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1. Rapid Mid-Infrared Spectral-Timing with JWST. I. The prototypical black hole X-ray Binary GRS 1915+105 during a MIR-bright and X-ray-obscured state

Author

Gandhi, P., Borowski, E. S., Byrom, J., Hynes, R. I., Maccarone, T. J., Shaw, A. W., Adegoke, O. K., Altamirano, D., Baglio, M. C., Bhargava, Y., Britt, C. T., Buckley, D. A. H., Buisson, D. J. K., Casella, P., Segura, N. Castro, Charles, P. A., Corral-Santana, J. M., Dhillon, V. S., Fender, R., Gúrpide, A., Heinke, C. O., Igl, A. B., Knigge, C., Markoff, S., Mastroserio, G., McCollough, M. L., Middleton, M., Miller, J. M., Miller-Jones, J. C. A., Motta, S. E., Paice, J. A., Pawar, D. D., Plotkin, R. M., Pradhan, P., Ressler, M. E., Russell, D. M., Russell, T. D., Santos-Sanz, P., Shahbaz, T., Sivakoff, G. R., Steeghs, D., Tetarenko, A. J., Tomsick, J. A., Vincentelli, F. M., George, M., Gurwell, M., and Rao, R.

Subjects
Astrophysics - High Energy Astrophysical Phenomena, Astrophysics - Solar and Stellar Astrophysics
Abstract

We present mid-infrared (MIR) spectral-timing measurements of the prototypical Galactic microquasar GRS 1915+105. The source was observed with the Mid-Infrared Instrument (MIRI) onboard JWST in June 2023 at a MIR luminosity L(MIR)~10^{36} erg/s exceeding past IR levels by about a factor of 10. By contrast, the X-ray flux is much fainter than the historical average, in the source's now-persistent 'obscured' state. The MIRI low-resolution spectrum shows a plethora of emission lines, the strongest of which are consistent with recombination in the hydrogen Pfund (Pf) series and higher. Low amplitude (~1%) but highly significant peak-to-peak photometric variability is found on timescales of ~1,000 s. The brightest Pf(6-5) emission line lags the continuum. Though difficult to constrain accurately, this lag is commensurate with light-travel timescales across the outer accretion disc or with expected recombination timescales inferred from emission line diagnostics. Using the emission line as a bolometric indicator suggests a moderate (~5-30% Eddington) intrinsic accretion rate. Multiwavelength monitoring shows that JWST caught the source close in-time to unprecedentedly bright MIR and radio long-term flaring. Assuming a thermal bremsstrahlung origin for the MIRI continuum suggests an unsustainably high mass-loss rate during this time unless the wind remains bound, though other possible origins cannot be ruled out. PAH features previously detected with Spitzer are now less clear in the MIRI data, arguing for possible destruction of dust in the interim. These results provide a preview of new parameter space for exploring MIR spectral-timing in XRBs and other variable cosmic sources on rapid timescales., Comment: Dedicated to the memory of our colleague, Tomaso Belloni. Submitted 2024 June 21; Comments welcome

Published
2024

2. Broadband Multi-wavelength Properties of M87 during the 2018 EHT Campaign including a Very High Energy Flaring Episode

Author

Algaba, J. C., Balokovic, M., Chandra, S., Cheong, W. Y., Cui, Y. Z., D'Ammando, F., Falcone, A. D., Ford, N. M., Giroletti, M., Goddi, C., Gurwell, M. A., Hada, K., Haggard, D., Jorstad, S., Kaur, A., Kawashima, T., Kerby, S., Kim, J. Y., Kino, M., Kravchenko, E. V., Lee, S. S., Lu, R. S., Markoff, S., Michail, J., Neilsen, J., Nowak, M. A., Principe, G., Ramakrishnan, V., Ripperda, B., Sasada, M., Savchenko, S. S., Sheridan, C., Akiyama, K., Alberdi, A., Alef, W., Anantua, R., Asada, K., Azulay, R., Bach, U., Baczko, A. -K., Ball, D., Bandyopadhyay, B., Barrett, J., Bauböck, M., Benson, B. A., Bintley, D., Blackburn, L., Blundell, R., Bouman, K. L., Bower, G. C., Boyce, H., Bremer, M., Brissenden, R., Britzen, S., Broderick, A. E., Broguiere, D., Bronzwaer, T., Bustamante, S., Carlstrom, J. E., Chael, A., Chan, C. -K., Chang, D. O., Chatterjee, K., Chatterjee, S., Chen, M. -T., Chen, Y., Cheng, X., Cho, I., Christian, P., Conroy, N. S., Conway, J. E., Crawford, T. M., Crew, G. B., Cruz-Osorio, A., Dahale, R., Davelaar, J., De Laurentis, M., Deane, R., Dempsey, J., Desvignes, G., Dexter, J., Dhruv, V., Dihingia, I. K., Doeleman, S. S., Dzib, S. A., Eatough, R. P., Emami, R., Falcke, H., Farah, J., Fish, V. L., Fomalont, E., Ford, H. A., Foschi, M., Fraga-Encinas, R., Freeman, W. T., Friberg, P., Fromm, C. M., Fuentes, A., Galison, P., Gammie, C. F., García, R., Gentaz, O., Georgiev, B., Gold, R., Gómez-Ruiz, A. I., Gómez, J. L., Gu, M., Hesper, R., Heumann, D., Ho, L. C., Ho, P., Honma, M., Huang, C. -W. L., Huang, L., Hughes, D. H., Ikeda, S., Impellizzeri, C. M. V., Inoue, M., Issaoun, S., James, D. J., Jannuzi, B. T., Janssen, M., Jeter, B., Jiang, W., Jiménez-Rosales, A., Johnson, M. D., Jones, A. C., Joshi, A. V., Jung, T., Karuppusamy, R., Keating, G. K., Kettenis, M., Kim, D. -J., Kim, J., Koay, J. Y., Kocherlakota, P., Kofuji, Y., Koch, P. M., Koyama, S., Kramer, C., Kramer, J. A., Kramer, M., Krichbaum, T. P., Kuo, C. -Y., La Bella, N., Levis, A., Li, Z., Lico, R., Lindahl, G., Lindqvist, M., Lisakov, M., Liu, J., Liu, K., Liuzzo, E., Lo, W. -P., Lobanov, A. P., Loinard, L., Lonsdale, C. J., Lowitz, A. E., MacDonald, N. R., Mao, J., Marchili, N., Marrone, D. P., Marscher, A. P., Martí-Vidal, I., Matsushita, S., Matthews, L. D., Medeiros, L., Menten, K. M., Mizuno, I., Mizuno, Y., Montgomery, J., Moran, J. M., Moriyama, K., Moscibrodzka, M., Mulaudzi, W., Müller, C., Müller, H., Mus, A., Musoke, G., Myserlis, I., Nagai, H., Nagar, N. M., Nair, D. G., Nakamura, M., Narayanan, G., Natarajan, I., Nathanail, A., Fuentes, S. Navarro, Ni, C., Oh, J., Okino, H., Olivares, H., Oyama, T., Özel, F., Palumbo, D. C. M., Paraschos, G. Filippos, Park, J., Parsons, H., Patel, N., Pen, U. -L., Pesce, D. W., Piétu, V., PopStefanija, A., Porth, O., Prather, B., Psaltis, D., Pu, H. -Y., Rao, R., Rawlings, M. G., Raymond, A. W., Rezzolla, L., Ricarte, A., Roelofs, F., Romero-Cañizales, C., Ros, E., Roshanineshat, A., Rottmann, H., Roy, A. L., Ruiz, I., Ruszczyk, C., Rygl, K. L. J., Sánchez, S., Sánchez-Argüelles, D., Sánchez-Portal, M., Satapathy, K., Savolainen, T., Schloerb, F. P., Schonfeld, J., Schuster, K. -F., Shao, L., Shen, Z., Small, D., Sohn, B. W., SooHoo, J., Salas, L. D. Sosapanta, Souccar, K., Stanway, J. S., Sun, H., Tazaki, F., Tetarenko, A. J., Tiede, P., Tilanus, R. P. J., Titus, M., Toma, K., Torne, P., Toscano, T., Traianou, E., Trent, T., Trippe, S., Turk, M., van Bemmel, I., van Langevelde, H. J., van Rossum, D. R., Vos, J., Wagner, J., Ward-Thompson, D., Wardle, J., Washington, J. E., Weintroub, J., Wharton, R., Wielgus, M., Wiik, K., Witzel, G., Wondrak, M. F., Wong, G. N., Wu, Q., Yadlapalli, N., Yamaguchi, P., Yfantis, A., Yoon, D., Young, A., Younsi, Z., Yu, W., Yuan, F., Yuan, Y. -F., Zensus, J. A., Zhang, S., Zhao, G. -Y., Zhao, S. -S., Bellazzini, R., Berenji, B., Bissaldi, E., Blandford, R. D., Bonino, R., Bruel, P., Cameron, R. A., Caraveo, P. A., Cavazzuti, E., Cheung, C. C., Ciprini, S., Orestano, P. Cristarella, Cutini, S., Di Lalla, N., Dinesh, A., Di Venere, L., Domínguez, A., Fegan, S. J., Franckowiak, A., Fukazawa, Y., Fusco, P., Gargano, F., Gasbarra, C., Germani, S., Giliberti, M., Grenier, I. A., Hays, E., Horan, D., Kuss, M., Larsson, S., Liodakis, I., Longo, F., Loparco, F., Lovellette, M. N., Maldera, S., Mazziotta, M. N., Mereu, I., Michelson, P. F., Mirabal, N., Mizuno, T., Monzani, M. E., Morselli, A., Negro, M., Omodei, N., Orlando, E., Persic, M., Rainò, S., Rani, B., Reimer, A., Reimer, O., Sánchez-Conde, M., Parkinson, P. M. Saz, Sgrò, C., Siskind, E. J., Spinelli, P., Suson, D. J., Tajima, H., Torres, D. F., Zaharijas, G., Aharonian, F., Benkhali, F. Ait, Aschersleben, J., Ashkar, H., Backes, M., Martins, V. Barbosa, Batzofin, R., Becherini, Y., Berge, D., Böttcher, M., Boisson, C., Bolmont, J., de Lavergne, M. de Bony, Borowska, J., Bouyahiaoui, M., Bradascio, F., Brose, R., Brown, A., Bruno, B., Bulik, T., Burger-Scheidlin, C., Casanova, S., Cecil, R., Celic, J., Cerruti, M., Chand, T., Chen, A., Chibueze, J., Chibueze, O., Czerny, T., Dainotti, M., Dubus, F., Dumm, J., D'Urso, G., Drouhin, A., Durouchoux, P., Fabbian, D., Franczak, D., Funk, M., Gabanyi, J., Gaggero, G., Garcia, N., Geiger, A., Giorgi, M. G., Gleeson, S., Gonzalez, S., Gauthier, G. T., Grasso, P., Hovatta, T., Hyman, J., Kaaret, C., Kirk, D., Lal, S., Lesch, T. M., Lohmann, K., Massaro, C., Mayer, M., Meintjes, P. J., Miral, E., Mirra, A., Neronov, J., Padovani, E., Paccagnella, F., Parisi, E., Piotrowska, A., Pohl, S., Puga, G., Ramirez, L. R., Reville, S., Rowell, D. S., Rudge, M., Rybka, G., Schlenstedt, M. S., Seo, E. S., Svirski, J., Taylor, J. R., Torres, F., Tsujimoto, K., Tosti, F., Volpi, S., Walraven, N. A., Welker, L., Zietkiewicz, M., Abdalla, G., Aleva, C., Benkhali, H. A. Ait, Aldous, M., Amin, M., Aschieri, M. A., de Deus, E., Santos, J. de Los, Fontanot, D., Jorfi, S., Levens, P., Zwart, A. E. E., Oliviero, S., Puglisi, D., Thiel, M., Zaharijas, C., Amaral, F., Boella, L., Holincheck, L., Queiroz, R., Sofue, H., Tellis, G., Wagner, G., Wierzcholska, A., Zacharias, M., Zdziarski, A. A., Zech, A., Zywucka, N., Abe, S., Abhir, J., Abhishek, A., Acciari, V. A., Aguasca-Cabot, A., Agudo, I., Aniello, T., Ansoldi, S., Antonelli, L. A., Engels, A. Arbet, Arcaro, C., Artero, M., Asano, K., Babic, A., de Almeida, U. Barres, Barrio, J. A., Batkovic, I., Bautista, A., Baxter, J., González, J. Becerra, Bednarek, W., Bernardini, E., Bernete, J., Berti, A., Besenrieder, J., Bigongiari, C., Biland, A., Blanch, O., Bonnoli, G., Bosnjak, Z., Bronzini, E., Burelli, I., Busetto, G., Campoy-Ordaz, A., Carosi, A., Carosi, R., Carretero-Castrillo, M., Castro-Tirado, A. J., Cerasole, D., Ceribella, G., Chai, Y., Cifuentes, A., 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., de Menezes, R., Delfino, M., Delgado, J., Mendez, C. Delgado, Di Pierro, F., Di Tria, R., Prester, D. Dominis, Donini, A., Dorner, D., Doro, M., Elsaesser, D., Escudero, J., Fariña, L., Fattorini, A., Foffano, L., Font, L., Fröse, S., Fukami, S., López, R. J. García, Garczarczyk, M., Gasparyan, S., Gaug, M., Paiva, J. G. Giesbrecht, Giglietto, N., Giordano, F., Gliwny, P., Godinovic, N., Gradetzke, T., Grau, R., Green, D., Green, J. G., Günther, P., Hadasch, D., Hahn, A., Hassan, T., Heckmann, L., Llorente, J. Herrera, Hrupec, D., Imazawa, R., Ishio, K., Martínez, I. Jiménez, Jormanainen, J., Kayanoki, T., Kerszberg, D., Kluge, G. W., Kobayashi, Y., Kouch, P. M., Kubo, H., Kushida, J., Laínez, M., Lamastra, A., Leone, F., Lindfors, E., Lombardi, S., López-Coto, R., López-Moya, M., López-Oramas, A., Loporchio, S., Lorini, A., Lyard, E., Fraga, B. Machado de Oliveira, Majumdar, P., Makariev, M., Maneva, G., Manganaro, M., Mangano, S., Mannheim, K., Mariotti, M., Martínez, M., Martínez-Chicharro, M., Mas-Aguilar, A., Mazin, D., Menchiari, S., Mender, S., Miceli, D., Miener, T., Miranda, J. M., Mirzoyan, R., González, M. Molero, Molina, E., Mondal, H. A., Moralejo, A., Morcuende, D., Nakamori, T., Nanci, C., Neustroev, V., Nickel, L., Rosillo, M. Nievas, Nigro, C., Nikolic, L., Nilsson, K., Nishijima, K., Ekoume, T. Njoh, Noda, K., Nozaki, S., Ohtani, Y., Okumura, A., Otero-Santos, J., Paiano, S., Paneque, D., Paoletti, R., Paredes, J. M., Peresano, M., Pihet, M., Pirola, G., Podobnik, F., Moroni, P. G. Prada, Prandini, E., Priyadarshi, C., Ribó, M., Rico, J., Righi, C., Sahakyan, N., Saito, T., Saturni, F. G., Schmidt, K., Schmuckermaier, F., Schubert, J. L., Schweizer, T., Sciaccaluga, A., Silvestri, G., Sitarek, J., Sliusar, V., Sobczynska, D., Spolon, A., Stamerra, A., Strišković, J., Strom, D., Strzys, M., Suda, Y., Suutarinen, S., Takahashi, M., Takeishi, R., Tavecchio, F., Temnikov, P., Terauchi, K., Terzic, T., Teshima, M., Truzzi, S., Tutone, A., Ubach, S., van Scherpenberg, J., Acosta, M. Vazquez, Ventura, S., Verna, G., Viale, I., Vigorito, C. F., Vitale, V., Vovk, I., Walter, R., Will, M., Wunderlich, C., Yamamoto, T., Acharyya, A., Adams, C. B., Bangale, P., Bartkoske, J. T., Benbow, W., Christiansen, J. L., Duerr, A., Errando, M., Feng, Q., Foote, G. M., Fortson, L., Furniss, A., Hanlon, W., Hervet, O., Hinrichs, C. E., Holder, J., Humensky, T. B., Jin, W., Johnson, M. N., Kaaret, P., Kertzman, M., Kieda, D., Kleiner, T. K., Korzoun, N., Krennrich, F., Kumar, S., Lang, M. J., Lundy, M., Maier, G., McGrath, C. E., Millard, M. J., Mooney, C. L., Moriarty, P., Mukherjee, R., Ning, W., O'Brien, S., Ong, R. A., Pohl, M., Pueschel, E., Quinn, J., Ragan, K., Reynolds, P. T., Ribeiro, D., Roache, E., Ryan, J. L., Sadeh, I., Saha, L., Santander, M., Sembroski, G. H., Shang, R., Splettstoesser, M., Talluri, A. K., Tucci, J. V., Valverde, J., Vassiliev, V. V., Williams, D. A., Wong, S. L., Chen, Z., Cui, L., Hirota, T., Li, B., Li, G., Liu, Q., Liu, X., Liu, Z., Ma, J., Niinuma, K., Ro, H., Sakai, N., Sawada-Satoh, S., Wajima, K., Wang, J., Wang, N., Xia, B., Yan, H., Yonekura, Y., Zhang, H., Zhao, R., Zhong, W., group, The Event Horizon Telescope - Multi-wavelength science working, Collaboration, The Event Horizon Telescope, Collaboration, The Fermi Large Area Telescope, Collaboration, H. E. S. S., Collaboration, MAGIC, Collaboration, VERITAS, and Collaboration, EAVN

Subjects
Astrophysics - High Energy Astrophysical Phenomena, Astrophysics - Astrophysics of Galaxies
Abstract

The nearby elliptical galaxy M87 contains one of the only two supermassive black holes whose emission surrounding the event horizon has been imaged by the Event Horizon Telescope (EHT). In 2018, more than two dozen multi-wavelength (MWL) facilities (from radio to gamma-ray energies) took part in the second M87 EHT campaign. The goal of this extensive MWL campaign was to better understand the physics of the accreting black hole M87*, the relationship between the inflow and inner jets, and the high-energy particle acceleration. Understanding the complex astrophysics is also a necessary first step towards performing further tests of general relativity. The MWL campaign took place in April 2018, overlapping with the EHT M87* observations. We present a new, contemporaneous spectral energy distribution (SED) ranging from radio to very high energy (VHE) gamma-rays, as well as details of the individual observations and light curves. We also conduct phenomenological modelling to investigate the basic source properties. We present the first VHE gamma-ray flare from M87 detected since 2010. The flux above 350 GeV has more than doubled within a period of about 36 hours. We find that the X-ray flux is enhanced by about a factor of two compared to 2017, while the radio and millimetre core fluxes are consistent between 2017 and 2018. We detect evidence for a monotonically increasing jet position angle that corresponds to variations in the bright spot of the EHT image. Our results show the value of continued MWL monitoring together with precision imaging for addressing the origins of high-energy particle acceleration. While we cannot currently pinpoint the precise location where such acceleration takes place, the new VHE gamma-ray flare already presents a challenge to simple one-zone leptonic emission model approaches, and emphasises the need for combined image and spectral modelling., Comment: 46 pages, 23 figures, accepted by Astronomy & Astrophysics on August. 29, 2024

Published
2024

3. Ordered magnetic fields around the 3C 84 central black hole

Author

Paraschos, G. F., Kim, J. -Y., Wielgus, M., Röder, J., Krichbaum, T. P., Ros, E., Agudo, I., Myserlis, I., Moscibrodzka, M., Traianou, E., Zensus, J. A., Blackburn, L., Chan, C. -K., Issaoun, S., Janssen, M., Johnson, M. D., Fish, V. L., Akiyama, K., Alberdi, A., Alef, W., Algaba, J. C., Anantua, R., Asada, K., Azulay, R., Bach, U., Baczko, A. -K., Ball, D., Baloković, M., Barrett, J., Bauböck, M., Benson, B. A., Bintley, D., Blundell, R., Bouman, K. L., Bower, G. C., Boyce, H., Bremer, M., Brinkerink, C. D., Brissenden, R., Britzen, S., Broderick, A. E., Broguiere, D., Bronzwaer, T., Bustamante, S., Byun, D. -Y., Carlstrom, J. E., Ceccobello, C., Chael, A., Chang, D. O., Chatterjee, K., Chatterjee, S., Chen, M. T., Chen, Y., Cheng, X., Cho, I., Christian, P., Conroy, N. S., Conway, J. E., Cordes, J. M., Crawford, T. M., Crew, G. B., Cruz-Osorio, A., Cui, Y., Dahale, R., Davelaar, J., De Laurentis, M., Deane, R., Dempsey, J., Desvignes, G., Dexter, J., Dhruv, V., Doeleman, S. S., Dougal, S., Dzib, S. A., Eatough, R. P., Emami, R., Falcke, H., Farah, J., Fomalont, E., Ford, H. A., Foschi, M., Fraga-Encinas, R., Freeman, W. T., Friberg, P., Fromm, C. M., Fuentes, A., Galison, P., Gammie, C. F., García, R., Gentaz, O., Georgiev, B., Goddi, C., Gold, R., Gómez-Ruiz, A. I., Gómez, J. L., Gu, M., Gurwell, M., Hada, K., Haggard, D., Haworth, K., Hecht, M. H., Hesper, R., Heumann, D., Ho, L. C., Ho, P., Honma, M., Huang, C. L., Huang, L., Hughes, D. H., Ikeda, S., Impellizzeri, C. M. V., Inoue, M., James, D. J., Jannuzi, B. T., Jeter, B., Jaing, W., Jiménez-Rosales, A., Jorstad, S., Joshi, A. V., Jung, T., Karami, M., Karuppusamy, R., Kawashima, T., Keating, G. K., Kettenis, M., Kim, D. -J., Kim, J., Kino, M., Koay, J. Y., Kocherlakota, P., Kofuji, Y., Koch, P. M., Koyama, S., Kramer, C., Kramer, J. A., Kramer, M., Kuo, C. -Y., La Bella, N., Lauer, T. R., Lee, D., Lee, S. -S., Leung, P. K., Levis, A., Li, Z., Lico, R., Lindahl, G., Lindqvist, M., Lisakov, M., Liu, J., Liu, K., Liuzzo, E., Lo, W. -P., Lobanov, A. P., Loinard, L., Lonsdale, C. J., Lowitz, A. E., Lu, R. -S., MacDonald, N. R., Mao, J., Marchili, N., Markoff, S., Marrone, D. P., Marscher, A. P., Martí-Vidal, I., Matsushita, S., Matthews, L. D., Medeiros, L., Menten, K. M., Michalik, D., Mizuno, I., Mizuno, Y., Moran, J. M., Moriyama, K., Mulaudzi, W., Müller, C., Müller, H., Mus, A., Musoke, G., Nadolski, A., Nagai, H., Nagar, N. M., Nakamura, M., Narayanan, G., Natarajan, I., Nathanail, A., Fuentes, S. Navarro, Neilsen, J., Neri, R., Ni, C., Noutsos, A., Nowak, M. A., Oh, J., Okino, H., Olivares, H., Ortiz-León, G. N., Oyama, T., Özel, F., Palumbo, D. C. M., Park, J., Parsons, H., Patel, N., Pen, U. -L., Piétu, V., Plambeck, R., PopStefanija, A., Porth, O., Pötzl, F. M., Prather, B., Preciado-López, J. A., Psaltis, D., Pu, H. -Y., Ramakrishnan, V., Rao, R., Rawlings, M. G., Raymond, A. W., Rezzolla, L., Ricarte, A., Ripperda, B., Roelofs, F., Rogers, A., Romero-Cañizales, C., Roshanineshat, A., Rottmann, H., Roy, A. L., Ruiz, I., Ruszczyk, C., Rygl, K. L. J., Sánchez, S., Sánchez-Argüelles, D., Sánchez-Portal, M., Sasada, M., Satapathy, K., Savolainen, T., Schloerb, F. P., Schonfeld, J., Schuster, K., Shao, L., Shen, Z., Small, D., Sohn, B. W., SooHoo, J., Salas, L. D. Sosapanta, Souccar, K., Sun, H., Tazaki, F., Tetarenko, A. J., Tiede, P., Tilanus, R. P. J., Titus, M., Torne, P., Toscano, T., Trent, T., Trippe, S., Turk, M., van Bemmel, I., van Langevelde, H. J., van Rossum, D. R., Vos, J., Wagner, J., Ward-Thompson, D., Wardle, J., Washington, J. E., Weintroub, J., Wharton, R., Wiik, K., Witzel, G., Wondrak, M. F., Wong, G. N., Wu, Q., Yadlapalli, N., Yamaguchi, P., Yfantis, A., Yoon, D., Young, A., Young, K., Younsi, Z., Yu, W., Yuan, F., Yuan, Y. -F., Zhang, S., Zhao, G. Y., and Zhao, S. -S.

Subjects
Astrophysics - High Energy Astrophysical Phenomena, Astrophysics - Astrophysics of Galaxies
Abstract

3C84 is a nearby radio source with a complex total intensity structure, showing linear polarisation and spectral patterns. A detailed investigation of the central engine region necessitates the use of VLBI above the hitherto available maximum frequency of 86GHz. Using ultrahigh resolution VLBI observations at the highest available frequency of 228GHz, we aim to directly detect compact structures and understand the physical conditions in the compact region of 3C84. We used EHT 228GHz observations and, given the limited (u,v)-coverage, applied geometric model fitting to the data. We also employed quasi-simultaneously observed, multi-frequency VLBI data for the source in order to carry out a comprehensive analysis of the core structure. We report the detection of a highly ordered, strong magnetic field around the central, SMBH of 3C84. The brightness temperature analysis suggests that the system is in equipartition. We determined a turnover frequency of $\nu_m=(113\pm4)$GHz, a corresponding synchrotron self-absorbed magnetic field of $B_{SSA}=(2.9\pm1.6)$G, and an equipartition magnetic field of $B_{eq}=(5.2\pm0.6)$G. Three components are resolved with the highest fractional polarisation detected for this object ($m_\textrm{net}=(17.0\pm3.9)$%). The positions of the components are compatible with those seen in low-frequency VLBI observations since 2017-2018. We report a steeply negative slope of the spectrum at 228GHz. We used these findings to test models of jet formation, propagation, and Faraday rotation in 3C84. The findings of our investigation into different flow geometries and black hole spins support an advection-dominated accretion flow in a magnetically arrested state around a rapidly rotating supermassive black hole as a model of the jet-launching system in the core of 3C84. However, systematic uncertainties due to the limited (u,v)-coverage, however, cannot be ignored., Comment: 15 pages, 6 figures, published in A&A

Published
2024
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4. 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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5. ReveaLLAGN 0: First Look at JWST MIRI data of Sombrero and NGC 1052

Author

Goold, K., Seth, A., Molina, M., Ohlson, D., Runnoe, J. C., Boeker, T., Davis, T. A., Dumont, A., Eracleous, M., Fernández-Ontiveros, J. A., Gallo, E., Goulding, A. D., Greene, J. E., Ho, L. C., Markoff, S. B., Neumayer, N., Plotkin, R., Prieto, A., Satyapal, S., Van De Ven, G., Walsh, J. L., Yuan, F., Feldmeier-Krause, A., Gültekin, K., Hoenig, S., Kirkpatrick, A., Lützgendorf, N., Reines, A. E., Strader, J., Trump, J. R., and Voggel, K. T.

Subjects
Astrophysics - Astrophysics of Galaxies
Abstract

We present the first results from the Revealing Low-Luminosity Active Galactic Nuclei (ReveaLLAGN) survey, a JWST survey of seven nearby LLAGN. We focus on two observations with the Mid-Infrared Instrument's (MIRI) Medium Resolution Spectrograph (MRS) of the nuclei of NGC 1052 and Sombrero (NGC 4594 / M104). We also compare these data to public JWST data of a higher-luminosity AGN, NGC 7319 and NGC 7469. JWST clearly separates the AGN spectrum from the galaxy light even in Sombrero, the faintest target in our survey; the AGN components have very red spectra. We find that the emission-line widths in both NGC 1052 and Sombrero increase with increasing ionization potential, with FWHM > 1000 km/s for lines with ionization potential > 50 eV. These lines are also significantly blue-shifted in both LLAGN. The high ionization potential lines in NGC 7319 show neither broad widths or significant blue shifts. Many of the lower ionization potential emission lines in Sombrero show significant blue wings extending > 1000 km/s. These features and the emission-line maps in both galaxies are consistent with outflows along the jet direction. Sombrero has the lowest luminosity high-ionization potential lines ([Ne V] and [O IV]) ever measured in the mid-IR, but the relative strengths of these lines are consistent with higher luminosity AGN. On the other hand, the [Ne V] emission is much weaker relative to the [Ne III] and [Ne II] lines of higher-luminosity AGN. These initial results show the great promise that JWST holds for identifying and studying the physical nature of LLAGN., Comment: Accepted to ApJ Feb 28, 2024

Published
2023

6. Multiwavelength astrophysics of the blazar OJ 287 and the project MOMO

Author

Komossa, S., Kraus, A., Grupe, D., Parker, M. L., Gonzalez, A., Gallo, L. C., Gurwell, M. A., Laine, S., Yao, S., Chandra, S., Dey, L., Gomez, J. L., Hada, A. Gopakumar. K., Haggard, D., Hollett, A. R., Jermak, H., Jorstad, S., Krichbaum, T. P., Markoff, S., McCall, C., Neilsen, J., and Nowak, M.

Subjects
Astrophysics - High Energy Astrophysical Phenomena, Astrophysics - Astrophysics of Galaxies
Abstract

We are carrying out the densest and longest multiyear, multiwavelength monitoring project of OJ 287 ever done. The project MOMO (Multiwavelength Observations and Modelling of OJ 287) covers wavelengths from the radio to the high-energy regime. A few selected observations are simultaneous with those of the Event Horizon Telescope (EHT). MOMO aims at understanding disk-jet physics and at testing predictions of the binary black hole scenario of OJ 287. Here, we present a discussion of extreme outburst and minima states in context, and then focus on the recent flux and spectral evolution between 2021 and May 2022, including an ongoing bright radio flare. Further, we show that there is no evidence for precursor flare activity in our optical-UV-X-ray light curves that would be associated with any secondary supermassive black hole (SMBH) disk impact and that was predicted to start as thermal flare on 2021 December 23., Comment: Submitted to AN. Contribution to the XMM-Newton Workshop 2022 (Madrid, Spain). 5 figures

Published
2022
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7. Multi-wavelength Variability of Sagittarius A* in July 2019

Author

Boyce, H., Haggard, D., Witzel, G., von Fellenberg, S., Willner, S. P., Becklin, E. E., Do, T., Eckart, A., Fazio, G. G., Gurwell, M. A., Hora, J. L., Markoff, S., Morris, M. R., Neilsen, J., Nowak, M., Smith, H. A., and Zhang, S.

Subjects
Astrophysics - High Energy Astrophysical Phenomena
Abstract

We report timing analysis of near-infrared (NIR), X-ray, and sub-millimeter (submm) data during a three-day coordinated campaign observing Sagittarius A*. Data were collected at 4.5 micron with the Spitzer Space Telescope, 2-8 keV with the Chandra X-ray Observatory, 3-70 keV with NuSTAR, 340 GHz with ALMA, and at 2.2 micron with the GRAVITY instrument on the Very Large Telescope Interferometer. Two dates show moderate variability with no significant lags between the submm and the infrared at 99% confidence. July 18 captured a moderately bright NIR flare (F_K ~ 15 mJy) simultaneous with an X-ray flare (F ~ 0.1 cts/s) that most likely preceded bright submm flux (F ~ 5.5 Jy) by about +34 (+14 -33) minutes at 99% confidence. The uncertainty in this lag is dominated by the fact that we did not observe the peak of the submm emission. A synchrotron source cooled through adiabatic expansion can describe a rise in the submm once the synchrotron-self-Compton NIR and X-ray peaks have faded. This model predicts high GHz and THz fluxes at the time of the NIR/X-ray peak and electron densities well above those implied from average accretion rates for Sgr A*. However, the higher electron density postulated in this scenario would be in agreement with the idea that 2019 was an extraordinary epoch with a heightened accretion rate. Since the NIR and X-ray peaks can also be fit by a non-thermal synchrotron source with lower electron densities, we cannot rule out an unrelated chance coincidence of this bright submm flare with the NIR/X-ray emission., Comment: Accepted for publication in The Astrophysical Journal

Published
2022
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8. The prototype X-ray binary GX 339-4: using TeV gamma-rays to assess LMXBs as Galactic cosmic ray accelerators

Author

Kantzas, D., Markoff, S., Lucchini, M., Ceccobello, C., Grinberg, V., Connors, R. M. T., and Uttley, P.

Subjects
Astrophysics - High Energy Astrophysical Phenomena
Abstract

Since the discovery of cosmic rays (CRs) over a century ago, their origin remains an open question. Galactic CRs with energy up to the knee ($10^{15}$ eV) are considered to originate from supernova remnants, but this scenario has recently been questioned due to lack of TeV $\gamma$-ray counterparts in many cases. Extragalactic CRs on the other hand, are thought to be associated with accelerated particles in the relativistic jets launched by supermassive accreting black holes at the center of galaxies. Scaled down versions of such jets have been detected in X-ray binaries hosting a stellar black hole (BHXBs). In this work, we investigate the possibility that the smaller-scale jets in transient outbursts of low-mass BHXBs could be sources of Galactic CRs. To better test this scenario, we model the entire electromagnetic spectrum of such sources focusing on the potential TeV regime, using the `canonical' low-mass BHXB GX 339-4 as a benchmark. Taking into account both the leptonic radiative processes and the $\gamma$-rays produced via neutral pion decay from inelastic hadronic interactions, we predict the GeV and TeV $\gamma$-ray spectrum of GX 339-4 using lower-frequency emission as constraints. Based on this test-case of GX 339-4 we investigate whether other, nearby low-mass BHXBs could be detected by the next-generation very-high-energy $\gamma$-ray facility the Cherenkov Telescope Array, which would establish them as additional and numerous potential sources of CRs in the Galaxy., Comment: 13 pages, 12 figures, accepted to MNRAS

Published
2022
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9. A Swift study of long-term changes in the X-ray flaring properties of Sagittarius A*

Author

Andrés, A., Eijnden, J. van den, Degenaar, N., Evans, P. A., Chatterjee, K., Reynolds, M., Miller, J. M., Kennea, J., Wijnands, R., Markoff, S., Altamirano, D., Heinke, C. O., Bahramian, A., Ponti, G., and Haggard, D.

Subjects
Astrophysics - High Energy Astrophysical Phenomena
Abstract

The radiative counterpart of the supermassive black hole at the Galactic Centre, Sagittarius A*, displays flaring emission in the X-ray band atop a steady, quiescent level. Flares are also observed in the near-infrared band. The physical process producing the flares is not fully understood and it is unclear if the flaring rate varies, although some recent works suggest it has reached unprecedented variability in recent years. Using over a decade of regular X-ray monitoring of Neil Gehrels Swift Observatory, we studied the variations in count rate of Sgr A* on time scales of years. We decomposed the X-ray emission into quiescent and flaring emission, modelled as a constant and power law process, respectively. We found that the complete, multi-year dataset cannot be described by a stationary distribution of flare fluxes, while individual years follow this model better. In three of the ten studied years, the data is consistent with a purely Poissonian quiescent distribution, while for five years only an upper limit of the flare flux distribution parameter could be determined. We find that these possible changes cannot be explained fully by the different number of observations per year. Combined, these results are instead consistent with a changing flaring rate of Sgr A*, appearing more active between 2006-2007 and 2017-2019, than between 2008-2012. Finally, we discuss this result in the context of flare models and the passing of gaseous objects, and discuss the extra statistical steps taken, for instance to deal with the background in the Swift observations., Comment: 14 pages, 10 figures, Accepted for publication in MNRAS

Published
2021
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10. EuCAPT White Paper: Opportunities and Challenges for Theoretical Astroparticle Physics in the Next Decade

Author

Batista, R. Alves, Amin, M. A., Barenboim, G., Bartolo, N., Baumann, D., Bauswein, A., Bellini, E., Benisty, D., Bertone, G., Blasi, P., Böhmer, C. G., Bošnjak, Ž., Bringmann, T., Burrage, C., Bustamante, M., Bustillo, J. Calderón, Byrnes, C. T., Calore, F., Catena, R., Cerdeño, D. G., Cerri, S. S., Chianese, M., Clough, K., Cole, A., Coloma, P., Coogan, A., Covi, L., Cutting, D., Davis, A. C., de Rham, C., di Matteo, A., Domènech, G., Drewes, M., Dietrich, T., Edwards, T. D. P., Esteban, I., Erdem, R., Evoli, C., Fasiello, M., Feeney, S. M., Ferreira, R. Z., Fialkov, A., Fornengo, N., Gabici, S., Galatyuk, T., Gaggero, D., Grasso, D., Guépin, C., Harz, J., Herrero-Valea, M., Hinderer, T., Hogg, N. B., Hooper, D. C., Iocco, F., Isern, J., Karchev, K., Kavanagh, B. J., Korsmeier, M., Kotera, K., Koyama, K., Krishnan, B., Lesgourgues, J., Said, J. Levi, Lombriser, L., Lorenz, C. S., Manconi, S., Mapelli, M., Marcowith, A., Markoff, S. B., Marsh, D. J. E., Martinelli, M., Martins, C. J. A. P., Matthews, J. H., Meli, A., Mena, O., Mifsud, J., Bertolami, M. M. Miller, Millington, P., Moesta, P., Nippel, K., Niro, V., O'Connor, E., Oikonomou, F., Paganini, C. F., Pagliaroli, G., Pani, P., Pfrommer, C., Pascoli, S., Pinol, L., Pizzuti, L., Porto, R. A., Pound, A., Quevedo, F., Raffelt, G. G., Raccanelli, A., Ramirez-Ruiz, E., Raveri, M., Renaux-Petel, S., Ricciardone, A., Khalifeh, A. Rida, Riotto, A., Roiban, R., Rubio, J., Sahlén, M., Sabti, N., Sagunski, L., Šarčević, N., Schmitz, K., Schwaller, P., Schwetz, T., Sedrakian, A., Sellentin, E., Serenelli, A., Serpico, P. D., Sfakianakis, E. I., Shalgar, S., Silvestri, A., Tamborra, I., Tanidis, K., Teresi, D., Tokareva, A. A., Tolos, L., Trojanowski, S., Trotta, R., Uhlemann, C., Urban, F. R., Vernizzi, F., van Vliet, A., Villante, F. L., Vincent, A., Vink, J., Vitagliano, E., Weniger, C., Wickenbrock, A., Winter, W., Zell, S., and Zeng, M.

Subjects
Astrophysics - High Energy Astrophysical Phenomena, Astrophysics - Cosmology and Nongalactic Astrophysics
Abstract

Astroparticle physics is undergoing a profound transformation, due to a series of extraordinary new results, such as the discovery of high-energy cosmic neutrinos with IceCube, the direct detection of gravitational waves with LIGO and Virgo, and many others. This white paper is the result of a collaborative effort that involved hundreds of theoretical astroparticle physicists and cosmologists, under the coordination of the European Consortium for Astroparticle Theory (EuCAPT). Addressed to the whole astroparticle physics community, it explores upcoming theoretical opportunities and challenges for our field of research, with particular emphasis on the possible synergies among different subfields, and the prospects for solving the most fundamental open questions with multi-messenger observations., Comment: White paper of the European Consortium for Astroparticle Theory (EuCAPT). 135 authors, 400 endorsers, 133 pages, 1382 references

Published
2021

11. Bhjet: a public multi-zone, steady state jet + thermal corona spectral model

Author

Lucchini, M., Ceccobello, C., Markoff, S., Kini, Y., Chhotray, A., Connors, R. M. T., Crumley, P., Falcke, H., Kantzas, D., and Maitra, D.

Subjects
Astrophysics - High Energy Astrophysical Phenomena
Abstract

Accreting black holes are sources of major interest in astronomy, particular those launching jets because of their ability to accelerate particles, and dramatically affect their surrounding environment up to very large distances. The spatial, energy and time scales at which a central active black hole radiates and impacts its environment depend on its mass. The implied scale-invariance of accretion/ejection physics between black hole systems of different central masses has been confirmed by several studies. Therefore, designing a self-consistent theoretical model that can describe such systems, regardless of their mass, is of crucial importance to tackle a variety of astrophysical sources. We present here a new and significantly improved version of a scale invariant, steady-state, multi-zone jet model, which we rename bhjet, resulting from the efforts of our group to advance the modelling of black hole systems. We summarise the model assumptions and basic equations, how they have evolved over time, and the additional features that we have recently introduced. These include additional input electron populations, the extension to cyclotron emission in near-relativistic regime, an improved multiple inverse Compton scattering method, external photon seeds typical of AGN and a magnetically-dominated jet dynamical model as opposed to the pressure-driven jet configuration present in older versions. In this paper, we publicly release the code on Github and, in order to facilitate the user's approach to its many possibilities, showcase a few applications as a tutorial., Comment: 28 pages, 16 figures, accepted for publication on MNRAS, code available at https://github.com/matteolucchini1/BHJet/, updated to the latest version of the manuscript

Published
2021
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12. Prospects for Galactic transient sources detection with the Cherenkov Telescope Array

Author

López-Oramas, A., Bulgarelli, A., Chaty, S., Chernyakova, M., Gnatyk, R., Hnatyk, B., Kantzas, D., Markoff, S., McKeague, S., Mereghetti, S., Mestre, E., di Piano, A., Romano, P., Sadeh, I., Sergijenko, O., Sidoli, L., Spolon, A., Wilhelmi, E. de Oña, Piano, G., and Zampieri, L.

Subjects
Astrophysics - High Energy Astrophysical Phenomena
Abstract

Several types of Galactic sources, like magnetars, microquasars, novae or pulsar wind nebulae flares, display transient emission in the X-ray band. Some of these sources have also shown emission at MeV--GeV energies. However, none of these Galactic transients have ever been detected in the very-high-energy (VHE; E$>$100 GeV) regime by any Imaging Air Cherenkov Telescope (IACT). The Galactic Transient task force is a part of the Transient Working group of the Cherenkov Telescope Array (CTA) Consortium. The task force investigates the prospects of detecting the VHE counterpart of such sources, as well as their study following Target of Opportunity (ToO) observations. In this contribution, we will show some of the results of exploring the capabilities of CTA to detect and observe Galactic transients; we assume different array configurations and observing strategies., Comment: 37th International Cosmic Ray Conference (ICRC2021)

Published
2021
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13. Constraining particle acceleration in Sgr A* with simultaneous GRAVITY, Spitzer, NuSTAR and Chandra observations

Author

Abuter, R., Amorim, A., Bauböck, M., Baganoff, F., Berge, J. P., Boyce, H., Bonnet, H., Brandner, W., Clénet, Y., Davies, R., de Zeeuw, P. T., Dexter, J., Dallilar, Y., Drescher, A., Eckart, A., Eisenhauer, F., Fazio, G. G., Schreiber, N. M. Förster, Foster, K., Gammie, C., Garcia, P., Gao, F., Gendron, E., Genzel, R., Ghisellini, G., Gillessen, S., Gurwell, M. A., Habibi, M., Haggard, D., Hailey, C., Harrison, F. A., Haubois, X., Heißel, G., Henning, T., Hippler, S., Hora, J. L., Horrobin, M., Jiménez-Rosales, A., Jochum, L., Jocou, L., Kaufer, A., Kervella, P., Lacour, S., Lapeyrère, V., Bouquin, J. -B. Le, Léna, P., Lowrance, P. J., Lutz, D., Markoff, S., Mori, K., Morris, M. R., Neilsen, J., Nowak, M., Ott, T., Paumard, T., Perraut, K., Perrin, G., Ponti, G., Pfuhl, O., Rabien, S., Rodríguez-Coira, G., Shangguan, J., Shimizu, T., Scheithauer, S., Smith, H. A., Stadler, J., Stern, D. K., Straub, O., Straubmeier, C., Sturm, E., Tacconi, L. J., Vincent, F., von Fellenberg, S., Waisberg, I., Widmann, F., Wieprecht, E., Wiezorrek, E., Willner, S. P., Witzel, G., Woillez, J., Yazici, S., Young, A., Zhang, S., and Zins, G.

Subjects
Astrophysics - High Energy Astrophysical Phenomena
Abstract

We report the time-resolved spectral analysis of a bright near-infrared and moderate X-ray flare of Sgr A*. We obtained light curves in the $M$-, $K$-, and $H$-bands in the mid- and near-infrared and in the $2-8~\mathrm{keV}$ and $2-70~\mathrm{keV}$ bands in the X-ray. The observed spectral slope in the near-infrared band is $\nu L_\nu\propto \nu^{0.5\pm0.2}$; the spectral slope observed in the X-ray band is $\nu L_\nu \propto \nu^{-0.7\pm0.5}$. We tested synchrotron and synchrotron self-Compton (SSC) scenarios. The observed near-infrared brightness and X-ray faintness, together with the observed spectral slopes, pose challenges for all models explored. We rule out a scenario in which the near-infrared emission is synchrotron emission and the X-ray emission is SSC. A one-zone model in which both the near-infrared and X-ray luminosity are produced by SSC and a model in which the luminosity stems from a cooled synchrotron spectrum can explain the flare. In order to describe the mean SED, both models require specific values of the maximum Lorentz factor $\gamma_{max}$, which however differ by roughly two orders of magnitude: the SSC model suggests that electrons are accelerated to $\gamma_{max}\sim 500$, while cooled synchrotron model requires acceleration up to $\gamma_{max}\sim5\times 10^{4}$. The SSC scenario requires electron densities of $10^{10}~\mathrm{cm^{-3}}$ much larger than typical ambient densities in the accretion flow, and thus require in an extraordinary accretion event. In contrast, assuming a source size of $1R_s$, the cooled synchrotron scenario can be realized with densities and magnetic fields comparable with the ambient accretion flow. For both models, the temporal evolution is regulated through the maximum acceleration factor $\gamma_{max}$, implying that sustained particle acceleration is required to explain at least a part of the temporal evolution of the flare., Comment: accepted for publication in Astronomy & Astrophysics; preview abstract shortened due to arXiv requirements

Published
2021
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14. 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

15. The Varying Kinematics of Multiple Ejecta from the Black Hole X-ray Binary MAXI J1820+070

Author

Wood, C. M., Miller-Jones, J. C. A., Homan, J., Bright, J. S., Motta, S. E., Fender, R. P., Markoff, S., Belloni, T. M., Körding, E. G., Maitra, D., Migliari, S., Russell, D. M., Russell, T. D., Sarazin, C. L., Soria, R., Tetarenko, A. J., and Tudose, V.

Subjects
Astrophysics - High Energy Astrophysical Phenomena
Abstract

During a 2018 outburst, the black hole X-ray binary MAXI J1820+070 was comprehensively monitored at multiple wavelengths as it underwent a hard to soft state transition. During this transition a rapid evolution in X-ray timing properties and a short-lived radio flare were observed, both of which were linked to the launching of bi-polar, long-lived relativistic ejecta. We provide detailed analysis of two Very Long Baseline Array observations, using both time binning and a new dynamic phase centre tracking technique to mitigate the effects of smearing when observing fast-moving ejecta at high angular resolution. We identify a second, earlier ejection, with a lower proper motion of $18.0\pm1.1$ mas day$^{-1}$. This new jet knot was ejected $4\pm1$ hours before the beginning of the rise of the radio flare, and $2\pm1$ hours before a switch from type-C to type-B X-ray quasi-periodic oscillations (QPOs). We show that this jet was ejected over a period of $\sim6$ hours and thus its ejection was contemporaneous with the QPO transition. Our new technique locates the original, faster ejection in an observation in which it was previously undetected. With this detection we revised the fits to the proper motions of the ejecta and calculated a jet inclination angle of $(64\pm5)^\circ$, and jet velocities of $0.97_{-0.09}^{+0.03}c$ for the fast-moving ejecta ($\Gamma>2.1$) and $(0.30\pm0.05)c$ for the newly-identified slow-moving ejection ($\Gamma=1.05\pm0.02$). We show that the approaching slow-moving component is predominantly responsible for the radio flare, and is likely linked to the switch from type-C to type-B QPOs, while no definitive signature of ejection was identified for the fast-moving ejecta., Comment: 11 pages including 5 figures. Accepted for publication in MNRAS

Published
2021
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16. X-ray spectral components of the blazar and binary black hole candidate OJ 287 (2005-2020)

Author

Komossa, S., Grupe, D., Parker, M. L., Gómez, J. L., Valtonen, M. J., Nowak, M. A., Jorstad, S. G., Haggard, D., Chandra, S., Ciprini, S., Dey, L., Gopakumar, A., Hada, K., Markoff, S., and Neilsen, J.

Subjects
Astrophysics - High Energy Astrophysical Phenomena, Astrophysics - Astrophysics of Galaxies
Abstract

We present a comprehensive analysis of all XMM-Newton spectra of OJ 287 spanning 15 years of X-ray spectroscopy of this bright blazar. We also report the latest results from our dedicated Swift UVOT and XRT monitoring of OJ 287 which started in 2015, along with all earlier public Swift data since 2005. During this time interval, OJ 287 was caught in extreme minima and outburst states. Its X-ray spectrum is highly variable and encompasses all states seen in blazars from very flat to exceptionally steep. The spectrum can be decomposed into three spectral components: Inverse Compton (IC) emission dominant at low-states, super-soft synchrotron emission which becomes increasingly dominant as OJ 287 brightens, and an intermediately-soft (Gamma_x=2.2) additional component seen at outburst. This last component extends beyond 10 keV and plausibly represents either a second synchrotron/IC component and/or a temporary disk corona of the primary supermassive black hole (SMBH). Our 2018 XMM-Newton observation, quasi-simultaneous with the Event Horizon Telescope observation of OJ 287, is well described by a two-component model with a hard IC component of Gamma_x=1.5 and a soft synchrotron component. Low-state spectra limit any long-lived accretion disk/corona contribution in X-rays to a very low value of L_x/L_Edd < 5.6 times 10^(-4) (for M_(BH, primary) = 1.8 times 10^10 M_sun). Some implications for the binary SMBH model of OJ 287 are discussed., Comment: 14 pages. MNRAS, in press

Published
2021
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17. Persistent Non-Gaussian Structure in the Image of Sagittarius A* at 86 GHz

Author

Issaoun, S., Johnson, M. D., Blackburn, L., Broderick, A., Tiede, P., Wielgus, M., Doeleman, S. S., Falcke, H., Akiyama, K., Bower, G. C., Brinkerink, C. D., Chael, A., Cho, I., Gómez, J. L., Hernández-Gómez, A., Hughes, D., Kino, M., Krichbaum, T. P., Liuzzo, E., Loinard, L., Markoff, S., Marrone, D. P., Mizuno, Y., Moran, J. M., Pidopryhora, Y., Ros, E., Rygl, K., Shen, Z. -Q., and Wagner, J.

Subjects
Astrophysics - Astrophysics of Galaxies, Astrophysics - High Energy Astrophysical Phenomena
Abstract

Observations of the Galactic Center supermassive black hole Sagittarius A* (Sgr A*) with very long baseline interferometry (VLBI) are affected by interstellar scattering along our line of sight. At long radio observing wavelengths ($\gtrsim1\,$cm), the scattering heavily dominates image morphology. At 3.5 mm (86 GHz), the intrinsic source structure is no longer sub-dominant to scattering, and thus the intrinsic emission from Sgr A* is resolvable with the Global Millimeter VLBI Array (GMVA). Long-baseline detections to the phased Atacama Large Millimeter/submillimeter Array (ALMA) in 2017 provided new constraints on the intrinsic and scattering properties of Sgr A*, but the stochastic nature of the scattering requires multiple observing epochs to reliably estimate its statistical properties. We present new observations with the GMVA+ALMA, taken in 2018, which confirm non-Gaussian structure in the scattered image seen in 2017. In particular, the ALMA-GBT baseline shows more flux density than expected for an anistropic Gaussian model, providing a tight constraint on the source size and an upper limit on the dissipation scale of interstellar turbulence. We find an intrinsic source extent along the minor axis of $\sim100\,\mu$as both via extrapolation of longer wavelength scattering constraints and direct modeling of the 3.5 mm observations. Simultaneously fitting for the scattering parameters, we find an at-most modestly asymmetrical (major-to-minor axis ratio of $1.5\pm 0.2$) intrinsic source morphology for Sgr A*., Comment: 18 pages, 10 figures, submitted to ApJ

Published
2021
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18. Broadband Multi-wavelength Properties of M87 during the 2017 Event Horizon Telescope Campaign

Author

Algaba, J. C., Anczarski, J., Asada, K., Balokovic, M., Chandra, S., Cui, Y. -Z., Falcone, A. D., Giroletti, M., Goddi, C., Hada, K., Haggard, D., Jorstad, S., Kaur, A., Kawashima, T., Keating, G., Kim, J. -Y., Kino, M., Komossa, S., Kravchenko, E. V., Krichbaum, T. P., Lee, S. -S., Lu, R. -S., Lucchini, M., Markoff, S., Neilsen, J., Nowak, M. A., Park, J., Principe, G., Ramakrishnan, V., Reynolds, M. T., Sasada, M., Savchenko, S. S., Williamson, K. E., Collaboration, The Event Horizon Telescope, Collaboration, The Fermi Large Area Telescope, Collaboration, H. E. S. S., Collaboration, MAGIC, Collaboration, VERITAS, and Collaboration, EAVN

Subjects
Astrophysics - High Energy Astrophysical Phenomena, Astrophysics - Cosmology and Nongalactic Astrophysics, Astrophysics - Astrophysics of Galaxies
Abstract

In 2017, the Event Horizon Telescope (EHT) Collaboration succeeded in capturing the first direct image of the center of the M87 galaxy. The asymmetric ring morphology and size are consistent with theoretical expectations for a weakly accreting supermassive black hole of mass approximately 6.5 x 10^9 M_solar. The EHTC also partnered with several international facilities in space and on the ground, to arrange an extensive, quasi-simultaneous multi-wavelength campaign. This Letter presents the results and analysis of this campaign, as well as the multi-wavelength data as a legacy data repository. We captured M87 in a historically low state, and the core flux dominates over HST-1 at high energies, making it possible to combine core flux constraints with the more spatially precise very long baseline interferometry data. We present the most complete simultaneous multi-wavelength spectrum of the active nucleus to date, and discuss the complexity and caveats of combining data from different spatial scales into one broadband spectrum. We apply two heuristic, isotropic leptonic single-zone models to provide insight into the basic source properties, but conclude that a structured jet is necessary to explain M87's spectrum. We can exclude that the simultaneous gamma-ray emission is produced via inverse Compton emission in the same region producing the EHT mm-band emission, and further conclude that the gamma-rays can only be produced in the inner jets (inward of HST-1) if there are strongly particle-dominated regions. Direct synchrotron emission from accelerated protons and secondaries cannot yet be excluded., Comment: 43 pages, 19 figures, 10 tables; complete author list available in manuscript; The Astrophysical Journal Letters, 2021, 911, L11; publication doi: 3847/2041-8213/abef71, data doi: 10.25739/mhh2-cw46

Published
2021
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19. LOFAR imaging of Cygnus A -- Direct detection of a turnover in the hotspot radio spectra

Author

McKean, J. P., Godfrey, L. E. H., Vegetti, S., Wise, M. W., Morganti, R., Hardcastle, M. J., Rafferty, D., Anderson, J., Avruch, I. M., Beck, R., Bell, M. E., van Bemmel, I., Bentum, M. J., Bernardi, G., Best, P., Blaauw, R., Bonafede, A., Breitling, F., Broderick, J. W., Bruggen, M., Cerrigone, L., Ciardi, B., de Gasperin, F., Deller, A., Duscha, S., Engels, D., Falcke, H., Fallows, R. A., Frieswijk, W., Garrett, M. A., Griessmeier, J. M., van Haarlem, M. P., Heald, G., Hoeft, M., van der Horst, A. J., Iacobelli, M., Intema, H., Juette, E., Karastergiou, A., Kondratiev, V. I., Koopmans, L. V. E., Kuniyoshi, M., Kuper, G., van Leeuwen, J., Maat, P., Mann, G., Markoff, S., McFadden, R., McKay-Bukowski, D., Mulcahy, D. D., Munk, H., Nelles, A., Orru, E., Paas, H., Pandey-Pommier, M., Pietka, M., Pizzo, R., Polatidis, A. G., Reich, W., Rottgering, H. J. A., Rowlinson, A., Scaife, A. M. M., Serylak, M., Shulevski, A., Sluman, J., Smirnov, O., Steinmetz, M., Stewart, A., Swinbank, J., Tagger, M., Thoudam, S., Toribio, M. C., Vermeulen, R., Vocks, C., van Weeren, R. J., Wucknitz, O., Yatawatta, S., and Zarka, P.

Subjects
Astrophysics - Astrophysics of Galaxies
Abstract

The low-frequency radio spectra of the hotspots within powerful radio galaxies can provide valuable information about the physical processes operating at the site of the jet termination. These processes are responsible for the dissipation of jet kinetic energy, particle acceleration, and magnetic-field generation. Here we report new observations of the powerful radio galaxy Cygnus A using the Low Frequency Array (LOFAR) between 109 and 183 MHz, at an angular resolution of ~3.5 arcsec. The radio emission of the lobes is found to have a complex spectral index distribution, with a spectral steepening found towards the centre of the source. For the first time, a turnover in the radio spectrum of the two main hotspots of Cygnus A has been directly observed. By combining our LOFAR imaging with data from the Very Large Array at higher frequencies, we show that the very rapid turnover in the hotspot spectra cannot be explained by a low-energy cut-off in the electron energy distribution, as has been previously suggested. Thermal (free-free) absorption or synchrotron self absorption models are able to describe the low-frequency spectral shape of the hotspots, however, as with previous studies, we find that the implied model parameters are unlikely, and interpreting the spectra of the hotspots remains problematic., Comment: 9 pages, 3 figures, accepted for publication in MNRAS

Published
2021
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20. Correlating spectral and timing properties in the evolving jet of the micro blazar MAXI J1836-194

Author

Lucchini, M., Russell, T. D., Markoff, S. B., Vincentelli, F., Gardenier, D., Ceccobello, C., and Uttley, P.

Subjects
Astrophysics - High Energy Astrophysical Phenomena
Abstract

During outbursts, the observational properties of black hole X-ray binaries (BHXBs) vary on timescales of days to months. These relatively short timescales make these systems ideal laboratories to probe the coupling between accreting material and outflowing jets as a the accretion rate varies. In particular, the origin of the hard X-ray emission is poorly understood and highly debated. This spectral component, which has a power-law shape, is due to Comptonisation of photons near the black hole, but it is unclear whether it originates in the accretion flow itself, or at the base of the jet, or possibly the interface region between them. In this paper we explore the disk-jet connection by modelling the multi-wavelength emission of MAXI J1836-194 during its 2011 outburst. We combine radio through X-ray spectra, X-ray timing information, and a robust joint-fitting method to better isolate the jet's physical properties. Our results demonstrate that the jet base can produce power-law hard X-ray emission in this system/outburst, provided that its base is fairly compact and that the temperatures of the emitting electrons are sub-relativistic. Because of energetic considerations, our model favours mildly pair-loaded jets carrying at least 20 pairs per proton. Finally, we find that the properties of the X-ray power spectrum are correlated with the jet properties, suggesting that an underlying physical process regulates both., Comment: 17 pages, 10 figures, accepted for publication on MNRAS

Published
2020
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21. Disk-jet coupling changes as a possible indicator for outbursts from GX 339-4 remaining within the X-ray hard state

Author

de Haas, S. E. M., Russell, T. D., Degenaar, N., Markoff, S., Tetarenko, A. J., Tetarenko, B. E., Eijnden, J. van den, Miller-Jones, J. C. A., Parikh, A. S., Plotkin, R. M., and Sivakoff, G. R.

Subjects
Astrophysics - High Energy Astrophysical Phenomena
Abstract

We present quasi-simultaneous radio, (sub-)millimetre, and X-ray observations of the Galactic black hole X-ray binary GX 339-4, taken during its 2017--2018 outburst, where the source remained in the hard X-ray spectral state. During this outburst, GX 339-4 showed no atypical X-ray behaviour that may act as a indicator for an outburst remaining within the hard state. However, quasi-simultaneous radio and X-ray observations showed a flatter than expected coupling between the radio and X-ray luminosities (with a best fit relation of $L_{\rm radio} \propto L_{\rm X}^{0.39 \pm 0.06}$), when compared to successful outbursts from this system ($L_{\rm radio} \propto L_{\rm X}^{0.62 \pm 0.02}$). While our 2017--2018 outburst data only span a limited radio and X-ray luminosity range ($\sim$1 order of magnitude in both, where more than 2-orders of magnitude in $L_{\rm X}$ is desired), including data from other hard-only outbursts from GX 339-4 extends the luminosity range to $\sim$1.2 and $\sim$2.8 orders of magnitude, respectively, and also results in a flatter correlation (where $L_{\rm radio} \propto L_{\rm X}^{0.46 \pm 0.04}$). This result is suggestive that for GX 339-4 a flatter radio -- X-ray correlation, implying a more inefficient coupling between the jet and accretion flow, could act as an indicator for a hard-only outburst. However, further monitoring of both successful and hard-only outbursts over larger luminosity ranges with strictly simultaneous radio and X-ray observations is required from different, single sources, to explore if this applies generally to the population of black hole X-ray binaries, or even GX 339-4 at higher hard-state luminosities., Comment: 14 pages, 9 figures, 4 tables. All data is provided in the appendices, accepted for publication in MNRAS

Published
2020
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22. A new lepto-hadronic model applied to the first simultaneous multiwavelength data set for Cygnus X--1

Author

Kantzas, D., Markoff, S., Beuchert, T., Lucchini, M., Chhotray, A., Ceccobello, C., Tetarenko, A. J., Miller-Jones, J. C. A., Bremer, M., Garcia, J. A., Grinberg, V., Uttley, P., and Wilms, J.

Subjects
Astrophysics - High Energy Astrophysical Phenomena
Abstract

Cygnus X--1 is the first Galactic source confirmed to host an accreting black hole. It has been detected across the entire electromagnetic spectrum from radio to GeV $\gamma$-rays. The source's radio through mid-infrared radiation is thought to originate from the relativistic jets. The observed high degree of linear polarisation in the MeV X-rays suggests that the relativistic jets dominate in this regime as well, whereas a hot accretion flow dominates the soft X-ray band. The origin of the GeV non-thermal emission is still debated, with both leptonic and hadronic scenarios deemed to be viable. In this work, we present results from a new semi-analytical, multi-zone jet model applied to the broad-band spectral energy distribution of Cygnus X--1 for both leptonic and hadronic scenarios. We try to break this degeneracy by fitting the first-ever high-quality, simultaneous multiwavelength data set obtained from the CHOCBOX campaign (Cygnus X--1 Hard state Observations of a Complete Binary Orbit in X-rays). Our model parameterises dynamical properties, such as the jet velocity profile, the magnetic field, and the energy density. Moreover, the model combines these dynamical properties with a self-consistent radiative transfer calculation including secondary cascades, both of leptonic and hadronic origin. We conclude that sensitive TeV $\gamma$-ray telescopes like Cherenkov Telescope Array (CTA) will definitively answer the question of whether hadronic processes occur inside the relativistic jets of Cygnus X--1., Comment: 16 pages, 4 figures, accepted for publication in MNRAS

Published
2020
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23. 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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24. Rapid compact jet quenching in the Galactic black hole candidate X-ray binary MAXI J1535-571

Author

Russell, T. D., Lucchini, M., Tetarenko, A. J., Miller-Jones, J. C. A., Sivakoff, G. R., Krauß, F., Mulaudzi, W., Baglio, M. C., Russell, D. M., Altamirano, D., Ceccobello, C., Corbel, S., Degenaar, N., Eijnden, J. van den, Fender, R., Heinz, S., Koljonen, K. I. I., Maitra, D., Markoff, S., Migliari, S., Parikh, A. S., Plotkin, R. M., Rupen, M., Sarazin, C., Soria, R., and Wijnands, R.

Subjects
Astrophysics - High Energy Astrophysical Phenomena
Abstract

We present results from six epochs of quasi-simultaneous radio, (sub-)millimetre, infrared, optical, and X-ray observations of the black hole X-ray binary MAXI~J1535$-$571. These observations show that as the source transitioned through the hard-intermediate X-ray state towards the soft intermediate X-ray state, the jet underwent dramatic and rapid changes. We observed the frequency of the jet spectral break, which corresponds to the most compact region in the jet where particle acceleration begins (higher frequencies indicate closer to the black hole), evolve from the IR band into the radio band (decreasing by $\approx$3 orders of magnitude) in less than a day. During one observational epoch, we found evidence of the jet spectral break evolving in frequency through the radio band. Estimating the magnetic field and size of the particle acceleration region shows that the rapid fading of the high-energy jet emission was not consistent with radiative cooling; instead the particle acceleration region seems to be moving away from the black hole on approximately dynamical timescales. This result suggests that the compact jet quenching is not caused by local changes to the particle acceleration, rather we are observing the acceleration region of the jet travelling away from the black hole with the jet flow. Spectral analysis of the X-ray emission show a gradual softening in the few days before the dramatic jet changes, followed by a more rapid softening $\sim$1--2\,days after the onset of the jet quenching., Comment: 17 pages, 6 figures, data provided in the appendices. Accepted for publication in MNRAS

Published
2020
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25. 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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26. Relativistic AGN jets III. Synthesis of synchrotron emission from Double-Double Radio Galaxies

Author

Walg, S., Achterberg, A., Markoff, S., Keppens, R., and Porth, O.

Subjects
Astrophysics - High Energy Astrophysical Phenomena, Astrophysics - Astrophysics of Galaxies
Abstract

The class of Double-Double Radio Galaxies (DDRGs) relates to episodic jet outbursts. How various regions and components add to the total intensity in radio images is less well known. In this paper we synthesize synchrotron images for DDRGs based on special relativistic hydrodynamic simulations, making advanced approximations for the magnetic fields. We study the synchrotron images for: Three different radial jet profiles; Ordered, entangled or mixed magnetic fields; Spectral ageing from synchrotron cooling; The contribution from different jet components; The viewing angle and Doppler (de-)boosting; The various epochs of the evolution of the DDRG. To link our results to observational data, we adopt to J1835+6204 as a reference source. In all cases the synthesized synchrotron images show two clear pairs of hotspots, in the inner and outer lobes. The best resemblance is obtained for the piecewise isochoric jet model, for a viewing angle of approximately $\vartheta \sim -71^{\circ}$, i.e. inclined with the lower jet towards the observer, with predominantly entangled ($\gtrsim 70$ per cent of the magnetic pressure) in turbulent, rather than ordered fields. The effects of spectral ageing become significant when the ratio of observation frequencies and cut-off frequency $\nu_{\rm obs}/\nu_{\infty,0} \gtrsim 10^{-3}$, corresponding to $\sim 3 \cdot 10^2$ MHz. For viewing angles $\vartheta \lesssim -30^{\circ}$, a DDRG morphology can no longer be recognized. The second jets must be injected within $\lesssim$ 4 per cent of the lifetime of the first jets for a DDRG structure to emerge, which is relevant for Active Galactic Nuclei feedback constraints., Comment: 24 pages, 8 figures

Published
2020
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27. SYMBA: An end-to-end VLBI synthetic data generation pipeline

Author

Roelofs, F., Janssen, M., Natarajan, I., Deane, R., Davelaar, J., Olivares, H., Porth, O., Paine, S. N., Bouman, K. L., Tilanus, R. P. J., van Bemmel, I. M., Falcke, H., Akiyama, K., Alberdi, A., Alef, W., Asada, K., Azulay, R., Baczko, A., Ball, D., Baloković, M., Barrett, J., Bintley, D., Blackburn, L., Boland, W., Bower, G. C., Bremer, M., Brinkerink, C. D., Brissenden, R., Britzen, S., Broderick, A. E., Broguiere, D., Bronzwaer, T., Byun, D., Carlstrom, J. E., Chael, A., Chan, C., Chatterjee, S., Chatterjee, K., Chen, M., Chen, Y., Cho, I., Christian, P., Conway, J. E., Cordes, J. M., Crew, G. B., Cui, Y., De Laurentis, M., Dempsey, J., Desvignes, G., Dexter, J., Doeleman, S. S., Eatough, R. P., Fish, V. L., Fomalont, E., Fraga-Encinas, R., Friberg, P., Fromm, C. M., Gómez, J. L., Galison, P., Gammie, C. F., García, R., Gentaz, O., Georgiev, B., Goddi, C., Gold, R., Gu, M., Gurwell, M., Hada, K., Hecht, M. H., Hesper, R., Ho, L. C., Ho, P., Honma, M., Huang, C. L., Huang, L., Hughes, D. H., Ikeda, S., Inoue, M., Issaoun, S., James, D. J., Jannuzi, B. T., Jeter, B., Jiang, W., Johnson, M. D., Jorstad, S., Jung, T., Karami, M., Karuppusamy, R., Kawashima, T., Keating, G. K., Kettenis, M., Kim, J., Kino, M., Koay, J. Yi, Koch, P. M., Koyama, S., Kramer, M., Kramer, C., Krichbaum, T. P., Kuo, C., Lauer, T. R., Lee, S., Li, Y., Li, Z., Lindqvist, M., Lico, R., Liu, K., Liuzzo, E., Lo, W., Lobanov, A. P., Loinard, L., Lonsdale, C., Lu, R., MacDonald, N. R., Mao, J., Markoff, S., Marrone, D. P., Marscher, A. P., Martí-Vidal, I., Matsushita, S., Matthews, L. D., Medeiros, L., Menten, K. M., Mizuno, Y., Mizuno, I., Moran, J. M., Moriyama, K., Moscibrodzka, M., Müller, C., Nagai, H., Nagar, N. M., Nakamura, M., Narayan, R., Narayanan, G., Neri, R., Ni, C., Noutsos, A., Okino, H., Ortiz-León, G. N., Oyama, T., Özel, F., Palumbo, D. C. M., Patel, N., Pen, U., Pesce, D. W., Piétu, V., Plambeck, R., PopStefanija, A., Prather, B., Preciado-López, J. A., Psaltis, D., Pu, H., Ramakrishnan, V., Rao, R., Rawlings, M. G., Raymond, A. W., Rezzolla, L., Ripperda, B., Rogers, A., Ros, E., Rose, M., Roshanineshat, A., Rottmann, H., Roy, A. L., Ruszczyk, C., Ryan, B. R., Rygl, K. L. J., Sánchez, S., Sánchez-Arguelles, D., Sasada, M., Savolainen, T., Schloerb, F. Peter, Schuster, K., Shao, L., Shen, Z., Small, D., Sohn, B. Won, SooHoo, J., Tazaki, F., Tiede, P., Titus, M., Toma, K., Torne, P., Trent, T., Trippe, S., Tsuda, S., van Langevelde, H. J., van Rossum, D. R., Wagner, J., Wardle, J., Ward-Thompson, D., Weintroub, J., Wex, N., Wharton, R., Wielgus, M., Wong, G. N., Wu, Q., Young, A., Young, K., Younsi, Z., Yuan, F., Yuan, Y., Zensus, J. A., Zhao, G., Zhao, S., and Zhu, Z.

Subjects
Astrophysics - Instrumentation and Methods for Astrophysics, Astrophysics - High Energy Astrophysical Phenomena
Abstract

Realistic synthetic observations of theoretical source models are essential for our understanding of real observational data. In using synthetic data, one can verify the extent to which source parameters can be recovered and evaluate how various data corruption effects can be calibrated. These studies are important when proposing observations of new sources, in the characterization of the capabilities of new or upgraded instruments, and when verifying model-based theoretical predictions in a comparison with observational data. We present the SYnthetic Measurement creator for long Baseline Arrays (SYMBA), a novel synthetic data generation pipeline for Very Long Baseline Interferometry (VLBI) observations. SYMBA takes into account several realistic atmospheric, instrumental, and calibration effects. We used SYMBA to create synthetic observations for the Event Horizon Telescope (EHT), a mm VLBI array, which has recently captured the first image of a black hole shadow. After testing SYMBA with simple source and corruption models, we study the importance of including all corruption and calibration effects. Based on two example general relativistic magnetohydrodynamics (GRMHD) model images of M87, we performed case studies to assess the attainable image quality with the current and future EHT array for different weather conditions. The results show that the effects of atmospheric and instrumental corruptions on the measured visibilities are significant. Despite these effects, we demonstrate how the overall structure of the input models can be recovered robustly after performing calibration steps. With the planned addition of new stations to the EHT array, images could be reconstructed with higher angular resolution and dynamic range. In our case study, these improvements allowed for a distinction between a thermal and a non-thermal GRMHD model based on salient features in reconstructed images., Comment: 20 pages, 15 figures, accepted for publication in A&A

Published
2020
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28. The Chandra High Resolution X-ray Spectrum of Quiescent Emission from Sgr A*

Author

Corrales, L., Baganoff, F. K., Wang, Q. D., Nowak, M., Neilsen, J., Markoff, S., Haggard, D., Davis, J., Houck, J., and Principe, D.

Subjects
Astrophysics - High Energy Astrophysical Phenomena, Physics - Space Physics
Abstract

In quiescence, Sgr A* is surprisingly dim, shining 100,000 times less than expected for its environment. This problem has motivated a host of theoretical models to explain radiatively inefficient accretion flows (RIAFs). The Chandra Galactic Center (GC) X-ray Visionary Program obtained approximately 3 Ms (one month) of Chandra HETG data, offering the only opportunity to examine the quiescent X-ray emission of Sgr A* with high resolution spectroscopy. Utilizing custom background regions and filters for removing overlapping point sources, this work provides the first ever look at stacked HETG spectra of Sgr A*. We model the background datasets with a cubic spline and fit the unbinned Sgr A* spectra with a simple parametric model of a power law plus Gaussian lines under the effects of interstellar extinction. We detect a strong 6.7 keV iron emission line in the HEG spectra and a 3.1 keV emission line in the MEG spectra. In all cases, the line centroids and equivalent widths are consistent with those measured from low-resolution CCD spectra. An examination of the unbinned, stacked HEG+/-1 spectrum reveals fine structure in the iron line complex. In addition to resolving the resonant and forbidden lines from He-like iron, there are apparent emission features arising with higher statistical significance at lower energy, potentially associated with FeXX-XXIV ions in a ~1 keV plasma arising near the Bondi radius of Sgr A*. With this work, we release the cleaned and stacked Sgr A* and background HETG spectra to the public as a special legacy dataset., Comment: Accepted by ApJ

Published
2020
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29. High-energy Cosmic Ray production in X-ray Binary Jets

Author

Cooper, A. J., Gaggero, D., Markoff, S., and Zhang, S.

Subjects
Astrophysics - High Energy Astrophysical Phenomena
Abstract

As smaller analogs of Active Galactic Nuclei (AGN), X-ray Binaries (XRBs) are also capable of launching jets that accelerate particles to high energies. In this work, we reexamine XRB jets as potential sources of high-energy cosmic rays (CRs) and explore whether they could provide a significant second Galactic component to the CR spectrum. In the most intriguing scenario, XRB-CRs could dominate the observed spectrum above the so-called "knee" feature at $\sim 3 \times 10^{15}$ eV, offering an explanation for several key issues in this transition zone from Galactic to extragalactic CRs. We discuss how such a scenario could be probed in the near future via multi-messenger observations of XRB jets, as well as diffuse Galactic neutrino flux measurements., Comment: 12 pages, 7 figures, accepted for publication in MNRAS

Published
2020
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30. H-AMR: A New GPU-accelerated GRMHD Code for Exascale Computing With 3D Adaptive Mesh Refinement and Local Adaptive Time-stepping

Author

Liska, M. T. P., Chatterjee, K., Issa, D., Yoon, D., Kaaz, N., Tchekhovskoy, A., van Eijnatten, D., Musoke, G., Hesp, C., Rohoza, V., Markoff, S., Ingram, A., and van der Klis, M.

Subjects
Astrophysics - High Energy Astrophysical Phenomena, Astrophysics - Astrophysics of Galaxies, Astrophysics - Solar and Stellar Astrophysics
Abstract

General-relativistic magnetohydrodynamic (GRMHD) simulations have revolutionized our understanding of black hole accretion. Here, we present a graphics processing unit (GPU) accelerated GRMHD code \hammer{} with multi-faceted optimizations that, collectively, accelerate computation by 2-5 orders of magnitude for a wide range of applications. Firstly, it introduces a spherical grid with 3D adaptive mesh refinement that operates in each of the 3 dimensions independently. This allows us to circumvent the Courant condition near the polar singularity, which otherwise cripples high-resolution computational performance. Secondly, we demonstrate that local adaptive time-stepping (LAT) on a logarithmic spherical-polar grid accelerates computation by a factor of $\lesssim10$ compared to traditional hierarchical time-stepping approaches. Jointly, these unique features lead to an effective speed of $\sim10^9$ zone-cycles-per-second-per-node on 5,400 NVIDIA V100 GPUs (i.e., 900 nodes of the OLCF Summit supercomputer). We illustrate \hammer{}'s computational performance by presenting the first GRMHD simulation of a tilted thin accretion disk threaded by a toroidal magnetic field around a rapidly spinning black hole. With an effective resolution of $13$,$440\times4$,$608\times8$,$092$ cells, and a total of $\lesssim22$ billion cells and $\sim0.65\times10^8$ timesteps, it is among the largest astrophysical simulations ever performed. We find that frame-dragging by the black hole tears up the disk into two independently precessing sub-disks. The innermost sub-disk rotation axis intermittently aligns with the black hole spin, demonstrating for the first time that such long-sought alignment is possible in the absence of large-scale poloidal magnetic fields., Comment: 21 pages, 10 figures, Accepted by ApJS, for the YouTube playlist see https://youtu.be/rIOjKUfzcvI

Published
2019
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31. A radio parallax to the black hole X-ray binary MAXI J1820+070

Author

Atri, P., Miller-Jones, J. C. A., Bahramian, A., Plotkin, R. M., Deller, A. T., Jonker, P. G., Maccarone, T. J., Sivakoff, G. R., Soria, R., Altamirano, D., Belloni, T., Fender, R., Koerding, E., Maitra, D., Markoff, S., Migliari, S., Russell, D., Russell, T., Sarazin, C. L., Tetarenko, A. J., and Tudose, V.

Subjects
Astrophysics - High Energy Astrophysical Phenomena
Abstract

Using the Very Long Baseline Array and the European Very Long Baseline Interferometry Network we have made a precise measurement of the radio parallax of the black hole X-ray binary MAXI\,J1820+070, providing a model-independent distance to the source. Our parallax measurement of ($0.348\pm0.033$) mas for MAXI J1820+070 translates to a distance of ($2.96\pm0.33$) kpc. This distance implies that the source reached ($15\pm3)\%$ of the Eddington luminosity at the peak of its outburst. Further, we use this distance to refine previous estimates of the jet inclination angle, jet velocity and the mass of the black hole in MAXI J1820+070 to be ($63\pm3)^{\circ}$, ($0.89\pm0.09)c$ and ($9.2\pm1.3) M_{\odot}$, respectively., Comment: 5 pages, 3 figures, Published in MNRAS

Published
2019
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32. A Black Hole X-ray Binary at $\sim$100 Hz: Multiwavelength Timing of MAXI J1820+070 with HiPERCAM and NICER

Author

Paice, J. A., Gandhi, P., Shahbaz, T., Uttley, P., Arzoumanian, Z., Charles, P. A., Dhillon, V. S., Gendreau, K. C., Littlefair, S. P., Malzac, J., Markoff, S., Marsh, T. R., Misra, R., Russell, D. M., and Veledina, A.

Subjects
Astrophysics - High Energy Astrophysical Phenomena
Abstract

We report on simultaneous sub-second optical and X-ray timing observations of the low mass X-ray binary black hole candidate MAXI J1820+070. The bright 2018 outburst rise allowed simultaneous photometry in five optical bands ($ugriz_s$) with HiPERCAM/GTC (Optical) at frame rates over 100 Hz, together with NICER/ISS observations (X-rays). Intense (factor of two) red flaring activity in the optical is seen over a broad range of timescales down to $\sim$10 ms. Cross-correlating the bands reveals a prominent anti-correlation on timescales of $\sim$seconds, and a narrow sub-second correlation at a lag of $\approx$+165 ms (optical lagging X-rays). This lag increases with optical wavelength, and is approximately constant over Fourier frequencies of $\sim$0.3-10 Hz. These features are consistent with an origin in the inner accretion flow and jet base within $\sim$5000 Gravitational radii. An additional $\sim$+5 s lag feature may be ascribable to disc reprocessing. MAXI J1820+070 is the third black hole transient to display a clear $\sim$0.1s optical lag, which may be common feature in such objects. The sub-second lag $variation$ with wavelength is novel, and may allow constraints on internal shock jet stratification models., Comment: MNRAS Letters, In Press

Published
2019
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33. Disk-jet coupling in the 2017/2018 outburst of the Galactic black hole candidate X-ray binary MAXI J1535-571

Author

Russell, T. D., Tetarenko, A. J., Miller-Jones, J. C. A., Sivakoff, G. R., Parikh, A. S., Rapisarda, S., Wijnands, R., Corbel, S., Tremou, E., Altamirano, D., Baglio, M. C., Ceccobello, C., Degenaar, N., Eijnden, J. van den, Fender, R., Heywood, I., Krimm, H. A., Lucchini, M., Markoff, S., Russell, D. M., Soria, R., and Woudt, P. A.

Subjects
Astrophysics - High Energy Astrophysical Phenomena
Abstract

MAXI J1535-571 is a Galactic black hole candidate X-ray binary that was discovered going into outburst in 2017 September. In this paper, we present comprehensive radio monitoring of this system using the Australia Telescope Compact Array (ATCA), as well as the MeerKAT radio observatory, showing the evolution of the radio jet during its outburst. Our radio observations show the early rise and subsequent quenching of the compact jet as the outburst brightened and then evolved towards the soft state. We constrain the compact jet quenching factor to be more than 3.5 orders of magnitude. We also detected and tracked (for 303 days) a discrete, relativistically-moving jet knot that was launched from the system. From the motion of the apparently superluminal knot, we constrain the jet inclination (at the time of ejection) and speed to $\leq 45^{\circ}$ and $\geq0.69$c, respectively. Extrapolating its motion back in time, our results suggest that the jet knot was ejected close in time to the transition from the hard intermediate state to soft intermediate state. The launching event also occurred contemporaneously with a short increase in X-ray count rate, a rapid drop in the strength of the X-ray variability, and a change in the type-C quasi-periodic oscillation (QPO) frequency that occurs $>$2.5 days before the first appearance of a possible type-B QPO., Comment: 19 pages, 9 figures, supplementary tables and figures included as appendices. Accepted for publication in ApJ

Published
2019
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34. Disc Tearing and Bardeen-Petterson Alignment in GRMHD Simulations of Highly Tilted Thin Accretion Discs

Author

Liska, M., Hesp, C., Tchekhovskoy, A., Ingram, A., van der Klis, M., Markoff, S. B., and Van Moer, M.

Subjects
Astrophysics - High Energy Astrophysical Phenomena, Astrophysics - Astrophysics of Galaxies, Astrophysics - Solar and Stellar Astrophysics
Abstract

Luminous active galactic nuclei (AGN) and X-Ray binaries (XRBs) often contain geometrically thin, radiatively cooled accretion discs. According to theory, these are -- in many cases -- initially highly misaligned with the black hole equator. In this work, we present the first general relativistic magnetohydrodynamic simulations of very thin (h/r~0.015-0.05) accretion discs around rapidly spinning (a~0.9) black holes and tilted by 45-65 degrees. We show that the inner regions of the discs with h/r<0.03 align with the black hole equator, though out to smaller radii than predicted by analytic work. The inner aligned and outer misaligned disc regions are separated by a sharp break in tilt angle accompanied by a sharp drop in density. We find that frame-dragging by the spinning black hole overpowers the disc viscosity, which is self-consistently produced by magnetized turbulence, tearing the disc apart and forming a rapidly precessing inner sub-disc surrounded by a slowly precessing outer sub-disc. We find that the system produces a pair of relativistic jets for all initial tilt values. At small distances the black hole launched jets precess rapidly together with the inner sub-disc, whereas at large distances they partially align with the outer sub-disc and precess more slowly. If the tearing radius can be modeled accurately in future work, emission model independent measurements of black hole spin based on precession-driven quasi-periodic oscillations may become possible., Comment: 8 pages, 5 figures, accompanying animations included in YouTube playlist: https://www.youtube.com/playlist?list=PLDO1oeU33GwlaPSME1TdCto1Y3P6yG91L

Published
2019
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35. The Size, Shape, and Scattering of Sagittarius A* at 86 GHz: First VLBI with ALMA

Author

Issaoun, S., Johnson, M. D., Blackburn, L., Brinkerink, C. D., Mościbrodzka, M., Chael, A., Goddi, C., Martí-Vidal, I., Wagner, J., Doeleman, S. S., Falcke, H., Krichbaum, T. P., Akiyama, K., Bach, U., Bouman, K. L., Bower, G. C., Broderick, A., Cho, I., Crew, G., Dexter, J., Fish, V., Gold, R., Gómez, J. L., Hada, K., Hernández-Gómez, A., Janßen, M., Kino, M., Kramer, M., Loinard, L., Lu, R. -S., Markoff, S., Marrone, D. P., Matthews, L. D., Moran, J. M., Müller, C., Roelofs, F., Ros, E., Rottmann, H., Sanchez, S., Tilanus, R. P. J., de Vicente, P., Wielgus, M., Zensus, J. A., and Zhao, G. -Y.

Subjects
Astrophysics - High Energy Astrophysical Phenomena
Abstract

The Galactic Center supermassive black hole Sagittarius A* (Sgr A*) is one of the most promising targets to study the dynamics of black hole accretion and outflow via direct imaging with very long baseline interferometry (VLBI). At 3.5 mm (86 GHz), the emission from Sgr A* is resolvable with the Global Millimeter VLBI Array (GMVA). We present the first observations of Sgr A* with the phased Atacama Large Millimeter/submillimeter Array (ALMA) joining the GMVA. Our observations achieve an angular resolution of ~87{\mu}as, improving upon previous experiments by a factor of two. We reconstruct a first image of the unscattered source structure of Sgr A* at 3.5 mm, mitigating effects of interstellar scattering. The unscattered source has a major axis size of 120 $\pm$ 34{\mu}as (12 $\pm$ 3.4 Schwarzschild radii), and a symmetrical morphology (axial ratio of 1.2$^{+0.3}_{-0.2}$), which is further supported by closure phases consistent with zero within 3{\sigma}. We show that multiple disk-dominated models of Sgr A* match our observational constraints, while the two jet-dominated models considered are constrained to small viewing angles. Our long-baseline detections to ALMA also provide new constraints on the scattering of Sgr A*, and we show that refractive scattering effects are likely to be weak for images of Sgr A* at 1.3 mm with the Event Horizon Telescope. Our results provide the most stringent constraints to date for the intrinsic morphology and refractive scattering of Sgr A*, demonstrating the exceptional contribution of ALMA to millimeter VLBI., Comment: Accepted for publication in ApJ

Published
2019
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36. A Phase Lag between Disk and Corona in GRMHD Simulations of Precessing Tilted Accretion Disks

Author

Liska, M., Hesp, C., Tchekhovskoy, A., Ingram, A., van der Klis, M., and Markoff, S. B.

Subjects
Astrophysics - High Energy Astrophysical Phenomena
Abstract

In the course of its evolution, a black hole (BH) accretes gas from a wide range of directions. Given a random accretion event, the typical angular momentum of an accretion disc would be tilted by $\sim$60$^\circ$ relative to the BH spin. Misalignment causes the disc to precess at a rate that increases with BH spin and tilt angle. We present the first general-relativistic magnetohydrodynamic (GRMHD) simulations spanning a full precession period of highly tilted (60$^\circ$), moderately thin ($h/r=0.1$) accretion discs around a rapidly spinning ($a\simeq0.9$) BH. While the disc and jets precess in phase, we find that the corona, sandwiched between the two, lags behind by $\gtrsim 10^{\circ}$. For spectral models of BH accretion, the implication is that hard non-thermal (corona) emission lags behind the softer (disc) emission, thus potentially explaining some properties of the hard energy lags seen in Type-C low frequency quasi-periodic oscillations in X-Ray binaries. While strong jets are unaffected by this disc-corona lag, weak jets stall when encountering the lagging corona at distances $r \sim 100$ black hole radii. This interaction may quench large-scale jet formation., Comment: 6 pages, 4 figures, Accepted in New Astronomy, see YouTube playlist for 3D renderings: https://www.youtube.com/playlist?list=PLDO1oeU33GwmwOV_Hp9s7572JdU8JPSSK

Published
2019
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37. Simultaneous X-ray and Infrared Observations of Sagittarius A*'s Variability

Author

Boyce, H., Haggard, D., Witzel, G., Willner, S. P., Neilsen, J., Hora, J. L., Markoff, S., Ponti, G., Baganoff, F., Becklin, E., Fazio, G., Lowrance, P., Morris, M. R., and Smith, H. A.

Subjects
Astrophysics - High Energy Astrophysical Phenomena
Abstract

Emission from Sgr A* is highly variable at both X-ray and infrared (IR) wavelengths. Observations over the last ~20 years have revealed X-ray flares that rise above a quiescent thermal background about once per day, while faint X-ray flares from Sgr A* are undetectable below the constant thermal emission. In contrast, the IR emission of Sgr A* is observed to be continuously variable. Recently, simultaneous observations have indicated a rise in IR flux density around the same time as every distinct X-ray flare, while the opposite is not always true (peaks in the IR emission may not be coincident with an X-ray flare). Characterizing the behaviour of these simultaneous X-ray/IR events and measuring any time lag between them can constrain models of Sgr A*'s accretion flow and the flare emission mechanism. Using 100+ hours of data from a coordinated campaign between the Spitzer Space Telescope and the Chandra X-ray Observatory, we present results of the longest simultaneous IR and X-ray observations of Sgr A* taken to date. The cross-correlation between the IR and X-ray light curves in this unprecedented dataset, which includes four modest X-ray/IR flares, indicates that flaring in the X-ray may lead the IR by approximately 10-20 minutes with 68% confidence. However, the 99.7% confidence interval on the time-lag also includes zero, i.e., the flaring remains statistically consistent with simultaneity. Long duration and simultaneous multiwavelength observations of additional bright flares will improve our ability to constrain the flare timing characteristics and emission mechanisms, and must be a priority for Galactic Center observing campaigns., Comment: 12 pages, 6 figures, 3 tables, accepted for publication in ApJ

Published
2018
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38. Breaking degeneracy in jet dynamics: multi-epoch joint modelling of the BL Lac PKS 2155-304

Author

Lucchini, M., Markoff, S., Crumley, P., Krauß, F., and Connors, R. M. T.

Subjects
Astrophysics - High Energy Astrophysical Phenomena
Abstract

Supermassive black holes can launch powerful jets which can be some of the most luminous multi-wavelength sources; decades after their discovery their physics and energetics are still poorly understood. The past decade has seen a dramatic improvement in the quality of available data, but despite this improvement the semi-analytical modelling of jets has advanced slowly: simple one-zone models are still the most commonly employed method of interpreting data, in particular for AGN jets. These models can roughly constrain the properties of jets but they cannot unambiguously couple their emission to the launching regions and internal dynamics, which can be probed with simulations. However, simulations are not easily comparable to observations because they cannot yet self-consistently predict spectra. We present an advanced semi-analytical model which accounts for the dynamics of the whole jet, starting from a simplified parametrization of Relativistic Magnetohydrodynamics in which the magnetic flux is converted into bulk kinetic energy. To benchmark the model we fit six quasisimultaneous, multi-wavelength spectral energy distributions of the BL Lac PKS 2155-304 obtained by the TANAMI program, and we address the degeneracies inherent to such a complex model by employing a state-of-the-art exploration of parameter space, which so far has been mostly neglected in the study of AGN jets. We find that this new approach is much more effective than a single-epoch fit in providing meaningful constraints on model parameters., Comment: Accepted for publication on MNRAS

Published
2018
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39. Tracking the variable jets of V404 Cygni during its 2015 outburst

Author

Tetarenko, A. J., Sivakoff, G. R., Miller-Jones, J. C. A., Bremer, M., Mooley, K. P., Fender, R. P., Rumsey, C., Bahramian, A., Altamirano, D., Heinz, S., Maitra, D., Markoff, S. B., Migliari, S., Rupen, M. P., Russell, D. M., Russell, T. D., and Sarazin, C. L.

Subjects
Astrophysics - High Energy Astrophysical Phenomena
Abstract

We present multi-frequency monitoring observations of the black hole X-ray binary V404 Cygni throughout its June 2015 outburst. Our data set includes radio and mm/sub-mm photometry, taken with the Karl G. Jansky Very Large Array, Arc-Minute MicroKelvin Imager Large Array, Sub-millimeter Array, James Clerk Maxwell Telescope, and the Northern Extended Millimetre Array, combined with publicly available infrared, optical, UV, and X-ray measurements. With these data, we report detailed diagnostics of the spectral and variability properties of the jet emission observed during different stages of this outburst. These diagnostics show that emission from discrete jet ejecta dominated the jet emission during the brightest stages of the outburst. We find that the ejecta became fainter, slower, less frequent, and less energetic, before the emission transitioned (over 1--2 days) to being dominated by a compact jet, as the outburst decayed toward quiescence. While the broad-band spectrum of this compact jet showed very little evolution throughout the outburst decay (with the optically thick to thin synchrotron jet spectral break residing in the near-infrared/optical bands; $\sim2-5\times10^{14}$ Hz), the emission still remained intermittently variable at mm/sub-mm frequencies. Additionally, we present a comparison between the radio jet emission throughout the 2015 and previous 1989 outbursts, confirming that the radio emission in the 2015 outburst decayed significantly faster than in 1989. Lastly, we detail our sub-mm observations taken during the December 2015 mini-outburst of V404 Cygni, which demonstrate that, similar to the main outburst, the source was likely launching jet ejecta during this short period of renewed activity., Comment: 24 pages, 12 Figures, Accepted to MNRAS

Published
2018
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40. A wildly flickering jet in the black hole X-ray binary MAXI J1535-571

Author

Baglio, M. C., Russell, D. M., Casella, P., Noori, H. Al, Yazeedi, A. Al, Belloni, T., Buckley, D. A. H., Bel, M. Cadolle, Ceccobello, C., Corbel, S., Zelati, F. Coti, Trigo, M. Diaz, Fender, R. P., Gallo, E., Gandhi, P., Homan, J., koljonen, K. I. I., lewis, F., Maccarone, T. J., Malzac, J., Markoff, S., Miller-Jones, J. C. A., O'Brien, K., Russell, T. D., Saikia, P., Shahbaz, T., Sivakoff, G. R., Soria, R., Testa, V., Tetarenko, A. J., Ancker, M. E. van den, and Vincentelli, F. M.

Subjects
Astrophysics - High Energy Astrophysical Phenomena, Astrophysics - Solar and Stellar Astrophysics
Abstract

We report on the results of optical, near-infrared (NIR) and mid-infrared observations of the black hole X-ray binary candidate (BHB) MAXI J1535-571 during its 2017/2018 outburst. During the first part of the outburst (MJD 58004-58012), the source shows an optical-NIR spectrum that is consistent with an optically thin synchrotron power-law from a jet. After MJD 58015, however, the source faded considerably, the drop in flux being much more evident at lower frequencies. Before the fading, we measure a de-reddened flux density of $\gtrsim$100 mJy in the mid-infrared, making MAXI J1535-571 one of the brightest mid-infrared BHBs known so far. A significant softening of the X-ray spectrum is evident contemporaneous with the infrared fade. We interpret it as due to the suppression of the jet emission, similar to the accretion-ejection coupling seen in other BHBs. However, MAXI J1535-571 did not transition smoothly to the soft state, instead showing X-ray hardness deviations, associated with infrared flaring. We also present the first mid-IR variability study of a BHB on minute timescales, with a fractional rms variability of the light curves of $\sim 15-22 \%$, which is similar to that expected from the internal shock jet model, and much higher than the optical fractional rms ($\lesssim 7 \%$). These results represent an excellent case of multi-wavelength jet spectral-timing and demonstrate how rich, multi-wavelength time-resolved data of X-ray binaries over accretion state transitions can help refining models of the disk-jet connection and jet launching in these systems., Comment: 20 pages, 8 figures. Accepted for publication in the ApJ

Published
2018
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41. LOFAR 150-MHz observations of SS 433 and W 50

Author

Broderick, J. W., Fender, R. P., Miller-Jones, J. C. A., Trushkin, S. A., Stewart, A. J., Anderson, G. E., Staley, T. D., Blundell, K. M., Pietka, M., Markoff, S., Rowlinson, A., Swinbank, J. D., van der Horst, A. J., Bell, M. E., Breton, R. P., Carbone, D., Corbel, S., Eislöffel, J., Falcke, H., Grießmeier, J. -M., Hessels, J. W. T., Kondratiev, V. I., Law, C. J., Molenaar, G. J., Serylak, M., Stappers, B. W., van Leeuwen, J., Wijers, R. A. M. J., Wijnands, R., Wise, M. W., and Zarka, P.

Subjects
Astrophysics - High Energy Astrophysical Phenomena, Astrophysics - Astrophysics of Galaxies
Abstract

We present LOFAR high-band data over the frequency range 115-189 MHz for the X-ray binary SS 433, obtained in an observing campaign from 2013 February - 2014 May. Our results include a deep, wide-field map, allowing a detailed view of the surrounding supernova remnant W 50 at low radio frequencies, as well as a light curve for SS 433 determined from shorter monitoring runs. The complex morphology of W 50 is in excellent agreement with previously published higher-frequency maps; we find additional evidence for a spectral turnover in the eastern wing, potentially due to foreground free-free absorption. Furthermore, SS 433 is tentatively variable at 150 MHz, with both a debiased modulation index of 11 per cent and a $\chi^2$ probability of a flat light curve of $8.2 \times 10^{-3}$. By comparing the LOFAR flux densities with contemporaneous observations carried out at 4800 MHz with the RATAN-600 telescope, we suggest that an observed $\sim$0.5-1 Jy rise in the 150-MHz flux density may correspond to sustained flaring activity over a period of approximately six months at 4800 MHz. However, the increase is too large to be explained with a standard synchrotron bubble model. We also detect a wealth of structure along the nearby Galactic plane, including the most complete detection to date of the radio shell of the candidate supernova remnant G 38.7-1.4. This further demonstrates the potential of supernova remnant studies with the current generation of low-frequency radio telescopes., Comment: 19 pages, 8 figures, 4 tables, accepted for publication in MNRAS

Published
2018
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42. Simultaneous X-Ray and Infrared Observations of Sagittarius A*'s Variability

Author

Boyce, H, Haggard, D, Witzel, G, Willner, SP, Neilsen, J, Hora, JL, Markoff, S, Ponti, G, Baganoff, F, Becklin, EE, Fazio, GG, Lowrance, P, Morris, MR, and Smith, HA

Subjects
Climate Action, accretion, accretion disks, black hole physics, Galaxy: center, radiation mechanisms: non-thermal, astro-ph.HE, Astronomical and Space Sciences, Atomic, Molecular, Nuclear, Particle and Plasma Physics, Physical Chemistry (incl. Structural), Astronomy & Astrophysics
Abstract

Emission from Saggitarius A* is highly variable at both X-ray and infrared (IR) wavelengths. Observations over the last ~20 yr have revealed X-ray flares that rise above a quiescent thermal background about once per day, while faint X-ray flares from Sgr A* are undetectable below the constant thermal emission. In contrast, the IR emission of Sgr A* is observed to be continuously variable. Recently, simultaneous observations have indicated a rise in IR flux density around the same time as every distinct X-ray flare, while the opposite is not always true (peaks in the IR emission may not be coincident with an X-ray flare). Characterizing the behavior of these simultaneous X-ray/IR events and measuring any time lag between them can constrain models of Sgr A*'s accretion flow and the flare emission mechanism. Using 100+ hours of data from a coordinated campaign between the Spitzer Space Telescope and the Chandra X-ray Observatory, we present results of the longest simultaneous IR and X-ray observations of Sgr A* taken to date. The cross-correlation between the IR and X-ray light curves in this unprecedented data set, which includes four modest X-ray/IR flares, indicates that flaring in the X-ray may lead the IR by approximately 10-20 min with 68% confidence. However, the 99.7% confidence interval on the time-lag also includes zero, i.e., the flaring remains statistically consistent with simultaneity. Long-duration and simultaneous multi-wavelength observations of additional bright flares will improve our ability to constrain the flare timing characteristics and emission mechanisms, and must be a priority for Galactic Center observing campaigns.

Published
2019

43. VLBA polarimetric monitoring of 3C 111

Author

Beuchert, T., Kadler, M., Perucho, M., Großberger, C., Schulz, R., Agudo, I., Casadio, C., Gómez, J. L., Gurwell, M., Homan, D., Kovalev, Y. Y., Lister, M. L., Markoff, S., Molina, S. N., Pushkarev, A. B., Ros, E., Savolainen, T., Steinbring, T., Thum, C., and Wilms, J.

Subjects
Astrophysics - Astrophysics of Galaxies
Abstract

We aim to better understand the dynamics within relativistic magneto-hydrodynamical flows in the extreme environment and close vicinity of supermassive black holes. To do so, we analyze the peculiar radio galaxy 3C 111, for which long-term polarimetric observations are available. We make use of the high spatial resolution of the VLBA network and the MOJAVE monitoring program, which provides high data quality also for single sources and allows us to study jet dynamics on parsec scales in full polarization with an evenly sampled time-domain. We additionally consider data from the IRAM 30-m Telescope as well as the SMA. Jet properties such as the electric vectors, the (polarized) flux density, feature size, and brightness temperature, describe a complex evolution of the polarized jet. The electric vector position angles (EVPAs) of features traveling down the jet perform a large and smooth rotation of $\gtrsim 180^{\circ}$ across a distance of about 20 pc. In contrast, the EVPAs are strongly variable within the first parsecs of the jet. We find a tendency towards transverse EVPAs across the jet with a local anomaly of aligned vectors in between. The transverse extent of the flow decreases coincident with a jump in brightness temperature around where we observe the EVPAs to turn into alignment with the jet flow. Also the gradients of the feature size and particle density with distance steepen in that region. We interpret the propagating polarized features with shocks and the observed local anomalies with the interaction of these shocks with a recollimation shock of the underlying flow. Together with a sheared magnetic field, this shock-shock interaction can explain the large rotation of the EVPA. The superimposed variability of the EVPAs close to the core is likely related to a clumpy Faraday screen, which also contributes significantly to the observed EVPA rotation in that region., Comment: 19 pages, 22 figures, 2 tables, accepted for publication by A&A

Published
2017
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44. 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. A., Mirabal, N., Mirzoyan, R., Mitchell, A., Mizuno, T., Moderski, R., Mohammed, M., Mohrmann, L., Montaruli, T., Moralejo, A., Morcuende-Parrilla, D., Mori, K., Morlino, G., Morris, P., Morselli, A., Moulin, E., Mukherjee, R., Mundell, C., Murach, T., Muraishi, H., Murase, K., Nagai, A., Nagataki, S., Nagayoshi, T., Naito, T., Nakamori, T., Nakamura, Y., Niemiec, J., Nieto, D., Nikołajuk, M., Nishijima, K., Noda, K., Nosek, D., Novosyadlyj, B., Nozaki, S., O'Brien, P., Oakes, L., Ohira, Y., Ohishi, M., Ohm, S., Okazaki, N., Okumura, A., Ong, R. A., Orienti, M., Orito, R., Osborne, J. P., Ostrowski, M., Otte, N., Oya, I., Padovani, M., Paizis, A., Palatiello, M., Palatka, M., Paoletti, R., Paredes, J. M., Pareschi, G., Parsons, R. D., Pe'er, A., Pech, M., Pedaletti, G., Perri, M., Persic, M., Petrashyk, A., Petrucci, P., Petruk, O., Peyaud, B., Pfeifer, M., Piano, G., Pisarski, A., Pita, S., Pohl, M., Polo, M., Pozo, D., Prandini, E., Prast, J., Principe, G., Prokhorov, D., Prokoph, H., Prouza, M., Pühlhofer, G., Punch, M., Pürckhauer, S., Queiroz, F., Quirrenbach, A., Rainò, S., Razzaque, S., Reimer, O., Reimer, A., Reisenegger, A., Renaud, M., Rezaeian, A. H., Rhode, W., Ribeiro, D., Ribó, M., Richtler, T., Rico, J., Rieger, F., Riquelme, M., Rivoire, S., Rizi, V., Rodriguez, J., Fernandez, G. Rodriguez, Vázquez, J. J. Rodríguez, Rojas, G., Romano, P., Romeo, G., Rosado, J., Rovero, A. C., Rowell, G., Rudak, B., Rugliancich, A., Rulten, C., Sadeh, I., Safi-Harb, S., Saito, T., Sakaki, N., Sakurai, S., Salina, G., Sánchez-Conde, M., Sandaker, H., Sandoval, A., Sangiorgi, P., Sanguillon, M., Sano, H., Santander, M., Sarkar, S., Satalecka, K., Saturni, F. G., Schioppa, E. J., Schlenstedt, S., Schneider, M., Schoorlemmer, H., Schovanek, P., Schulz, A., Schussler, F., Schwanke, U., Sciacca, E., Scuderi, S., Seitenzahl, I., Semikoz, D., Sergijenko, O., Servillat, M., Shalchi, A., Shellard, R. C., Sidoli, L., Siejkowski, H., Sillanpää, A., Sironi, G., Sitarek, J., Sliusar, V., Slowikowska, A., Sol, H., Stamerra, A., Stanič, S., Starling, R., Stawarz, Ł., Stefanik, S., Stephan, M., Stolarczyk, T., Stratta, G., Straumann, U., Suomijarvi, T., Supanitsky, A. D., Tagliaferri, G., Tajima, H., Tavani, M., Tavecchio, F., Tavernet, J. -P., Tayabaly, K., Tejedor, L. A., Temnikov, P., Terada, Y., Terrier, R., Terzic, T., Teshima, M., Testa, V., Thoudam, S., Tian, W., Tibaldo, L., Tluczykont, M., Peixoto, C. J. Todero, Tokanai, F., Tomastik, J., Tonev, D., Tornikoski, M., Torres, D. F., Torresi, E., Tosti, G., Tothill, N., Tovmassian, G., Travnicek, P., Trichard, C., Trifoglio, M., Pujadas, I. Troyano, Tsujimoto, S., Umana, G., Vagelli, V., Vagnetti, F., Valentino, M., Vallania, P., Valore, L., van Eldik, C., Vandenbroucke, J., Varner, G. S., Vasileiadis, G., Vassiliev, V., Acosta, M. Vázquez, Vecchi, M., Vega, A., Vercellone, S., Veres, P., Vergani, S., Verzi, V., Vettolani, G. P., Viana, A., Vigorito, C., Villanueva, J., Voelk, H., Vollhardt, A., Vorobiov, S., Vrastil, M., Vuillaume, T., Wagner, S. J., Wagner, R., Walter, R., Ward, J. E., Warren, D., Watson, J. J., Werner, F., White, M., White, R., Wierzcholska, A., Wilcox, P., Will, M., Williams, D. A., Wischnewski, R., Wood, M., Yamamoto, T., Yamazaki, R., Yanagita, S., Yang, L., Yoshida, T., Yoshiike, S., Yoshikoshi, T., Zacharias, M., Zaharijas, G., Zampieri, L., Zandanel, F., Zanin, R., Zavrtanik, M., Zavrtanik, D., Zdziarski, A. A., Zech, A., Zechlin, H., Zhdanov, V. I., Ziegler, A., and Zorn, J.

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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45. Paving the way to simultaneous multi-wavelength astronomy

Author

Middleton, M. J., Casella, P., Gandhi, P., Bozzo, E., Anderson, G., Degenaar, N., Donnarumma, I., Israel, G., Knigge, C., Lohfink, A., Markoff, S., Marsh, T., Rea, N., Tingay, S., Wiersema, K., Altamirano, D., Bhattacharya, D., Brandt, W. N., Carey, S., Charles, P., Trigo, M. Diaz, Done, C., Kotze, M., Eikenberry, S., Fender, R., Ferruit, P., Fuerst, F., Greiner, J., Ingram, A., Heil, L., Jonker, P., Komossa, S., Leibundgut, B., Maccarone, T., Malzac, J., McBride, V., Miller-Jones, J., Page, M., Rossi, E. M., Russell, D. M., Shahbaz, T., Sivakoff, G. R., Tanaka, M., Thompson, D. J., Uemura, M., Uttley, P., van Moorsel, G., Van Doesburgh, M., Warner, B., Wilkes, B., Wilms, J., and Woudt, P.

Subjects
Astrophysics - Instrumentation and Methods for Astrophysics
Abstract

Whilst astronomy as a science is historically founded on observations at optical wavelengths, studying the Universe in other bands has yielded remarkable discoveries, from pulsars in the radio, signatures of the Big Bang at submm wavelengths, through to high energy emission from accreting, gravitationally-compact objects and the discovery of gamma-ray bursts. Unsurprisingly, the result of combining multiple wavebands leads to an enormous increase in diagnostic power, but powerful insights can be lost when the sources studied vary on timescales shorter than the temporal separation between observations in different bands. In July 2015, the workshop "Paving the way to simultaneous multi-wavelength astronomy" was held as a concerted effort to address this at the Lorentz Center, Leiden. It was attended by 50 astronomers from diverse fields as well as the directors and staff of observatories and spaced-based missions. This community white paper has been written with the goal of disseminating the findings of that workshop by providing a concise review of the field of multi-wavelength astronomy covering a wide range of important source classes, the problems associated with their study and the solutions we believe need to be implemented for the future of observational astronomy. We hope that this paper will both stimulate further discussion and raise overall awareness within the community of the issues faced in a developing, important field., Comment: 52 pages, 15 figures, accepted, invited review (to appear in New Astronomy Reviews), v3: updated figure and text

Published
2017
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46. Cherenkov Telescope Array Contributions to the 35th International Cosmic Ray Conference (ICRC2017)

Author

Acero, F., Acharya, B. S., Portella, V. Acín, Adams, C., Agudo, I., Aharonian, F., Samarai, I. Al, Alberdi, A., Alcubierre, M., Alfaro, R., Alfaro, J., Alispach, C., Aloisio, R., Batista, R. Alves, Amans, J. -P., Amato, E., Ambrogi, L., Ambrosi, G., Ambrosio, M., Anderson, J., Anduze, M., Angüner, E. O., Antolini, E., Antonelli, L. A., Antonuccio, V., Antoranz, P., Aramo, C., Araya, M., Arcaro, C., Armstrong, T., Arqueros, F., Arrabito, L., Arrieta, M., Asano, K., Asano, A., Ashley, M., Aubert, P., Singh, C. B., Babic, A., Backes, M., Bajtlik, S., Balazs, C., Balbo, M., Ballester, O., Ballet, J., Ballo, L., Balzer, A., Bamba, A., Bandiera, R., Barai, P., Barbier, C., Barcelo, M., Barkov, M., de Almeida, U. Barres, Barrio, J. A., Bastieri, D., Bauer, C., Becciani, U., Becherini, Y., Tjus, J. Becker, Bednarek, W., Belfiore, A., Benbow, W., Benito, M., Berge, D., Bernardini, E., Bernardini, M. G., Bernardos, M., Bernhard, S., Bernlöhr, K., Salucci, C. Bertinelli, Bertucci, B., Besel, M. -A., Beshley, V., Bettane, J., Bhatt, N., Bhattacharyya, W., Bhattachryya, S., Biasuzzi, B., Bicknell, G., Bigongiari, C., Biland, A., Bilinsky, A., Bird, R., Bissaldi, E., Biteau, J., Bitossi, M., Blanch, O., Blasi, P., Blazek, J., Boccato, C., Bockermann, C., Boehm, C., Bohacova, M., Boisson, C., Bolmont, J., Bonanno, G., Bonardi, A., Bonavolontà, C., Bonnoli, G., Borkowski, J., Bose, R., Bosnjak, Z., Böttcher, M., Boutonnet, C., Bouyjou, F., Bowman, L., Bozhilov, V., Braiding, C., Brau-Nogué, S., Bregeon, J., Briggs, M., Brill, A., Brisken, W., Bristow, D., Britto, R., Brocato, E., Brown, A. M., Brown, S., Brügge, K., Brun, P., Brun, F., Brunetti, L., Brunetti, G., Bruno, P., Bryan, M., Buckley, J., Bugaev, V., Bühler, R., Bulgarelli, A., Bulik, T., Burton, M., Burtovoi, A., Busetto, G., Buson, S., Buss, J., Byrum, K., Caccianiga, A., Cameron, R., Canelli, F., Canestrari, R., Capalbi, M., Capasso, M., Capitanio, F., Caproni, A., Capuzzo-Dolcetta, R., Caraveo, P., Cárdenas, V., Cardenzana, J., Cardillo, M., Carlile, C., Caroff, S., Carosi, R., Carosi, A., Carquín, E., Carr, J., Casandjian, J. -M., Casanova, S., Cascone, E., Castro-Tirado, A. J., Mora, J. Castroviejo, Catalani, F., Catalano, O., Cauz, D., Silva, C. Celestino, Celli, S., Cerruti, M., Chabanne, E., Chadwick, P., Chakraborty, N., Champion, C., Chatterjee, A., Chaty, S., Chaves, R., Chen, A., Chen, X., Cheng, K., Chernyakova, M., Chikawa, M., Chitnis, V. R., Christov, A., Chudoba, J., Cieślar, M., Clark, P., Coco, V., Colafrancesco, S., Colin, P., Colombo, E., Colome, J., Colonges, S., Conforti, V., Connaughton, V., Conrad, J., Contreras, J. L., Cornat, R., Cortina, J., Costa, A., Costantini, H., Cotter, G., Courty, B., Covino, S., Covone, G., Cristofari, P., Criswell, S. J., Crocker, R., Croston, J., Crovari, C., Cuadra, J., Cuevas, O., Cui, X., Cumani, P., Cusumano, G., D'Aì, A., D'Ammando, F., D'Avanzo, P., D'Urso, D., Da Vela, P., Dale, Ø., Dang, V. T., Dangeon, L., Daniel, M., Davids, I., Dawson, B., Dazzi, F., De Angelis, A., De Caprio, V., Anjos, R. de Cássia dos, De Cesare, G., De Franco, A., De Frondat, F., Pino, E. M. de Gouveia Dal, de la Calle, I., De Lisio, C., Lopez, R. de los Reyes, De Lotto, B., De Luca, A., De Lucia, M., Neto, J. R. T. de Mello, de Naurois, M., Wilhelmi, E. de Oña, De Palma, F., De Persio, F., de Souza, V., Decock, J., Deil, C., Deiml, P., Del Santo, M., Delagnes, E., Deleglise, G., Reznicek, M. 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Rodríguez, Rojas, G., Romano, P., Romeo, G., Roncadelli, M., Rosado, J., Rosen, S., Lees, S. Rosier, Rousselle, J., Rovero, A. C., Rowell, G., Rudak, B., Rugliancich, A., del Mazo, J. E. Ruíz, Rujopakarn, W., Rulten, C., Russo, F., Saavedra, O., Sabatini, S., Sacco, B., Sadeh, I., Hatlen, E. Sæther, Safi-Harb, S., Sahakian, V., Sailer, S., Saito, T., Sakaki, N., Sakurai, S., Salek, D., Greus, F. Salesa, Salina, G., Sanchez, D., Sánchez-Conde, M., Sandaker, H., Sandoval, A., Sangiorgi, P., Sanguillon, M., Sano, H., Santander, M., Santangelo, A., Santos, E. M., Sanuy, A., Sapozhnikov, L., Sarkar, S., Satalecka, K., Sato, Y., Saturni, F. G., Savalle, R., Sawada, M., Schanne, S., Schioppa, E. J., Schlenstedt, S., Schmidt, T., Schmoll, J., Schneider, M., Schoorlemmer, H., Schovanek, P., Schulz, A., Schussler, F., Schwanke, U., Schwarz, J., Schweizer, T., Schwemmer, S., Sciacca, E., Scuderi, S., Seglar-Arroyo, M., Segreto, A., Seitenzahl, I., Semikoz, D., Sergijenko, O., Serre, N., Servillat, M., Seweryn, K., Shah, K., Shalchi, A., Sharma, M., Shellard, R. C., Shilon, I., Sidoli, L., Sidz, M., Siejkowski, H., Silk, J., Sillanpää, A., Simone, D., Singh, B. B., Sironi, G., Sitarek, J., Sizun, P., Sliusar, V., Slowikowska, A., Smith, A., Sobczyńska, D., Sokolenko, A., Sol, H., Sottile, G., Springer, W., Stahl, O., Stamerra, A., Stanič, S., Starling, R., Staszak, D., Stawarz, Ł., Steenkamp, R., Stefanik, S., Stegmann, C., Steiner, S., Stella, C., Stephan, M., Sternberger, R., Sterzel, M., Stevenson, B., Stodulska, M., Stodulski, M., Stolarczyk, T., Stratta, G., Straumann, U., Stuik, R., Suchenek, M., Suomijarvi, T., Supanitsky, A. 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J., Webb, N., Wegner, P., Weiner, O., Weinstein, A., Weniger, C., Werner, F., Wetteskind, H., White, M., White, R., Wierzcholska, A., Wiesand, S., Wijers, R., Wilcox, P., Wilhelm, A., Wilkinson, M., Will, M., Williams, D. A., Winter, M., Wojcik, P., Wolf, D., Wood, M., Wörnlein, A., Wu, T., Yadav, K. K., Yaguna, C., Yamamoto, T., Yamamoto, H., Yamane, N., Yamazaki, R., Yanagita, S., Yang, L., Yelos, D., Yoshida, T., Yoshida, M., Yoshiike, S., Yoshikoshi, T., Yu, P., Zaborov, D., Zacharias, M., Zaharijas, G., Zajczyk, A., Zampieri, L., Zandanel, F., Zanin, R., Sanchez, R. Zanmar, Zaric, D., Zavrtanik, M., Zavrtanik, D., Zdziarski, A. A., Zech, A., Zechlin, H., Zhdanov, V. I., Ziegler, A., Ziemann, J., Ziętara, K., Zink, A., Ziółkowski, J., Zitelli, V., Zoli, A., and Zorn, J.

Subjects
Astrophysics - High Energy Astrophysical Phenomena
Abstract

List of contributions from the Cherenkov Telescope Array Consortium presented at the 35th International Cosmic Ray Conference, July 12-20 2017, Busan, Korea., Comment: Index of Cherenkov Telescope Array conference proceedings at the ICRC2017, Busan, Korea

Published
2017

47. Single-dish and VLBI observations of Cygnus X-3 during the 2016 giant flare episode

Author

Egron, E., Pellizzoni, A., Giroletti, M., Righini, S., Stagni, M., Orlati, A., Migoni, C., Melis, A., Concu, R., Barbas, L., Buttaccio, S., Cassaro, P., De Vicente, P., Gawronski, M. P., Lindqvist, M., Maccaferri, G., Stanghellini, C., Wolak, P., Yang, J., Navarrini, A., Loru, S., Pilia, M., Bachetti, M., Iacolina, M. N., Buttu, M., Corbel, S., Rodriguez, J., Markoff, S., Wilms, J., Pottschmidt, K., Bel, M. Cadolle, Kalemci, E., Belloni, T., Grinberg, V., Marongiu, M., Vargiu, G. P., and Trois, A.

Subjects
Astrophysics - High Energy Astrophysical Phenomena
Abstract

In September 2016, the microquasar Cygnus X-3 underwent a giant radio flare, which was monitored for 6 days with the Medicina Radio Astronomical Station and the Sardinia Radio Telescope. Long observations were performed in order to follow the evolution of the flare on a hourly scale, covering six frequency ranges from 1.5 GHz to 25.6 GHz. The radio emission reached a maximum of 13.2 +/- 0.7 Jy at 7.2 GHz and 10 +/- 1 Jy at 18.6 GHz. Rapid flux variations were observed at high radio frequencies at the peak of the flare, together with rapid evolution of the spectral index: alpha steepened from 0.3 to 0.6 within 5 hours. This is the first time that such fast variations are observed, giving support to the evolution from optically thick to optically thin plasmons in expansion moving outward from the core. Based on the Italian network (Noto, Medicina and SRT) and extended to the European antennas (Torun, Yebes, Onsala), VLBI observations were triggered at 22 GHz on five different occasions, four times prior to the giant flare, and once during its decay phase. Flux variations of 2-hour duration were recorded during the first session. They correspond to a mini-flare that occurred close to the core ten days before the onset of the giant flare. From the latest VLBI observation we infer that four days after the flare peak the jet emission was extended over 30 mas., Comment: 13 pages, 9 figures. Accepted for publication in MNRAS

Published
2017
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48. ESO-Athena Synergy White Paper

Author

Padovani, P., Combes, F., Trigo, M. Diaz, Ettori, S., Hatziminaoglou, E., Jonker, P., Salvato, M., Viti, S., Adami, C., Aird, J., Alexander, D., Casella, P., Ceccarelli, C., Churazov, E., Cirasuolo, M., Daddi, E., Edge, A., Feruglio, C., Mainieri, V., Markoff, S., Merloni, A., Nicastro, F., O'Brien, P., Oskinova, L., Panessa, F., Pointecouteau, E., Rau, A., Robrade, J., Schaye, J., Stoehr, F., Testi, L., and Tombesi, F.

Subjects
Astrophysics - High Energy Astrophysical Phenomena, Astrophysics - Cosmology and Nongalactic Astrophysics, Astrophysics - Astrophysics of Galaxies, Astrophysics - Instrumentation and Methods for Astrophysics, Astrophysics - Solar and Stellar Astrophysics
Abstract

The Advanced Telescope for High ENergy Astrophysics (Athena) is the X-ray observatory mission selected by ESA within its Cosmic Vision 2015-2025 programme to address the Hot and Energetic Universe scientific theme. The ESO-Athena Synergy Team (EAST) has been tasked to single out the potential scientific synergies between Athena and optical/near-infrared (NIR) and sub/mm ground based facilities, in particular those of ESO (i.e., the VLT and ELT, ALMA and APEX), by producing a White Paper to identify and develop the: 1. needs to access ESO ground-based facilities to achieve the formulated Athena science objectives; 2. needs to access Athena to achieve the formulated science objectives of ESO facilities contemporary to Athena; 3. science areas where the synergetic use of Athena and ESO facilities in the late 2020s will result in scientific added value. Community input to the process happened primarily via a dedicated ESO - Athena Synergy Workshop that took place on Sept. 14 - 16, 2016 at ESO, Garching. This White Paper presents the results of the EAST's work, sorted by synergy area, and deals with the following topics: 1. the Hot Universe: Early groups and clusters and their evolution, Physics of the Intracluster medium, Missing baryons in cosmic filaments; 2. the Energetic Universe: Supermassive black hole (SMBH) history, SMBH accretion disks, Active Galactic Nuclei feedback - Molecular outflows, Ultra-fast outflows, Accretion Physics, Transient Science; 3. Observatory Science: Star Formation, Stars. It then discusses the optical-NIR-sub-mm perspective by providing details on VLT/MOONS, the E-ELT instruments, in particular the MOS, VISTA/4MOST, the ESO and ALMA archives, future ALMA and ESO developments, and finally the (likely) ESO - Athena astronomical scene in the 2020s. (abridged), Comment: 70 pages, 16 figures

Published
2017

49. Extreme Jet Ejections from the Black Hole X-ray Binary V404 Cygni

Author

Tetarenko, A. J., Sivakoff, G. R., Miller-Jones, J. C. A, Rosolowsky, E. W., Petitpas, G., Gurwell, M., Wouterloot, J., Fender, R., Heinz, S., Maitra, D., Markoff, S. B., Migliari, S., Rupen, M. P., Rushton, A. P., Russell, D. M., Russell, T. D., and Sarazin, C. L.

Subjects
Astrophysics - High Energy Astrophysical Phenomena
Abstract

We present simultaneous radio through sub-mm observations of the black hole X-ray binary (BHXB) V404 Cygni during the most active phase of its June 2015 outburst. Our $4$ hour long set of overlapping observations with the Very Large Array, the Sub-millimeter Array, and the James Clerk Maxwell Telescope (SCUBA-2), covers 8 different frequency bands (including the first detection of a BHXB jet at $666 \,{\rm GHz}/450\mu m$), providing an unprecedented multi-frequency view of the extraordinary flaring activity seen during this period of the outburst. In particular, we detect multiple rapidly evolving flares, which reach Jy-level fluxes across all of our frequency bands. With this rich data set we performed detailed MCMC modeling of the repeated flaring events. Our custom model adapts the van der Laan synchrotron bubble model to include twin bi-polar ejections, propagating away from the black hole at bulk relativistic velocities, along a jet axis that is inclined to the line of sight. The emission predicted by our model accounts for projection effects, relativistic beaming, and the geometric time delay between the approaching and receding ejecta in each ejection event. We find that a total of 8 bi-polar, discrete jet ejection events can reproduce the emission that we observe in all of our frequency bands remarkably well. With our best fit model, we provide detailed probes of jet speed, structure, energetics, and geometry. Our analysis demonstrates the paramount importance of the mm/sub-mm bands, which offer a unique, more detailed view of the jet than can be provided by radio frequencies alone., Comment: 25 pages, 11 figures, Accepted to MNRAS

Published
2017
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50. Mass-scaling as a method to constrain outflows and particle acceleration from low-luminosity accreting black holes

Author

Connors, R. M. T., Markoff, S., Nowak, M. A., Neilsen, J., Ceccobello, C., Crumley, P., Froning, C. S., Gallo, E., and Nip, J. E.

Subjects
Astrophysics - High Energy Astrophysical Phenomena
Abstract

The `fundamental plane of black hole accretion' (FP), a relation between the radio luminosities ($L_R$), X-ray luminosities ($L_X$), and masses ($M_{BH}$) of hard/quiescent state black hole binaries and low-luminosity active galactic nuclei, suggests some aspects of black hole accretion may be scale invariant. However, key questions still exist concerning the relationship between the inflow/outflow behaviour in the `classic' hard state and quiescence, which may impact this scaling. We show that the broadband spectra of A0620-00 and~\sgra~(the least luminous stellar mass/supermassive black holes on the FP) can be modelled simultaneously with a physically-motivated outflow-dominated model where the jet power and all distances are scaled by the black hole mass. We find we can explain the data of both A0620-00 and~\sgra~(in its non-thermal flaring state) in the context of two outflow-model scenarios: (1) a synchrotron-self-Compton dominated state in which the jet plasma reaches highly sub-equipartition conditions (for the magnetic field with respect to that of the radiating particles), and (2) a synchrotron dominated state in the fast-cooling regime in which particle acceleration occurs within the inner few gravitational radii of the black hole and plasma is close to equipartition. We show that it may be possible to further discriminate between models (1) and (2) through future monitoring of its submm/IR/X-ray emission, in particular via time lags between the variable emission in these bands., Comment: 19 pages (including appendix), 6 figures, 5 tables. Accepted for publication in MNRAS

Published
2016
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