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1,270 results on '"ORIENTI M."'

1. Search for Extended GeV Sources in the Inner Galactic Plane

Author: Abdollahi, S., Acero, F., Acharyya, A., Adelfio, A., Ajello, M., Baldini, L., Ballet, J., Bartolini, C., Gonzalez, J. Becerra, Bellazzini, R., Bissaldi, E., Bonino, R., Bruel, P., Cameron, R. A., Caraveo, P. A., Castro, D., Cavazzuti, E., Cheung, C. C., Cibrario, N., Ciprini, S., Cozzolongo, G., Orestano, P. Cristarella, Cuoco, A., Cutini, S., D'Ammando, F., Di Lalla, N., Dinesh, A., Di Venere, L., Domínguez, A., Fiori, A., Funk, S., Fusco, P., Gargano, F., Gasbarra, C., Gasparrini, D., Germani, S., Giacchino, F., Giglietto, N., Giliberti, M., Giordano, F., Giroletti, M., Green, D., Grenier, I. A., Guillemot, L., Guiriec, S., Gupta, R., Hashizume, M., Hays, E., Hewitt, J. W., Horan, D., Hou, X., Kayanoki, T., Kuss, M., Laviron, A., Lemoine-Goumard, M., Liguori, A., Li, J., Liodakis, I., Loizzo, P., Longo, F., Loparco, F., Lorusso, L., Lovellette, M. N., Lubrano, P., Maldera, S., Malyshev, D., Martí-Devesa, G., Martin, P., Mazziotta, M. N., Mereu, I., Michelson, P. F., Mirabal, N., Mitthumsiri, W., Mizuno, T., Monti-Guarnieri, P., Monzani, M. E., Morselli, A., Moskalenko, I. V., Negro, M., Omodei, N., Orienti, M., Orlando, E., Paneque, D., Panzarini, G., Persic, M., Pesce-Rollins, M., Pillera, R., Porter, T. A., Rainò, S., Rando, R., Razzano, M., Reimer, A., Reimer, O., Bernal, M. Rocamora, Sánchez-Conde, M., Parkinson, P. M. Saz, Serini, D., Sgrò, C., Siskind, E. J., Smith, D. A., Spandre, G., Spinelli, P., Strong, A. W., Suson, D. J., Tajima, H., Thayer, J. B., Torres, D. F., Valverde, J., Wadiasingh, Z., Wood, K., and Zaharijas, G.
Subjects: Astrophysics - High Energy Astrophysical Phenomena
Abstract: The recent detection of extended $\gamma$-ray emission around middle-aged pulsars is interpreted as inverse-Compton scattering of ambient photons by electron-positron pairs escaping the pulsar wind nebula, which are confined near the system by unclear mechanisms. This emerging population of $\gamma$-ray sources was first discovered at TeV energies and remains underexplored in the GeV range. To address this, we conducted a systematic search for extended sources along the Galactic plane using 14 years of Fermi-LAT data above 10 GeV, aiming to identify a number of pulsar halo candidates and extend our view to lower energies. The search covered the inner Galactic plane ($\lvert l\rvert\leq$ 100$^{\circ}$, $\lvert b\rvert\leq$ 1$^{\circ}$) and the positions of known TeV sources and bright pulsars, yielding broader astrophysical interest. We found 40 such sources, forming the Second Fermi Galactic Extended Sources Catalog (2FGES), most with 68% containment radii smaller than 1.0$^{\circ}$ and relatively hard spectra with photon indices below 2.5. We assessed detection robustness using field-specific alternative interstellar emission models and by inspecting significance maps. Noting 13 sources previously known as extended in the 4FGL-DR3 catalog and five dubious sources from complex regions, we report 22 newly detected extended sources above 10 GeV. Of these, 13 coincide with H.E.S.S., HAWC, or LHAASO sources; six coincide with bright pulsars (including four also coincident with TeV sources); six are associated with 4FGL point sources only; and one has no association in the scanned catalogs. Notably, six to eight sources may be related to pulsars as classical pulsar wind nebulae or pulsar halos., Comment: 43 pages, 17 figures, 11 tables
Published: 2024

2. GRB 221009A: the B.O.A.T Burst that Shines in Gamma Rays

Author: Axelsson, M., Ajello, M., Arimoto, M., Baldini, L., Ballet, J., Baring, M. G., Bartolini, C., Bastieri, D., Gonzalez, J. Becerra, Bellazzini, R., Berenji, B., Bissaldi, E., Blandford, R. D., Bonino, R., Bruel, P., Buson, S., Cameron, R. A., Caputo, R., Caraveo, P. A., Cavazzuti, E., Cheung, C. C., Chiaro, G., Cibrario, N., Ciprini, S., Cozzolongo, G., Orestano, P. Cristarella, Crnogorcevic, M., Cuoco, A., Cutini, S., D'Ammando, F., De Gaetano, S., Di Lalla, N., Dinesh, A., Di Tria, R., Di Venere, L., Domínguez, A., Fegan, S. J., Ferrara, E. C., Fiori, A., Franckowiak, A., Fukazawa, Y., Funk, S., Fusco, P., Galanti, G., Gargano, F., Gasbarra, C., Germani, S., Giacchino, F., Giglietto, N., Giliberti, M., Gill, R., Giordano, F., Giroletti, M., Granot, J., Green, D., Grenier, I. A., Guiriec, S., Gustafsson, M., Hashizume, M., Hays, E., Hewitt, J. W., Horan, D., Kayanoki, T., Kuss, M., Laviron, A., Li, J., Liodakis, I., Longo, F., Loparco, F., Lorusso, L., Lott, B., Lovellette, M. N., Lubrano, P., Maldera, S., Malyshev, D., Manfreda, A., Martí-Devesa, G., Martinelli, R., Castellanos, I. Martinez, Mazziotta, M. N., McEnery, J. E., Mereu, I., Meyer, M., Michelson, P. F., Mirabal, N., Mitthumsiri, W., Mizuno, T., Monti-Guarnieri, P., Monzani, M. E., Morishita, T., Morselli, A., Moskalenko, I. V., Negro, M., Niwa, R., Omodei, N., Orienti, M., Orlando, E., Paneque, D., Panzarini, G., Persic, M., Pesce-Rollins, M., Petrosian, V., Pillera, R., Piron, F., Porter, T. A., Principe, G., Racusin, J. L., Rainò, S., Rando, R., Rani, B., Razzano, M., Razzaque, S., Reimer, A., Reimer, O., Ryde, F., Sánchez-Conde, M., Parkinson, P. M. Saz, Serini, D., Sgrò, C., Sharma, V., Siskind, E. J., Spandre, G., Spinelli, P., Suson, D. J., Tajima, H., Tak, D., Thayer, J. B., Torres, D. F., Valverde, J., Zaharijas, G., Lesage, S., Briggs, M. S., Burns, E., Bala, S., Bhat, P. N., Cleveland, W. H., Dalessi, S., de Barra, C., Gibby, M., Giles, M. M., Hamburg, R., Hristov, B. A., Hui, C. M., Kocevski, D., Mailyan, B., Malacaria, C., McBreen, S., Poolakkil, S., Roberts, O. J., Scotton, L., Veres, P., von Kienlin, A., Wilson-Hodge, C. A., and Wood, J.
Subjects: Astrophysics - High Energy Astrophysical Phenomena
Abstract: We present a complete analysis of Fermi Large Area Telescope (LAT) data of GRB 221009A, the brightest Gamma-Ray Burst (GRB) ever detected. The burst emission above 30 MeV detected by the LAT preceded by 1 s the low-energy (< 10 MeV) pulse that triggered the Fermi Gamma-Ray Burst Monitor (GBM), as has been observed in other GRBs. The prompt phase of GRB 221009A lasted a few hundred seconds. It was so bright that we identify a Bad Time Interval (BTI) of 64 seconds caused by the extremely high flux of hard X-rays and soft gamma rays, during which the event reconstruction efficiency was poor and the dead time fraction quite high. The late-time emission decayed as a power law, but the extrapolation of the late-time emission during the first 450 seconds suggests that the afterglow started during the prompt emission. We also found that high-energy events observed by the LAT are incompatible with synchrotron origin, and, during the prompt emission, are more likely related to an extra component identified as synchrotron self-Compton (SSC). A remarkable 400 GeV photon, detected by the LAT 33 ks after the GBM trigger and directionally consistent with the location of GRB 221009A, is hard to explain as a product of SSC or TeV electromagnetic cascades, and the process responsible for its origin is uncertain. Because of its proximity and energetic nature, GRB 221009A is an extremely rare event., Comment: 60 pages, 38 figures, 9 tables
Published: 2024

3. Jetted Subgalactic-Size Radio Sources in Merging Galaxies -- A Jet Redirection Scenario

Author: Stanghellini, C., Orienti, M., Spingola, C., Zanichelli, A., Dallacasa, D., Cassaro, P., O'Dea, C. P., Baum, S. A., and Pérez-Torres, M.
Subjects: Astrophysics - Astrophysics of Galaxies
Abstract: The long-standing question concerning Jetted Sub-Galactic Size (JSS) radio sources is whether they will evolve into large radio galaxies, die before escaping the host galaxy, or remain indefinitely confined to their compact size. Our main goal is to propose a scenario that explains the relative number of JSS radio sources and their general properties. We studied the parsec-scale radio morphology of a complete sample of 21 objects using Very Long Baseline Interferometry (VLBI) observations at various frequencies and analyzed the morphological characteristics of their optical hosts. Many of these radio sources exhibit radio morphologies consistent with transverse motions of their bright edges and are located in dynamically disturbed galaxies. VLBI images provide evidence for large-angle, short-period precessing jets, and the orbital motion of the radio-loud AGN in a dual or binary system. The majority of JSS radio sources are in systems in different stages of their merging evolution. We propose a scenario where the rapid jet redirection, through precession or orbital motion, prevents the jet from penetrating the interstellar medium (ISM) sufficiently to escape the host galaxy. Most JSS radio sources remain compact due to their occurrence in merging galaxies, Comment: 34 pages, 24 figures, 3 tables, submitted to A&A
Published: 2024

4. A high-resolution radio morphology and polarization of the kpc-scale X-ray jet of PKS 1127-145

Author: Orienti, M., Siemiginowska, A., D'Ammando, F., and Migliori, G.
Subjects: Astrophysics - High Energy Astrophysical Phenomena
Abstract: We report on new multi-frequency Very Large Array (VLA) radio observations and Chandra X-ray observations of a radio-loud quasar with a ~300 kpc long jet, PKS 1127-145, during a flaring event detected in $\gamma$-rays by the Fermi Large Area Telescope in 2020 December. The high angular resolution of the new radio images allows us to disentangle for the first time the inner kpc-scale jet from the core contribution. The inner radio jet, up to 15 kpc from the core, is highly polarized (33 per cent) and the magnetic field is parallel to the jet axis. At about 18 arcsec from the core the jet slightly bends and we observe a re-brightening of the radio emission and a 90-degree rotation of the magnetic field, likely highlighting the presence of a shock that is compressing the magnetic field to a plane perpendicular to the jet axis and where efficient particle acceleration takes place. At the same position the X-ray emission fades, suggesting a deceleration of the bulk velocity of the jet after the bend. A change in velocity and collimation of the jet is supported by the widening of the jet profile and the detection of a limb-brightened structure connecting the bending region with the jet termination. The limb-brightened structure might indicate the co-existence of both longitudinal and transverse velocity gradients at the jet bending. There is no evidence for significant brightening of the kpc-scale jet in the radio or X-ray band during the $\gamma$-ray flare. The X-ray flux, $F_{\rm 2-10\,keV} = (6.24\pm0.57)\times10^{-12}$ ergs s$^{-1}$ cm$^{-2}$, measured by Chandra from the quasar core is consistent with the flux measured by the X-Ray Telescope on board the Neil Gehrels Swift Observatory after the high-energy flare. Our results indicate that the $\gamma$-ray flaring region is located within the VLA source core., Comment: 10 pages, 8 figures, accepted for publication in A&A
Published: 2024
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5. Dark Matter Line Searches with the Cherenkov Telescope Array

Author: Abe, S., Abhir, J., Abhishek, A., Acero, F., Acharyya, A., Adam, R., Aguasca-Cabot, A., Agudo, I., Aguirre-Santaella, A., Alfaro, J., Alfaro, R., Alvarez-Crespo, N., Batista, R. Alves, Amans, J. -P., Amato, E., Ambrosi, G., Angel, L., Aramo, C., Arcaro, C., Arnesen, T. T. H., Arrabito, L., Asano, K., Ascasibar, Y., Aschersleben, J., Ashkar, H., Backes, M., Baktash, A., Balazs, C., Balbo, M., Larriva, A. Baquero, Martins, V. Barbosa, de Almeida, U. Barres, Barrio, J. A., Batković, I., Batzofin, R., Baxter, J., González, J. Becerra, Beck, G., Benbow, W., Berge, D., Bernardini, E., Bernete, J., Bernlöhr, K., Berti, A., Bertucci, B., Bhattacharjee, P., Bhattacharyya, S., Bigongiari, C., Biland, A., Bissaldi, E., Biteau, J., Blanch, O., Blazek, J., Bocchino, F., Boisson, C., Bolmont, J., Bonnoli, G., Bonollo, A., Bordas, P., Bosnjak, Z., Bottacini, E., Böttcher, M., Bringmann, T., Bronzini, E., Brose, R., Brown, A. M., Brunelli, G., Bulgarelli, A., Bulik, T., Burelli, I., Burmistrov, L., Burton, M., Buscemi, M., Bylund, T., Cailleux, J., Campoy-Ordaz, A., Cantlay, B. K., Capasso, G., Caproni, A., Capuzzo-Dolcetta, R., Caraveo, P., Caroff, S., Carosi, A., Carosi, R., Carquin, E., Carrasco, M. -S., Cassol, F., Castaldini, L., Castrejon, N., Castro-Tirado, A. J., Cerasole, D., Cerruti, M., Chadwick, P. M., Chaty, S., Chen, A. W., Chernyakova, M., Chiavassa, A., Chudoba, J., Chytka, L., Cicciari, G. M., Cifuentes, A., Araujo, C. H. Coimbra, Colapietro, M., Conforti, V., Conte, F., Contreras, J. L., Costa, A., Costantini, H., Cotter, G., Cristofari, P., Cuevas, O., Curtis-Ginsberg, Z., D'Amico, G., D'Ammando, F., Dai, S., Dalchenko, M., Dazzi, F., De Angelis, A., de Lavergne, M. de Bony, De Caprio, V., Pino, E. M. de Gouveia Dal, De Lotto, B., De Lucia, M., de Menezes, R., de Naurois, M., de Souza, V., del Peral, L., del Valle, M. V., Giler, A. G. Delgado, Mengual, J. Delgado, Delgado, C., Dell'aiera, M., della Volpe, D., Depaoli, D., Di Girolamo, T., Di Piano, A., Di Pierro, F., Di Tria, R., Di Venere, L., Díaz, C., Diebold, S., Dinesh, A., Djuvsland, J., Dominik, R. M., Prester, D. Dominis, Donini, A., Dorner, D., Dörner, J., Doro, M., Dournaux, J. -L., Duangchan, C., Dubos, C., Ducci, L., Dwarkadas, V. V., Ebr, J., Eckner, C., Egberts, K., Einecke, S., Elsässer, D., Emery, G., Errando, M., Escanuela, C., Escarate, P., Godoy, M. Escobar, Escudero, J., Esposito, P., Ettori, S., Falceta-Goncalves, D., Fedorova, E., Fegan, S., Feng, Q., Ferrand, G., Ferrarotto, F., Fiandrini, E., Fiasson, A., Filipovic, M., Fioretti, V., Fiori, M., Foffano, L., Guiteras, L. Font, Fontaine, G., Fröse, S., Fukazawa, Y., Fukui, Y., Furniss, A., Galanti, G., Galaz, G., Galelli, C., Gallozzi, S., Gammaldi, V., Garczarczyk, M., Gasbarra, C., Gasparrini, D., Ghalumyan, A., Gianotti, F., Giarrusso, M., Paiva, J. G. Giesbrecht Formiga, Giglietto, N., Giordano, F., Giuffrida, R., Glicenstein, J. -F., Glombitza, J., Goldoni, P., González, J. M., González, M. M., Coelho, J. Goulart, Gradetzke, T., Granot, J., Grasso, D., Grau, R., Gréaux, L., Green, D., Green, J. G., Grolleron, G., Guedes, L. M. V., Gueta, O., Hackfeld, J., Hadasch, D., Hamal, P., Hanlon, W., Hara, S., Harvey, V. M., Hassan, T., Hayashi, K., Heß, B., Heckmann, L., Heller, M., Cadena, S. Hernández, Hervet, O., Hinton, J., Hiroshima, N., Hnatyk, B., Hnatyk, R., Hofmann, W., Holder, J., Horan, D., Horvath, P., Hovatta, T., Hrabovsky, M., Hrupec, D., Iarlori, M., Inada, T., Incardona, F., Inoue, S., Inoue, Y., Iocco, F., Iori, M., Ishio, K., Jamrozy, M., Janecek, P., Jankowsky, F., Jean, P., Quiles, J. Jimenez, Jin, W., Juramy-Gilles, C., Jurysek, J., Kagaya, M., Kalekin, O., Karas, V., Katagiri, H., Kataoka, J., Kaufmann, S., Kazanas, D., Kerszberg, D., Kieda, D. B., Kleiner, T., Kluge, G., Kobayashi, Y., Kohri, K., Komin, N., Kornecki, P., Kosack, K., Kowal, G., Kubo, H., Kushida, J., La Barbera, A., La Palombara, N., Láinez, M., Lamastra, A., Lapington, J., Laporte, P., Lazarević, S., Lazendic-Galloway, J., Lemoine-Goumard, M., Lenain, J. -P., Leone, F., Leonora, E., Leto, G., Lindfors, E., Linhoff, M., Liodakis, I., Lipniacka, A., Lombardi, S., Longo, F., López-Coto, R., López-Moya, M., López-Oramas, A., Loporchio, S., Bahilo, J. Lozano, Luque-Escamilla, P. L., Macias, O., Majumdar, P., Mallamaci, M., Malyshev, D., Mandat, D., Manicò, G., Mariotti, M., Márquez, I., Marquez, P., Marsella, G., Martí, J., Martínez, G. A., Martínez, M., Martinez, O., Marty, C., Mas-Aguilar, A., Mastropietro, M., Mazin, D., Menchiari, S., Mestre, E., Meunier, J. -L., Meyer, D. M. -A., Meyer, M., Miceli, D., Miceli, M., Michailidis, M., Michałowski, J., Miener, T., Miranda, J. M., Mitchell, A., Mizote, M., Mizuno, T., Moderski, R., Molero, M., Molfese, C., Molina, E., Montaruli, T., Moralejo, A., Morcuende, D., Morselli, A., Moulin, E., Zamanillo, V. Moya, Munari, K., Murach, T., Muraczewski, A., Muraishi, H., Nakamori, T., Nayak, A., Nemmen, R., Neto, J. P., Nickel, L., Niemiec, J., Nieto, D., Rosillo, M. Nievas, Nikołajuk, M., Nikolić, L., Nishijima, K., Noda, K., Nosek, D., Novotny, V., Nozaki, S., Ohishi, M., Ohtani, Y., Okumura, A., Olive, J. -F., Ong, R. A., Orienti, M., Orito, R., Orlandini, M., Orlando, E., Orlando, S., Ostrowski, M., Otero-Santos, J., Oya, I., Pagano, I., Pagliaro, A., Palatiello, M., Panebianco, G., Paneque, D., Pantaleo, F. R., Paredes, J. M., Parmiggiani, N., Patricelli, B., Pe'er, A., Pech, M., Pecimotika, M., Pensec, U., Peresano, M., Pérez-Romero, J., Persic, M., Peters, K. P., Petruk, O., Piano, G., Pierre, E., Pietropaolo, E., Pihet, M., Pinchbeck, L., Pirola, G., Pittori, C., Plard, C., Podobnik, F., Pohl, M., Pollet, V., Ponti, G., Prandini, E., Principe, G., Priyadarshi, C., Produit, N., Prouza, M., Pueschel, E., Pühlhofer, G., Pumo, M. L., Queiroz, F., Quirrenbach, A., Rainò, S., Rando, R., Razzaque, S., Regeard, M., Reimer, A., Reimer, O., Reisenegger, A., Rhode, W., Ribeiro, D., Ribó, M., Ricci, C., Richtler, T., Rico, J., Rieger, F., Riitano, L., Rizi, V., Roache, E., Fernandez, G. Rodriguez, Frías, M. D. Rodríguez, Rodríguez-Vázquez, J. J., Romano, P., Romeo, G., Rosado, J., de Leon, A. Rosales, Rowell, G., Rudak, B., Ruiter, A. J., Rulten, C. B., Sadeh, I., Saha, L., Saito, T., Salzmann, H., Sánchez-Conde, M., Sandaker, H., Sangiorgi, P., Sano, H., Santander, M., Santos-Lima, R., Sapienza, V., Šarić, T., Sarkar, A., Sarkar, S., Saturni, F. G., Savarese, S., Scherer, A., Schiavone, F., Schipani, P., Schleicher, B., Schovanek, P., Schubert, J. L., Schwanke, U., Arroyo, M. Seglar, Seitenzahl, I. R., Sergijenko, O., Servillat, M., Siegert, T., Siejkowski, H., Siqueira, C., Sliusar, V., Slowikowska, A., Sol, H., Spencer, S. T., Spiga, D., Stamerra, A., Stanič, S., Starecki, T., Starling, R., Stawarz, Ł., Steppa, C., Hatlen, E. Sæther, Stolarczyk, T., Strišković, J., Suda, Y., Świerk, P., Tajima, H., Tak, D., Takahashi, M., Takeishi, R., Tavernier, T., Tejedor, L. A., Terauchi, K., Teshima, M., Testa, V., Tian, W. W., Tibaldo, L., Tibolla, O., Peixoto, C. J. Todero, Torradeflot, F., Torres, D. F., Tosti, G., Tothill, N., Toussenel, F., Tramacere, A., Travnicek, P., Tripodo, G., Trois, A., Truzzi, S., Tutone, A., Vaclavek, L., Vacula, M., Vallania, P., Vallés, R., van Eldik, C., van Scherpenberg, J., Vandenbroucke, J., Vassiliev, V., Acosta, M. Vázquez, Vecchi, M., Ventura, S., Vercellone, S., Verna, G., Viana, A., Viaux, N., Vigliano, A., Vignatti, J., Vigorito, C. F., Villanueva, J., Visentin, E., Vitale, V., Vodeb, V., Voisin, V., Voitsekhovskyi, V., Vorobiov, S., Voutsinas, G., Vovk, I., Vuillaume, T., Wagner, S. J., Walter, R., White, M., White, R., Wierzcholska, A., Will, M., Williams, D. A., Wohlleben, F., Wolter, A., Yamamoto, T., Yang, L., Yoshida, T., Yoshikoshi, T., Zaharijas, G., Zampieri, L., Sanchez, R. Zanmar, Zavrtanik, D., Zavrtanik, M., Zdziarski, A. A., Zech, A., Zhang, W., Zhdanov, V. I., Ziętara, K., Živec, M., and Zuriaga-Puig, J.
Subjects: High Energy Physics - Phenomenology, Astrophysics - High Energy Astrophysical Phenomena, High Energy Physics - Experiment
Abstract: Monochromatic gamma-ray signals constitute a potential smoking gun signature for annihilating or decaying dark matter particles that could relatively easily be distinguished from astrophysical or instrumental backgrounds. We provide an updated assessment of the sensitivity of the Cherenkov Telescope Array (CTA) to such signals, based on observations of the Galactic centre region as well as of selected dwarf spheroidal galaxies. We find that current limits and detection prospects for dark matter masses above 300 GeV will be significantly improved, by up to an order of magnitude in the multi-TeV range. This demonstrates that CTA will set a new standard for gamma-ray astronomy also in this respect, as the world's largest and most sensitive high-energy gamma-ray observatory, in particular due to its exquisite energy resolution at TeV energies and the adopted observational strategy focussing on regions with large dark matter densities. Throughout our analysis, we use up-to-date instrument response functions, and we thoroughly model the effect of instrumental systematic uncertainties in our statistical treatment. We further present results for other potential signatures with sharp spectral features, e.g.~box-shaped spectra, that would likewise very clearly point to a particle dark matter origin., Comment: 44 pages JCAP style (excluding author list and references), 19 figures; minor changes to match published version
Published: 2024
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6. Investigating X-ray Emission in the GeV-emitting Compact Symmetric Objects PKS 1718-649 and TXS 1146+596

Author: Bronzini, E., Migliori, G., Vignali, C., Sobolewska, M., Stawarz, Ł., Siemiginowska, A., Orienti, M., D'Ammando, F., Giroletti, M., Principe, G., and Balasubramaniam, K.
Subjects: Astrophysics - High Energy Astrophysical Phenomena, Astrophysics - Astrophysics of Galaxies
Abstract: Compact Symmetric Objects (CSOs) are thought to represent the first step in the evolutionary path of radio galaxies. In this work, we investigate the X-ray emission of two CSOs confirmed to emit at GeV energies: PKS 1718-649 and TXS 1146+596. Unveiling the origin of their observed high-energy emission is crucial to establishing the physical parameters of the radio source and understanding how CSOs interact with the surrounding medium. We combined archival and new NuSTAR observations of PKS 1718-649 and TXS 1146+596 to have a broadband X-ray coverage. For both sources, we model the broadband spectral energy distribution, from radio band up to $\gamma$-rays, to derive their physical parameters. We also discuss the role of the ambient medium in confining the source expansion, which we investigate using X-ray obscuration. For the first time, we report on X-ray detections of PKS 1718-649 and 1146+596 with NuSTAR at energies higher than 10 keV. Combining Chandra and NuSTAR observations of TXS 1146+596, we reveal the presence of a multi-temperature thermal component dominating the soft X-ray spectrum, and we interpret this finding as indicative of an AGN feedback process in action in this source. In addition, we show that two emitting electrons populations are necessary to reproduce the observed broadband spectral energy distribution of TXS 1146+596: in our models, the X-ray emission could be produced either by synchrotron radiation or by a weak X-ray corona or an ADAF-type emission. Interestingly, an additional X-ray component, i.e. a weak corona, is also required for PKS 1718-649. Moreover, we argue that heavily obscured, and possibly frustrated, sources tend to show different radio sizes with respect to unobscured, free to expand, ones., Comment: Accepted for publication in A&A, 16 pages, 7 figures
Published: 2024

7. Prospects for $\gamma$-ray observations of the Perseus galaxy cluster with the Cherenkov Telescope Array

Author: Consortium, The Cherenkov Telescope Array, Abe, K., Abe, S., Acero, F., Acharyya, A., Adam, R., Aguasca-Cabot, A., Agudo, I., Aguirre-Santaella, A., Alfaro, J., Alfaro, R., Alvarez-Crespo, N., Batista, R. Alves, Amans, J. -P., Amato, E., Angüner, E. O., Antonelli, L. A., Aramo, C., Araya, M., Arcaro, C., Arrabito, L., Asano, K., Ascasíbar, Y., Aschersleben, J., Ashkar, H., Stuani, L. Augusto, Baack, D., Backes, M., Baktash, A., Balazs, C., Balbo, M., Ballester, O., Larriva, A. Baquero, Martins, V. Barbosa, de Almeida, U. Barres, Barrio, J. A., Batista, P. I., Batkovic, I., Batzofin, R., Baxter, J., González, J. Becerra, Beck, G., Tjus, J. Becker, Benbow, W., Medrano, J. Bernete, Bernlöhr, K., Berti, A., Bertucci, B., Beshley, V., Bhattacharjee, P., Bhattacharyya, S., Bi, B., Biederbeck, N., Biland, A., Bissaldi, E., Biteau, J., Blanch, O., Blazek, J., Boisson, C., Bolmont, J., Bordas, P., Bosnjak, Z., Bottacini, E., Bradascio, F., Braiding, C., Bronzini, E., Brose, R., Brown, A. M., Brun, F., Brunetti, G., Bucciantini, N., Bulgarelli, A., Burelli, I., Burmistrov, L., Burton, M., Bylund, T., Calisse, P. G., Campoy-Ordaz, A., Cantlay, B. K., Capalbi, M., Caproni, A., Capuzzo-Dolcetta, R., Caraveo, P., Caroff, S., Carosi, R., Carquin, E., Carrasco, M. -S., Cascone, E., Cassol, F., Castro-Tirado, A. J., Cerasole, D., Cerruti, M., Chadwick, P., Chaty, S., Chen, A. W., Chernyakova, M., Chiavassa, A., Chudoba, J., Chytka, L., Cifuentes, A., Araujo, C. H. Coimbra, Conforti, V., Conte, F., Contreras, J. L., Cortina, J., Costa, A., Costantini, H., Cotter, G., Cristofari, P., Cuevas, O., Curtis-Ginsberg, Z., D'Amico, G., D'Ammando, F., Dalchenko, M., Dazzi, F., de Lavergne, M. de Bony, De Caprio, V., Laadim, F. De Frondat, Pino, E. M. de Gouveia Dal, De Lotto, B., De Lucia, M., De Martino, D., de Menezes, R., de Naurois, M., De Simone, N., de Souza, V., del Valle, M. V., Delagnes, E., Giler, A. G. Delgado, Delgado, C., Dell'aiera, M., della Volpe, D., Depaoli, D., Di Girolamo, T., Di Piano, A., Di Pierro, F., Di Tria, R., Di Venere, L., Diebold, S., Djannati-Ataï, A., Djuvsland, J., Dominik, R. M., Donini, A., Dorner, D., Dörner, J., Doro, M., Anjos, R. D. C. dos, Dournaux, J. -L., Duangchan, C., Dubos, C., Dumora, D., Dwarkadas, V. V., Ebr, J., Eckner, C., Egberts, K., Einecke, S., Elsässer, D., Emery, G., Godoy, M. Escobar, Escudero, J., Esposito, P., Ettori, S., Evoli, C., Falceta-Goncalves, D., Ramazani, V. Fallah, Fattorini, A., Faure, A., Fedorova, E., Fegan, S., Feijen, K., Feng, Q., Ferrand, G., Ferrarotto, F., Fiandrini, E., Fiasson, A., Filipovic, M., Fioretti, V., Foffano, L., Guiteras, L. Font, Fontaine, G., Fröse, S., Fukazawa, Y., Fukui, Y., Gaggero, D., Galanti, G., Gallozzi, S., Gammaldi, V., Garczarczyk, M., Gasbarra, C., Gasparrini, D., Gaug, M., Ghalumyan, A., Gianotti, F., Giarrusso, M., Giesbrecht, J., Giglietto, N., Giordano, F., Glicenstein, J. -F., Göksu, H., Goldoni, P., González, J. M., González, M. M., Coelho, J. Goulart, Granot, J., Grau, R., Gréaux, L., Green, D., Green, J. G., Grenier, I., Grolleron, G., Grube, J., Gueta, O., Hackfeld, J., Hadasch, D., Hamal, P., Hanlon, W., Hara, S., Harvey, V. M., Hassan, T., Heckmann, L., Heller, M., Cadena, S. Hernández, Hervet, O., Hie, J., Hiroshima, N., Hnatyk, B., Hnatyk, R., Hoang, J., Hoffmann, D., Hofmann, W., Holder, J., Horan, D., Horvath, P., Hrupec122, D., Hütten, M., Iarlori, M., Inada, T., Incardona, F., Inoue, S., Iocco, F., Iori, M., Jamrozy, M., Janecek, P., Jankowsky, F., Jarnot, C., Jean, P., Martínez, I. Jiménez, Jin, W., Juramy-Gilles, C., Jurysek, J., Kagaya, M., Kantzas, D., Karas, V., Katagiri, H., Kataoka, J., Kaufmann, S., Kerszberg, D., Khélifi, B., Kissmann, R., Kleiner, T., Kluge, G., Kluźniak, W., Knödlseder, J., Kobayashi, Y., Kohri, K., Komin, N., Kornecki, P., Kosack, K., Kowal, G., Kubo, H., Kushida, J., La Barbera, A., La Palombara, N., Láinez, M., Lamastra, A., Lapington, J., Laporte, P., Lazarević, S., Leitgeb, F., Lemoine-Goumard, M., Lenain, J. -P., Leone, F., Leto, G., Leuschner, F., Lindfors, E., Linhoff, M., Liodakis, I., Lombardi, S., Longo, F., López-Coto, R., López-Moya, M., López-Oramas, A., Loporchio, S., Luque-Escamilla, P. L., Macias, O., Mackey, J., Majumdar, P., Malyshev, D., Mandat, D., Manganaro, M., Manicò, G., Mariotti, M., Markoff, S., Márquez, I., Marquez, P., Marsella, G., Martínez, G. A., Martínez, M., Martinez, O., Marty, C., Mas-Aguilar, A., Mastropietro, M., Maurin, G., Mazin, D., Melkumyan, D., Mello, A. J. T. S., Meunier, J. -L., Meyer, D. M. -A., Meyer, M., Miceli, D., Michailidis, M., Michałowski, J., Miener, T., Miranda, J. M., Mitchell, A., Mizote, M., Mizuno, T., Moderski, R., Molero, M., Molfese, C., Molina, E., Montaruli, T., Morcuende, D., Morik, K., Morlino, G., Morselli, A., Moulin, E., Zamanillo, V. Moya, Munari, K., Murach, T., Muraczewski, A., Muraishi, H., Nagataki, S., Nakamori, T., Nemmen, R., Neyroud, N., Nickel, L., Niemiec, J., Nieto, D., Rosillo, M. Nievas, Nikołajuk, M., Nishijima, K., Noda, K., Nosek, D., Novotny, V., Nozaki, S., O'Brien, P., Ohishi, M., Ohtani, Y., Okumura, A., Olive, J. -F., Olmi, B., Ong, R. A., Orienti, M., Orito, R., Orlandini, M., Orlando, E., Ostrowski, M., Oya, I., Pagliaro, A., Palatiello, M., Panebianco, G., Paneque, D., Pantaleo, F. R., Paoletti, R., Paredes, J. M., Parmiggiani, N., Patel, S. R., Patricelli, B., Pavlović, D., Pech, M., Pecimotika, M., Pensec, U., Peresano, M., Pérez-Romero, J., Peron, G., Persic, M., Petrucci, P. -O., Petruk, O., Piano, G., Pierre, E., Pietropaolo, E., Pintore, F., Pirola, G., Pita, S., Plard, C., Podobnik, F., Pohl, M., Polo, M., Pons, E., Ponti, G., Prandini, E., Prast, J., Principe, G., Priyadarshi, C., Produit, N., Pueschel, E., Pühlhofer, G., Pumo, M. L., Punch, M., Queiroz, F., Quirrenbach, A., Rainò, S., Rando, R., Razzaque, S., Recchia, S., Regeard, M., Reichherzer, P., Reimer, A., Reimer, O., Reisenegger, A., Rhode, W., Ribeiro, D., Ribó, M., Richtler, T., Rico, J., Rieger, F., Righi, C., Riitano, L., Rizi, V., Roache, E., Fernandez, G. Rodriguez, Rodríguez-Vázquez, J. J., Romano, P., Romeo, G., Rosado, J., de Leon, A. Rosales, Rowell, G., Rudak, B., Rulten, C. B., Russo, F., Sadeh, I., Saha, L., Saito, T., Salzmann, H., Sanchez, D., Sánchez-Conde, M., Sangiorgi, P., Sano, H., Santander, M., Santangelo, A., Santos-Lima, R., Sanuy, A., Šarić, T., Sarkar, A., Sarkar, S., Satalecka, K., Saturni, F. G., Savchenko, V., Scherer, A., Schipani, P., Schleicher, B., Schubert, J. L., Schussler, F., Schwanke, U., Schwefer, G., Arroyo, M. Seglar, Seiji, S., Semikoz, D., Sergijenko, O., Servillat, M., Sguera, V., Shang, R. Y., Sharma, P., Siejkowski, H., Sinha, A., Siqueira, C., Sliusar, V., Slowikowska, A., Sol, H., Specovius, A., Spencer, S. T., Spiga, D., Stamerra, A., Stanič, S., Starecki, T., Starling, R., Stawarz, Ł., Steppa, C., Stolarczyk, T., Strišković, J., Suda, Y., Suomijärvi, T., Tajima, H., Tak, D., Takahashi, M., Takeishi, R., Tanaka, S. J., Tavernier, T., Tejedor, L. A., Terauchi, K., Terrier, R., Teshima, M., Tian, W. W., Tibaldo, L., Tibolla, O., Torradeflot, F., Torres, D. F., Torresi, E., Tosti, G., Tosti, L., Tothill, N., Toussenel, F., Touzard, V., Tramacere, A., Travnicek, P., Tripodo, G., Truzzi, S., Tsiahina, A., Tutone, A., Vacula, M., Vallage, B., Vallania, P., van Eldik, C., van Scherpenberg, J., Vandenbroucke, J., Vassiliev, V., Acosta, M. Vázquez, Vecchi, M., Ventura, S., Vercellone, S., Verna, G., Viana, A., Viaux, N., Vigliano, A., Vigorito, C. F., Vitale, V., Vodeb, V., Voisin, V., Vorobiov, S., Voutsinas, G., Vovk, I., Vuillaume, T., Wagner, S. J., Walter, R., Wechakama, M., White, R., Wierzcholska, A., Will, M., Williams, D. A., Wohlleben, F., Wolter, A., Yamamoto, T., Yamazaki, R., Yoshida, T., Yoshikoshi, T., Zacharias, M., Zaharijas, G., Zavrtanik, D., Zavrtanik, M., Zdziarski, A. A., Zech, A., Zhdanov, V. I., Živec, M., Zuriaga-Puig, J., and Luque, P. De la Torre
Subjects: Astrophysics - High Energy Astrophysical Phenomena, Astrophysics - Cosmology and Nongalactic Astrophysics, High Energy Physics - Phenomenology
Abstract: Galaxy clusters are expected to be dark matter (DM) reservoirs and storage rooms for the cosmic-ray protons (CRp) that accumulate along the cluster's formation history. Accordingly, they are excellent targets to search for signals of DM annihilation and decay at gamma-ray energies and are predicted to be sources of large-scale gamma-ray emission due to hadronic interactions in the intracluster medium. We estimate the sensitivity of the Cherenkov Telescope Array (CTA) to detect diffuse gamma-ray emission from the Perseus galaxy cluster. We perform a detailed spatial and spectral modelling of the expected signal for the DM and the CRp components. For each, we compute the expected CTA sensitivity. The observing strategy of Perseus is also discussed. In the absence of a diffuse signal (non-detection), CTA should constrain the CRp to thermal energy ratio within the radius $R_{500}$ down to about $X_{500}<3\times 10^{-3}$, for a spatial CRp distribution that follows the thermal gas and a CRp spectral index $\alpha_{\rm CRp}=2.3$. Under the optimistic assumption of a pure hadronic origin of the Perseus radio mini-halo and depending on the assumed magnetic field profile, CTA should measure $\alpha_{\rm CRp}$ down to about $\Delta\alpha_{\rm CRp}\simeq 0.1$ and the CRp spatial distribution with 10% precision. Regarding DM, CTA should improve the current ground-based gamma-ray DM limits from clusters observations on the velocity-averaged annihilation cross-section by a factor of up to $\sim 5$, depending on the modelling of DM halo substructure. In the case of decay of DM particles, CTA will explore a new region of the parameter space, reaching models with $\tau_{\chi}>10^{27}$s for DM masses above 1 TeV. These constraints will provide unprecedented sensitivity to the physics of both CRp acceleration and transport at cluster scale and to TeV DM particle models, especially in the decay scenario., Comment: 93 pages (including author list, appendix and references), 143 figures. Submitted to JCAP
Published: 2023
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8. Young but fading radio sources: searching for remnants among compact steep-spectrum radio sources

Author: Orienti, M., Murgia, M., Dallacasa, D., Migliori, G., and D'Ammando, F.
Subjects: Astrophysics - Astrophysics of Galaxies
Abstract: The incidence of young but fading radio sources provides important information on the life cycle of radio emission in radio-loud active galactic nuclei. Despite its importance for constraining the models of radio source evolution, there are no systematic studies of remnants in complete samples of young radio sources. We report results on the study of 18 compact steep-spectrum (CSS) radio sources, selected from the statistically complete B3-VLA CSS sample, characterized by a steep optically-thin spectrum (alpha > 1.0) and no core detection in earlier studies. Our deep multi-frequency Very Large Array (VLA), pc-scale Very Long Baseline Array (VLBA), and eMERLIN observations allowed us to locate the core component in 10 objects. In 3 CSS sources there is no clear evidence of present-time active regions, suggesting they are likely in a remnant phase. Among sources with core detection, we find 3 objects that have no clear active regions (hotspots) at the edges of the radio structure, suggesting that the radio emission may have just restarted. Our results support a power-law distribution of the source ages, although the poor statistics prevents us from setting solid constraints on the percentage of remnants and restarted sources in sub-populations of radio sources., Comment: 33 pages, 8 figures, 7 tables. Accepted for publication in MNRAS
Published: 2023
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9. Sensitivity of the Cherenkov Telescope Array to spectral signatures of hadronic PeVatrons with application to Galactic Supernova Remnants

Author: Consortium, The Cherenkov Telescope Array, Acero, F., Acharyya, A., Adam, R., Aguasca-Cabot, A., Agudo, I., Aguirre-Santaella, A., Alfaro, J., Aloisio, R., Crespo, N. Álvarez, Batista, R. Alves, Amati, L., Amato, E., Ambrosi, G., Angüner, E. O., Aramo, C., Arcaro, C., Armstrong, T., Asano, K., Ascasibar, Y., Aschersleben, J., Backes, M., Baktash, A., Balazs, C., Balbo, M., Ballet, J., Larriva, A. Baquero, Martins, V. Barbosa, de Almeida, U. Barres, Barrio, J. A., Bastieri, D., Baxter, J. R., Tjus, J. Becker, Benbow, W., Bernardos-Martín, M. I., Bernete, J., Berti, A., Bertucci, B., Beshley, V., Bhattacharjee, P., Bhattacharyya, S., Biland, A., Bissaldi, E., Biteau, J., Blanch, O., Bordas, P., Bottacini, E., Bregeon, J., Brose, R., Bucciantini, N., Bulgarelli, A., Capasso, M., Dolcetta, R. A. Capuzzo, Caraveo, P., Cardillo, M., Carosi, R., Casanova, S., Cascone, E., Cassol, F., Catalani, F., Cerruti, M., Chadwick, P., Chaty, S., Chen, A., Chernyakova, M., Chiavassa, A., Chudoba, J., Coimbra-Araujo, C., Conforti, V., Contreras, J. L., Costa, A., Costantini, H., Cristofari, P., Crocker, R., D'Amico, G., D'Ammando, F., De Angelis, A., De Caprio, V., Pino, E. M. de Gouveia Dal, Wilhelmi, E. de Ona, de Souza, V., Delgado, C., della Volpe, D., Depaoli, D., Di Girolamo, T., Di Pierro, F., Di Tria, R., Di Venere, L., Diebold, S., Djuvsland, J. I., Donini, A., Doro, M., Anjos, R. d. C. Dos, Dwarkadas, V. V., Einecke, S., Elsässer, D., Emery, G., Evoli, C., Falceta-Goncalves, D., Fedorova, E., Fegan, S., Ferrand, G., Fiandrini, E., Filipovic, M., Fioretti, V., Fiori, M., Foffano, L., Fontaine, G., Fukami, S., Galanti, G., Galaz, G., Gammaldi, V., Gasbarra, C., Ghalumyan, A., Ghirlanda, G., Giarrusso, M., Giavitto, G., Giglietto, N., Giordano, F., Giroletti, M., Giuliani, A., Giunti, L., Godinovic, N., Coelho, J. Goulart, Gréaux, L., Green, D., Grondin, M-H., Gueta, O., Gunji, S., Hassan, T., Heller, M., Hernández-Cadena, S., Hinton, J., Hnatyk, B., Hnatyk, R., Hoffmann, D., Hofmann, W., Holder, J., Horan, D., Horvath, P., Hrabovsky, M., Hrupec, D., Inada, T., Incardona, F., Inoue, S., Ishio, K., Jamrozy, M., Janecek, P., Martínez, I. Jiménez, Jin, W., Jung-Richardt, I., Jurysek, J., Kaaret, P., Karas, V., Katz, U., Kerszberg, D., Khélifi, B., Kieda, D. B., Kissmann, R., Kleiner, T., Kluge, G., Kluzniak, W., Knödlseder, J., Kobayashi, Y., Kohri, K., Komin, N., Kornecki, P., Kubo, H., La Palombara, N., Láinez, M., Lamastra, A., Lapington, J., Lemoine-Goumard, M., Lenain, J. -P., Leone, F., Leto, G., Leuschner, F., Lindfors, E., Liodakis, I., Lohse, T., Lombardi, S., Longo, F., López-Coto, R., López-Moya, M., López-Oramas, A., Loporchio, S., Luque-Escamilla, P. L., Macias, O., Mackey, J., Majumdar, P., Mandat, D., Manganaro, M., Manicò, G., Marconi, M., Martí, J., Martínez, G., Martinez, M., Martinez, O., Mello, A. J. T. S., Menchiari, S., Meyer, D. M. -A., Micanovic, S., Miceli, D., Miceli, M., Michalowski, J., Miener, T., Miranda, J. M., Mitchell, A., Mode, B., Moderski, R., Mohrmann, L., Molina, E., Montaruli, T., Morcuende, D., Morlino, G., Morselli, A., Mosè, M., Moulin, E., Mukherjee, R., Munari, K., Murach, T., Nagai, A., Nagataki, S., Nemmen, R., Niemiec, J., Nieto, D., Rosillo, M. Nievas, Nikolajuk, M., Nishijima, K., Noda, K., Novosyadlyj, B., Nozaki, S., Ohishi, M., Ohm, S., Ohtani, Y., Okumura, A., Olmi, B., Ong, R. A., Orienti, M., Orito, R., Orlandini, M., Orlando, E., Orlando, S., Ostrowski, M., Oya, I., Pantaleo, F. R., Paredes, J. M., Patricelli, B., Pecimotika, M., Peresano, M., Pérez-Romero, J., Persic, M., Petruk, O., Piano, G., Pietropaolo, E., Pirola, G., Pittori, C., Pohl, M., Ponti, G., Prandini, E., Principe, G., Priyadarshi, C., Pueschel, E., Pühlhofer, G., Pumo, M. L., Quirrenbach, A., Rando, R., Razzaque, S., Reichherzer, P., Reimer, A., Reimer, O., Renaud, M., Reposeur, T., Ribó, M., Richtler, T., Rico, J., Rieger, F., Rigoselli, M., Riitano, L., Rizi, V., Roache, E., Romano, P., Romeo, G., Rosado, J., Rowell, G., Rudak, B., Sadeh, I., Safi-Harb, S., Saha, L., Sailer, S., Sánchez-Conde, M., Sarkar, S., Satalecka, K., Saturni, F. G., Scherer, A., Schovánek, P., Schussler, F., Schwanke, U., Scuderi, S., Seglar-Arroyo, M., Sergijenko, O., Servillat, M., Shang, R-Y., Sharma, P., Siejkowski, H., Sliusar, V., Słowikowska, A., Sol, H., Specovius, A., Spencer, S. T., Spengler, G., Stamerra, A., Stanič, S., Starecki, T., Starling, R., Stolarczyk, T., Pereira, L. A. Stuani, Suda, Y., Suomijarvi, T., Sushch, I., Tajima, H., Tam, P-H. T., Tanaka, S. J., Tavecchio, F., Testa, V., Tian, W., Tibaldo, L., Torres, D. F., Tothill, N., Vallage, B., Vallania, P., van Eldik, C., van Scherpenberg, J., Vandenbroucke, J., Acosta, M. Vazquez, Vecchi, M., Vercellone, S., Verna, G., Viana, A., Vignatti, J., Vitale, V., Vodeb, V., Vorobiov, S., Vuillaume, T., Wagner, S. J., Walter, R., White, M., Wierzcholska, A., Will, M., Williams, D., Yang, L., Yoshida, T., Yoshikoshi, T., Zaharijas, G., Zampieri, L., Zavrtanik, D., Zavrtanik, M., Zhdanov, V. I., and Živec, M.
Subjects: Astrophysics - High Energy Astrophysical Phenomena, Astrophysics - Instrumentation and Methods for Astrophysics
Abstract: The local Cosmic Ray (CR) energy spectrum exhibits a spectral softening at energies around 3~PeV. Sources which are capable of accelerating hadrons to such energies are called hadronic PeVatrons. However, hadronic PeVatrons have not yet been firmly identified within the Galaxy. Several source classes, including Galactic Supernova Remnants (SNRs), have been proposed as PeVatron candidates. The potential to search for hadronic PeVatrons with the Cherenkov Telescope Array (CTA) is assessed. The focus is on the usage of very high energy $\gamma$-ray spectral signatures for the identification of PeVatrons. Assuming that SNRs can accelerate CRs up to knee energies, the number of Galactic SNRs which can be identified as PeVatrons with CTA is estimated within a model for the evolution of SNRs. Additionally, the potential of a follow-up observation strategy under moonlight conditions for PeVatron searches is investigated. Statistical methods for the identification of PeVatrons are introduced, and realistic Monte--Carlo simulations of the response of the CTA observatory to the emission spectra from hadronic PeVatrons are performed. Based on simulations of a simplified model for the evolution for SNRs, the detection of a $\gamma$-ray signal from in average 9 Galactic PeVatron SNRs is expected to result from the scan of the Galactic plane with CTA after 10 hours of exposure. CTA is also shown to have excellent potential to confirm these sources as PeVatrons in deep observations with $\mathcal{O}(100)$ hours of exposure per source., Comment: 34 pages, 16 figures, Accepted for publication in Astroparticle Physics
Published: 2023
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10. Panning for gold, but finding helium: discovery of the ultra-stripped supernova SN2019wxt from gravitational-wave follow-up observations

Author: Agudo, I., Amati, L., An, T., Bauer, F. E., Benetti, S., Bernardini, M. G., Beswick, R., Bhirombhakdi, K., de Boer, T., Branchesi, M., Brennan, S. J., Caballero-García, M. D., Cappellaro, E., Rodríguez, N. Castro, Castro-Tirado, A. J., Chambers, K. C., Chassande-Mottin, E., Chaty, S., Chen, T. -W., Coleiro, A., Covino, S., D'Ammando, F., D'Avanzo, P., D'Elia, V., Fiore, A., Flörs, A., Fraser, M., Frey, S., Frohmaier, C., Galbany, L., Gall, C., Gao, H., García-Rojas, J., Ghirlanda, G., Giarratana, S., Gillanders, J. H., Giroletti, M., Gompertz, B. P., Gromadzki, M., Heintz, K. E., Hu, Y. -D., Huber, M. E., Inkenhaag, A., Izzo, L., Jin, Z. P., Jonker, P. G., Kann, D. A., Kool, E. C., Kotak, R., Leloudas, G., Levan, A. J., Lin, C. -C., Lyman, J. D., Magnier, E. A., Maguire, K., Mandel, I., Marcote, B., Sánchez, D. Mata, Mattila, S., Melandri, A., Michałowski, M. J., Moldon, J., Nicholl, M., Guelbenzu, A. Nicuesa, Oates, S. R., Onori, F., Orienti, M., Paladino, R., Paragi, Z., Perez-Torres, M., Pian, E., Pignata, G., Piranomonte, S., Quirola-Vásquez, J., Ragosta, F., Rau, A., Ronchini, S., Rossi, A., Sánchez-Ramírez, R., Salafia, O. S., Schulze, S., Smartt, S. J., Smith, K. W., Sollerman, J., Srivastav, S., Starling, R. L. C., Steeghs, D., Stevance, H. F., Testa, V., Torres, M. A. P., Vergani, S. D., Vescovi, D., Wainscost, R., Watson, D., Wiersema, K., Wyrzykowski, Ł., Yang, J., Yang, S., and Young, D. R.
Subjects: Astrophysics - High Energy Astrophysical Phenomena, Astrophysics - Solar and Stellar Astrophysics
Abstract: We present the results from multi-wavelength observations of a transient discovered during the follow-up of S191213g, a gravitational wave (GW) event reported by the LIGO-Virgo Collaboration as a possible binary neutron star merger in a low latency search. This search yielded SN2019wxt, a young transient in a galaxy whose sky position (in the 80\% GW contour) and distance ($\sim$150\,Mpc) were plausibly compatible with the localisation uncertainty of the GW event. Initially, the transient's tightly constrained age, its relatively faint peak magnitude ($M_i \sim -16.7$\,mag) and the $r-$band decline rate of $\sim 1$\,mag per 5\,days appeared suggestive of a compact binary merger. However, SN2019wxt spectroscopically resembled a type Ib supernova, and analysis of the optical-near-infrared evolution rapidly led to the conclusion that while it could not be associated with S191213g, it nevertheless represented an extreme outcome of stellar evolution. By modelling the light curve, we estimated an ejecta mass of $\sim 0.1\,M_\odot$, with $^{56}$Ni comprising $\sim 20\%$ of this. We were broadly able to reproduce its spectral evolution with a composition dominated by helium and oxygen, with trace amounts of calcium. We considered various progenitors that could give rise to the observed properties of SN2019wxt, and concluded that an ultra-stripped origin in a binary system is the most likely explanation. Disentangling electromagnetic counterparts to GW events from transients such as SN2019wxt is challenging: in a bid to characterise the level of contamination, we estimated the rate of events with properties comparable to those of SN2019wxt and found that $\sim 1$ such event per week can occur within the typical GW localisation area of O4 alerts out to a luminosity distance of 500\,Mpc, beyond which it would become fainter than the typical depth of current electromagnetic follow-up campaigns., Comment: By the ENGRAVE collaboration (engrave-eso.org). 35 pages, 20 figures, final version accepted by A&A
Published: 2022
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11. Search for new cosmic-ray acceleration sites within the 4FGL catalog Galactic plane sources

Author: Collaboration, Fermi-LAT, Abdollahi, S., Acero, F., Ackermann, M., Baldini, L., Ballet, J., Barbiellini, G., Bastieri, D., Bellazzini, R., Berenji, B., Berretta, A., Bissaldi, E., Blandford, R. D., Bonino, R., Bruel, P., Buson, S., Cameron, R. A., Caputo, R., Caraveo, P. A., Castro, D., Chiaro, G., Cibrario, N., Ciprini, S., Coronado-Blázquez, J., Crnogorcevic, M., Cutini, S., D'Ammando, F., De Gaetano, S., Di Lalla, N., Dirirsa, F., Di Venere, L., Domínguez, A., Fegan, S. J., Fiori, A., Fleischhack, H., Franckowiak, A., Fukazawa, Y., Fusco, P., Gammaldi, V., Gargano, F., Gasparrini, D., Giacchino, F., Giglietto, N., Giordano, F., Giroletti, M., Glanzman, T., Green, D., Grenier, I. A., Grondin, M. -H., Guiriec, S., Gustafsson, M., Harding, A. K., Hays, E., Hewitt, J. W., Horan, D., Hou, X., Jóhannesson, G., Kayanoki, T., Kerr, M., Kuss, M., Larsson, S., Latronico, L., Lemoine-Goumard, M., Li, J., Longo, F., Loparco, F., Lubrano, P., Maldera, S., Malyshev, D., Manfreda, A., Martí-Devesa, G., Mazziotta, M. N., Mereu, I., Michelson, P. F., Mirabal, N., Mitthumsiri, W., Mizuno, T., Monzani, M. E., Morselli, A., Moskalenko, I. V., Nuss, E., Omodei, N., Orienti, M., Orlando, E., Ormes, J. F., Paneque, D., Pei, Z., Persic, M., Pesce-Rollins, M., Pillera, R., Poon, H., Porter, T. A., Principe, G., Rainò, S., Rando, R., Rani, B., Razzano, M., Razzaque, S., Reimer, A., Reimer, O., Reposeur, T., Sánchez-Conde, M., Parkinson, P. M. Saz, Scotton, L., Serini, D., Sgrò, C., Siskind, E. J., Spandre, G., Spinelli, P., Sueoka, K., Suson, D. J., Tajima, H., Tak, D., Thayer, J. B., Torres, D. F., Troja, E., Valverde, J., Wadiasingh, Z., Wood, K., and Zaharijas, G.
Subjects: Astrophysics - High Energy Astrophysical Phenomena
Abstract: Cosmic rays are mostly composed of protons accelerated to relativistic speeds. When those protons encounter interstellar material, they produce neutral pions which in turn decay into gamma rays. This offers a compelling way to identify the acceleration sites of protons. A characteristic hadronic spectrum, with a low-energy break around 200 MeV, was detected in the gamma-ray spectra of four Supernova Remnants (SNRs), IC 443, W44, W49B and W51C, with the Fermi Large Area Telescope. This detection provided direct evidence that cosmic-ray protons are (re-)accelerated in SNRs. Here, we present a comprehensive search for low-energy spectral breaks among 311 4FGL catalog sources located within 5 degrees from the Galactic plane. Using 8 years of data from the Fermi Large Area Telescope between 50 MeV and 1 GeV, we find and present the spectral characteristics of 56 sources with a spectral break confirmed by a thorough study of systematic uncertainty. Our population of sources includes 13 SNRs for which the proton-proton interaction is enhanced by the dense target material; the high-mass gamma-ray binary LS~I +61 303; the colliding wind binary eta Carinae; and the Cygnus star-forming region. This analysis better constrains the origin of the gamma-ray emission and enlarges our view to potential new cosmic-ray acceleration sites., Comment: Accepted for publication in The Astrophysical Journal
Published: 2022
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12. A Gamma-ray Pulsar Timing Array Constrains the Nanohertz Gravitational Wave Background

Author: Ajello, M., Atwood, W. B., Baldini, L., Ballet, J., Barbiellini, G., Bastieri, D., Bellazzini, R., Berretta, A., Bhattacharyya, B., Bissaldi, E., Blandford, R. D., Bloom, E., Bonino, R., Bruel, P., Buehler, R., Burns, E., Buson, S., Cameron, R. A., Caraveo, P. A., Cavazzuti, E., Cibrario, N., Ciprini, S., Clark, C. J., Cognard, I., Coronado-Blázquez, J., Crnogorcevic, M., Cromartie, H., Crowter, K., Cutini, S., D'Ammando, F., Gaetano, S. D., Palma, F. d., Digel, S. W., Lalla, N. D., Dirirsa, F. Fan., Venere, L. D., Domínguez, A., Ferrara, E. C., Fiori, A., Franckowiak, A., Fukazawa, Y., Funk, S., Fusco, P., Gammaldi, V., Gargano, F., Gasparrini, D., Giglietto, N., Giordano, F., Giroletti, M., Green, D., Grenier, I. A., Guillemot, L., Guiriec, S., Gustafsson, M., Harding, A. K., Hays, E., Hewitt, J. W., Horan, D., Hou, X., Jóhannesson, G., Keith, M. J., Kerr, M., Kramer, M., Kuss, M., Larsson, S., Latronico, L., Li, J., Longo, F., Loparco, F., Lovellette, M. N., Lubrano, P., Maldera, S., Manfreda, A., Martí-Devesa, G., Mazziotta, M. N., Mereu, I., Michelson, P. F., Mirabal, N., Mitthumsiri, W., Mizuno, T., Monzani, M. E., Morselli, A., Negro, M., Nieder, L., Ojha, R., Omodei, N., Orienti, M., Orlando, E., Ormes, J. F., Paneque, D., Parthasarathy, A., Pei, Z., Persic, M., Pesce-Rollins, M., Pillera, R., Poon, H., Porter, T. A., Principe, G., Racusin, J. L., Rainò, S., Rando, R., Rani, B., Ransom, S. M., Ray, P. S., Razzano, M., Razzaque, S., Reimer, A., Reimer, O., Roy, J., Sánchez-Conde, M., Parkinson, P. M. Sa., Scargle, J., Scotton, L., Serini, D., Sgrò, C., Siskind, E. J., Smith, D. A., Spandre, G., Spiewak, R., Spinelli, P., Stairs, I., Suson, D. J., Swihart, S. J., Tabassum, S., Thayer, J. B., Theureau, G., Torres, D. F., Troja, E., Valverde, J., Wadiasingh, Z., Wood, K., and Zaharijas, G.
Subjects: Astrophysics - High Energy Astrophysical Phenomena
Abstract: After large galaxies merge, their central supermassive black holes are expected to form binary systems whose orbital motion generates a gravitational wave background (GWB) at nanohertz frequencies. Searches for this background utilize pulsar timing arrays, which perform long-term monitoring of millisecond pulsars (MSPs) at radio wavelengths. We use 12.5 years of Fermi Large Area Telescope data to form a gamma-ray pulsar timing array. Results from 35 bright gamma-ray pulsars place a 95\% credible limit on the GWB characteristic strain of $1.0\times10^{-14}$ at 1 yr$^{-1}$, which scales as the observing time span $t_{\mathrm{obs}}^{-13/6}$. This direct measurement provides an independent probe of the GWB while offering a check on radio noise models., Comment: 3 figures in the main text. 3 figures and 8 tables are in the supplementary material
Published: 2022
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13. RadioAstron discovery of a mini-cocoon around the restarted parsec-scale jet in 3C 84

Author: Savolainen, T., Giovannini, G., Kovalev, Y. Y., Perucho, M., Anderson, J. M., Bruni, G., Edwards, P. G., Fuentes, A., Giroletti, M., Gómez, J. L., Hada, K., Lee, S. S., Lisakov, M. M., Lobanov, A. P., López-Miralles, J., Orienti, M., Petrov, L., Plavin, A. V., Sohn, B. W., Sokolovsky, K. V., Voitsik, P. A., and Zensus, J. A.
Subjects: Astrophysics - High Energy Astrophysical Phenomena
Abstract: We present RadioAstron space-based very long baseline interferometry (VLBI) observations of the nearby radio galaxy 3C84 (NGC1275) at the centre of the Perseus cluster. The observations were carried out on September 21-22, 2013 and involved a global array of 24 ground radio telescopes observing at 5 GHz and 22 GHz, together with the Space Radio Telescope (SRT). Furthermore, the Very Long Baseline Array (VLBA) and the phased Very Large Array (VLA) observed the source quasi-simultaneously at 15 GHz and 43 GHz. Fringes between the ground array and the SRT were detected on baseline lengths up to 8.1 times the Earth's diameter, providing unprecedented resolution for 3C 84 at these wavelengths. We note that the corresponding fringe spacing is 125 microarcsec at 5 GHz and 27 microarcsec at 22 GHz. Our space-VLBI images reveal a previously unseen sub-structure inside the compact 1 pc long jet that was ejected about ten years earlier. In the 5 GHz image, we detected, for the first time, low-intensity emission from a cocoon-like structure around the restarted jet. Our results suggest that the increased power of the young jet is inflating a bubble of hot plasma as it carves its way through the ambient medium of the central region of the galaxy. Here, we estimate the minimum energy stored in the mini-cocoon, along with its pressure, volume, expansion speed, and the ratio of heavy particles to relativistic electrons, as well as the density of the ambient medium. About half of the energy delivered by the jet is dumped into the mini-cocoon and the quasi-spherical shape of the bubble suggests that this energy may be transferred to a significantly larger volume of the interstellar medium than what would be accomplished by the well-collimated jet on its own. The pressure of the hot mini-cocoon also provides a natural explanation for the almost cylindrical jet profile seen in the 22 GHz RadioAstron image., Comment: To be published in Astronomy & Astrophysics
Published: 2021
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14. First detection of VHE gamma-ray emission from TXS~1515--273, study of its X-ray variability and spectral energy distribution

Author: MAGIC Collaboration, Acciari, V. A., Ansoldi, S., Antonelli, L. A., Engels, A. Arbet, Artero, M., Asano, K., Baack, D., Babić, A., Baquero, A., de Almeida, U. Barres, Barrio, J. A., Batković, I., González, J. Becerra, Bednarek, W., Bellizzi, L., Bernardini, E., Bernardos, M., Berti, A., Besenrieder, J., Bhattacharyya, W., Bigongiari, C., Biland, A., Blanch, O., Bošnjak, Ž., Busetto, G., Carosi, R., Ceribella, G., Cerruti, M., Chai, Y., Chilingarian, A., Cikota, S., Colak, S. M., Colombo, E., Contreras, J. L., Cortina, J., Covino, S., D'Amico, G., D'Elia, V., Da Vela, P., Dazzi, F., De Angelis1, A., De Lotto, B., Delfino, M., Delgado, J., Mendez, C. Delgado, Depaoli, D., Di Pierro, F., Di Venere, L., Espiñeira, E. Do Souto, Prester, D. Dominis, Donini, A., Dorner, D., Doro, M., Elsaesser, D., Ramazani, V. Fallah, Fattorini, A., Ferrara, G., Fonseca, M. V., Font, L., Fruck, C., Fukami, S., López, R. J. García, Garczarczyk, M., Gasparyan, S., Gaug, M., Giglietto, N., Giordano, F., Gliwny, P., Godinović, N., Green, J. G., Green, D., Hadasch, D., Hahn, A., Heckmann, L., Herrera, J., Hoang, J., Hrupec, D., Hütten, M., Inada, T., Inoue, S., Ishio, K., Iwamura, Y., Jiménez, I., Jormanainen, J., Jouvin, L., Kajiwara, Y., Karjalainen, M., Kerszberg, D., Kobayashi, Y., Kubo, H., Kushida, J., Lamastra, A., Lelas, D., Leone, F., Lindfors, E., Lombardi, S., Longo, F., López-Coto, R., López-Moya, M., López-Oramas, A., Loporchio, S., Fraga, B. Machado de Oliveira, Maggio, C., Majumdar, P., Makariev, M., Mallamaci, M., Maneva, G., Manganaro, M., Mannheim, K., Maraschi, L., Mariotti, M., Martínez, M., Mazin, D., Menchiari, S., Mender, S., Mićanović, S., Miceli, D., Miener, T., Minev, M., Miranda, J. M., Mirzoyan, R., Molina, E., Moralejo, A., Morcuende, D., Moreno, V., Moretti, E., Neustroev, V., Nigro, C., Nilsson, K., Nishijima, K., Noda, K., Nozaki, S., Ohtani, Y., Oka, T., Otero-Santos, J., Paiano, S., Palatiello, M., Paneque, D., Paoletti, R., Paredes, J. M., Pavletić, L., Peñi, P., Perennes, C., Persic, M., Moroni, P. G. Prada, Prandini, E., Priyadarshi, C., Puljak, I., Rhode, W., Ribó, M., Rico, J., Righi, C., Rugliancich, A., Saha, L., Sahakyan, N., Saito, T., Sakurai, S., Satalecka, K., Saturni, F. G., Schleicher, B., Schmidt, K., Schweizer, T., Sitarek, J., Šnidarić, I., Sobczynska, D., Spolon, A., Stamerra, A., Strom, D., Strzys, M., Suda, Y., Surić, T., Takahashi, M., Tavecchio, F., Temnikov, P., Terzić, T., Teshima, M., Tosti, L., Truzzi, S., Tutone, A., Ubach, S., van Scherpenberg, J., Vanzo, G., Acosta, M. Vazquez, Ventura, S., Verguilov, V., Vigorito, C. F., Vitale, V., Vovk, I., Will, M., Wunderlich, C., Zaric, D., Bissaldi, E., Bonnoli, G., Cutini, S., D'Ammando, F., Nabizadeh, A., Marchini, A., and Orienti, M.
Subjects: Astrophysics - High Energy Astrophysical Phenomena
Abstract: We report here on the first multi-wavelength (MWL) campaign on the blazar TXS 1515-273, undertaken in 2019 and extending from radio to very-high-energy gamma rays (VHE). Up until now, this blazar had not been the subject of any detailed MWL observations. It has a rather hard photon index at GeV energies and was considered a candidate extreme high-synchrotronpeaked source. MAGIC observations resulted in the first-time detection of the source in VHE with a statistical significance of 7.6$\sigma$. The average integral VHE flux of the source is 6 $\pm$ 1% of the Crab nebula flux above 400 GeV. X-ray coverage was provided by Swift-XRT, XMMNewton, and NuSTAR. The long continuous X-ray observations were separated by $\sim$ 9 h, both showing clear hour scale flares. In the XMM-Newton data, both the rise and decay timescales are longer in the soft X-ray than in the hard X-ray band, indicating the presence of a particle cooling regime. The X-ray variability timescales were used to constrain the size of the emission region and the strength of the magnetic field. The data allowed us to determine the synchrotron peak frequency and classify the source as a flaring high, but not extreme, synchrotron peaked object. Considering the constraints and variability patterns from the X-ray data, we model the broad-band spectral energy distribution. We applied a simple one-zone model, which could not reproduce the radio emission and the shape of the optical emission, and a two-component leptonic model with two interacting components, enabling us to reproduce the emission from radio to VHE band.
Published: 2021
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15. Fermi Large Area Telescope Performance After 10 Years Of Operation

Author: The Fermi LAT Collaboration, Ajello, M., Atwood, W. B., Axelsson, M., Bagagli, R., Bagni, M., Baldini, L., Bastieri, D., Bellardi, F., Bellazzini, R., Bissaldi, E., Bloom, E. D., Bonino, R., Bregeon, J., Brez, A., Bruel, P., Buehler, R., Buson, S., Cameron, R. A., Caraveo, P. A., Cavazzuti, E., Ceccanti, M., Chen, S., Cheung, C. C., Ciprini, S., Cognard, I., Cohen-Tanugi, J., Cutini, S., D'Ammando, F., Luque, P. de la Torre, de Palma, F., Digel, S. W., Dirirsa, F., Di Lalla, N., Di Venere, L., Domínguez, A., Fabiani, D., Ferrara, E. C., Fiori, A., Foglia, G., Fukazawa, Y., Fusco, P., Gargano, F., Gasparrini, D., Giroletti, M., Glanzman, T., Green, D., Griffin, S., Grondin, M. -H., Grove, J. E., Guillemot, L., Guiriec, S., Gustafsson, M., Hays, E., Horan, D., Jóhannesson, G., Johnson, T. J., Kamae, T., Kerr, M., Kuss, M., Larsson, S., Latronico, L., Lemoine-Goumard, M., Li, J., Liodakis, I., Longo, F., Loparco, F., Lovellette, M. N., Lubrano, P., Maldera, S., Manfreda, A., Martí-Devesa, G., Mazziotta, M. N., Menon, N., Mereu, I., Meyer, M., Michelson, P. F., Minuti, M., Mitthumsiri, W., Mizuno, T., Mongelli, M., Monzani, M. E., Moskalenko, I. V., Negro, M., Nuss, E., Ojha, R., Orienti, M., Orlando, E., Paccagnella, A., Paliya, V. S., Paneque, D., Pei, Z., Perkins, J. S., Pesce-Rollins, M., Pinchera, M., Piron, F., Poon, H., Porter, T. A., Primavera, R., Principe, G., Racusin, J. L., Rainò, S., Rando, R., Rani, B., Rapposelli, E., Razzano, M., Razzaque, S., Reimer, A., Reimer, O., Russell, J. J., Saggini, N., Parkinson, P. M. Saz, Scolieri, N., Serini, D., Sgrò, C., Siskind, E. J., Smith, D. A., Spandre, G., Spinelli, P., Suson, D. J., Tajima, H., Thayer, J. G., Thompson, D. J., Tibaldo, L., Torres, D. F., Tosti, G., Valverde, J., Vigiani, L., and Zaharijas, G.
Subjects: Astrophysics - Instrumentation and Methods for Astrophysics
Abstract: The Large Area Telescope (LAT), the primary instrument for the Fermi Gamma-ray Space Telescope (Fermi) mission, is an imaging, wide field-of-view, high-energy gamma-ray telescope, covering the energy range from 30 MeV to more than 300 GeV. We describe the performance of the instrument at the 10-year milestone. LAT performance remains well within the specifications defined during the planning phase, validating the design choices and supporting the compelling case to extend the duration of the Fermi mission. The details provided here will be useful when designing the next generation of high-energy gamma-ray observatories., Comment: 60 pages, 28 figures. Published in ApJS
Published: 2021
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16. Multi-wavelength view of the close-by GRB 190829A sheds light on gamma-ray burst physics

Author: Salafia, O. S., Ravasio, M. E., Yang, J., An, T., Orienti, M., Ghirlanda, G., Nava, L., Giroletti, M., Mohan, P., Spinelli, R., Zhang, Y., Marcote, B., Cimò, G., Wu, X., and Li, Z.
Subjects: Astrophysics - High Energy Astrophysical Phenomena
Abstract: Gamma-ray bursts are produced as a result of cataclysmic events such as the collapse of a massive star or the merger of two neutron stars. We monitored the position of the close-by gamma-ray burst GRB~190829A, which originated from a massive star collapse, through very long baseline interferometry (VLBI) observations with the EVN and the VLBA, involving a total of 30 telescopes across 4 continents. We carried out a total of 9 observations between 9 and 117 days after the gamma-ray burst at 5 and 15 GHz, with a typical resolution of few milliarcseconds (mas). We obtained limits on the source size and expansion rate. The limits are in agreement with the size evolution entailed by a detailed modelling of the multi-wavelength light curves with a forward plus reverse shock model, which agrees with the observations across almost 18 orders of magnitude in frequency (including the High Energy Stereoscopic System data at TeV photon energies) and more than 4 orders of magnitude in time. Thanks to the broad, high-cadence coverage of the afterglow, afterglow degeneracies are broken to a large extent, allowing us to capture some unique physical insights: we find a low prompt emission efficiency $\lesssim 10^{-3}$; we constrain the fraction of electrons that are accelerated to relativistic speeds in the forward shock to be $\chi_e<13\%$ at the 90\% credible level; we find that the magnetic field energy density in the reverse shock downstream must decay rapidly after the shock crossing. While our model assumes an on-axis jet, our VLBI astrometric measurements alone are not sufficiently tight as to exclude any off-axis viewing angle. On the other hand, we can firmly exclude the line of sight to have been more than $2\,\mathrm{deg}$ away from the border of the region that produced the prompt gamma-ray emission based on compactness arguments., Comment: 35 pages, 30 figures, submitted to ApJL. Supplementay materials at http://doi.org/10.5281/zenodo.6412088
Published: 2021
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17. Probing extreme environments with the Cherenkov Telescope Array

Author: Boisson, C., Brown, A. M., Burtovoi, A., Cerruti, M., Chernyakova, M., Hassan, T., Lenain, J. -P., Manganaro, M., Romano, P., Sol, H., Tavecchio, F., Vercellone, S., Zampieri, L., Zanin, R., Zech, A., Agudo, I., Batista, R. Alves, Anguner, E. O., Antonelli, L. A., Backes, M., Balazs, C., González, J. Becerra, Bigongiari, C., Bissaldi, E., Bolmont, J., Bordas, P., Bošnjak, Ž., Böttcher, M., Burton, M., Cangemi, F., Caraveo, P., Cardillo, M., Caroff, S., Carosi, A., Casanova, S., Chaty, S., Contreras, J. L., Coelho, J. G., Cotter, G., D'Aì, A., D'Ammando, F., Pino, E. M. de Gouveia Dal, de Martino, D., Delgado, C., della Volpe, D., Djannati-Ataï, A., Anjos, R. C. Dos, Wilhelmi, E. de Oña, Dwarkadas, V., Emery, G., Fedorova, E., Fegan, S., Filipovic, M. D., Galanti, G., Gasparrini, D., Ghirlanda, G., Goldoni, P., Granot, J., Green, J. G., Heller, M., Hnatyk, B., Hnatyk, R., Horan, D., Hovatta, T., Inoue, S., Jamrozy, M., Khélifi, B., Komin, N., Kohri, K., Lamastra, A., La Palombara, N., Lindfors, E., Liodakis, I., Lombardi, S., Longo, F., Lucarelli, F., Luque-Escamilla, P. L., Marti, J., Martinez, M., Mazin, D., Mbarubucyeye, J. D., Menchiari, S., Mohrmann, L., Montaruli, T., Olaizola, A. Moralejo, Morcuende, D., Morlino, G., Morselli, A., Mundell, C. G., Murach, T., Nagai, A., Nayerhoda, A., Niemiec, J., Nikolajuk, M., Olmi, B., Orienti, M., Paredes, J. M., Pareschi, G., Pe'er, A., Pühlhofer, G., Punch, M., Reimer, O., Ribó, M., Rieger, F., Rodriguez, G., Rodriguez, J., Romeo, G., Roncadelli, M., Rowell, G., Rudak, B., Sadeh, I., Greus, F. Salesa, Sawangwit, U., Schüssler, F., Sergijenko, O., Shellard, R. C., Saturni, F. G., Stamerra, A., Stolarczyk, Th., Tagliaferri, G., Testa, V., Tibaldo, L., Ventura, S., Viana, A., Vink, J., Vitale, V., Vorobiov, S., Wierzcholska, A., Zacharias, M., and Zavrtanik, D.
Subjects: Astrophysics - Instrumentation and Methods for Astrophysics, Astrophysics - High Energy Astrophysical Phenomena
Abstract: The physics of the non-thermal Universe provides information on the acceleration mechanisms in extreme environments, such as black holes and relativistic jets, neutron stars, supernovae or clusters of galaxies. In the presence of magnetic fields, particles can be accelerated towards relativistic energies. As a consequence, radiation along the entire electromagnetic spectrum can be observed, and extreme environments are also the most likely sources of multi-messenger emission. The most energetic part of the electromagnetic spectrum corresponds to the very-high-energy (VHE, E>100 GeV) gamma-ray regime, which can be extensively studied with ground based Imaging Atmospheric Cherenkov Telescopes (IACTs). The results obtained by the current generation of IACTs, such as H.E.S.S., MAGIC, and VERITAS, demonstrate the crucial importance of the VHE band in understanding the non-thermal emission of extreme environments in our Universe. In some objects, the energy output in gamma rays can even outshine the rest of the broadband spectrum. The Cherenkov Telescope Array (CTA) is the next generation of IACTs, which, with cutting edge technology and a strategic configuration of ~100 telescopes distributed in two observing sites, in the northern and southern hemispheres, will reach better sensitivity, angular and energy resolution, and broader energy coverage than currently operational IACTs. With CTA we can probe the most extreme environments and considerably boost our knowledge of the non-thermal Universe., Comment: Submitted as input to ASTRONET Science Vision and Infrastructure roadmap on behalf of the CTA consortium
Published: 2021

18. Multi-messenger and transient astrophysics with the Cherenkov Telescope Array

Author: Bošnjak, Ž., Brown, A. M., Carosi, A., Chernyakova, M., Cristofari, P., Longo, F., López-Oramas, A., Santander, M., Satalecka, K., Schüssler, F., Sergijenko, O., Stamerra, A., Agudo, I., Batista, R. Alves, Amato, E., Anguner, E. O., Antonelli, L. A., Backes, M., Balazs, Csaba, Baroncelli, L., Tjus, J. Becker, Bigongiari, C., Bissaldi, E., Boisson, C., Bolmont, J., Böttcher, M., Bordas, P., Braiding, C., Bregeon, J., Bucciantini, N., Bulgarelli, A., Burton, M., Cangemi, F., Caraveo, P., Cardillo, M., Caroff, S., Casanova, S., Chaty, S., Coelho, J. G., Cotter, G., D'Aì, A., D'Ammando, F., Pino, E. M. de Gouveia Dal, della Volpe, D., de Martino, D., Di Girolamo, T., Di Piano, A., Djannati-Ataï, A., Dwarkadas, V., Wilhelmi, E. de Ona, Anjos, R. C. Dos, Emery, G., Fedorova, E., Fegan, S., Fiasson, A., Fioretti, V., Filipovic, M. D., Gaggero, D., Galanti, G., Gasparrini, D., Ghirlanda, G., Goldoni, P., Granot, J., Green, J. G., Heller, M., Hnatyk, B., Hnatyk, R., Horan, D., Hovatta, T., Inoue, S., Jamrozy, M., Kantzas, D., Khélifi, B., Komin, N., Lamastra, A., La Palombara, N., Lenain, J. P., Lindfors, E., Liodakis, I., Lombardi, S., Lucarelli, F., Luque-Escamilla, P. L., Majumdar, P., Marcowith, A., Markoff, S., Marti, J., Martinez, M., Mazin, D., McKeague, S., Mereghetti, S., Mestre, E., Montaruli, T., Morlino, G., Morselli, A., Mundell, C., Murach, T., Nava, L., Nayerhoda, A., Nicastro, L., Niemiec, J., Nikolajuk, M., Olmi, B., Ong, R., Orienti, M., Osborne, J. P., Paredes, Josep M., Pareschi, G., Parmiggiani, N., Patricelli, B., Pe'er, A., Piano, G., Pühlhofer, G., Punch, M., Reimer, O., Ribó, M., Rodriguez, G., Rodriguez, J., Romano, P., Romeo, G., Roncadelli, M., Rowell, G., Rudak, B., Sadeh, I., Greus, F. Salesa, Saturni, F. G., Sawangwit, U., Seglar-Arroyo, M., Shellard, R. C., Sol, H., Starling, R., Stolarczyk, T., Tagliaferri, G., Tavecchio, F., Tibaldo, L., Testa, V., Vercellone, S., Viana, A., Vink, J., Vitale, V., Vergani, S. D., Vorobiov, S., Wierzcholska, A., Yang, L., Zavrtanik, D., and Zhdanov, V.
Subjects: Astrophysics - High Energy Astrophysical Phenomena
Abstract: The discovery of gravitational waves, high-energy neutrinos or the very-high-energy counterpart of gamma-ray bursts has revolutionized the high-energy and transient astrophysics community. The development of new instruments and analysis techniques will allow the discovery and/or follow-up of new transient sources. We describe the prospects for the Cherenkov Telescope Array (CTA), the next-generation ground-based gamma-ray observatory, for multi-messenger and transient astrophysics in the decade ahead. CTA will explore the most extreme environments via very-high-energy observations of compact objects, stellar collapse events, mergers and cosmic-ray accelerators., Comment: Submitted to ASTRONET roadmap on behalf of the CTA consortium
Published: 2021

19. Catalog of Long-Term Transient Sources in the First 10 Years of Fermi-LAT Data

Author: Baldini, L., Ballet, J., Bastieri, D., Gonzalez, J. Becerra, Bellazzini, R., Berretta, A., Bissaldi, E., Blandford, R. D., Bloom, E. D., Bonino, R., Bottacini, E., Bruel, P., Buson, S., Cameron, R. A., Caraveo, P. A., Cavazzuti, E., Chen, S., Chiaro, G., Ciangottini, D., Ciprini, S., Orestano, P. Cristarella, Crnogorcevic, M., Cutini, S., D'Ammando, F., Luque, P. de la Torre, de Palma, F., Digel, S. W., Di Lalla, N., Dirirsa, F., Di Venere, L., Domínguez, A., Fiori, A., Fleischhack, H., Franckowiak, A., Fukazawa, Y., Funk, S., Fusco, P., Gargano, F., Gasparrini, D., Germani, S., Giglietto, N., Giordano, F., Giroletti, M., Green, D., Grenier, I. A., Griffin, S., Guiriec, S., Gustafsson, M., Hewitt, J. W., Horan, D., Imazawa, R., Jóhannesson, G., Kerr, M., Kocevski, D., Kuss, M., Larsson, S., Latronico, L., Li, J., Liodakis, I., Longo, F., Loparco, F., Lovellette, M. N., Lubrano, P., Maldera, S., Manfreda, A., Martí-Devesa, G., Matake, H., Mazziotta, M. N., Mereu, I., Meyer, M., Mirabal, N., Mitthumsiri, W., Mizuno, T., Monzani, M. E., Morselli, A., Moskalenko, I. V., Nagasawa, S., Negro, M., Ojha, R., Orienti, M., Orlando, E., Palatiello, M., Paliya, V., Paneque, D., Pei, Z., Persic, M., Pesce-Rollins, M., Petrosian, V., Poon, H., Porter, T. A., Principe, G., Racusin, J. L., Rainò, S., Rando, R., Rani, B., Razzano, M., Razzaque, S., Reimer, A., Reimer, O., Parkinson, P. M. Saz, Scotton, L., Serini, D., Sgrò, C., Siskind, E. J., Spandre, G., Spinelli, P., Suson, D. J., Tajima, H., Tak, D., Torres, D. F., Tosti, G., Troja, E., Wood, K., Yassine, M., and Zaharijas, G.
Subjects: Astrophysics - High Energy Astrophysical Phenomena
Abstract: We present the first Fermi Large Area Telescope (LAT) catalog of long-term $\gamma$-ray transient sources (1FLT). This comprises sources that were detected on monthly time intervals during the first decade of Fermi-LAT operations. The monthly time scale allows us to identify transient and variable sources that were not yet reported in other Fermi-LAT catalogs. The monthly datasets were analyzed using a wavelet-based source detection algorithm that provided the candidate new transient sources. The search was limited to the extragalactic regions of the sky to avoid the dominance of the Galactic diffuse emission at low Galactic latitudes. The transient candidates were then analyzed using the standard Fermi-LAT Maximum Likelihood analysis method. All sources detected with a statistical significance above 4$\sigma$ in at least one monthly bin were listed in the final catalog. The 1FLT catalog contains 142 transient $\gamma$-ray sources that are not included in the 4FGL-DR2 catalog. Many of these sources (102) have been confidently associated with Active Galactic Nuclei (AGN): 24 are associated with Flat Spectrum Radio Quasars; 1 with a BL Lac object; 70 with Blazars of Uncertain Type; 3 with Radio Galaxies; 1 with a Compact Steep Spectrum radio source; 1 with a Steep Spectrum Radio Quasar; 2 with AGN of other types. The remaining 40 sources have no candidate counterparts at other wavelengths. The median $\gamma$-ray spectral index of the 1FLT-AGN sources is softer than that reported in the latest Fermi-LAT AGN general catalog. This result is consistent with the hypothesis that detection of the softest $\gamma$-ray emitters is less efficient when the data are integrated over year-long intervals., Comment: 41 pages, 17 figures, 7 tables; Accepted by ApJS on 24 May 2021; Contact Authors: I. Mereu, S. Cutini, E. Cavazzuti, G. Tosti
Published: 2021
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20. VLBI images at 327 MHz of compact steep spectrum and GHz-peaked spectrum sources from the 3C and PW samples

Author: Dallacasa, D., Orienti, M., Fanti, C., and Fanti, R.
Subjects: Astrophysics - Astrophysics of Galaxies
Abstract: We present results on global very long baseline interferometry (VLBI) observations at 327 MHz of eighteen compact steep-spectrum (CSS) and GHz-peaked spectrum (GPS) radio sources from the 3C and the Peacock & Wall catalogues. About 80 per cent of the sources have a 'double/triple' structure. The radio emission at 327 MHz is dominated by steep-spectrum extended structures, while compact regions become predominant at higher frequencies. As a consequence, we could unambiguously detect the core region only in three sources, likely due to self-absorption affecting its emission at this low frequency. Despite their low surface brightness, lobes store the majority of the source energy budget, whose correct estimate is a key ingredient in tackling the radio source evolution. Low-frequency VLBI observations able to disentangle the lobe emission from that of other regions are therefore the best way to infer the energetics of these objects. Dynamical ages estimated from energy budget arguments provide values between 2x10^3 and 5x10^4 yr, in agreement with the radiative ages estimated from the fit of the integrated synchrotron spectrum, further supporting the youth of these objects. A discrepancy between radiative and dynamical ages is observed in a few sources where the integrated spectrum is dominated by hotspots. In this case the radiative age likely represents the time spent by the particles in these regions, rather than the source age., Comment: 14 pages, 21 figures, and 5 tables. Accepted for publication in Monthly Notices of the Royal Astronomical Society
Published: 2021
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21. Multi-wavelength flare observations of the blazar S5 1803+784

Author: Nesci, R., Cutini, S., Stanghellini, C., Martinelli, F., Maselli, A., Lipunov, V. M., Kornilov, V., Lopez, R. R., Siviero, A., Giroletti, M., and Orienti, M.
Subjects: Astrophysics - High Energy Astrophysical Phenomena
Abstract: The radio, optical, and $\gamma$-ray light curves of the blazar S5 1803+784, from the beginning of the {\it Fermi} Large Area Telescope (LAT) mission in August 2008 until December 2018, are presented. The aim of this work is to look for correlations among different wavelengths useful for further theoretical studies. We analyzed all the data collected by {\it Fermi} LAT for this source, taking into account the presence of nearby sources, and we collected optical data from our own observations and public archive data to build the most complete optical and $\gamma$-ray light curve possible. Several $\gamma$-ray flares ($\mathrm{F>2.3~10^{-7} ph(E>0.1 GeV)~cm^{-2}~s^{-1}}$) with optical coverage were detected, all but one with corresponding optical enhancement; we also found two optical flares without a $\gamma$-ray counterpart. We obtained two {\it Swift} Target of Opportunity observations during the strong flare of 2015. Radio observations performed with VLBA and EVN through our proposals in the years 2016-2020 were analyzed to search for morphological changes after the major flares. The optical/$\gamma$-ray flux ratio at the flare peak varied for each flare. Very minor optical V-I color changes were detected during the flares. The X-ray spectrum was well fitted by a power law with photon spectral index $\alpha$=1.5, nearly independent of the flux level: no clear correlation with the optical or the $\gamma$-ray emission was found. The $\gamma$-ray spectral shape was well fitted by a power law with average photon index $\alpha$= 2.2. These findings support an Inverse Compton origin for the high-energy emission of the source, nearly co-spatial with the optically emitting region. The radio maps showed two new components originating from the core and moving outwards, with ejection epochs compatible with the dates of the two largest $\gamma$-ray flares., Comment: Twelve pages, 12 figures, accepted for MNRAS
Published: 2021
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22. The First Fermi-LAT Solar Flare Catalog

Author: Ajello, M., Baldini, L., Bastieri, D., Bellazzini, R., Berretta, A., Bissaldi, E., Blandford, R. D., Bonino, R., Bruel, P., Buson, S., Cameron, R. A., Caputo, R., Cavazzuti, E., Cheung, C. C., Chiaro, G., Costantin, D., Cutini, S., D'Ammando, F., de Palma, F., Desiante, R., Di Lalla, N., Di Venere, L., Dirirsa, F. Fana, Fegan, S. J., Fukazawa, Y., Funk, S., Fusco, P., Gargano, F., Gasparrini, D., Giordano, F., Giroletti, M., Green, D., Guiriec, S., Hays, E., Hewitt, J. W., Horan, D., Johannesson, G., Kovacevic, M., Kuss, M., Larsson, S., Latronico, L., Li, J., Longo, F., Lovellette, M. N., Lubrano, P., Maldera, S., Manfreda, A., Marti-Devesa, G., Mazziotta, M. N., Mereu, I., Michelson, P. F., Mizuno, T., Monzani, M. E., Morselli, A., Moskalenko, I. V., Negro, M., Omodei, N., Orienti, M., Orlando, E., Paneque, D., Pei, Z., Persic, M., Pesce-Rollins, M., Petrosian, V., Piron, F., Porter, T. A., Principe, G., Racusin, J. L., Raino, S., Rando, R., Rani, B., Razzano, M., Razzaque, S., Reimer, A., Reimer, O., Serini, D., Sgro, C., Siskind, E. J., Spandre, G., Spinelli, P., Tak, D., Troja, E., Valverde, J., Wood, K., and Zaharijas, G.
Subjects: Astrophysics - High Energy Astrophysical Phenomena, Astrophysics - Solar and Stellar Astrophysics
Abstract: We present the first Fermi - Large Area Telescope (LAT) solar flare catalog covering the 24 th solar cycle. This catalog contains 45 Fermi -LAT solar flares (FLSFs) with emission in the gamma-ray energy band (30 MeV - 10 GeV) detected with a significance greater than 5 sigma over the years 2010-2018. A subsample containing 37 of these flares exhibit delayed emission beyond the prompt-impulsive hard X-ray phase with 21 flares showing delayed emission lasting more than two hours. No prompt-impulsive emission is detected in four of these flares. We also present in this catalog the observations of GeV emission from 3 flares originating from Active Regions located behind the limb (BTL) of the visible solar disk. We report the light curves, spectra, best proton index and localization (when possible) for all the FLSFs. The gamma-ray spectra is consistent with the decay of pions produced by >300 MeV protons. This work contains the largest sample of high-energy gamma-ray flares ever reported and provides the unique opportunity to perform population studies on the different phases of the flare and thus allowing to open a new window in solar physics., Comment: Published in ApJS
Published: 2021
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23. VHE gamma-ray detection of FSRQ QSO B1420+326 and modeling of its enhanced broadband state in 2020

Author: Acciari, V. A., Ansoldi, S., Antonelli, L. A., Engels, A. Arbet, Artero, M., Asano, K., Baack, D., Babić, A., Baquero, A., de Almeida, U. Barres, Barrio, J. A., González, J. Becerra, Bednarek, W., Bellizzi, L., Bernardini, E., Bernardos, M., Berti, A., Besenrieder, J., Bhattacharyya, W., Bigongiari, C., Biland, A., Blanch, O., Bonnoli, G., Bošnjak, Ž., Busetto, G., Carosi, R., Ceribella, G., Cerruti, M., Chai, Y., Chilingarian, A., Cikota, S., Colak, S. M., Colombo, E., Contreras, J. L., Cortina, J., Covino, S., D'Amico, G., D'Elia, V., Da Vela, P., Dazzi, F., De Angelis, A., De Lotto, B., Delfino, M., Delgado, J., Mendez, C. Delgado, Depaoli, D., Di Pierro, F., Di Venere, L., Espiñeira, E. Do Souto, Prester, D. Dominis, Donini, A., Dorner, D., Doro, M., Elsaesser, D., Ramazani, V. Fallah, Fattorini, A., Ferrara, G., Foffano, L., Fonseca, M. V., Font, L., Fruck, C., Fukami, S., López, R. J. García, Garczarczyk, M., Gasparyan, S., Gaug, M., Giglietto, N., Giordano, F., Gliwny, P., Godinović, N., Green, J. G., Green, D., Hadasch, D., Hahn, A., Heckmann, L., Herrera, J., Hoang, J., Hrupec, D., Hütten, M., Inada, T., Inoue, S., Ishio, K., Iwamura, Y., Jormanainen, J., Jouvin, L., Kajiwara, Y., Karjalainen, M., Kerszberg, D., Kobayashi, Y., Kubo, H., Kushida, J., Lamastra, A., Lelas, D., Leone, F., Lindfors, E., Lombardi, S., Longo, F., López-Coto, R., López-Moya, M., López-Oramas, A., Loporchio, S., Fraga, B. Machado de Oliveira, Maggio, C., Majumdar, P., Makariev, M., Mallamaci, M., Maneva, G., Manganaro, M., Mannheim, K., Maraschi, L., Mariotti, M., Martínez, M., Mazin, D., Mender, S., Mićanović, S., Miceli, D., Miener, T., Minev, M., Miranda, J. M., Mirzoyan, R., Molina, E., Moralejo, A., Morcuende, D., Moreno, V., Moretti, E., Neustroev, V., Nigro, C., Nilsson, K., Ninci, D., Nishijima, K., Noda, K., Nozaki, S., Ohtani, Y., Oka, T., Otero-Santos, J., Paiano, S., Palatiello, M., Paneque, D., Paoletti, R., Paredes, J. M., Pavletić, L., Peñil, P., Perennes, C., Persic, M., Moroni, P. G. Prada, Prandini, E., Priyadarshi, C., Puljak, I., Rhode, W., Ribó, M., Rico, J., Righi, C., Rugliancich, A., Saha, L., Sahakyan, N., Saito, T., Sakurai, S., Satalecka, K., Saturni, F. G., Schleicher, B., Schmidt, K., Schweizer, T., Sitarek, J., Šnidarić, I., Sobczynska, D., Spolon, A., Stamerra, A., Strom, D., Strzys, M., Suda, Y., Surić, T., Takahashi, M., Tavecchio, F., Temnikov, P., Terzić, T., Teshima, M., Torres-Albà, N., Tosti, L., Truzzi, S., Tutone, A., van Scherpenberg, J., Vanzo, G., Acosta, M. Vazquez, Ventura, S., Verguilov, V., Vigorito, C. F., Vitale, V., Vovk, I., Will, M., Zarić, D., Angioni, R., D'Ammando, F., Ciprini, S., Cheung, C. C., Orienti, M., Pacciani, L., Prajapati, P., Kumar, P., Ganesh, S., Kurtenkov, A., Marchini, A., Carrasco, L., Escobedo, G., Porras, A., Recillas, E., Lähteenmäki, A., Tornikoski, M., Berton, M., Tammi, J., Vera, R. J. C., Jorstad, S. G., Marscher, A. P., Weaver, Z. R., Hart, M., Hallum, M. K., Larionov, V. M., Borman, G. A., Grishina, T. S., Kopatskaya, E. N., Larionova, E. G., Nikiforova, A. A., Morozova, D. A., Savchenko, S. S., Troitskaya, Yu. V., Troitsky, I. S., Vasilyev, A. A., Hodges, M., Hovatta, T., Kiehlmann, S., Max-Moerbeck, W., Readhead, A. C. S., Reeves, R., and Pearson, T. J.
Subjects: Astrophysics - High Energy Astrophysical Phenomena
Abstract: Context. QSO B1420+326 is a blazar classified as a Flat Spectrum Radio Quasar (FSRQ). In the beginning of 2020 it underwent an enhanced flux state. An extensive multiwavelength campaign allowed us to trace the evolution of the flare. Aims. We search for VHE gamma-ray emission from QSO B1420+326 during this flaring state. We aim to characterize and model the broadband emission of the source over different phases of the flare. Methods. The source was observed with a number of instruments in radio, near infrared, optical (including polarimetry and spectroscopy), ultra-violet, X-ray and gamma-ray bands. We use dedicated optical spectroscopy results to estimate the accretion disk and the dust torus luminosity. We perform spectral energy distribution modeling in the framework of combined Synchrotron-Self-Compton and External Compton scenario in which the electron energy distribution is partially determined from acceleration and cooling processes. Results. During the enhanced state the flux of both SED components drastically increased and the peaks were shifted to higher energies. Follow up observations with the MAGIC telescopes led to the detection of very-high-energy gamma-ray emission from this source, making it one of only a handful of FSRQs known in this energy range. Modeling allows us to constrain the evolution of the magnetic field and electron energy distribution in the emission region. The gamma-ray flare was accompanied by a rotation of the optical polarization vector during a low polarization state. Also, a new, superluminal radio knot contemporaneously appeared in the radio image of the jet. The optical spectroscopy shows a prominent FeII bump with flux evolving together with the continuum emission and a MgII line with varying equivalent width., Comment: 20 pages, 15 figures, 7 tables, accepted for publication in A&A
Published: 2020
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24. Parsec-scale properties of the radio brightest jetted AGN at z > 6

Author: Spingola, C., Dallacasa, D., Belladitta, S., Caccianiga, A., Giroletti, M., Moretti, A., and Orienti, M.
Subjects: Astrophysics - High Energy Astrophysical Phenomena, Astrophysics - Cosmology and Nongalactic Astrophysics
Abstract: We present Director's Discretionary Time multi-frequency observations obtained with the Jansky Very Large Array (VLA) and the Very Long Baseline Array (VLBA) of the blazar PSO J030947.49+271757.31 (hereafter PSO J0309+27) at $z = 6.10\pm0.03$. The milliarcsecond angular resolution of our VLBA observations at 1.5, 5 and 8.4 GHz unveils a bright one-sided jet extended for $\sim500$ parsecs in projection. This high-z radio-loud AGN is resolved into multiple compact sub-components, embedded in a more diffuse and faint radio emission, which enshrouds them in a continuous jet structure. We derive limits on some physical parameters directly from the observable quantities, such as viewing angle, Lorentz and Doppler factors. If PSO J0309+27 is a genuine blazar, as suggested by its X-ray properties, then we find that its bulk Lorentz factor must be relatively low (less than 5). Such value would be in favour of a scenario currently proposed to reconcile the paucity of high-z blazars with respect to current predictions. Nevertheless, we cannot exclude that PSO J0309+27 is seen under a larger viewing angle, which would imply that the X-ray emission must be enhanced, for example, by inverse Compton with the Cosmic Microwave Background. More stringent constraints on the bulk Lorentz factor in PSO J0309+27 and the other high-z blazars are necessary to test whether their properties are intrinsically different with respect to the low-z blazar population., Comment: 10 pages, 5 figures, accepted for publication in A&A Letters
Published: 2020
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25. Sensitivity of the Cherenkov Telescope Array for probing cosmology and fundamental physics with gamma-ray propagation

Author: Consortium, The Cherenkov Telescope Array, Abdalla, H., Abe, H., Acero, F., Acharyya, A., Adam, R., Agudo, I., Aguirre-Santaella, A., Alfaro, R., Alfaro, J., Alispach, C., Aloisio, R., B, R. Alves, Amati, L., Amato, E., Ambrosi, G., Angüner, E. O., Araudo, A., Armstrong, T., Arqueros, F., Arrabito, L., Asano, K., Ascasíbar, Y., Ashley, M., Backes, M., Balazs, C., Balbo, M., Balmaverde, B., Larriva, A. Baquero, Martins, V. Barbosa, Barkov, M., Baroncelli, L., de Almeida, U. Barres, Barrio, J. A., Batista, P., Becerra, J., Becherini, Y., Beck, G., Tjus, J. Becker, Belmont, R., Benbow, W., Bernardini, E., Berti, A., Berton, M., Bertucci, B., Beshley, V., Bi, B., Biasuzzi, B., Biland, A., Bissaldi, E., Biteau, J., Blanch, O., Bocchino, F., Boisson, C., Bolmont, J., Bonanno, G., Arbeletche, L. Bonneau, Bonnoli, G., Bordas, P., Bottacini, E., Böttcher, M., Bozhilov, V., Bregeon, J., Brill, A., Brown, A. M., Bruno, P., Bruno, A., Bulgarelli, A., Burton, M., Buscemi, M., Caccianiga, A., Cameron, R., Capasso, M., Caprai, M., Caproni, A., Capuzzo-Dolcetta, R., Caraveo, P., Carosi, R., Carosi, A., Casanova, S., Cascone, E., Cauz, D., Cerny, K., Cerruti, M., Chadwick, P., Chaty, S., Chen, A., Chernyakova, M., Chiaro, G., Chiavassa, A., Chytka, L., Conforti, V., Conte, F., Contreras, J. L., Coronado-Blazquez, J., Cortina, J., Costa, A., Costantini, H., Covino, S., Cristofari, P., Cuevas, O., D'Ammando, F., Daniel, M. K., Davies, J., Dazzi, F., De Angelis, A., de Lavergne, M. de Bony, De Caprio, V., Anjos, R. de Cássia dos, Pino, E. M. de Gouveia Dal, De Lotto, B., De Martino, D., de Naurois, M., Wilhelmi, E. de Oña, De Palma, F., de Souza, V., Delgado, C., Della Ceca, R., della Volpe, D., Depaoli, D., Di Girolamo, T., Di Pierro, F., Díaz, C., Díaz-Bahamondes, C., Diebold, S., Djannati-Ataï, A., Dmytriiev, A., Domínguez, A., Donini, A., Dorner, D., Doro, M., Dournaux, J., Dwarkadas, V. V., Ebr, J., Eckner, C., Einecke, S., Ekoume, T. R. N., Elsässer, D., Emery, G., Evoli, C., Fairbairn, M., Falceta-Goncalves, D., Fegan, S., Feng, Q., Ferrand, G., Fiandrini, E., Fiasson, A., Fioretti, V., Foffano, L., Fonseca, M. V., Font, L., Fontaine, G., Franco, F. J., Coromina, L. Freixas, Fukami, S., Fukazawa, Y., Fukui, Y., Gaggero, D., Galanti, G., Gammaldi, V., Garcia, E., Garczarczyk, M., Gascon, D., Gaug, M., Gent, A., Ghalumyan, A., Ghirlanda, G., Gianotti, F., Giarrusso, M., Giavitto, G., Giglietto, N., Giordano, F., Glicenstein, J., Goldoni, P., González, J. M., Gourgouliatos, K., Grabarczyk, T., Grandi, P., Granot, J., Grasso, D., Green, J., Grube, J., Gueta, O., Gunji, S., Halim, A., Harvey, M., Collado, T. Hassan, Hayashi, K., Heller, M., Cadena, S. Hernández, Hervet, O., Hinton, J., Hiroshima, N., Hnatyk, B., Hnatyk, R., Hoffmann, D., Hofmann, W., Holder, J., Horan, D., Hörandel, J., Horvath, P., Hovatta, T., Hrabovsky, M., Hrupec, D., Hughes, G., Hütten, M., Iarlori, M., Inada, T., Inoue, S., Insolia, A., Ionica, M., Iori, M., Jacquemont, M., Jamrozy, M., Janecek, P., Martínez, I. Jiménez, Jin, W., Jung-Richardt, I., Jurysek, J., Kaaret, P., Karas, V., Karkar, S., Kawanaka, N., Kerszberg, D., Khélifi, B., Kissmann, R., Knödlseder, J., Kobayashi, Y., Kohri, K., Komin, N., Kong, A., Kosack, K., Kubo, H., La Palombara, N., Lamanna, G., Lang, R. G., Lapington, J., Laporte, P., Lemoine-Goumard, M., Lenain, J., Leone, F., Leto, G., Leuschner, F., Lindfors, E., Lloyd, S., Lohse, T., Lombardi, S., Longo, F., Lopez, A., López, M., López-Coto, R., Loporchio, S., Lucarelli, F., Luque-Escamilla, P. L., Lyard, E., Maggio, C., Majczyna, A., Makariev, M., Mallamaci, M., Mandat, D., Maneva, G., Manganaro, M., Manicò, G., Marcowith, A., Marculewicz, M., Markoff, S., Marquez, P., Martí, J., Martinez, O., Martínez, M., Martínez, G., Martínez-Huerta, H., Maurin, G., Mazin, D., Mbarubucyeye, J. D., Miranda, D. Medina, Meyer, M., Micanovic, S., Miener, T., Minev, M., Miranda, J. M., Mitchell, A., Mizuno, T., Mode, B., Moderski, R., Mohrmann, L., Molina, E., Montaruli, T., Moralejo, A., Merino, J. Morales, Morcuende-Parrilla, D., Morselli, A., Mukherjee, R., Mundell, C., Murach, T., Muraishi, H., Nagai, A., Nakamori, T., Nemmen, R., Niemiec, J., Nieto, D., Nievas, M., Nikołajuk, M., Nishijima, K., Noda, K., Nosek, D., Nozaki, S., O'Brien, P., Ohira, Y., Ohishi, M., Oka, T., Ong, R. A., Orienti, M., Orito, R., Orlandini, M., Orlando, E., Osborne, J. P., Ostrowski, M., Oya, I., Pagliaro, A., Palatka, M., Paneque, D., Pantaleo, F. R., Paredes, J. M., Parmiggiani, N., Patricelli, B., Pavletić, L., Pe'er, A., Pech, M., Pecimotika, M., Peresano, M., Persic, M., Petruk, O., Pfrang, K., Piatteli, P., Pietropaolo, E., Pillera, R., Pilszyk, B., Pimentel, D., Pintore, F., Pita, S., Pohl, M., Poireau, V., Polo, M., Prado, R. R., Prast, J., Principe, G., Produit, N., Prokoph, H., Prouza, M., Przybilski, H., Pueschel, E., Pühlhofer, G., Pumo, M. L., Punch, M., Queiroz, F., Quirrenbach, A., Rando, R., Razzaque, S., Rebert, E., Recchia, S., Reichherzer, P., Reimer, O., Reimer, A., Renier, Y., Reposeur, T., Rhode, W., Ribeiro, D., Ribó, M., Richtler, T., Rico, J., Rieger, F., Rizi, V., Rodriguez, J., Fernandez, G. Rodriguez, Ramirez, J. C. Rodriguez, Vázquez, J. J. Rodríguez, Romano, P., Romeo, G., Roncadelli, M., Rosado, J., de Leon, A. Rosales, Rowell, G., Rudak, B., Rujopakarn, W., Russo, F., Sadeh, I., Saha, L., Saito, T., Greus, F. Salesa, Sanchez, D., Sánchez-Conde, M., Sangiorgi, P., Sano, H., Santander, M., Santos, E. M., Sanuy, A., Sarkar, S., Saturni, F. G., Sawangwit, U., Scherer, A., Schleicher, B., Schovanek, P., Schussler, F., Schwanke, U., Sciacca, E., Scuderi, S., Arroyo, M. Seglar, Sergijenko, O., Servillat, M., Seweryn, K., Shalchi, A., Sharma, P., Shellard, R. C., Siejkowski, H., Sinha, A., Sliusar, V., Slowikowska, A., Sokolenko, A., Sol, H., Specovius, A., Spencer, S., Spiga, D., Stamerra, A., Stanič, S., Starling, R., Stolarczyk, T., Straumann, U., Strišković, J., Suda, Y., Świerk, P., Tagliaferri, G., Takahashi, H., Takahashi, M., Tavecchio, F., Taylor, L., Tejedor, L. A., Temnikov, P., Terrier, R., Terzic, T., Testa, V., Tian, W., Tibaldo, L., Tonev, D., Torres, D. F., Torresi, E., Tosti, L., Tothill, N., Tovmassian, G., Travnicek, P., Truzzi, S., Tuossenel, F., Umana, G., Vacula, M., Vagelli, V., Valentino, M., Vallage, B., Vallania, P., van Eldik, C., Varner, G. S., Vassiliev, V., Acosta, M. Vázquez, Vecchi, M., Veh, J., Vercellone, S., Vergani, S., Verguilov, V., Vettolani, G. P., Viana, A., Vigorito, C. F., Vitale, V., Vorobiov, S., Vovk, I., Vuillaume, T., Wagner, S. J., Walter, R., Watson, J., White, M., White, R., Wiemann, R., Wierzcholska, A., Will, M., Williams, D. A., Wischnewski, R., Wolter, A., Yamazaki, R., Yanagita, S., Yang, L., Yoshikoshi, T., Zacharias, M., Zaharijas, G., Zaric, D., Zavrtanik, M., Zavrtanik, D., Zech, A., Zechlin, H., Zhdanov, V. I., and Živec, M.
Subjects: Astrophysics - High Energy Astrophysical Phenomena, Astrophysics - Cosmology and Nongalactic Astrophysics
Abstract: The Cherenkov Telescope Array (CTA), the new-generation ground-based observatory for $\gamma$-ray astronomy, provides unique capabilities to address significant open questions in astrophysics, cosmology, and fundamental physics. We study some of the salient areas of $\gamma$-ray cosmology that can be explored as part of the Key Science Projects of CTA, through simulated observations of active galactic nuclei (AGN) and of their relativistic jets. Observations of AGN with CTA will enable a measurement of $\gamma$-ray absorption on the extragalactic background light with a statistical uncertainty below 15% up to a redshift $z=2$ and to constrain or detect $\gamma$-ray halos up to intergalactic-magnetic-field strengths of at least 0.3pG. Extragalactic observations with CTA also show promising potential to probe physics beyond the Standard Model. The best limits on Lorentz invariance violation from $\gamma$-ray astronomy will be improved by a factor of at least two to three. CTA will also probe the parameter space in which axion-like particles could constitute a significant fraction, if not all, of dark matter. We conclude on the synergies between CTA and other upcoming facilities that will foster the growth of $\gamma$-ray cosmology., Comment: 71 pages (including affiliations and references), 13 figures, 6 tables. Accepted in JCAP; matches published version. Corresponding authors: Jonathan Biteau, Julien Lefaucheur, Humberto Martinez-Huerta, Manuel Meyer, Santiago Pita, Ievgen Vovk
Published: 2020
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26. Variability and parsec-scale radio structure of candidate compact symmetric objects

Author: Orienti, M. and Dallacasa, D.
Subjects: Astrophysics - Astrophysics of Galaxies
Abstract: We report results on multi-epoch Very Large Array (VLA) and pc-scale Very Long Baseline Array (VLBA) observations of candidate compact symmetric objects (CSOs) from the faint sample of high frequency peakers. New VLBA observations could resolve the radio structure in about 42 per cent of the observed sources, showing double components that may be either mini-lobes or core-jet structures. Almost all the sources monitored by the VLA show some variability on time scale of a decade, and only 1 source does not show any significant variation. In 17 sources the flux density changes randomly as it is expected in blazars, and in 4 sources the spectrum becomes flat in the last observing epoch, confirming that samples selected in the GHz regime are highly contaminated by beamed objects. In 16 objects, the pc-scale and variability properties are consistent with a young radio source in adiabatic expansion, with a steady decrease of the flux density in the optically-thin part of the spectrum, and a flux density increase in the optically-thick part. For these sources we estimate dynamical ages between a few tens to a few hundreds years. The corresponding expansion velocity is generally between 0.1c and 0.7c, similar to values found in CSOs with different approaches. The fast evolution that we observe in some CSO candidates suggests that not all the objects would become classical Fanaroff-Riley radio sources., Comment: 18 pages, 4 figures; accepted for publication in MNRAS
Published: 2020
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27. Sensitivity of the Cherenkov Telescope Array to a dark matter signal from the Galactic centre

Author: Consortium, The Cherenkov Telescope Array, Acharyya, A., Adam, R., Adams, C., Agudo, I., Aguirre-Santaella, A., Alfaro, R., Alfaro, J., Alispach, C., Aloisio, R., Batista, R. Alves, Amati, L., Ambrosi, G., Angüner, E. O., Antonelli, L. A., Aramo, C., Araudo, A., Armstrong, T., Arqueros, F., Asano, K., Ascasíbar, Y., Ashley, M., Balazs, C., Ballester, O., Larriva, A. Baquero, Martins, V. Barbosa, Barkov, M., de Almeida, U. Barres, Barrio, J. A., Bastieri, D., Becerra, J., Beck, G., Tjus, J. Becker, Benbow, W., Benito, M., Berge, D., Bernardini, E., Bernlöhr, K., Berti, A., Bertucci, B., Beshley, V., Biasuzzi, B., Biland, A., Bissaldi, E., Biteau, J., Blanch, O., Blazek, J., Bocchino, F., Boisson, C., Arbeletche, L. Bonneau, Bordas, P., Bosnjak, Z., Bottacini, E., Bozhilov, V., Bregeon, J., Brill, A., Bringmann, T., Brown, A. M., Brun, P., Brun, F., Bruno, P., Bulgarelli, A., Burton, M., Burtovoi, A., Buscemi, M., Cameron, R., Capasso, M., Caproni, A., Capuzzo-Dolcetta, R., Caraveo, P., Carosi, R., Carosi, A., Casanova, S., Cascone, E., Cassol, F., Catalani, F., Cauz, D., Cerruti, M., Chadwick, P., Chaty, S., Chen, A., Chernyakova, M., Chiaro, G., Chiavassa, A., Chikawa, M., Chudoba, J., Çolak, M., Conforti, V., Coniglione, R., Conte, F., Contreras, J. L., Coronado-Blazquez, J., Costa, A., Costantini, H., Cotter, G., Cristofari, P., D'Aì, A., D'Ammando, F., Damone, L. A., Daniel, M. K., Dazzi, F., De Angelis, A., De Caprio, V., Anjos, R. de Cássia dos, Pino, E. M. de Gouveia Dal, De Lotto, B., De Martino, D., Wilhelmi, E. de Oña, De Palma, F., de Souza, V., Delgado, C., Giler, A. G. Delgado, della Volpe, D., Depaoli, D., Di Girolamo, T., Di Pierro, F., Di Venere, L., Diebold, S., Dmytriiev, A., Domínguez, A., Donini, A., Doro, M., Ebr, J., Eckner, C., Edwards, T. D. P., Ekoume, T. R. N., Elsässer, D., Evoli, C., Falceta-Goncalves, D., Fedorova, E., Fegan, S., Feng, Q., Ferrand, G., Ferrara, G., Fiandrini, E., Fiasson, A., Filipovic, M., Fioretti, V., Fiori, M., Foffano, L., Fontaine, G., Fornieri, O., Franco, F. J., Fukami, S., Fukui, Y., Gaggero, D., Galaz, G., Gammaldi, V., Garcia, E., Garczarczyk, M., Gascon, D., Gent, A., Ghalumyan, A., Gianotti, F., Giarrusso, M., Giavitto, G., Giglietto, N., Giordano, F., Giuliani, A., Glicenstein, J., Gnatyk, R., Goldoni, P., González, M. M., Gourgouliatos, K., Granot, J., Grasso, D., Green, J., Grillo, A., Gueta, O., Gunji, S., Halim, A., Hassan, T., Heller, M., Cadena, S. Hernández, Hiroshima, N., Hnatyk, B., Hofmann, W., Holder, J., Horan, D., Hörandel, J., Horvath, P., Hovatta, T., Hrabovsky, M., Hrupec, D., Hughes, G., Humensky, T. B., Hütten, M., Iarlori, M., Inada, T., Inoue, S., Iocco, F., Iori, M., Jamrozy, M., Janecek, P., Jin, W., Jouvin, L., Jurysek, J., Karukes, E., Katarzyński, K., Kazanas, D., Kerszberg, D., Kherlakian, M. C., Kissmann, R., Knödlseder, J., Kobayashi, Y., Kohri, K., Komin, N., Kubo, H., Kushida, J., Lamanna, G., Lapington, J., Laporte, P., de Oliveira, M. A. Leigui, Lenain, J., Leone, F., Leto, G., Lindfors, E., Lohse, T., Lombardi, S., Longo, F., Lopez, A., López, M., López-Coto, R., Loporchio, S., Luque-Escamilla, P. L., Mach, E., Maggio, C., Maier, G., Mallamaci, M., de Almeida, R. Malta Nunes, Mandat, D., Manganaro, M., Mangano, S., Manicò, G., Marculewicz, M., Mariotti, M., Markoff, S., Marquez, P., Martí, J., Martinez, O., Martínez, M., Martínez, G., Martínez-Huerta, H., Maurin, G., Mazin, D., Mbarubucyeye, J. D., Miranda, D. Medina, Meyer, M., Miceli, M., Miener, T., Minev, M., Miranda, J. M., Mirzoyan, R., Mizuno, T., Mode, B., Moderski, R., Mohrmann, L., Molina, E., Montaruli, T., Moralejo, A., Morcuende-Parrilla, D., Morselli, A., Mukherjee, R., Mundell, C., Nagai, A., Nakamori, T., Nemmen, R., Niemiec, J., Nieto, D., Nikołajuk, M., Ninci, D., Noda, K., Nosek, D., Nozaki, S., Ohira, Y., Ohishi, M., Ohtani, Y., Oka, T., Okumura, A., Ong, R. A., Orienti, M., Orito, R., Orlandini, M., Orlando, S., Orlando, E., Ostrowski, M., Oya, I., Pagano, I., Pagliaro, A., Palatiello, M., Pantaleo, F. R., Paredes, J. M., Pareschi, G., Parmiggiani, N., Patricelli, B., Pavletić, L., Pe'er, A., Pecimotika, M., Pérez-Romero, J., Persic, M., Petruk, O., Pfrang, K., Piano, G., Piatteli, P., Pietropaolo, E., Pillera, R., Pilszyk, B., Pintore, F., Pohl, M., Poireau, V., Prado, R. R., Prandini, E., Prast, J., Principe, G., Prokoph, H., Prouza, M., Przybilski, H., Pühlhofer, G., Pumo, M. L., Queiroz, F., Quirrenbach, A., Rainò, S., Rando, R., Razzaque, S., Recchia, S., Reimer, O., Reisenegger, A., Renier, Y., Rhode, W., Ribeiro, D., Ribó, M., Richtler, T., Rico, J., Rieger, F., Rinchiuso, L., Rizi, V., Rodriguez, J., Fernandez, G. Rodriguez, Ramirez, J. C. Rodriguez, Rojas, G., Romano, P., Romeo, G., Rosado, J., Rowell, G., Rudak, B., Russo, F., Sadeh, I., Hatlen, E. Sæther, Safi-Harb, S., Greus, F. Salesa, Salina, G., Sanchez, D., Sánchez-Conde, M., Sangiorgi, P., Sano, H., Santander, M., Santos, E. M., Santos-Lima, R., Sanuy, A., Sarkar, S., Saturni, F. G., Sawangwit, U., Schussler, F., Schwanke, U., Sciacca, E., Scuderi, S., Seglar-Arroyo, M., Sergijenko, O., Servillat, M., Seweryn, K., Shalchi, A., Sharma, P., Shellard, R. C., Siejkowski, H., Silk, J., Siqueira, C., Sliusar, V., Słowikowska, A., Sokolenko, A., Sol, H., Spencer, S., Stamerra, A., Stanič, S., Starling, R., Stolarczyk, T., Straumann, U., Strišković, J., Suda, Y., Suomijarvi, T., Świerk, P., Tavecchio, F., Taylor, L., Tejedor, L. A., Teshima, M., Testa, V., Tibaldo, L., Peixoto, C. J. Todero, Tokanai, F., Tonev, D., Tosti, G., Tosti, L., Tothill, N., Truzzi, S., Travnicek, P., Vagelli, V., Vallage, B., Vallania, P., van Eldik, C., Vandenbroucke, J., Varner, G. S., Vassiliev, V., Acosta, M. Vázquez, Vecchi, M., Ventura, S., Vercellone, S., Vergani, S., Verna, G., Viana, A., Vigorito, C. F., Vink, J., Vitale, V., Vorobiov, S., Vovk, I., Vuillaume, T., Wagner, S. J., Walter, R., Watson, J., Weniger, C., White, R., White, M., Wiemann, R., Wierzcholska, A., Will, M., Williams, D. A., Wischnewski, R., Yanagita, S., Yang, L., Yoshikoshi, T., Zacharias, M., Zaharijas, G., Zakaria, A. A., Zampieri, L., Zanin, R., Zaric, D., Zavrtanik, M., Zavrtanik, D., Zdziarski, A. A., Zech, A., Zechlin, H., Zhdanov, V. I., and Živec, M.
Subjects: Astrophysics - High Energy Astrophysical Phenomena, High Energy Physics - Phenomenology
Abstract: We provide an updated assessment of the power of the Cherenkov Telescope Array (CTA) to search for thermally produced dark matter at the TeV scale, via the associated gamma-ray signal from pair-annihilating dark matter particles in the region around the Galactic centre. We find that CTA will open a new window of discovery potential, significantly extending the range of robustly testable models given a standard cuspy profile of the dark matter density distribution. Importantly, even for a cored profile, the projected sensitivity of CTA will be sufficient to probe various well-motivated models of thermally produced dark matter at the TeV scale. This is due to CTA's unprecedented sensitivity, angular and energy resolutions, and the planned observational strategy. The survey of the inner Galaxy will cover a much larger region than corresponding previous observational campaigns with imaging atmospheric Cherenkov telescopes. CTA will map with unprecedented precision the large-scale diffuse emission in high-energy gamma rays, constituting a background for dark matter searches for which we adopt state-of-the-art models based on current data. Throughout our analysis, we use up-to-date event reconstruction Monte Carlo tools developed by the CTA consortium, and pay special attention to quantifying the level of instrumental systematic uncertainties, as well as background template systematic errors, required to probe thermally produced dark matter at these energies. "Full likelihood tables complementing our analysis are provided here [ https://doi.org/10.5281/zenodo.4057987 ]", Comment: 68 pages (including references) and 26 figures; text identical to the version published in JCAP
Published: 2020
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28. Jansky VLA observations of synchrotron emitting optical hotspots of 3C 227 and 3C 445 radio galaxies

Author: Orienti, M., Migliori, G., Brunetti, G., Nagai, H., D'Ammando, F., Mack, K. -H., and Prieto, M. A.
Subjects: Astrophysics - High Energy Astrophysical Phenomena
Abstract: We report results on deep Jansky Very Large Array A-configuration observations at 22 GHz of the hotspots of the radio galaxies 3C227 and 3C445. Synchrotron emission in the optical on scales up to a few kpc was reported for the four hotspots. Our VLA observations point out the presence of unresolved regions with upper limit to their linear size of about 100 pc. This is the first time that such compact components in hotspots have been detected in a mini-sample, indicating that they are not a peculiar characteristic of a few individual hotspots. The polarization may reach values up to 70 per cent in compact (about 0.1 kpc scale) regions within the hotspot, indicating a highly ordered magnetic field with size up to a hundred parsecs. On larger scales, the average polarization of the hotspot component is about 30-45 per cent, suggesting the presence of a significant random field component, rather than an ordered magnetic field. This is further supported by the displacement between the peaks in polarized intensity and in total intensity images that is observed in all the four hotspots. The electric vector position angle is not constant, but changes arbitrarily in the central part of the hotspot regions, whereas it is usually perpendicular to the total intensity contours of the outermost edge of the hotspot structure, likely marking the large-scale shock front. The misalignment between X-ray and radio-to-optical emission suggests that the former is tracing the current particle acceleration, whereas the latter marks older shock fronts., Comment: 12 pages, 13 figures, published in MNRAS
Published: 2020
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29. Particle acceleration in low-power hotspots: modelling the broad-band spectral energy distribution

Author: Migliori, G., Orienti, M., Coccato, L., Brunetti, G., D'Ammando, F., Mack, K. -H., and Prieto, M. A.
Subjects: Astrophysics - High Energy Astrophysical Phenomena
Abstract: The acceleration and radiative processes active in low-power radio hotspots are investigated by means of new deep near-infrared (NIR) and optical VLT observations, complemented with archival, high-sensitivity VLT, radio VLA and X-ray Chandra data. For the three studied radio galaxies (3C 105, 3C 195 and 3C 227), we confirm the detection of NIR/optical counterparts of the observed radio hotspots. We resolve multiple components in 3C 227 West and in 3C 105 South and characterize the diffuse NIR/optical emission of the latter. We show that the linear size of this component ($\gtrsim$4 kpc) makes 3C 105 South a compelling case for particles' re-acceleration in the post-shock region. Modeling of the radio-to-X-ray spectral energy distribution (SED) of 3C 195 South and 3C 227 W1 gives clues on the origin of the detected X-ray emission. In the context of inverse Compton models, the peculiarly steep synchrotron curve of 3C 195 South sets constraints on the shape of the radiating particles' spectrum that are testable with better knowledge of the SED shape at low ($\lesssim$GHz) radio frequencies and in X-rays. The X-ray emission of 3C 227 W1 can be explained with an additional synchrotron component originating in compact ($<$100 pc) regions, such those revealed by radio observations at 22 GHz, provided that efficient particle acceleration ($\gamma\gtrsim$10$^7$) is ongoing. The emerging picture is that of systems in which different acceleration and radiative processes coexist., Comment: 16 pages, 10 figures, accepted for publication in MNRAS
Published: 2020
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30. NGC 3894: a young radio galaxy seen by Fermi-LAT

Author: Principe, G., Migliori, G., Johnson, T. J., D'Ammando, F., Giroletti, M., Orienti, M., Stanghellini, C., Taylor, G. B., Torresi, E., and Cheung, C. C.
Subjects: Astrophysics - Astrophysics of Galaxies, Astrophysics - High Energy Astrophysical Phenomena
Abstract: Context. According to radiative models, radio galaxies may produce gamma-ray emission from the first stages of their evolution. However, very few such galaxies have been detected by the Fermi Large Area Telescope (LAT) so far. Aims. NGC 3894 is a nearby (z = 0.0108) object that belongs to the class of compact symmetric objects (CSOs, i.e., the most compact and youngest radio galaxies), which is associated with a gamma-ray counterpart in the Fourth Fermi-LAT source catalog. Here we present a study of the source in the gamma-ray and radio bands aimed at investigating its high-energy emission and assess its young nature. Methods. We analyzed 10.8 years of Fermi-LAT data between 100 MeV and 300 GeV and determined the spectral and variability characteristics of the source. Multi-epoch very long baseline array (VLBA) observations between 5 and 15 GHz over a period of 35 years were used to study the radio morphology of NGC 3894 and its evolution. Results. NGC 3894 is detected in gamma-rays with a significance >9 sigma over the full period, and no significant variability has been observed in the gamma-ray flux on a yearly time-scale. The spectrum is modeled with a flat power law ($\Gamma$ = 2.0$\pm$0.1) and a flux on the order of 2.2 $\times$ 10$^{-9}$ ph cm$^{-2}$ s$^{-1}$. For the first time, the VLBA data allow us to constrain with high precision the apparent velocity of the jet and counter-jet side to be $\beta_{\mathrm{app,NW}}$ = 0.132$\pm$0.004 and $\beta_{\mathrm{app,SE}}$ = 0.065$\pm$0.003, respectively. Conclusions. Fermi-LAT and VLBA results favor the youth scenario for the inner structure of this object, with an estimated dynamical age of 59$\pm$5 years. The estimated range of viewing angle (10{\deg} < $\theta$ < 21{\deg}) does not exclude a possible jet-like origin of the gamma-ray emission., Comment: Accepted by A&A on February 28, 2020. 8 pages, 7 figures
Published: 2020
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31. A parsec-scale wobbling jet in the high-synchrotron peaked blazar PG 1553+113

Author: Lico, Rocco, Liu, J., Giroletti, M., Orienti, M., Gomez, J. L., Piner, B. G., MacDonald, N. R., D'Ammando, F., and Fuentes, A.
Subjects: Astrophysics - High Energy Astrophysical Phenomena, Astrophysics - Astrophysics of Galaxies
Abstract: PG 1553+113 is the first blazar showing an approximately two-year quasi-periodic pattern in its gamma-ray light curve. Such quasi-periodicity might have a geometrical origin, possibly related to the precessing nature of the jet, or could be intrinsic to the source and related to pulsational accretion flow instabilities. By means of a ~2yr very long baseline array (VLBA) monitoring at 15, 24, and 43 GHz we investigate the source pc-scale properties during an entire cycle of gamma-ray activity in the period 2015-2017. In contrast to the well-defined periodicity in the gamma-ray emission, at radio frequencies no clear periodic pattern can be recognized. The jet position angle, constrained by means of the total intensity ridge line, varies across the different observing epochs in the range 40-60 deg. We also investigate the time evolution of the source polarization properties, including the rotation measure. The brightness temperature is found to decrease as the frequency increases with an intrinsic value of ~1.5 x 10^10 K and the estimated Doppler factor is ~1.4., Comment: 11 pages, 7 images, 5 tables. Accepted for publication in Astronomy and Astrophysics
Published: 2020
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32. On the connection between radio and gamma rays

Author: Orienti M., D’Ammando F., Giroletti M., Dallacasa D., Venturi T., and Giovannini G.
Subjects: Physics, QC1-999
Abstract: Relativistic jets are one of the most powerful manifestations of the release of energy produced around supermassive black holes at the centre of active galactic nuclei (AGN). Their emission is observed across the entire electromagnetic spectrum, from the radio band to gamma rays. Despite decades of efforts, many aspects of the physics of relativistic jets remain elusive. In particular, the location and the mechanisms responsible for the high-energy emission and the connection of the variability at different wavelengths are among the greatest challenges in the study of AGN. From the comparison of the radio and gamma-ray light curves of gamma-ray flaring objects, there is evidence that some flares, either in radio or in gamma rays, have not an obvious connection at the other extreme of the electromagnetic spectrum, like in the case of the Narrow-Line Seyfert 1 SBS 0846+513. An intriguing aspect pointed out by high resolution radio observations is the change of the polarization properties close in time with some high energy flares. In particular, in PKS 1510–089 and 3C 454.3 a rotation of almost 90 degrees has been observed after strong gamma-ray flares. The swing of the polarization angle may be related either to the propagation of a shock along the jet that orders the magnetic field, or a change of the opacity regime.
Published: 2013
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33. Relativistic jets in narrow-line Seyfert 1 galaxies. New discoveries and open questions

Author: D’Ammando F., Orienti M., Finke J., Larsson J., and Giroletti M.
Subjects: Physics, QC1-999
Abstract: Before the launch of the Fermi satellite only two classes of AGNs were known to produce relativistic jets and thus emit up to the γ-ray energy range: blazars and radio galaxies, both hosted in giant elliptical galaxies. The first four years of observations by the Large Area Telescope on board Fermi confirmed that these two are the most numerous classes of identified sources in the extragalactic γ-ray sky, but the discovery of γ-ray emission from 5 radio-loud narrow-line Seyfert 1 galaxies revealed the presence of a possible emerging third class of AGNs with relativistic jets. Considering that narrow-line Seyfert 1 galaxies seem to be typically hosted in spiral galaxy, this finding poses intriguing questions about the nature of these objects, the onset of production of relativistic jets, and the cosmological evolution of radio-loud AGN. Here, we discuss the radio-to-γ-rays properties of the γ-ray emitting narrow-line Seyfert 1 galaxies, also in comparison with the blazar scenario.
Published: 2013
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34. Very Long Baseline Polarimetric monitoring at 15 GHz of the TeV blazar Markarian 421

Author: Lico R., Casadio C., Gómez J.L., Giroletti M., Orienti M., Giovannini G., Blasi M.G., Cotton W., Edwards P. G., Fuhrmann L., Jorstad S., Kino M., Kovalev Y.Y., Krichbaum T.P., Marscher A., Paneque D., Perez-Torres M.A., Piner G., and Sokolovsky K.V.
Subjects: Physics, QC1-999
Abstract: Thanks to high resolution radio observations it is possible to obtain a direct imaging of the innermost regions of Active Galactic Nuclei; in particular, it is possible to investigate about the jet’s morphology and any proper motions, and the time evolution of physical parameters, such as flux densities and spectral index. Furthermore, with the study of the polarization properties, it is possible to obtain important information about the magnetic field structure and the emission mechanisms. In this work we present recent results about the nearby (z=0.031) TeV blazar Mrk 421. We analyzed data obtained with the Very Long Baseline Array (VLBA),both in total and polarized intensity, at twelve epochs (one observation per month from January to December 2011) at 15, 24 and 43 GHz, in the context of a broadband campaign from the radio to gamma-ray. We investigate the inner jet structure on parsec scale through the study of model-fit components for each epoch. At these frequencies the source shows a compact (about 0.13 mas, or 0.08 pc) and bright component, with a one sided jet detected out to about 10 mas. All model-fit components in the jet appear to be almost stationary during our observation period, and the spectral index is fairly flat in the core region and steepens along the jet’s length. In particular, we present a preliminary study of the polarization properties for the 15 GHz dataset: we found a degree of polarization of ∼ 1% for the core region and for the C3 component, at near 1 mas from the core, we found a value of near 14%.
Published: 2013
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35. Radio VLBA polarization and multi-band monitoring of the high-redshift quasar S5 0836+710 during a high activity period

Author: Orienti, M., D'Ammando, F., Giroletti, M., Dallacasa, D., Giovannini, G., and Ciprini, S.
Subjects: Astrophysics - High Energy Astrophysical Phenomena
Abstract: We report on results of a multi-band monitoring campaign from radio to gamma rays of the high-redshift flat spectrum radio quasar S5 0836+710 during a high activity period detected by the Large Area Telescope on board the Fermi Gamma-ray Space Telescope. Two major flares were detected, in 2015 August and November. In both episodes, the apparent isotropic gamma-ray luminosity exceeds 10^50 erg/s, with a doubling time scale of about 3 hours. The high gamma-ray activity may be related to a superluminal knot that emerged from the core in 2015 April at the peak of the radio activity and is moving downstream along the jet. The low variability observed in X-rays may indicate that X-ray emission is produced by the low-energy tail of the same electron population that produces the gamma-ray emission. The analysis of full-polarization pc-scale radio observations suggests the presence of a limb-brightened polarization structure at about 1 mas from the core in which a rotation measure gradient with a sign change is observed transverse to the jet direction. These characteristics are consistent with a scenario in which Faraday rotation is produced by a sheath of thermal electrons with a toroidal magnetic field surrounding the emitting jet., Comment: 26 pages, 13 figures, and 7 tables. Accepted for publication in Monthly Notices of the Royal Astronomical Society
Published: 2019
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36. Sensitivity of the Cherenkov Telescope Array to spectral signatures of hadronic PeVatrons with application to Galactic Supernova Remnants

Author: Acero, F., Acharyya, A., Adam, R., Aguasca-Cabot, A., Agudo, I., Aguirre-Santaella, A., Alfaro, J., Aloisio, R., Crespo, N. Álvarez, Batista, R. Alves, Amati, L., Amato, E., Ambrosi, G., Angüner, E.O., Aramo, C., Arcaro, C., Armstrong, T., Asano, K., Ascasibar, Y., Aschersleben, J., Backes, M., Baktash, A., Balazs, C., Balbo, M., Ballet, J., Larriva, A. Baquero, Martins, V. Barbosa, de Almeida, U. Barres, Barrio, J.A., Bastieri, D., Baxter, J.R., Tjus, J. Becker, Benbow, W., Bernardos-Martín, M.I., Bernete, J., Berti, A., Bertucci, B., Beshley, V., Bhattacharjee, P., Bhattacharyya, S., Biland, A., Bissaldi, E., Biteau, J., Blanch, O., Bordas, P., Bottacini, E., Bregeon, J., Brose, R., Bucciantini, N., Bulgarelli, A., Capasso, M., Dolcetta, R.A. Capuzzo, Caraveo, P., Cardillo, M., Carosi, R., Casanova, S., Cascone, E., Cassol, F., Catalani, F., Cerruti, M., Chadwick, P., Chaty, S., Chen, A., Chernyakova, M., Chiavassa, A., Chudoba, J., Coimbra-Araujo, C., Conforti, V., Contreras, J.L., Costa, A., Costantini, H., Cristofari, P., Crocker, R., D’Amico, G., D’Ammando, F., De Angelis, A., De Caprio, V., de Gouveia Dal Pino, E.M., de Ona Wilhelmi, E., de Souza, V., Delgado, C., della Volpe, D., Depaoli, D., Di Girolamo, T., Di Pierro, F., Di Tria, R., Di Venere, L., Diebold, S., Djuvsland, J.I., Donini, A., Doro, M., Dos Anjos, R.d.C., Dwarkadas, V.V., Einecke, S., Elsässer, D., Emery, G., Evoli, C., Falceta-Goncalves, D., Fedorova, E., Fegan, S., Ferrand, G., Fiandrini, E., Filipovic, M., Fioretti, V., Fiori, M., Foffano, L., Fontaine, G., Fukami, S., Galanti, G., Galaz, G., Gammaldi, V., Gasbarra, C., Ghalumyan, A., Ghirlanda, G., Giarrusso, M., Giavitto, G., Giglietto, N., Giordano, F., Giroletti, M., Giuliani, A., Giunti, L., Godinovic, N., Coelho, J. Goulart, Gréaux, L., Green, D., Grondin, M.-H., Gueta, O., Gunji, S., Hassan, T., Heller, M., Hernández-Cadena, S., Hinton, J., Hnatyk, B., Hnatyk, R., Hoffmann, D., Hofmann, W., Holder, J., Horan, D., Horvath, P., Hrabovsky, M., Hrupec, D., Inada, T., Incardona, F., Inoue, S., Ishio, K., Jamrozy, M., Janecek, P., Martínez, I. Jiménez, Jin, W., Jung-Richardt, I., Jurysek, J., Kaaret, P., Karas, V., Katz, U., Kerszberg, D., Khélifi, B., Kieda, D.B., Kissmann, R., Kleiner, T., Kluge, G., Kluzniak, W., Knödlseder, J., Kobayashi, Y., Kohri, K., Komin, N., Kornecki, P., Kubo, H., La Palombara, N., Láinez, M., Lamastra, A., Lapington, J., Lemoine-Goumard, M., Lenain, J.-P., Leone, F., Leto, G., Leuschner, F., Lindfors, E., Liodakis, I., Lohse, T., Lombardi, S., Longo, F., López-Coto, R., López-Moya, M., López-Oramas, A., Loporchio, S., Luque-Escamilla, P.L., Macias, O., Mackey, J., Majumdar, P., Mandat, D., Manganaro, M., Manicò, G., Marconi, M., Martí, J., Martínez, G., Martinez, M., Martinez, O., Mello, A.J.T.S., Menchiari, S., Meyer, D.M.-A., Micanovic, S., Miceli, D., Miceli, M., Michalowski, J., Miener, T., Miranda, J.M., Mitchell, A., Mode, B., Moderski, R., Mohrmann, L., Molina, E., Montaruli, T., Morcuende, D., Morlino, G., Morselli, A., Mosè, M., Moulin, E., Mukherjee, R., Munari, K., Murach, T., Nagai, A., Nagataki, S., Nemmen, R., Niemiec, J., Nieto, D., Rosillo, M. Nievas, Nikolajuk, M., Nishijima, K., Noda, K., Novosyadlyj, B., Nozaki, S., Ohishi, M., Ohm, S., Ohtani, Y., Okumura, A., Olmi, B., Ong, R.A., Orienti, M., Orito, R., Orlandini, M., Orlando, E., Orlando, S., Ostrowski, M., Oya, I., Pantaleo, F.R., Paredes, J.M., Patricelli, B., Pecimotika, M., Peresano, M., Pérez-Romero, J., Persic, M., Petruk, O., Piano, G., Pietropaolo, E., Pirola, G., Pittori, C., Pohl, M., Ponti, G., Prandini, E., Principe, G., Priyadarshi, C., Pueschel, E., Pühlhofer, G., Pumo, M.L., Quirrenbach, A., Rando, R., Razzaque, S., Reichherzer, P., Reimer, A., Reimer, O., Renaud, M., Reposeur, T., Ribó, M., Richtler, T., Rico, J., Rieger, F., Rigoselli, M., Riitano, L., Rizi, V., Roache, E., Romano, P., Romeo, G., Rosado, J., Rowell, G., Rudak, B., Sadeh, I., Safi-Harb, S., Saha, L., Sailer, S., Sánchez-Conde, M., Sarkar, S., Satalecka, K., Saturni, F.G., Scherer, A., Schovánek, P., Schussler, F., Schwanke, U., Scuderi, S., Seglar-Arroyo, M., Sergijenko, O., Servillat, M., Shang, R.-Y., Sharma, P., Siejkowski, H., Sliusar, V., Słowikowska, A., Sol, H., Specovius, A., Spencer, S.T., Spengler, G., Stamerra, A., Stanič, S., Starecki, T., Starling, R., Stolarczyk, T., Pereira, L.A. Stuani, Suda, Y., Suomijarvi, T., Sushch, I., Tajima, H., Tam, P.-H.T., Tanaka, S.J., Tavecchio, F., Testa, V., Tian, W., Tibaldo, L., Torres, D.F., Tothill, N., Vallage, B., Vallania, P., van Eldik, C., van Scherpenberg, J., Vandenbroucke, J., Acosta, M. Vazquez, Vecchi, M., Vercellone, S., Verna, G., Viana, A., Vignatti, J., Vitale, V., Vodeb, V., Vorobiov, S., Vuillaume, T., Wagner, S.J., Walter, R., White, M., Wierzcholska, A., Will, M., Williams, D., Yang, L., Yoshida, T., Yoshikoshi, T., Zaharijas, G., Zampieri, L., Zavrtanik, D., Zavrtanik, M., Zhdanov, V.I., and Z̆ivec, M.
Published: 2023
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37. Fermi and Swift Observations of GRB 190114C: Tracing the Evolution of High-Energy Emission from Prompt to Afterglow

Author: Ajello, M., Arimoto, M., Axelsson, M., Baldini, L., Barbiellini, G., Bastieri, D., Bellazzini, R., Berretta, A., Bissaldi, E., Blandford, R. D., Bonino, R., Bottacini, E., Bregeon, J., Bruel, P., Buehler, R., Burns, E., Buson, S., Cameron, R. A., Caputo, R., Caraveo, P. A., Cavazzuti, E., Chen, S., Chiaro, G., Ciprini, S., Cohen-Tanugi, J., Costantin, D., Cutini, S., D'Ammando, F., DeKlotz, M., Luque, P. de la Torre, de Palma, F., Desai, A., Di Lalla, N., Di Venere, L., Dirirsa, F. Fana, Fegan, S. J., Franckowiak, A., Fukazawa, Y., Funk, S., Fusco, P., Gargano, F., Gasparrini, D., Giglietto, N., Gill, R., Giordano, F., Giroletti, M., Granot, J., Green, D., Grenier, I. A., Grondin, M. H., Guiriec, S., Hays, E., Horan, D., Jóhannesson, G., Kocevski, D., Kovac'evic', M., Kuss, M., Larsson, S., Latronico, L., Lemoine-Goumard, M., Li, J., Liodakis, I., Longo, F., Loparco, F., Lovellette, M. N., Lubrano, P., Maldera, S., Malyshev, D., Manfreda, A., Martí-Devesa, G., Mazziotta, M. N., McEnery, J. E., Mereu, I., Meyer, M., Michelson, P. F., Mitthumsiri, W., Mizuno, T., Monzani, M. E., Moretti, E., Morselli, A., Moskalenko, I. V., Negro, M., Nuss, E., Omodei, N., Orienti, M., Orlando, E., Palatiello, M., Paliya, V. S., Paneque, D., Pei, Z., Persic, M., Pesce-Rollins, M., Petrosian, V., Piron, F., Poon, H., Porter, T. A., Principe, G., Racusin, J. L., Rainò, S., Rando, R., Rani, B., Razzano, M., Razzaque, S., Reimer, A., Reimer, O., Ryde, F., Parkinson, P. M. Saz, Serini, D., Sgrò, C., Siskind, E. J., Spandre, G., Spinelli, P., Tajima, H., Takagi, K., Takahashi, M. N., Tak, D., Thayer, J. B., Thompson, D. J., Torres, D. F., Troja, E., Valverde, J., Van Klaveren, B., Wood, K., Yassine, M., Zaharijas, G., Bhat, P. N., Briggs, M. S., Cleveland, W., Giles, M., Goldstein, A., Hui, M., Malacaria, C., Preece, R., Roberts, O., Veres, P., von Kienlin, A., Cenko, S. B., O'Brien, P., Beardmore, A. P., Lien, A., Osborne, J. P., Tohuvavohu, A., D'Elia, V., D'A, A., Perri, M., Gropp, J., Klingler, N., Capalbi, M., Tagliaferri, G., and Stamatikos, M.
Subjects: Astrophysics - High Energy Astrophysical Phenomena
Abstract: We report on the observations of gamma-ray burst (GRB) 190114C by the Fermi Gamma-ray Space Telescope and the Neil Gehrels Swift Observatory. The early-time observations reveal multiple emission components that evolve independently, with a delayed power-law component that exhibits significant spectral attenuation above 40 MeV in the first few seconds of the burst. This power-law component transitions to a harder spectrum that is consistent with the afterglow emission observed at later times. This afterglow component is clearly identifiable in the GBM and BAT light curves as a slowly fading emission component on which the rest of the prompt emission is superimposed. As a result, we are able to constrain the transition from internal shock to external shock dominated emission. We find that the temporal and spectral evolution of the broadband afterglow emission can be well modeled as synchrotron emission from a forward shock propagating into a wind-like circumstellar environment and find that high-energy photons observed by Fermi LAT are in tension with the theoretical maximum energy that can be achieved through synchrotron emission from a shock. These violations of the maximum synchrotron energy are further compounded by the detection of very high energy (VHE) emission above 300 GeV by MAGIC concurrent with our observations. We conclude that the observations of VHE photons from GRB 190114C necessitates either an additional emission mechanism at very high energies that is hidden in the synchrotron component in the LAT energy range, an acceleration mechanism that imparts energy to the particles at a rate that is faster than the electron synchrotron energy loss rate, or revisions of the fundamental assumptions used in estimating the maximum photon energy attainable through the synchrotron process., Comment: 24 pages, 9 figures, Accepted to ApJ
Published: 2019
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38. Monte Carlo studies for the optimisation of the Cherenkov Telescope Array layout

Author: Acharyya, A., Agudo, I., Angüner, E. O., Alfaro, R., Alfaro, J., Alispach, C., Aloisio, R., Batista, R. Alves, Amans, J. -P., Amati, L., Amato, E., Ambrosi, G., Antonelli, L. A., Aramo, C., Armstrong, T., Arqueros, F., Arrabito, L., Asano, K., Ashkar, H., Balazs, C., Balbo, M., Balmaverde, B., Barai, P., Barbano, A., Barkov, M., de Almeida, U. Barres, Barrio, J. A., Bastieri, D., González, J. Becerra, Tjus, J. Becker, Bellizzi, L., Benbow, W., Bernardini, E., Bernardos, M. I., Bernlöhr, K., Berti, A., Berton, M., Bertucci, B., Beshley, V., Biasuzzi, B., Bigongiari, C., Bird, R., Bissaldi, E., Biteau, J., Blanch, O., Blazek, J., Boisson, C., Bonanno, G., Bonardi, A., Bonavolontà, C., Bonnoli, G., Bordas, P., Böttcher, M., Bregeon, J., Brill, A., Brown, A. M., Brügge, K., Brun, P., Bruno, P., Bulgarelli, A., Bulik, T., Burton, M., Burtovoi, A., Busetto, G., Cameron, R., Canestrari, R., Capalbi, M., Caproni, A., Capuzzo-Dolcetta, R., Caraveo, P., Caroff, S., Carosi, R., Casanova, S., Cascone, E., Cassol, F., Catalani, F., Catalano, O., Cauz, D., Cerruti, M., Chaty, S., Chen, A., Chernyakova, M., Chiaro, G., Cieślar, M., Colak, S. M., Conforti, V., Congiu, E., Contreras, J. L., Cortina, J., Costa, A., Costantini, H., Cotter, G., Cristofari, P., Cumani, P., Cusumano, G., D'Aì, A., D'Ammando, F., Dangeon, L., Da Vela, P., Dazzi, F., De Angelis, A., De Caprio, V., Anjos, R. de Cássia dos, De Frondat, F., Pino, E. M. de Gouveia Dal, De Lotto, B., De Martino, D., de Naurois, M., Wilhelmi, E. de Oña, de Palma, F., de Souza, V., Del Santo, M., Delgado, C., della Volpe, D., Di Girolamo, T., Di Pierro, F., Di Venere, L., Díaz, C., Diebold, S., Djannati-Ataï, A., Dmytriiev, A., Prester, D. Dominis, Donini, A., Dorner, D., Doro, M., Dournaux, J. -L., Ebr, J., Ekoume, T. R. N., Elsässer, D., Emery, G., Falceta-Goncalves, D., Fedorova, E., Fegan, S., Feng, Q., Ferrand, G., Fiandrini, E., Fiasson, A., Filipovic, M., Fioretti, V., Fiori, M., Flis, S., Fonseca, M. V., Fontaine, G., Coromina, L. Freixas, Fukami, S., Fukui, Y., Funk, S., Füßling, M., Gaggero, D., Galanti, G., López, R. J. Garcia, Garczarczyk, M., Gascon, D., Gasparetto, T., Gaug, M., Ghalumyan, A., Gianotti, F., Giavitto, G., Giglietto, N., Giordano, F., Giroletti, M., Gironnet, J., Glicenstein, J. -F., Gnatyk, R., Goldoni, P., González, J. M., González, M. M., Gourgouliatos, K. N., Grabarczyk, T., Granot, J., Green, D., Greenshaw, T., Grondin, M. -H., Gueta, O., Hadasch, D., Hassan, T., Hayashida, M., Heller, M., Hervet, O., Hinton, J., Hiroshima, N., Hnatyk, B., Hofmann, W., Horvath, P., Hrabovsky, M., Hrupec, D., Humensky, T. B., Hütten, M., Inada, T., Iocco, F., Ionica, M., Iori, M., Iwamura, Y., Jamrozy, M., Janecek, P., Jankowsky, D., Jean, P., Jouvin, L., Jurysek, J., Kaaret, P., Kadowaki, L. H. S., Karkar, S., Kerszberg, D., Khélifi, B., Kieda, D., Kimeswenger, S., Kluźniak, W., Knapp, J., Knödlseder, J., Kobayashi, Y., Koch, B., Kocot, J., Komin, N., Kong, A., Kowal, G., Krause, M., Kubo, H., Kushida, J., Kushwaha, P., La Parola, V., La Rosa, G., Arquillo, M. Lallena, Lang, R. G., Lapington, J., Blanc, O. Le, Lefaucheur, J., de Oliveira, M. A. Leigui, Lemoine-Goumard, M., Lenain, J. -P., Leto, G., Lico, R., Lindfors, E., Lohse, T., Lombardi, S., Longo, F., Lopez, A., López, M., Lopez-Oramas, A., López-Coto, R., Loporchio, S., Luque-Escamilla, P. L., Lyard, E., Maccarone, M. C., Mach, E., Maggio, C., Majumdar, P., Malaguti, G., Mallamaci, M., Mandat, D., Maneva, G., Manganaro, M., Mangano, S., Marculewicz, M., Mariotti, M., Martí, J., Martínez, M., Martínez, G., Martínez-Huerta, H., Masuda, S., Maxted, N., Mazin, D., Meunier, J. -L., Meyer, M., Micanovic, S., Millul, R., Minaya, I. A., Mitchell, A., Mizuno, T., Moderski, R., Mohrmann, L., Montaruli, T., Moralejo, A., Morcuende, D., Morlino, G., Morselli, A., Moulin, E., Mukherjee, R., Munar, P., Mundell, C., Murach, T., Nagai, A., Nagayoshi, T., Naito, T., Nakamori, T., Nemmen, R., Niemiec, J., Nieto, D., Rosillo, M. Nievas, Nikołajuk, M., Ninci, D., Nishijima, K., Noda, K., Nosek, D., Nöthe, M., Nozaki, S., Ohishi, M., Ohtani, Y., Okumura, A., Ong, R. A., Orienti, M., Orito, R., Ostrowski, M., Otte, N., Ou, Z., Oya, I., Pagliaro, A., Palatiello, M., Palatka, M., Paoletti, R., Paredes, J. M., Pareschi, G., Parmiggiani, N., Parsons, R. D., Patricelli, B., Pe'er, A., Pech, M., Del Campo, P. Peñil, Pérez-Romero, J., Perri, M., Persic, M., Petrucci, P. -O., Petruk, O., Pfrang, K., Piel, Q., Pietropaolo, E., Pohl, M., Polo, M., Poutanen, J., Prandini, E., Produit, N., Prokoph, H., Prouza, M., Przybilski, H., Pühlhofer, G., Punch, M., Queiroz, F., Quirrenbach, A., Rainò, S., Rando, R., Razzaque, S., Reimer, O., Renault-Tinacci, N., Renier, Y., Ribeiro, D., Ribó, M., Rico, J., Rieger, F., Rizi, V., Fernandez, G. Rodriguez, Rodriguez-Ramirez, J. C., Vázquez, J. J. Rodríguez, Romano, P., Romeo, G., Roncadelli, M., Rosado, J., Rowell, G., Rudak, B., Rugliancich, A., Rulten, C., Sadeh, I., Saha, L., Saito, T., Sakurai, S., Greus, F. Salesa, Sangiorgi, P., Sano, H., Santander, M., Santangelo, A., Santos-Lima, R., Sanuy, A., Satalecka, K., Saturni, F. G., Sawangwit, U., Schlenstedt, S., Schovanek, P., Schussler, F., Schwanke, U., Sciacca, E., Scuderi, S., Sedlaczek, K., Seglar-Arroyo, M., Sergijenko, O., Seweryn, K., Shalchi, A., Shellard, R. C., Siejkowski, H., Sillanpää, A., Sinha, A., Sironi, G., Sliusar, V., Slowikowska, A., Sol, H., Specovius, A., Spencer, S., Spengler, G., Stamerra, A., Stanič, S., Stawarz, Ł., Stefanik, S., Stolarczyk, T., Straumann, U., Suomijarvi, T., Świerk, P., Szepieniec, T., Tagliaferri, G., Tajima, H., Tam, T., Tavecchio, F., Taylor, L., Tejedor, L. A., Temnikov, P., Terzic, T., Testa, V., Tibaldo, L., Peixoto, C. J. Todero, Tokanai, F., Tomankova, L., Tonev, D., Torres, D. F., Tosti, G., Tosti, L., Tothill, N., Toussenel, F., Tovmassian, G., Travnicek, P., Trichard, C., Umana, G., Vagelli, V., Valentino, M., Vallage, B., Vallania, P., Valore, L., Vandenbroucke, J., Varner, G. S., Vasileiadis, G., Vassiliev, V., Acosta, M. Vázquez, Vecchi, M., Vercellone, S., Vergani, S., Vettolani, G. P., Viana, A., Vigorito, C. F., Vink, J., Vitale, V., Voelk, H., Vollhardt, A., Vorobiov, S., Wagner, S. J., Walter, R., Werner, F., White, R., Wierzcholska, A., Will, M., Williams, D. A., Wischnewski, R., Yang, L., Yoshida, T., Yoshikoshi, T., Zacharias, M., Zampieri, L., Zavrtanik, M., Zavrtanik, D., Zdziarski, A. A., Zech, A., Zechlin, H., Zenin, A., Zhdanov, V. I., Zimmer, S., and Zorn, J.
Subjects: Astrophysics - Instrumentation and Methods for Astrophysics
Abstract: The Cherenkov Telescope Array (CTA) is the major next-generation observatory for ground-based very-high-energy gamma-ray astronomy. It will improve the sensitivity of current ground-based instruments by a factor of five to twenty, depending on the energy, greatly improving both their angular and energy resolutions over four decades in energy (from 20 GeV to 300 TeV). This achievement will be possible by using tens of imaging Cherenkov telescopes of three successive sizes. They will be arranged into two arrays, one per hemisphere, located on the La Palma island (Spain) and in Paranal (Chile). We present here the optimised and final telescope arrays for both CTA sites, as well as their foreseen performance, resulting from the analysis of three different large-scale Monte Carlo productions., Comment: 48 pages, 16 figures, accepted for publication in Astroparticle Physics
Published: 2019
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39. From radio-quiet to radio-silent: low luminosity Seyfert radio cores

Author: Chiaraluce, E., Bruni, G., Panessa, F., Giroletti, M., Orienti, M., Rampadarath, H., Vagnetti, F., and Tombesi, F.
Subjects: Astrophysics - Astrophysics of Galaxies
Abstract: A strong effort has been devoted to understand the physical origin of radio emission from low-luminosity AGN (LLAGN), but a comprehensive picture is still missing. We used high-resolution ($\le$1 arcsec), multi-frequency (1.5, 5.5, 9 and 14 GHz) NSF's Karl G. Jansky Very Large Array (VLA) observations to characterise the state of the nuclear region of ten Seyfert nuclei, which are the faintest members of a complete, distance-limited sample of 28 sources. With the sensitivity and resolution guaranteed by the VLA-A configuration, we measured radio emission for six sources (NGC3185, NGC3941, NGC4477, NGC4639, NGC4698 and NGC4725), while for the remaining four (NGC0676, NGC1058, NGC2685 and NGC3486) we put upper limits at tens uJy/beam level, below the previous 0.12 mJy/beam level of Ho&Ulvestad (2001), corresponding to luminosities down to L$\le10^{19}$ W/Hz at 1.5 GHz for the highest RMS observation. Two sources, NGC4639 and NGC4698, exhibit spectral slopes compatible with inverted spectra ($\alpha\le$0, $S_{\nu}\,\propto\,{\nu}^{-\alpha}$), hint for radio emission from an optically-thick core, while NGC4477 exhibits a steep (+0.52$\pm$0.09) slope. The detected sources are mainly compact on scales $\le$ arcseconds, predominantly unresolved, except NGC3185 and NGC3941, in which the resolved radio emission could be associated to star-formation processes. A significant X-ray - radio luminosities correlation is extended down to very low luminosities, with slope consistent with inefficient accretion, expected at such low Eddington ratios. Such sources will be one of the dominant Square Kilometre Array (SKA) population, allowing a deeper understanding of the physics underlying such faint AGN., Comment: accepted for publication on MNRAS (19 pages, 26 figures)
Published: 2019
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40. MAGIC and Fermi-LAT gamma-ray results on unassociated HAWC sources

Author: Ahnen, M. L., Ansoldi, S., Antonelli, L. A., Arcaro, C., Baack, D., Babić, A., Banerjee, B., Bangale, P., de Almeida, U. Barres, Barrio, J. A., González, J. Becerra, Bednarek, W., Bernardini, E., Berse, R. Ch., Berti, A., Bhattacharyya, W., Biland, A., Blanch, O., Bonnoli, G., Carosi, R., Carosi, A., Ceribella, G., Chatterjee, A., Colak, S. M., Colin, P., Colombo, E., Contreras, J. L., Cortina, J., Covino, S., Cumani, P., Da Vela, P., Dazzi, F., De Angelis, A., De Lotto, B., Delfino, M., Delgado, J., Di Pierro, F., Domínguez, A., Prester, D. Dominis, Dorner, D., Doro, M., Einecke, S., Elsaesser, D., Ramazani, V. Fallah, Fernández-Barral, A., Fidalgo, D., Fonseca, M. V., Font, L., Fruck, C., Galindo, D., López, R. J. García, Garczarczyk, M., Gaug, M., Giammaria, P., Godinović, N., Gora, D., Guberman, D., Hadasch, D., Hahn, A., Hassan, T., Hayashida, M., Herrera, J., Hose, J., Hrupec, D., Ishio, K., Konno, Y., Kubo, H., Kushida, J., Kuveždić, D., Lelas, D., Lindfors, E., Lombardi, S., Longo, F., López, M., Maggio, C., Majumdar, P., Makariev, M., Maneva, G., Manganaro, M., Mannheim, K., Maraschi, L., Mariotti, M., Martínez, M., Masuda, S., Mazin, D., Mielke, K., Minev, M., Miranda, J. M., Mirzoyan, R., Moralejo, A., Moreno, V., Moretti, E., Nagayoshi, T., Neustroev, V., Niedzwiecki, A., Rosillo, M. Nievas, Nigro, C., Nilsson, K., Ninci, D., Nishijima, K., Noda, K., Nogués, L., Paiano, S., Palacio, J., Paneque, D., Paoletti, R., Paredes, J. M., Pedaletti, G., Peresano, M., Persic, M., Moroni, P. G. Prada, Prandini, E., Puljak, I., Garcia, J. R., Reichardt, I., Rhode, W., Ribó, M., Rico, J., Righi, C., Rugliancich, A., Saito, T., Satalecka, K., Schweizer, T., Sitarek, J., Šnidarić, I., Sobczynska, D., Stamerra, A., Strzys, M., Surić, T., Takahashi, M., Takalo, L., Tavecchio, F., Temnikov, P., Terzić, T., Teshima, M., Torres-Albà, N., Treves, A., Tsujimoto, S., Vanzo, G., Acosta, M. Vazquez, Vovk, I., Ward, J. E., Will, M., Zarić, D., Albert, A., Alfaro, R., Alvarez, C., Arceo, R., Arteaga-Velázquez, J. C., Rojas, D. Avila, Solares, H. A. Ayala, Becerril, A., Belmont-Moreno, E., BenZvi, S. Y., Bernal, A., Braun, J., Caballero-Mora, K. S., Capistrán, T., Carramiñana, A., Casanova, S., Castillo, M., Cotti, U., Cotzomi, J., de León, S. Coutiño, De León, C., De la Fuente, E., Hernandez, R. Diaz, Dichiara, S., Dingus, B. L., DuVernois, M. A., Díaz-Vélez, J. C., Ellsworth, R. W., Engel, K., Enriquez-Rivera, O., Fiorino, D. W., Fleischhack, H., Fraija, N., García-González, J. A., Garfias, F., González-Muñoz, A., González, M. M., Goodman, J. A., Hampel-Arias, Z., Harding, J. P., Hernandez, S., Hueyotl-Zahuantitla, F., Hui, C. M., Hüntemeyer, P., Iriarte, A., Jardin-Blicq, A., Joshi, V., Kaufmann, S., Lara, A., Lauer, R. J., Lee, W. H., Lennarz, D., Vargas, H. León, Linnemann, J. T., Longinotti, A. L., Luis-Raya, G., Luna-García, R., López-Coto, R., Malone, K., Marinelli, S. S., Martinez, O., Martinez-Castellanos, I., Martínez-Castro, J., Martínez-Huerta, H., Matthews, J. A., Miranda-Romagnoli, P., Moreno, E., Mostafá, M., Nayerhoda, A., Nellen, L., Newbold, M., Nisa, M. U., Noriega-Papaqui, R., Pelayo, R., Pretz, J., Pérez-Pérez, E. G., Ren, Z., Rho, C. D., Rivière, C., Rosa-González, D., Rosenberg, M., Ruiz-Velasco, E., Greus, F. Salesa, Sandoval, A., Schneider, M., Arroyo, M. Seglar, Sinnis, G., Smith, A. J., Springer, R. W., Surajbali, P., Taboada, I., Tibolla, O., Tollefson, K., Torres, I., Ukwatta, T. N., Vianello, G., Villaseñor, L., Werner, F., Westerhoff, S., Wood, J., Yapici, T., Yodh, G., Zepeda, A., Zhou, H., Álvarez, J. D., Ajello, M., Baldini, L., Barbiellini, G., Berenji, B., Bissaldi, E., Blandford, R. D., Bonino, R., Bottacini, E., Brandt, T. J., Bregeon, J., Bruel, P., Cameron, R. A., Caputo, R., Caraveo, P. A., Castro, D., Cavazzuti, E., Chiaro, G., Ciprini, S., Costantin, D., D'Ammando, F., de Palma, F., Desai, A., Di Lalla, N., Di Mauro, M., Di Venere, L., Favuzzi, C., Fukazawa, Y., Funk, S., Fusco, P., Gargano, F., Gasparrini, D., Giglietto, N., Giordano, F., Giroletti, M., Glanzman, T., Green, D., Grenier, I. A., Guiriec, S., Harding, A. K., Hays, E., Hewitt, J. W., Horan, D., Jóhannesson, G., Kuss, M., Larsson, S., Liodakis, I., Loparco, F., Lubrano, P., Magill, J. D., Maldera, S., Manfreda, A., Mazziotta, M. N., Mereu, I., Michelson, P. F., Mizuno, T., Monzani, M. E., Morselli, A., Moskalenko, I. V., Negro, M., Nuss, E., Omodei, N., Orienti, M., Orlando, E., Ormes, J. F., Palatiello, M., Paliya, V. S., Pesce-Rollins, M., Petrosian, V., Piron, F., Porter, T. A., Principe, G., Rainò, S., Rani, B., Razzano, M., Razzaque, S., Reimer, A., Reimer, O., Sgrò, C., Siskind, E. J., Spandre, G., Spinelli, P., Tajima, H., Thayer, J. B., Thompson, D. J., Torres, D. F., Torresi, E., Troja, E., Valverde, J., Wood, K., and Yassine, M.
Subjects: Astrophysics - High Energy Astrophysical Phenomena
Abstract: The HAWC Collaboration released the 2HWC catalog of TeV sources, in which 19 show no association with any known high-energy (HE; E > 10 GeV) or very-high-energy (VHE; E > 300 GeV) sources. This catalog motivated follow-up studies by both the MAGIC and Fermi-LAT observatories with the aim of investigating gamma-ray emission over a broad energy band. In this paper, we report the results from the first joint work between HAWC, MAGIC and Fermi-LAT on three unassociated HAWC sources: 2HWC J2006+341, 2HWC J1907+084* and 2HWC J1852+013*. Although no significant detection was found in the HE and VHE regimes, this investigation shows that a minimum 1 degree extension (at 95% confidence level) and harder spectrum in the GeV than the one extrapolated from HAWC results are required in the case of 2HWC J1852+013*, while a simply minimum extension of 0.16 degrees (at 95% confidence level) can already explain the scenario proposed by HAWC for the remaining sources. Moreover, the hypothesis that these sources are pulsar wind nebulae is also investigated in detail., Comment: 12 pages, 3 figures. Accepted for publication in MNRAS
Published: 2019
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41. Unresolved Gamma-Ray Sky through its Angular Power Spectrum

Author: Ackermann, M., Ajello, M., Baldini, L., Ballet, J., Barbiellini, G., Bastieri, D., Bellazzini, R., Bissaldi, E., Blandford, R. D., Bonino, R., Bottacini, E., Bregeon, J., Bruel, P., Buehler, R., Burns, E., Buson, S., Cameron, R. A., Caputo, R., Caraveo, P. A., Cavazzuti, E., Chen, S., Chiaro, G., Ciprini, S., Costantin, D., Cuoco, A., Cutini, S., D'Ammando, F., Luque, P. de la Torre, de Palma, F., Desai, A., Digel, S. W., Di Lalla, N., Di Mauro, M., Di Venere, L., Dirirsa, F. Fana, Favuzzi, C., Franckowiak, A., Fukazawa, Y., Funk, S., Fusco, P., Gargano, F., Gasparrini, D., Giglietto, N., Giordano, F., Giroletti, M., Green, D., Grenier, I. A., Guillemot, L., Guiriec, S., Horan, D., Johannesson, G., Kuss, M., Larsson, S., Latronico, L., Li, J., Liodakis, I., Longo, F., Loparco, F., Lubrano, P., Magill, J. D., Maldera, S., Malyshev, D., Manfreda, A., Mazziotta, M. N., Mereu, I., Michelson, P. F., Mitthumsiri, W., Mizuno, T., Monzani, M. E., Morselli, A., Moskalenko, I. V., Negro, M., Nuss, E., Orienti, M., Orlando, E., Palatiello, M., Paliya, V. S., Paneque, D., Persic, M., Pesce-Rollins, M., Petrosian, V., Piron, F., Porter, T. A., Principe, G., Raino, S., Rando, R., Razzano, M., Razzaque, S., Reimer, A., Reimer, O., Serini, D., Sgro, C., Siskind, E. J., Spandre, G., Spinelli, P., Suson, D. J., Tajima, H., Takahashi, M., Thayer, J. B., Tibaldo, L., Torres, D. F., Troja, E., Venters, T. M., Vianello, G., Wood, K., Yassine, M., Zaharijas, G., Ammazzalorso, S., Fornengo, N., and Regis, M.
Subjects: Astrophysics - High Energy Astrophysical Phenomena, Astrophysics - Cosmology and Nongalactic Astrophysics, High Energy Physics - Phenomenology
Abstract: The gamma-ray sky has been observed with unprecedented accuracy in the last decade by the Fermi large area telescope (LAT), allowing us to resolve and understand the high-energy Universe. The nature of the remaining unresolved emission (unresolved gamma-ray background, UGRB) below the LAT source detection threshold can be uncovered by characterizing the amplitude and angular scale of the UGRB fluctuation field. This work presents a measurement of the UGRB autocorrelation angular power spectrum based on eight years of Fermi LAT Pass 8 data products. The analysis is designed to be robust against contamination from resolved sources and noise systematics. The sensitivity to subthreshold sources is greatly enhanced with respect to previous measurements. We find evidence (with $\sim$3.7$\sigma$ significance) that the scenario in which two classes of sources contribute to the UGRB signal is favored over a single class. A double power law with exponential cutoff can explain the anisotropy energy spectrum well, with photon indices of the two populations being 2.55 $\pm$ 0.23 and 1.86 $\pm$ 0.15., Comment: 8 + 12 (SOM) pages, Contact author: Michela Negro (michela.negro@to.infn.it). (Typos in Tab. VII in previous versions)
Published: 2018
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42. AGILE, Fermi, Swift, and GASP-WEBT multi-wavelength observations of the high-redshift blazar 4C $+$71.07 in outburst

Author: Vercellone, S., Romano, P., Piano, G., Vittorini, V., Donnarumma, I., Munar-Adrover, P., Raiteri, C. M., Villata, M., Verrecchia, F., Lucarelli, F., Pittori, C., Bulgarelli, A., Fioretti, V., Tavani, M., Acosta-Pulido, J. A., Agudo, I., Arkharov, A. A., Bach, U., Bachev, R., Borman, G. A., Butuzova, M. S., Carnerero, M. I., Casadio, C., Damljanovic, G., D'Ammando, F., Di Paola, A., Doroshenko, V. T., Efimova, N. V., Ehgamberdiev, Sh. A., Giroletti, M., Gómez, J. L., Grishina, T. S., Järvelä, E., Klimanov, S. A., Kopatskaya, E. N., Kurtanidze, O. M., Lähteenmäki, A., Larionov, V. M., Larionova, L. V., Mihov, B., Mirzaqulov, D. O., Molina, S. N., Morozova, D. A., Nazarov, S. V., Orienti, M., Righini, S., Savchenko, S. S., Semkov, E., Slavcheva-Mihova, L., Strigachev, A., Tornikoski, M., Troitskaya, Yu. V., Vince, O., Cattaneo, P. W., Colafrancesco, S., Longo, F., Morselli, A., Paoletti, F., and Parmiggiani, N.
Subjects: Astrophysics - High Energy Astrophysical Phenomena
Abstract: The flat-spectrum radio quasar 4C $+$71.07 is a high-redshift ($z=2.172$), $\gamma$-loud blazar whose optical emission is dominated by the thermal radiation from accretion disc. 4C $+$71.07 has been detected in outburst twice by the AGILE $\gamma$-ray satellite during the period end of October - mid November 2015, when it reached a $\gamma$-ray flux of the order of $F_{\rm E>100\,MeV} = (1.2 \pm 0.3)\times 10^{-6}$ photons cm$^{-2}$ s$^{-1}$ and $F_{\rm E>100\,MeV} = (3.1 \pm 0.6)\times 10^{-6}$ photons cm$^{-2}$ s$^{-1}$, respectively, allowing us to investigate the properties of the jet and of the emission region. We investigated its spectral energy distribution by means of almost simultaneous observations covering the cm, mm, near-infrared, optical, ultra-violet, X-ray and $\gamma$-ray energy bands obtained by the GASP-WEBT Consortium, the Swift and the AGILE and Fermi satellites. The spectral energy distribution of the second $\gamma$-ray flare (the one whose energy coverage is more dense) can be modelled by means of a one-zone leptonic model, yielding a total jet power of about $4\times10^{47}$ erg s$^{-1}$. During the most prominent $\gamma$-ray flaring period our model is consistent with a dissipation region within the broad-line region. Moreover, this class of high-redshift, large-mass black-hole flat-spectrum radio quasars might be good targets for future $\gamma$-ray satellites such as e-ASTROGAM., Comment: Accepted for publication in A&A. 9 pages, 4 Figures, 3 Tables
Published: 2018
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43. VERITAS and Fermi-LAT observations of new HAWC sources

Author: VERITAS Collaboration, Abeysekara, A. U., Archer, A., Benbow, W., Bird, R., Brose, R., Buchovecky, M., Buckley, J. H., Bugaev, V., Chromey, A. J., Connolly, M. P., Cui, W., Daniel, M. K., Falcone, A., Feng, Q., Finley, J. P., Fortson, L., Furniss, A., Hutten, M., Hanna, D., Hervet, O., Holder, J., Hughes, G., Humensky, T. B., Johnson, C. A., Kaaret, P., Kar, P., Kertzman, M., Kieda, D., Krause, M., Krennrich, F., Kumar, S., Lang, M. J., Lin, T. T. Y., McArthur, S., Moriarty, P., Mukherjee, R., O'Brien, S., Ong, R. A., Otte, A. N., Park, N., Petrashyk, A., Pohl, M., Pueschel, E., Quinn, J., Ragan, K., Reynolds, P. T., Richards, G. T., Roache, E., Rulten, C., Sadeh, I., Santander, M., Sembroski, G. H., Shahinyan, K., Sushch, I., Tyler, J., Wakely, S. P., Weinstein, A., Wells, R. M., Wilcox, P., Wilhelm, A., Williams, D. A., Williamson, T. J., Zitzer, B., Collaboration, Fermi-LAT, Abdollahi, S., Ajello, M., Baldini, L., Barbiellini, G., Bastieri, D., Bellazzini, R., Berenji, B., Bissaldi, E., Blandford, R. D., Bonino, R., Bottacini, E., Brandt, T. J., Bruel, P., Buehler, R., Cameron, R. A., Caputo, R., Caraveo, P. A., Castro, D., Cavazzuti, E., Charles, E., Chiaro, G., Ciprini, S., Cohen-Tanugi, J., Costantin, D., Cutini, S., D'Ammando, F., de Palma, F., Di Lalla, N., Di Mauro, M., Di Venere, L., Dominguez, A., Favuzzi, C., Fegan, S. J., Franckowiak, A., Fukazawa, Y., Funk, S., Fusco, P., Gargano, F., Gasparrini, D., Giglietto, N., Giordano, F., Giroletti, M., Green, D., Grenier, I. A., Guillemot, L., Guiriec, S., Hays, E., Hewitt, J. W., Horan, D., Johannesson, G., Kensei, S., Kuss, M., Larsson, S., Latronico, L., Lemoine-Goumard, M., Li, J., Longo, F., Loparco, F., Lovellette, M. N., Lubrano, P., Magill, J. D., Maldera, S., Mazziotta, M. N., McEnery, J. E., Michelson, P. F., Mitthumsiri, W., Mizuno, T., Monzani, M. E., Morselli, A., Moskalenko, I. V., Negro, M., Nuss, E., Ojha, R., Omodei, N., Orienti, M., Orlando, E., Palatiello, M., Paliya, V. S., Paneque, D., Perkins, J. S., Persic, M., Pesce-Rollins, M., Petrosian, V., Piron, F., Porter, T. A., Principe, G., Raino, S., Rando, R., Rani, B., Razzano, M., Razzaque, S., Reimer, A., Reimer, O., Reposeur, T., Sgro, C., Siskind, E. J., Spandre, G., Spinelli, P., Suson, D. J., Tajima, H., Thayer, J. B., Thompson, D. J., Torres, D. F., Tosti, G., Troja, E., Valverde, J., Vianello, G., Vogel, M., Wood, K., Yassine, M., Collaboration, HAWC, Alfaro, R., Alvarez, C., Alvarez, J. D., Arceo, R., Arteaga-Velazquez, J. C., Rojas, D. Avila, Solares, H. A. Ayala, Becerril, A., Belmont-Moreno, E., BenZvi, S. Y., Bernal, A., Braun, J., Brisbois, C., Caballero-Mora, K. S., Capistran, T., Carraminana, A., Casanova, S., Castillo, M., Cotti, U., Cotzomi, J., de Leon, S. Coutino, De Leon, C., De la Fuente, E., Dichiara, S., Dingus, B. L., DuVernois, M. A., Diaz-Velez, J. C., Engel, K., Enriquez-Rivera, O., Fiorino, D. W., Fleischhack, H., Fraija, N., Garcia-Gonzalez, J. A., Garfias, F., Munoz, A. Gonzalez, Gonzalez, M. M., Goodman, J. A., Hampel-Arias, Z., Harding, J. P., Hernandez, S., Hernandez-Almada, A., Hona, B., Hueyotl-Zahuantitla, F., Hui, C. M., Huntemeyer, P., Iriarte, A., Jardin-Blicq, A., Joshi, V., Kaufmann, S., Lara, A., Lauer, R. J., Lee, W. H., Lennarz, D., Vargas, H. Leon, Linnemann, J. T., Longinotti, A. L., Luis-Raya, G., Luna-Garcia, R., Lopez-Coto, R., Malone, K., Marinelli, S. S., Martinez, O., Martinez-Castellanos, I., Martinez-Castro, J., Martinez-Huerta, H., Matthews, J. A., Miranda-Romagnoli, P., Moreno, E., Mostafa, M., Nayerhoda, A., Nellen, L., Newbold, M., Nisa, M. U., Noriega-Papaqui, R., Pelayo, R., Pretz, J., Perez-Perez, E. G., Ren, Z., Rho, C. D., Riviere, C., Rosa-Gonzalez, D., Rosenberg, M., Ruiz-Velasco, E., Salazar, H., Greus, F. Salesa, Sandoval, A., Schneider, M., Arroyo, M. Seglar, Sinnis, G., Smith, A. J., Springer, R. W., Surajbali, P., Taboada, I., Tibolla, O., Tollefson, K., Torres, I., Ukwatta, T. N., Villasenor, L., Weisgarber, T., Westerhoff, S., Wisher, I. G., Wood, J., Yapici, T., Yodh, G., Zepeda, A., and Zhou, H.
Subjects: Astrophysics - High Energy Astrophysical Phenomena
Abstract: The HAWC (High Altitude Water Cherenkov) collaboration recently published their 2HWC catalog, listing 39 very high energy (VHE; >100~GeV) gamma-ray sources based on 507 days of observation. Among these, there are nineteen sources that are not associated with previously known TeV sources. We have studied fourteen of these sources without known counterparts with VERITAS and Fermi-LAT. VERITAS detected weak gamma-ray emission in the 1~TeV-30~TeV band in the region of DA 495, a pulsar wind nebula coinciding with 2HWC J1953+294, confirming the discovery of the source by HAWC. We did not find any counterpart for the selected fourteen new HAWC sources from our analysis of Fermi-LAT data for energies higher than 10 GeV. During the search, we detected GeV gamma-ray emission coincident with a known TeV pulsar wind nebula, SNR G54.1+0.3 (VER J1930+188), and a 2HWC source, 2HWC J1930+188. The fluxes for isolated, steady sources in the 2HWC catalog are generally in good agreement with those measured by imaging atmospheric Cherenkov telescopes. However, the VERITAS fluxes for SNR G54.1+0.3, DA 495, and TeV J2032+4130 are lower than those measured by HAWC and several new HAWC sources are not detected by VERITAS. This is likely due to a change in spectral shape, source extension, or the influence of diffuse emission in the source region., Comment: Accepted for publication in the ApJ, Corresponding author: Nahee Park (VERITAS Collaboration), John W. Hewitt (Fermi-LAT Collaboration), Ignacio Taboada (HAWC Collaboration), 30 pages, 12 figures
Published: 2018
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44. Evidence of jet-clump interaction: a flip of the radio jet head of 3C~84

Author: Kino, M., Wajima, K., Kawakatu, N., Nagai, H., Orienti, M., Giovannini, G., Hada, K., Niinuma, K., and Giroletti, M.
Subjects: Astrophysics - High Energy Astrophysical Phenomena
Abstract: Radio jets in active galaxies have been expected to interact with circumnuclear environments in their early phase evolutions. By performing the multi-epoch monitoring observation with the KVN and VERA Array (KaVA) at 43~GHz, we investigate the kinematics of the notable newborn bright component C3 located at the tip of the recurrent jet of 3C~84. During 2015 August-September, we discover the flip of C3 and the amount of the flip is about 0.4~milli-arcsecond in angular scale, which corresponds to 0.14 parsec in physical scale. After the flip of C3, it wobbled at the same location for a few months and then it restarted to propagate towards the southern direction. The flux density of C3 coherently showed the monotonic increase during the observation period. The flip is in good agreement with hydrodynamical simulations of jets in clumpy ambient medium. We estimate the number density of the putative clump based on the momentum balance between the jet thrust and the ram pressure from the clump and it is about $10^{3-5}~{\rm cm^{-3}}$. We briefly discuss possible origins of the clump., Comment: 11 pages, 6 figures, 1 table. Accepted for publication in ApJ
Published: 2018
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45. A wide and collimated radio jet in 3C 84 on the scale of a few hundred gravitational radii

Author: Giovannini, G., Savolainen, T., Orienti, M., Nakamura, M., Nagai, H., Kino, M., Giroletti, M., Hada, K., Bruni, G., Kovalev, Y. Y., Anderson, J. M., D'Ammando, F., Hodgson, J., Honma, M., Krichbaum, T. P., Lee, S. -S., Lico, R., Lisakov, M. M., Lobanov, A. P., Petrov, L., Sohn, B. W., Sokolovsky, K. V., Voitsik, P. A., Zensus, J. A., and Tingay, S.
Subjects: Astrophysics - Astrophysics of Galaxies, Astrophysics - High Energy Astrophysical Phenomena
Abstract: Understanding the launching, acceleration, and collimation of jets powered by active galactic nuclei remains an outstanding problem in relativistic astrophysics. This is partly because observational tests of jet formation models suffer from the limited angular resolution of ground-based very long baseline interferometry that has thus far been able to probe the transverse jet structure in the acceleration and collimation zone of only two sources. Here we report radio interferometric observations of 3C 84 (NGC 1275), the central galaxy of the Perseus cluster, made with an array including the orbiting radio telescope of the RadioAstron mission. The obtained image transversely resolves the edge-brightened jet in 3C 84 only 30 microarcseconds from the core, which is ten times closer to the central engine than what has been possible in previous ground-based observations, and it allows us to measure the jet collimation profile from ~ 100 to ~10000 gravitational radii from the black hole. The previously found, almost cylindrical jet profile on scales larger than a few thousand r_g is now seen to continue at least down to a few hundred r_g from the black hole and we find a broad jet with a transverse radius larger than about 250 r_g at only 350 r_g from the core. If the bright outer jet layer is launched by the black hole ergosphere, it has to rapidly expand laterally on scales smaller than 100 r_g. If this is not the case, then this jet sheath is likely launched from the accretion disk., Comment: Unedited, revised manuscript of the Letter published as Advance Online Publication (AOP) on the Nature Astronomy website on 02 April 2018. 15 pages, 3 figures
Published: 2018
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46. FBQS J1644+2619: multiwavelength properties and its place in the class of gamma-ray emitting Narrow Line Seyfert 1s

Author: Larsson, J., D'Ammando, F., Falocco, S., Giroletti, M., Orienti, M., Piconcelli, E., and Righini, S.
Subjects: Astrophysics - High Energy Astrophysical Phenomena, Astrophysics - Astrophysics of Galaxies
Abstract: A small fraction of Narrow Line Seyfert 1s (NLSy1s) are observed to be gamma-ray emitters. Understanding the properties of these sources is of interest since the majority of NLSy1s are very different from typical blazars. Here, we present a multi-frequency analysis of FBQS J1644+2619, one of the most recently discovered gamma-ray emitting NLSy1s. We analyse an ~80 ks XMM-Newton observation obtained in 2017, as well as quasi-simultaneous multi-wavelength observations covering the radio - gamma-ray range. The spectral energy distribution of the source is similar to the other gamma-ray NLSy1s, confirming its blazar-like nature. The X-ray spectrum is characterised by a hard photon index (Gamma = 1.66) above 2 keV and a soft excess at lower energies.The hard photon index provides clear evidence that inverse Compton emission from the jet dominates the spectrum, while the soft excess can be explained by a contribution from the underlying Seyfert emission. This contribution can be fitted by reflection of emission from the base of the jet, as well as by Comptonisation in a warm, optically thick corona. We discuss our results in the context of the other gamma-ray NLSy1s and note that the majority of them have similar X-ray spectra, with properties intermediate between blazars and radio-quiet NLSy1s., Comment: Accepted for publication in MNRAS
Published: 2018
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47. On the radio and GeV-TeV gamma-ray emission connection in Fermi blazars

Author: Lico, R., Giroletti, M., Orienti, M., Costamante, L., Pavlidou, V., D'Ammando, F., and Tavecchio, F.
Subjects: Astrophysics - High Energy Astrophysical Phenomena
Abstract: The Fermi-LAT revealed that the census of the gamma-ray sky is dominated by blazars. Looking for a possible connection between radio and gamma-ray emission is a central issue for understanding the blazar physics, and various works were dedicated to this topic. However, while a strong and significant correlation was found between radio and gamma-ray emission in the 0.1-100 GeV energy range, the connection between radio and very high energy (VHE, E>0.1 TeV) emission is still elusive. The main reason is the lack of a homogeneous VHE sky coverage, due to the operational mode of the imaging atmospheric Cherenkov telescopes. With the present work we aim to quantify and assess the significance of the possible connection between high-resolution radio emission, on milliarcsecond scale, and GeV-TeV gamma-ray emission in blazars. For achieving our goal we extract two large and unbiased blazar samples from the 1FHL and 2FHL Fermi catalogs, above 10 GeV and 50 GeV, respectively. To investigate how the correlation evolves as the gamma-ray energy increases, we perform the same analysis by using the 0.1-300 GeV 3FGL gamma-ray energy fluxes. When we consider the 0.1-300 GeV gamma-ray energy range, we find a strong and significant correlation for all of the blazar sub-classes. Conversely, when we consider the gamma-ray emission above 10 GeV the correlation with the radio emission vanishes, with the exception of the blazar sub-class of high synchrotron peaked objects., Comment: 6 pages, 2 figures, 1 table. For the proceedings of the 7th International Fermi Symposium
Published: 2017

48. Science with e-ASTROGAM (A space mission for MeV-GeV gamma-ray astrophysics)

Author: De Angelis, A., Tatischeff, V., Grenier, I. A., McEnery, J., Mallamaci, M., Tavani, M., Oberlack, U., Hanlon, L., Walter, R., Argan, A., Von Ballmoos, P., Bulgarelli, A., Bykov, A., Hernanz, M., Kanbach, G., Kuvvetli, I., Pearce, M., Zdziarski, A., Conrad, J., Ghisellini, G., Harding, A., Isern, J., Leising, M., Longo, F., Madejski, G., Martinez, M., Mazziotta, M. N., Paredes, J. M., Pohl, M., Rando, R., Razzano, M., Aboudan, A., Ackermann, M., Addazi, A., Ajello, M., Albertus, C., Alvarez, J. M., Ambrosi, G., Anton, S., Antonelli, L. A., Babic, A., Baibussinov, B., Balbo, M., Baldini, L., Balman, S., Bambi, C., de Almeida, U. Barres, Barrio, J. A., Bartels, R., Bastieri, D., Bednarek, W., Bernard, D., Bernardini, E., Bernasconi, T., Bertucci, B., Biland, A., Bissaldi, E., Boettcher, M., Bonvicini, V., Ramon, V. Bosch, Bottacini, E., Bozhilov, V., Bretz, T., Branchesi, M., Brdar, V., Bringmann, T., Brogna, A., Jorgensen, C. Budtz, Busetto, G., Buson, S., Busso, M., Caccianiga, A., Camera, S., Campana, R., Caraveo, P., Cardillo, M., Carlson, P., Celestin, S., Cermeno, M., Chen, A., Cheung, C. C, Churazov, E., Ciprini, S., Coc, A., Colafrancesco, S., Coleiro, A., Collmar, W., Coppi, P., da Silva, R. Curado, Cutini, S., DAmmando, F., De Lotto, B., de Martino, D., De Rosa, A., Del Santo, M., Delgado, L., Diehl, R., Dietrich, S., Dolgov, A. D., Dominguez, A., Prester, D. Dominis, Donnarumma, I., Dorner, D., Doro, M., Dutra, M., Elsaesser, D., Fabrizio, M., FernandezBarral, A., Fioretti, V., Foffano, L., Formato, V., Fornengo, N., Foschini, L., Franceschini, A., Franckowiak, A., Funk, S., Fuschino, F., Gaggero, D., Galanti, G., Gargano, F., Gasparrini, D., Gehrz, R., Giammaria, P., Giglietto, N., Giommi, P., Giordano, F., Giroletti, M., Ghirlanda, G., Godinovic, N., Gouiffes, C., Grove, J. E., Hamadache, C., Hartmann, D. H., Hayashida, M., Hryczuk, A., Jean, P., Johnson, T., Jose, J., Kaufmann, S., Khelifi, B., Kiener, J., Knodlseder, J., Kole, M., Kopp, J., Kozhuharov, V., Labanti, C., Lalkovski, S., Laurent, P., Limousin, O., Linares, M., Lindfors, E., Lindner, M., Liu, J., Lombardi, S., Loparco, F., LopezCoto, R., Moya, M. Lopez, Lott, B., Lubrano, P., Malyshev, D., Mankuzhiyil, N., Mannheim, K., Marcha, M. J., Marciano, A., Marcote, B., Mariotti, M., Marisaldi, M., McBreen, S., Mereghetti, S., Merle, A., Mignani, R., Minervini, G., Moiseev, A., Morselli, A., Moura, F., Nakazawa, K., Nava, L., Nieto, D., Orienti, M., Orio, M., Orlando, E., Orleanski, P., Paiano, S., Paoletti, R., Papitto, A., Pasquato, M., Patricelli, B., PerezGarcia, M. A., Persic, M., Piano, G., Pichel, A., Pimenta, M., Pittori, C., Porter, T., Poutanen, J., Prandini, E., Prantzos, N., Produit, N., Profumo, S., Queiroz, F. S., Raino, S., Raklev, A., Regis, M., Reichardt, I., Rephaeli, Y., Rico, J., Rodejohann, W., Fernandez, G. Rodriguez, Roncadelli, M., Roso, L., Rovero, A., Ruffini, R., Sala, G., SanchezConde, M. A., Santangelo, A., Parkinson, P. Saz, Sbarrato, T., Shearer, A., Shellard, R., Short, K., Siegert, T., Siqueira, C., Spinelli, P., Stamerra, A., Starrfield, S., Strong, A., Strumke, I., Tavecchio, F., Taverna, R., Terzic, T., Thompson, D. J., Tibolla, O., Torres, D. F., Turolla, R., Ulyanov, A., Ursi, A., Vacchi, A., Abeele, J. Van den, Kirilovai, G. Vankova, Venter, C., Verrecchia, F., Vincent, P., Wang, X., Weniger, C., Wu, X., Zaharijas, G., Zampieri, L., Zane, S., Zimmer, S., Zoglauer, A., and collaboration, the eASTROGAM
Subjects: Astrophysics - High Energy Astrophysical Phenomena, Astrophysics - Instrumentation and Methods for Astrophysics, Astrophysics - Solar and Stellar Astrophysics, High Energy Physics - Experiment
Abstract: e-ASTROGAM (enhanced ASTROGAM) is a breakthrough Observatory space mission, with a detector composed by a Silicon tracker, a calorimeter, and an anticoincidence system, dedicated to the study of the non-thermal Universe in the photon energy range from 0.3 MeV to 3 GeV - the lower energy limit can be pushed to energies as low as 150 keV for the tracker, and to 30 keV for calorimetric detection. The mission is based on an advanced space-proven detector technology, with unprecedented sensitivity, angular and energy resolution, combined with polarimetric capability. Thanks to its performance in the MeV-GeV domain, substantially improving its predecessors, e-ASTROGAM will open a new window on the non-thermal Universe, making pioneering observations of the most powerful Galactic and extragalactic sources, elucidating the nature of their relativistic outflows and their effects on the surroundings. With a line sensitivity in the MeV energy range one to two orders of magnitude better than previous generation instruments, e-ASTROGAM will determine the origin of key isotopes fundamental for the understanding of supernova explosion and the chemical evolution of our Galaxy. The mission will provide unique data of significant interest to a broad astronomical community, complementary to powerful observatories such as LIGO-Virgo-GEO600-KAGRA, SKA, ALMA, E-ELT, TMT, LSST, JWST, Athena, CTA, IceCube, KM3NeT, and LISA., Comment: Published on Journal of High Energy Astrophysics (Elsevier)
Published: 2017
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49. Science with the Cherenkov Telescope Array

Author: Consortium, The Cherenkov Telescope Array, Acharya, B. S., Agudo, I., Samarai, I. Al, Alfaro, R., Alfaro, J., Alispach, C., Batista, R. Alves, Amans, J. -P., Amato, E., Ambrosi, G., Antolini, E., Antonelli, L. A., Aramo, C., Araya, M., Armstrong, T., Arqueros, F., Arrabito, L., Asano, K., Ashley, M., Backes, M., Balazs, C., Balbo, M., Ballester, O., Ballet, J., Bamba, A., Barkov, M., de Almeida, U. Barres, Barrio, J. A., Bastieri, D., Becherini, Y., Belfiore, A., Benbow, W., Berge, D., Bernardini, E., Bernardini, M. G., Bernardos, M., Bernlöhr, K., Bertucci, B., Biasuzzi, B., Bigongiari, C., Biland, A., Bissaldi, E., Biteau, J., Blanch, O., Blazek, J., Boisson, C., Bolmont, J., Bonanno, G., Bonardi, A., Bonavolontà, C., Bonnoli, G., Bosnjak, Z., Böttcher, M., Braiding, C., Bregeon, J., Brill, A., Brown, A. M., Brun, P., Brunetti, G., Buanes, T., Buckley, J., Bugaev, V., Bühler, R., Bulgarelli, A., Bulik, T., Burton, M., Burtovoi, A., Busetto, G., Canestrari, R., Capalbi, M., Capitanio, F., Caproni, A., Caraveo, P., Cárdenas, V., Carlile, C., Carosi, R., Carquín, E., Carr, J., Casanova, S., Cascone, E., Catalani, F., Catalano, O., Cauz, D., Cerruti, M., Chadwick, P., Chaty, S., Chaves, R. C. G., Chen, A., Chen, X., Chernyakova, M., Chikawa, M., Christov, A., Chudoba, J., Cieślar, M., Coco, V., Colafrancesco, S., Colin, P., Conforti, V., Connaughton, V., Conrad, J., Contreras, J. L., Cortina, J., Costa, A., Costantini, H., Cotter, G., Covino, S., Crocker, R., Cuadra, J., Cuevas, O., Cumani, P., D'Aì, A., D'Ammando, F., D'Avanzo, P., D'Urso, D., Daniel, M., Davids, I., Dawson, B., Dazzi, F., De Angelis, A., Anjos, R. de Cássia dos, De Cesare, G., De Franco, A., Pino, E. M. de Gouveia Dal, de la Calle, I., Lopez, R. de los Reyes, De Lotto, B., De Luca, A., De Lucia, M., de Naurois, M., Wilhelmi, E. de Oña, De Palma, F., De Persio, F., de Souza, V., Deil, C., Del Santo, M., Delgado, C., della Volpe, D., Di Girolamo, T., Di Pierro, F., Di Venere, L., Díaz, C., Dib, C., Diebold, S., Djannati-Ataï, A., Domínguez, A., Prester, D. Dominis, Dorner, D., Doro, M., Drass, H., Dravins, D., Dubus, G., Dwarkadas, V. V., Ebr, J., Eckner, C., Egberts, K., Einecke, S., Ekoume, T. R. N., Elsässer, D., Ernenwein, J. -P., Espinoza, C., Evoli, C., Fairbairn, M., Falceta-Goncalves, D., Falcone, A., Farnier, C., Fasola, G., Fedorova, E., Fegan, S., Fernandez-Alonso, M., Fernández-Barral, A., Ferrand, G., Fesquet, M., Filipovic, M., Fioretti, V., Fontaine, G., Fornasa, M., Fortson, L., Coromina, L. Freixas, Fruck, C., Fujita, Y., Fukazawa, Y., Funk, S., Füßling, M., Gabici, S., Gadola, A., Gallant, Y., Garcia, B., López, R. Garcia, Garczarczyk, M., Gaskins, J., Gasparetto, T., Gaug, M., Gerard, L., Giavitto, G., Giglietto, N., Giommi, P., Giordano, F., Giro, E., Giroletti, M., Giuliani, A., Glicenstein, J. -F., Gnatyk, R., Godinovic, N., Goldoni, P., Gómez-Vargas, G., González, M. M., González, J. M., Götz, D., Graham, J., Grandi, P., Granot, J., Green, A. J., Greenshaw, T., Griffiths, S., Gunji, S., Hadasch, D., Hara, S., Hardcastle, M. J., Hassan, T., Hayashi, K., Hayashida, M., Heller, M., Helo, J. C., Hermann, G., Hinton, J., Hnatyk, B., Hofmann, W., Holder, J., Horan, D., Hörandel, J., Horns, D., Horvath, P., Hovatta, T., Hrabovsky, M., Hrupec, D., Humensky, T. B., Hütten, M., Iarlori, M., Inada, T., Inome, Y., Inoue, S., Inoue, T., Inoue, Y., Iocco, F., Ioka, K., Iori, M., Ishio, K., Iwamura, Y., Jamrozy, M., Janecek, P., Jankowsky, D., Jean, P., Jung-Richardt, I., Jurysek, J., Kaaret, P., Karkar, S., Katagiri, H., Katz, U., Kawanaka, N., Kazanas, D., Khélifi, B., Kieda, D. B., Kimeswenger, S., Kimura, S., Kisaka, S., Knapp, J., Knödlseder, J., Koch, B., Kohri, K., Komin, N., Kosack, K., Kraus, M., Krause, M., Krauß, F., Kubo, H., Mezek, G. Kukec, Kuroda, H., Kushida, J., La Palombara, N., Lamanna, G., Lang, R. G., Lapington, J., Blanc, O. Le, Leach, S., Lees, J. -P., Lefaucheur, J., de Oliveira, M. A. Leigui, Lenain, J. -P., Lico, R., Limon, M., Lindfors, E., Lohse, T., Lombardi, S., Longo, F., López, M., López-Coto, R., Lu, C. -C., Lucarelli, F., Luque-Escamilla, P. L., Lyard, E., Maccarone, M. C., Maier, G., Majumdar, P., Malaguti, G., Mandat, D., Maneva, G., Manganaro, M., Mangano, S., Marcowith, A., Marín, J., Markoff, S., Martí, J., Martin, P., Martínez, M., Martínez, G., Masetti, N., Masuda, S., Maurin, G., Maxted, N., Mazin, D., Medina, C., Melandri, A., Mereghetti, S., Meyer, M., Minaya, I. 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Subjects: Astrophysics - Instrumentation and Methods for Astrophysics, Astrophysics - High Energy Astrophysical Phenomena, High Energy Physics - Experiment
Abstract: The Cherenkov Telescope Array, CTA, will be the major global observatory for very high energy gamma-ray astronomy over the next decade and beyond. The scientific potential of CTA is extremely broad: from understanding the role of relativistic cosmic particles to the search for dark matter. CTA is an explorer of the extreme universe, probing environments from the immediate neighbourhood of black holes to cosmic voids on the largest scales. Covering a huge range in photon energy from 20 GeV to 300 TeV, CTA will improve on all aspects of performance with respect to current instruments. The observatory will operate arrays on sites in both hemispheres to provide full sky coverage and will hence maximize the potential for the rarest phenomena such as very nearby supernovae, gamma-ray bursts or gravitational wave transients. With 99 telescopes on the southern site and 19 telescopes on the northern site, flexible operation will be possible, with sub-arrays available for specific tasks. CTA will have important synergies with many of the new generation of major astronomical and astroparticle observatories. Multi-wavelength and multi-messenger approaches combining CTA data with those from other instruments will lead to a deeper understanding of the broad-band non-thermal properties of target sources. The CTA Observatory will be operated as an open, proposal-driven observatory, with all data available on a public archive after a pre-defined proprietary period. Scientists from institutions worldwide have combined together to form the CTA Consortium. This Consortium has prepared a proposal for a Core Programme of highly motivated observations. The programme, encompassing approximately 40% of the available observing time over the first ten years of CTA operation, is made up of individual Key Science Projects (KSPs), which are presented in this document., Comment: 213 pages, including references and glossary. Version 2: credits and references updated, some figures updated, and author list updated
Published: 2017
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50. Enhanced Polarized Emission from the One-Parsec-Scale Hotspot of 3C 84 as a Result of the Interaction with Clumpy Ambient Medium

Author: Nagai, H., Fujita, Y., Nakamura, M., Orienti, M., Kino, M., Asada, K., and Giovannini, G.
Subjects: Astrophysics - High Energy Astrophysical Phenomena
Abstract: We present Very Long Baseline Array polarimetric observations of the innermost jet of 3C$\sim$84 (NGC$\sim$1275) at 43$\sim$GHz. A significant polarized emission is detected at the hotspot of the innermost re-started jet, which is located $\sim$1 pc south from the radio core. While the previous report presented a hotspot at the southern end of the western limb, the hotspot location has been moved to the southern end of the eastern limb. Faraday rotation is detected within an entire bandwidth of the 43-GHz band. The measured rotation measure (RM) is at most (6.3$\pm$1.9)$\times10^{5}$$\sim$rad$\sim$m$^{-2}$ and might be slightly time variable on the timescale of a month by a factor of a few. Our measured RM and the RM previously reported by the CARMA and SMA observations cannot be consistently explained by the spherical accretion flow with a power-law profile. We propose that a clumpy/inhomogeneous ambient medium is responsible for the observed rotation measure. Using equipartition magnetic field, we derive the electron density of $2\times10^{4}$$\sim$cm$^{-3}$. Such an electron density is consistent with the cloud of narrow line emission region around the central engine. We also discuss the magnetic field configuration from black hole scale to pc scale and the origin of low polarization., Comment: 8 pages, 8 figures, accepted for publication in ApJ
Published: 2017
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