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

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

2. The Radio Spectra of High Luminosity Compact Symmetric Objects (CSO-2s): Implications for Studies of Compact Jetted Active Galactic Nuclei

Author: de la Parra, P. V., Readhead, A. C. S, Herbig, T., Kiehlmann, S., Lister, M. L., Pavlidou, V., Reeves, R. A., Siemiginowska, A., Sullivan, A. G., Surti, T., Synani, A., Tassis, K., Taylor, G. B., Wilkinson, P. N., Aller, M. F., Blandford, R. D., Globus, N., Lawrence, C. R., Molina, B., O'Neill, S., and Pearson, T. J.
Subjects: Astrophysics - High Energy Astrophysical Phenomena, Astrophysics - Astrophysics of Galaxies
Abstract: This paper addresses, for the first time, a key aspect of the phenomenology of Compact Symmetric Objects (CSOs) -- the characteristics of their radio spectra. We present a radio-spectrum description of a complete sample of high luminosity CSOs (CSO-2s), which shows that they exhibit the \textit{complete} range of spectral types, including flat-spectrum sources ($\alpha \ge -0.5$), steep-spectrum sources ($\alpha < -0.5$), and peaked-spectrum sources. We show that there is no clear correlation between spectral type and size, but there is a correlation between the high-frequency spectral index and both object type and size. We also show that, to avoid biasing the data and to understand the various classes of jetted-AGN involved, the complete range of spectral types should be included in studying the general phenomenology of compact jetted-AGN, and that complete samples must be used, selected over a wide range of frequencies. We discuss examples that demonstrate these points. We find that the high-frequency spectral indices of CSO-2s span $-1.3 <\alpha_{\rm hi} < -0.3$, and hence that radio spectral signatures cannot be used to discriminate definitively between CSO-2s, binary galactic nuclei, and millilensed objects, unless they have $\alpha_{\rm hi} >-0.3$.
Published: 2024

3. PKS~J0805$-$0111: A Second Owens Valley Radio Observatory Blazar Showing Highly Significant Sinusoidal Radio Variability -- The Tip of the Iceberg

Author: de la Parra, P. V., Kiehlmann, S., Mroz, P., Readhead, A. C. S., Synani, A., Begelman, M. C., Blandford, R. D., Ding, Y., Harrison, F., Liodakis, I., Max-Moerbeck, W., Pavlidou, V., Reeves, R., Vallisneri, M., Aller, M. F., Graham, M. J., Hovatta, T., Lawrence, C. R., Lazio, T. J. W., Mahabal, A. A., Molina, B., O'Neill, S., Pearson, T. J., Ravi, V., Tassis, K., and Zensus, J. A.
Subjects: Astrophysics - High Energy Astrophysical Phenomena, Astrophysics - Astrophysics of Galaxies
Abstract: Owens Valley Radio Observatory (OVRO) observations of supermassive black hole binary (SMBHB) candidate PKS~2131$-$021 revealed, for the first time, six likely characteristics of the phenomenology exhibited by SMBHB in blazars, of which the most unexpected and critical is sinusoidal flux density variations. We have now identified a second blazar, PKS~J0805$-$0111, showing significant sinusoidal variations, with an observed period that translates to $1.422 \pm 0.005$ yr in the rest frame of the $z = 1.388$ object. We generate $10^6$ simulated light curves to reproduce the radio variability characteristics of PKS~J0805$-$0111, and show that the global probability, considering the \textit{look-elsewhere effect}, indicates that the observed periodicity can be attributed to the red noise tail of the power spectral density, with a $p_0$ value of $7.8 \times 10^{-5}$ (i.e. 3.78$\sigma$). PKS J0805$-$0111 displays all six characteristics observed in PKS 2131$-$021. Taking into account the well-defined OVRO sample size, the false positive probability $\sim 0.22$, but the rare behavior makes this a strong SMBHB candidate. The discovery of a second SMBHB candidate exhibiting these rare characteristics reveals that PKS~2131$-$021 is not a unique, isolated case. With these two strong cases we are clearly seeing only the tip of the iceberg. We estimate that the number of SMBHB candidates amongst blazars $\sim$ 1 in 100.
Published: 2024

4. Fermi-GBM Discovery of GRB 221009A: An Extraordinarily Bright GRB from Onset to Afterglow

Author: Lesage, S., Veres, P., Briggs, M. S., Goldstein, A., Kocevski, D., Burns, E., Wilson-Hodge, C. A., Bhat, P. N., Huppenkothen, D., Fryer, C. L., Hamburg, R., Racusin, J., Bissaldi, E., Cleveland, W. H., Dalessi, S., Fletcher, C., Giles, M. M., Hristov, B. A., Hui, C. M., Mailyan, B., Malacaria, C., Poolakkil, S., Roberts, O. J., von Kienlin, A., Wood, J., Ajello, M., Arimoto, M., Baldini, L., Ballet, J., Baring, M. G., Bastieri, D., Gonzalez, J. Becerra, Bellazzini, R., Blandford, R. D., Bonino, R., Bruel, P., Buson, S., Cameron, R. A., Caputo, R., Caraveo, P. A., Cavazzuti, E., Chiaro, G., Cibrario, N., Ciprini, S., Orestano, P. Cristarella, Crnogorcevic, M., Cuoco, A., Cutini, S., DAmmando, F., De Gaetano, S., Di Lalla, N., Di Venere, L., Dominguez, A., Fegan, S. J., Ferrara, E. C., Fleischhack, H., Fukazawa, Y., Funk, S., Fusco, P., Galanti, G., Gammaldi, V., Gargano, F., Gasbarra, C., Gasparrini, D., Germani, S., Giacchino, F., Giglietto, N., Gill, R., Giroletti, M., Granot, J., Green, D., Grenier, I. A., Guiriec, S., Gustafsson, M., Hays, E., Hewitt, J. W., Horan, D., Hou, X., Kuss, M., Latronico, L., Laviron, A., Lemoine-Goumard, M., Li, J., Liodakis, I., Longo, F., Loparco, F., Lorusso, L., Lovellette, M. N., Lubrano, P., Maldera, S., Manfreda, A., Marti-Devesa, G., Mazziotta, M. N., McEnery, J. E., Mereu, I., Meyer, M., Michelson, P. F., Mizuno, T., Monzani, M. E., Morselli, A., Moskalenko, I. V., Negro, M., Nuss, E., Omodei, N., Orlando, E., Ormes, J. F., Paneque, D., Panzarini, G., Persic, M., Pesce-Rollins, M., Pillera, R., Piron, F., Poon, H., Porter, T. A., Principe, G., Raino, S., Rando, R., Rani, B., Razzano, M., Razzaque, S., Reimer, A., Reimer, O., Ryde, F., Sanchez-Conde, M., Parkinson, P. M. Saz, Scotton, L., Serini, D., Sgro, C., Sharma, V., Siskind, E. J., Spandre, G., Spinelli, P., Tajima, H., Torres, D. F., Valverde, J., Venters, T., Wadiasingh, Z., Wood, K., and Zaharijas, G.
Subjects: Astrophysics - High Energy Astrophysical Phenomena
Abstract: We report the discovery of GRB 221009A, the highest flux gamma-ray burst ever observed by the Fermi Gamma-ray Burst Monitor (GBM). This GRB has continuous prompt emission lasting more than 600 seconds which smoothly transitions to afterglow visible in the GBM energy range (8 keV--40 MeV), and total energetics higher than any other burst in the GBM sample. By using a variety of new and existing analysis techniques we probe the spectral and temporal evolution of GRB 221009A. We find no emission prior to the GBM trigger time (t0; 2022 October 9 at 13:16:59.99 UTC), indicating that this is the time of prompt emission onset. The triggering pulse exhibits distinct spectral and temporal properties suggestive of the thermal, photospheric emission of shock-breakout, with significant emission up to $\sim$15 MeV. We characterize the onset of external shock at t0+600 s and find evidence of a plateau region in the early-afterglow phase which transitions to a slope consistent with Swift-XRT afterglow measurements. We place the total energetics of GRB 221009A in context with the rest of the GBM sample and find that this GRB has the highest total isotropic-equivalent energy ($\textrm{E}_{\gamma,\textrm{iso}}=1.0\times10^{55}$ erg) and second highest isotropic-equivalent luminosity ($\textrm{L}_{\gamma,\textrm{iso}}=9.9\times10^{53}$ erg/s) based on redshift of z = 0.151. These extreme energetics are what allowed us to observe the continuously emitting central engine of GBM from the beginning of the prompt emission phase through the onset of early afterglow., Comment: 26 pages 7 figures - accepted for publication in ApJL
Published: 2023
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5. The Evolution of Compact Symmetric Objects -- A Possible Connection with Tidal Disruption Events

Author: Readhead, A. C. S., Ravi, V., Blandford, R. D., Sullivan, A. G., Somalwar, J., Liodakis, I., Lister, M. L., Taylor, G. B., Wilkinson, P. N., Globus, N., Kiehlmann, S., Lawrence, C. R., O'Neill, S., Pavlidou, V., Pearson, T. J., Sheldahl, E., Siemiginowska, A., and Tassis, K.
Subjects: Astrophysics - High Energy Astrophysical Phenomena, Astrophysics - Astrophysics of Galaxies
Abstract: Compact Symmetric Objects (CSOs) form a distinct class of jetted active galactic nuclei (jetted-AGN). We examine a carefully selected sample of 54 CSOs, and confirm that there are two unrelated classes: an edge-dimmed, low-luminosity class (CSO 1), and an edge-brightened, high-luminosity class (CSO 2). Using statistically significant blind tests, we show that CSO 2s themselves consist of two morphologically distinct classes: CSO 2.0, having prominent hot-spots at the leading edges of narrow jets and/or narrow lobes; and CSO 2.2, without prominent hot-spots, and with broad jets and/or lobes. An intermediate class, CSO 2.1, exhibits mixed properties. The four classes occupy different, overlapping, portions of the luminosity-size plane, with the sizes of largest CSOs being $\sim 500$pc. We advance the hypothesis that CSO 2.0s are young and evolve through CSO 2.1s into CSO 2.2s, which are old (up to $\sim 5000$ yr). Thus CSOs do not evolve into larger types of jetted-AGN, but spend their whole life cycle as CSOs. The radio emission region energies in the CSO 2s we have studied range from $\sim 10^{-4}\, M_\odot {c}^2$ to $\sim 7 \, M_\odot {c}^2$. We show that the transient nature of CSO 2s, and their birthrate, can be explained through ignition in the tidal disruption events of giant stars. We also consider possibilities for tapping the spin energy of the supermassive black hole, and tapping the energy of the accretion disk, in a manner similar to, but not the same as, that which occurs in dwarf novae. Our results demonstrate conclusively that CSOs constitute a large family of AGN in which we have thus far studied only the brightest. More comprehensive radio studies, with higher sensitivity, resolution, and dynamic range, will revolutionize our understanding of AGN and the central engines that power them., Comment: 41 pages, 13 figures, 10 tables
Published: 2023

6. Absence of the predicted 2022 October outburst of OJ 287 and implications for binary SMBH scenarios

Author: Komossa, S., Grupe, D., Kraus, A., Gurwell, M. A., Haiman, Z., Liu, F. K., Tchekhovskoy, A., Gallo, L. C., Berton, M., Blandford, R., Gomez, J. L., and Gonzalez, A. G.
Subjects: Astrophysics - High Energy Astrophysical Phenomena, Astrophysics - Astrophysics of Galaxies
Abstract: The project MOMO (Multiwavelength Observations and Modelling of OJ 287) was set up to test predictions of binary supermassive black hole (SMBH) scenarios and to understand disk-jet physics of the blazar OJ 287. After a correction, the precessing binary (PB) SMBH model predicted the next main outburst of OJ 287 in 2022 October, no longer in July, making the outburst well observable and the model testable. We have densely covered this period in our ongoing multi-frequency radio, optical, UV, and X-ray monitoring. The predicted outburst was not detected. Instead, OJ 287 was at low optical-UV emission levels, declining further into November. The predicted thermal bremsstrahlung spectrum was not observed either, at any epoch. Further, applying scaling relations, we estimate a SMBH mass of OJ 287 of 10^8 M_sun. The latest in a sequence of deep low-states that recur every 1-2 yrs is used to determine an upper limit on the Eddington ratio and on the accretion-disk luminosity. This limit is at least a factor of 10 lower than required by the PB model with its massive primary SMBH of >10^{10} M_sun. All these results favor alternative binary SMBH models of OJ 287 that neither require strong orbital precession nor a very large mass of the primary SMBH., Comment: MNRAS Letter, in press
Published: 2023
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7. The hunt for extraterrestrial high-energy neutrino counterparts

Author: Liodakis, I., Hovatta, T., Pavlidou, V., Readhead, A. C. S., Blandford, R. D., Kiehlmann, S., Lindfors, E., Max-Moerbeck, W., Pearson, T. J., and Petropoulou, M.
Subjects: Astrophysics - High Energy Astrophysical Phenomena
Abstract: The origin of Petaelectronvolt (PeV) astrophysical neutrinos is fundamental to our understanding of the high-energy Universe. Apart from the technical challenges of operating detectors deep below ice, oceans, and lakes, the phenomenological challenges are even greater than those of gravitational waves; the sources are unknown, hard to predict, and we lack clear signatures. Neutrino astronomy therefore represents the greatest challenge faced by the astronomy and physics communities thus far. The possible neutrino sources range from accretion disks and tidal disruption events, to relativistic jets and galaxy clusters with blazar TXS~0506+056 the most compelling association thus far. Since that association, immense effort has been put into proving or disproving that jets are indeed neutrino emitters, but to no avail. By generating simulated neutrino counterpart samples, we explore the potential of detecting a significant correlation of neutrinos with jets from active galactic nuclei. We find that, given the existing challenges, even our best experiments could not have produced a $>3\sigma$ result. Larger programs over the next few years will be able to detect a significant correlation only if the brightest radio sources, rather than all jetted active galactic nuclei, are neutrino emitters. We discuss the necessary strategies required to steer future efforts into successful experiments., Comment: 8 pages, 1 figure, 1 table, accepted for publication in A&A
Published: 2022
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8. Search for new cosmic-ray acceleration sites within the 4FGL catalog Galactic plane sources

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

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

Author: Wilkins, D. R., Gallo, L. C., Costantini, E., Brandt, W. N., and Blandford, R. D.
Subjects: Astrophysics - High Energy Astrophysical Phenomena
Abstract: We report on X-ray flares that were observed from the active galactic nucleus I Zwicky 1 (I Zw 1) in 2020 January by the NuSTAR and XMM-Newton observatories. The X-ray spectrum is well-described by a model comprised of the continuum emission from the corona and its reflection from the accretion disc around a rapidly spinning (a > 0.94) black hole. In order to model the broadband spectrum, it is necessary to account for the variation in ionisation across the disc. Analysis of the X-ray spectrum in time periods before, during and after the flares reveal the underlying changes to the corona associated with the flaring. During the flares, the reflection fraction drops significantly, consistent with the acceleration of the corona away from the accretion disc. We find the first evidence that during the X-ray flares, the temperature drops from 140(-20,+100)keV before to 45(-9,+40)keV during the flares. The profile of the iron K line reveals the emissivity profile of the accretion disc, showing it to be illuminated by a compact corona extending no more than 7(-2,+4)rg over the disc before the flares, but with tentative evidence that the corona expands as it is accelerated during the flares. Once the flares subsided, the corona had collapsed to a radius of 6(-2,+2)rg. The rapid timescale of the flares suggests that they arise within the black-hole magnetosphere rather than in the accretion disc, and the variation of the corona is consistent with the continuum arising from the Comptonisation of seed photons from the disc., Comment: 15 pages, 10 figures. Accepted for publication in MNRAS
Published: 2022
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11. New Tests of Millilensing in the Blazar PKS 1413+135

Author: Peirson, A. L., Liodakis, I., Readhead, A. C. S., Lister, M. L., Perlman, E. S., Aller, M. F., Blandford, R. D., Grainge, K. J. B., Green, D. A., Gurwell, M. A., Hodges, M. W., Hovatta, T., Kiehlmann, S., Lähteenmäki, A., Max-Moerbeck, W., Mcaloone, T., O'Neill, S., Pavlidou, V., Pearson, T. J., Ravi, V., Reeves, R. A., Scott, P. F., Taylor, G. B., Titterington, D. J., Tornikoski, M., Vedantham, H. K., Wilkinson, P. N., Williams, D. T., and Zensus, J. A.
Subjects: Astrophysics - Astrophysics of Galaxies, Astrophysics - High Energy Astrophysical Phenomena
Abstract: Symmetric Achromatic Variability (SAV) is a rare form of radio variability in blazars that has been attributed to gravitational millilensing by a ~$10^2 - 10^5$ $M_\odot$ mass condensate. Four SAVs have been identified between 1980 and 2020 in the long-term radio monitoring data of the blazar PKS 1413+135. We show that all four can be fitted with the same, unchanging, gravitational lens model. If SAV is due to gravitational millilensing, PKS 1413+135 provides a unique system for studying active galactic nuclei with unprecedented microarcsecond resolution, as well as for studying the nature of the millilens itself. We discuss two possible candidates for the putative millilens: a giant molecular cloud hosted in the intervening edge-on spiral galaxy, and an undetected dwarf galaxy with a massive black hole. We find a significant dependence of SAV crossing time on frequency, which could indicate a fast shock moving in a slower underlying flow. We also find tentative evidence for a 989-day periodicity in the SAVs, which, if real, makes possible the prediction of future SAVs: the next three windows for possible SAVs begin in August 2022, May 2025, and February 2028., Comment: Accepted to ApJ
Published: 2022
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12. The Unanticipated Phenomenology of the Blazar PKS~2131$-$021: A Unique Super-Massive Black Hole Binary Candidate

Author: O'Neill, S., Kiehlmann, S., Readhead, A. C. S., Aller, M. F., Blandford, R. D., Liodakis, I., Lister, M. L., Mróz, P., O'Dea, C. P., Pearson, T. J., Ravi, V., Vallisneri, M., Cleary, K. A., Graham, M. J., Grainge, K. J. B., Hodges, M. W., Hovatta, T., Lähteenmäki, A., Lamb, J. W., Lazio, T. J. W., Max-Moerbeck, W., Pavlidou, V., Prince, T. A., Reeves, R. A., Tornikoski, M., de la Para, P. Vergara, and Zensus, J. A.
Subjects: Astrophysics - High Energy Astrophysical Phenomena
Abstract: Most large galaxies host supermassive black holes in their nuclei and are subject to mergers, which can produce a supermassive black hole binary (SMBHB), and hence periodic signatures due to orbital motion. We report unique periodic radio flux density variations in the blazar PKS~2131$-$021, which strongly suggest an SMBHB with an orbital separation of $\sim 0.001-0.01$ pc. Our 45.1-year radio light curve shows two epochs of strong sinusoidal variation with the same period and phase to within $<2\%$ and $\sim 10\%$, respectively, straddling a 20-year period when this variation was absent. Our simulated light curves accurately reproduce the ``red noise'' of this object, and Lomb-Scargle, weighted wavelet Z-transform, and least-squares sine wave analyses demonstrate conclusively, at the $4.6\sigma$ significance level, that the periodicity in this object is not due to random fluctuations in flux density. The observed period translates to $2.082\pm 0.003$ years in the rest frame at the $z=1.285$ redshift of PKS~2131$-$021. The periodic variation in PKS~2131$-$021 is remarkably sinusoidal. We present a model in which orbital motion, combined with the strong Doppler boosting of the approaching relativistic jet, produces a sine-wave modulation in the flux density which easily fits the observations. Given the rapidly-developing field of gravitational wave experiments with pulsar timing arrays, closer counterparts to PKS~2131$-$021 and searches using the techniques we have developed are strongly motivated. These results constitute a compelling demonstration that the phenomenology, not the theory, must provide the lead in this field., Comment: 24 pages, 13 figure, 3 Tables, accepted for publication in APJL
Published: 2021
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13. Light bending and X-ray echoes from behind a supermassive black hole

Author: Wilkins, D. R., Gallo, L. C., Costantini, E., Brandt, W. N., and Blandford, R. D.
Subjects: Astrophysics - High Energy Astrophysical Phenomena, General Relativity and Quantum Cosmology
Abstract: The innermost regions of accretion disks around black holes are strongly irradiated by X-rays that are emitted from a highly variable, compact corona, in the immediate vicinity of the black hole. The X-rays that are seen reflected from the disk and the time delays, as variations in the X-ray emission echo or reverberate off the disk provide a view of the environment just outside the event horizon. I Zwicky 1 (I Zw 1), is a nearby narrow line Seyfert 1 galaxy. Previous studies of the reverberation of X-rays from its accretion disk revealed that the corona is composed of two components; an extended, slowly varying component over the surface of the inner accretion disk, and a collimated core, with luminosity fluctuations propagating upwards from its base, which dominates the more rapid variability. Here we report observations of X-ray flares emitted from around the supermassive black hole in I Zw 1. X-ray reflection from the accretion disk is detected through a relativistically broadened iron K line and Compton hump in the X-ray emission spectrum. Analysis of the X-ray flares reveals short flashes of photons consistent with the re-emergence of emission from behind the black hole. The energy shifts of these photons identify their origins from different parts of the disk. These are photons that reverberate off the far side of the disk and bent around the black hole and magnified by the strong gravitational field. Observing photons bent around the black hole confirms a key prediction of General Relativity., Comment: Preprint version. 22 pages, 8 figures. Published in Nature
Published: 2021
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14. Catalog of Long-Term Transient Sources in the First 10 Years of Fermi-LAT Data

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

Author: Meinecke, J., Tzeferacos, P., Ross, J. S., Bott, A. F. A., Feister, S., Park, H. -S., Bell, A. R., Blandford, R., Berger, R. L., Bingham, R., Casner, A., Chen, L. E., Foster, J., Froula, D. H., Goyon, C., Kalantar, D., Koenig, M., Lahmann, B., Li, C. -K., Lu, Y., Palmer, C. A. J., Petrasso, R., Poole, H., Remington, B., Reville, B., Reyes, A., Rigby, A., Ryu, D., Swadling, G., Zylstra, A., Miniati, F., Sarkar, S., Schekochihin, A. A., Lamb, D. Q., and Gregori, G.
Subjects: Physics - Plasma Physics, Astrophysics - High Energy Astrophysical Phenomena
Abstract: Galaxy clusters are filled with hot, diffuse X-ray emitting plasma, with a stochastically tangled magnetic field whose energy is close to equipartition with the energy of the turbulent motions \cite{zweibel1997, Vacca}. In the cluster cores, the temperatures remain anomalously high compared to what might be expected considering that the radiative cooling time is short relative to the Hubble time \cite{cowie1977,fabian1994}. While feedback from the central active galactic nuclei (AGN) \cite{fabian2012,birzan2012,churazov2000} is believed to provide most of the heating, there has been a long debate as to whether conduction of heat from the bulk to the core can help the core to reach the observed temperatures \cite{narayan2001,ruszkowski2002,kunz2011}, given the presence of tangled magnetic fields. Interestingly, evidence of very sharp temperature gradients in structures like cold fronts implies a high degree of suppression of thermal conduction \cite{markevitch2007}. To address the problem of thermal conduction in a magnetized and turbulent plasma, we have created a replica of such a system in a laser laboratory experiment. Our data show a reduction of local heat transport by two orders of magnitude or more, leading to strong temperature variations on small spatial scales, as is seen in cluster plasmas \cite{markevitch2003}.
Published: 2021
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16. HAWC observations of the acceleration of very-high-energy cosmic rays in the Cygnus Cocoon

Author: Abeysekara, A. U., Albert, A., Alfaro, R., Alvarez, C., Camacho, J. R. Angeles, Arteaga-Velazquez, J. C., Arunbabu, K. P., Rojas, D. Avila, Solares, H. A. Ayala, Baghmanyan, V., Belmont-Moreno, E., BenZvi, S. Y., Blandford, R., Brisbois, C., Caballero-Mora, K. S., Capistran, T., Carraminana, A., Casanova, S., Cotti, U., de Leon, S. Coutino, De la Fuente, E., Hernandez, R. Diaz, Dingus, B. L., DuVernois, M. A., Durocher, M., Diaz-Velez, J. C., Ellsworth, R. W., Engel, K., Espinoza, C., Fan, K. L., Fang, K., Fleischhack, H., Fraija, N., Galvan-Gamez, A., Garcia, D., Garcıa-Gonzalez, J. A., Garfias, F., Giacinti, G., Gonzalez, M. M., Goodman, J. A., Harding, J. P., Hernandez, S., Hinton, J., Hona, B., Huang, D., Hueyotl-Zahuantitla, F., Huntemeyer, P., Iriarte, A., Jardin-Blicq, A., Joshi, V., Kieda, D., Lara, A., Lee, W. H., Vargas, H. Leon, Linnemann, J. T., Longinotti, A. L., Luis-Raya, G., Lundeen, J., Malone, K., Martinez, O., Martinez-Castellanos, I., Martinez-Castro, J., Matthews, J. A., Miranda-Romagnoli, P., Soto, J. A. Morales, Moreno, E., Mostafa, M., Nayerhoda, A., Nellen, L., Newbold, M., Nisa, M. U., Noriega-Papaqui, R., Olivera-Nieto, L., Omodei, N., Peisker, A., Araujo, Y. Perez, Perez-Perez, E. G., Ren, Z., Rho, C. D., Rosa-Gonzalez, D., Ruiz-Velasco, E., Salazar, H., Greus, F. Salesa, Sandova, A., Schneider, M., Schoorlemmer, H., Serna, F., Smith, A. J., Springer, R. W., Surajbali, P., Tollefson, K., Torres, I., Torres-Escobedo, R., Urena-Mena, F., Weisgarber, T., Werner, F., Willox, E., Zepeda, A., Zhou, H., on, C. De Le, and Alvarez, J. D.
Subjects: Astrophysics - High Energy Astrophysical Phenomena
Abstract: Cosmic rays with energies up to a few PeV are known to be accelerated within the Milky Way. Traditionally, it has been presumed that supernova remnants were the main source of very-high-energy cosmic rays but theoretically it is difficult to get protons to PeV energies and observationally there simply is no evidence to support the remnants as sources of hadrons with energies above a few tens of TeV. One possible source of protons with those energies is the Galactic Center region. Here we report observations of 1-100 TeV gamma rays coming from the 'Cygnus Cocoon', which is a superbubble surrounding a region of OB2 massive star formation. These gamma rays are likely produced by 10-1000 TeV freshly accelerated CRs originating from the enclosed star forming region Cygnus OB2. Hitherto it was not known that such regions could accelerate particles to these energies. The measured flux is likely originated by hadronic interactions. The spectral shape and the emission profile of the Cocoon changes from GeV to TeV energies, which reveals the transport of cosmic particles and historical activity in the superbubble.
Published: 2021
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17. The First Fermi-LAT Solar Flare Catalog

Author: Ajello, M., Baldini, L., Bastieri, D., Bellazzini, R., Berretta, A., Bissaldi, E., Blandford, R. D., Bonino, R., Bruel, P., Buson, S., Cameron, R. A., Caputo, R., Cavazzuti, E., Cheung, C. C., Chiaro, G., Costantin, D., Cutini, S., D'Ammando, F., de Palma, F., Desiante, R., Di Lalla, N., Di Venere, L., Dirirsa, F. Fana, Fegan, S. J., Fukazawa, Y., Funk, S., Fusco, P., Gargano, F., Gasparrini, D., Giordano, F., Giroletti, M., Green, D., Guiriec, S., Hays, E., Hewitt, J. W., Horan, D., Johannesson, G., Kovacevic, M., Kuss, M., Larsson, S., Latronico, L., Li, J., Longo, F., Lovellette, M. N., Lubrano, P., Maldera, S., Manfreda, A., Marti-Devesa, G., Mazziotta, M. N., Mereu, I., Michelson, P. F., Mizuno, T., Monzani, M. E., Morselli, A., Moskalenko, I. V., Negro, M., Omodei, N., Orienti, M., Orlando, E., Paneque, D., Pei, Z., Persic, M., Pesce-Rollins, M., Petrosian, V., Piron, F., Porter, T. A., Principe, G., Racusin, J. L., Raino, S., Rando, R., Rani, B., Razzano, M., Razzaque, S., Reimer, A., Reimer, O., Serini, D., Sgro, C., Siskind, E. J., Spandre, G., Spinelli, P., Tak, D., Troja, E., Valverde, J., Wood, K., and Zaharijas, G.
Subjects: Astrophysics - High Energy Astrophysical Phenomena, Astrophysics - Solar and Stellar Astrophysics
Abstract: We present the first Fermi - Large Area Telescope (LAT) solar flare catalog covering the 24 th solar cycle. This catalog contains 45 Fermi -LAT solar flares (FLSFs) with emission in the gamma-ray energy band (30 MeV - 10 GeV) detected with a significance greater than 5 sigma over the years 2010-2018. A subsample containing 37 of these flares exhibit delayed emission beyond the prompt-impulsive hard X-ray phase with 21 flares showing delayed emission lasting more than two hours. No prompt-impulsive emission is detected in four of these flares. We also present in this catalog the observations of GeV emission from 3 flares originating from Active Regions located behind the limb (BTL) of the visible solar disk. We report the light curves, spectra, best proton index and localization (when possible) for all the FLSFs. The gamma-ray spectra is consistent with the decay of pions produced by >300 MeV protons. This work contains the largest sample of high-energy gamma-ray flares ever reported and provides the unique opportunity to perform population studies on the different phases of the flare and thus allowing to open a new window in solar physics., Comment: Published in ApJS
Published: 2021
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18. The Relativistic Jet Orientation and Host Galaxy of the Peculiar Blazar PKS 1413+135

Author: Readhead, A. C. S., Ravi, V., Liodakis, I., Lister, M. L., Singh, V., Aller, M. F., Blandford, R. D., Browne, I. W. A., Gorjian, V., Grainge, K. J. B., Gurwell, M. A., Hodges, M. W., Hovatta, T., Kiehlmann, S., Lähteenmäki, A., McAloone, T., Max-Moerbeck, W., Pavlidou, V., Pearson, T. J., Peirson, A. L., Perlman, E. S., Reeves, R. A., Soifer, B. T., Taylor, G. B., Tornikoski, M., Vedantham, H. K., Werner, M., Wilkinson, P. N., and Zensus, J. A.
Subjects: Astrophysics - Astrophysics of Galaxies, Astrophysics - High Energy Astrophysical Phenomena
Abstract: PKS 1413+135 is one of the most peculiar blazars known. Its strange properties led to the hypothesis almost four decades ago that it is gravitationally lensed by a mass concentration associated with an intervening galaxy. It exhibits symmetric achromatic variability, a rare form of variability that has been attributed to gravitational milli-lensing. It has been classified as a BL Lac object, and is one of the rare objects in this class with a visible counterjet. BL Lac objects have jet axes aligned close to the line of sight. It has also been classified as a compact symmetric object, which have jet axes not aligned close to the line of sight. Intensive efforts to understand this blazar have hitherto failed to resolve even the questions of the orientation of the relativistic jet, and the host galaxy. Answering these two questions is important as they challenge our understanding of jets in active galactic nuclei and the classification schemes we use to describe them. We show that the jet axis is aligned close to the line of sight and PKS 1413+135 is almost certainly not located in the apparent host galaxy, but is a background object in the redshift range $0.247 < z < 0.5$. The intervening spiral galaxy at $z = 0.247$ provides a natural host for the putative lens responsible for symmetric achromatic variability and is shown to be a Seyfert 2 galaxy. We also show that, as for the radio emission, a "multizone" model is needed to account for the high-energy emission., Comment: Accepted for publication in The Astrophysical Journal. 28 pages, 15 figures
Published: 2020
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19. Fermi and Swift Observations of GRB 190114C: Tracing the Evolution of High-Energy Emission from Prompt to Afterglow

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

Author: Uzdensky, D., Begelman, M., Beloborodov, A., Blandford, R., Boldyrev, S., Cerutti, B., Fiuza, F., Giannios, D., Grismayer, T., Kunz, M., Loureiro, N., Lyutikov, M., Medvedev, M., Petropoulou, M., Philippov, A., Quataert, E., Schekochihin, A., Schoeffler, K., Silva, L., Sironi, L., Spitkovsky, A., Werner, G., Zhdankin, V., Zrake, J., and Zweibel, E.
Subjects: Astrophysics - High Energy Astrophysical Phenomena, Physics - Plasma Physics
Abstract: This is a science white paper submitted to the Astro-2020 and Plasma-2020 Decadal Surveys. The paper describes the present status and emerging opportunities in Extreme Plasma Astrophysics -- a study of astrophysically-relevant plasma processes taking place under extreme conditions that necessitate taking into account relativistic, radiation, and QED effects., Comment: A science white paper submitted to the Astro-2020 and Plasma-2020 Decadal Surveys. 7 pages including cover page and references. Paper updated in late March 2019 to include a several additional co-authors and references, and a few small changes
Published: 2019

21. MAGIC and Fermi-LAT gamma-ray results on unassociated HAWC sources

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

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

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

Author: Vedantham, H. K., Readhead, A. C. S., Hovatta, T., Pearson, T. J., Blandford, R. D., Gurwell, M. A., Lähteenmäki, A., Max-Moerbeck, W., Pavlidou, V., Ravi, V., Reeves, R. A., Richards, J. L., Tornikoski, M., and Zensus, J. A.
Subjects: Astrophysics - High Energy Astrophysical Phenomena, Astrophysics - Astrophysics of Galaxies
Abstract: We report the discovery of a rare new form of long-term radio variability in the light-curves of active galaxies (AG) --- Symmetric Achromatic Variability (SAV) --- a pair of opposed and strongly skewed peaks in the radio flux density observed over a broad frequency range. We propose that SAV arises through gravitational milli-lensing when relativistically moving features in AG jets move through gravitational lensing caustics created by $10^3-10^6 \;{\rm M}_{\odot}$ subhalo condensates or black holes located within intervening galaxies. The lower end of this mass range has been inaccessible with previous gravitational lensing techniques. This new interpretation of some AG variability can easily be tested and if it passes these tests, will enable a new and powerful probe of cosmological matter distribution on these intermediate mass scales, as well as provide, for the first time, micro-arcsecond resolution of the nuclei of AG --- a factor of 30--100 greater resolution than is possible with ground-based millimeter VLBI., Comment: Submitted version
Published: 2017
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25. The peculiar light-curve of J1415+1320: A case study in extreme scattering events

Author: Vedantham, H. K., Readhead, A. C. S., Hovatta, T., Koopmans, L. V. E., Pearson, T. J., Blandford, R. D., Gurwell, M. A., Lähteenmäki, A., Max-Moerbeck, W., Pavlidou, V., Ravi, V., Reeves, R. A., Richards, J. L., Tornikoski, M., and Zensus, J. A.
Subjects: Astrophysics - Astrophysics of Galaxies, Astrophysics - High Energy Astrophysical Phenomena
Abstract: The radio light-curve of J1415+1320 (PKS 1413+135) shows time-symmetric and recurring U-shaped features across the cm-wave and mm-wave bands. The symmetry of these features points to lensing by an intervening object as the cause. U-shaped events in radio light curves in the cm-wave band have previously been attributed to Extreme scattering events (ESE). ESEs are thought to be the result of lensing by compact plasma structures in the Galactic interstellar medium, but the precise nature of these plasma structures remains unknown. Since the strength of a plasma lens evolves with wavelength $\lambda$ as $\lambda^2$, the presence of correlated variations at over a wide wavelength range casts doubt on the canonical ESE interpretation for J1415+1320. In this paper, we critically examine the evidence for plasma lensing in J1415+1320. We compute limits on the lensing strength, and the associated free-free opacity of the putative plasma lenses. We compare the observed and model ESE light curves, and also derive a lower limit on the lens distance based on the effects of parallax due to the Earth's orbit around the Sun. We conclude that plasma lensing is not a viable interpretation for J1415+1320's light curves and that symmetric U-shaped features in the radio light curves of extragalactic sources do not present {\em prima facie} evidence for ESEs. The methodology presented here is generic enough to be applicable to any plasma lensing candidate., Comment: Submitted version
Published: 2017
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26. The second catalog of flaring gamma-ray sources from the Fermi All-sky Variability Analysis

Author: Abdollahi, S., Ackermann, M., Ajello, M., Albert, A., Baldini, L., Ballet, J., Barbiellini, G., Bastieri, D., Gonzalez, J. Becerra, Bellazzini, R., Bissaldi, E., Blandford, R. D., Bloom, E. D., Bonino, R., Bottacini, E., Bregeon, J., Bruel, P., Buehler, R., Buson, S., Cameron, R. A., Caragiulo, M., Caraveo, P. A., Cavazzuti, E., Cecchi, C., Chekhtman, A., Cheung, C. C., Chiaro, G., Ciprini, S., Conrad, J., Costantin, D., Costanza, F., Cutini, S., D'Ammando, F., de Palma, F., Desai, A., Desiante, R., Digel, S. W., Di Lalla, N., Di Mauro, M., Di Venere, L., Donaggio, B., Drell, P. S., Favuzzi, C., Fegan, S. J., Ferrara, E. C., Focke, W. B., Franckowiak, A., Fukazawa, Y., Funk, S., Fusco, P., Gargano, F., Gasparrini, D., Giglietto, N., Giomi, M., Giordano, F., Giroletti, M., Glanzman, T., Green, D., Grenier, I. A., Grove, J. E., Guillemot, L., Guiriec, S., Hays, E., Horan, D., Jogler, T., Jóhannesson, G., Johnson, A. S., Kocevski, D., Kuss, M., La Mura, G., Larsson, S., Latronico, L., Li, J., Longo, F., Loparco, F., Lovellette, M. N., Lubrano, P., Magill, J. D., Maldera, S., Manfreda, A., Mayer, M., Mazziotta, M. N., Michelson, P. F., Mitthumsiri, W., Mizuno, T., Monzani, M. E., Morselli, A., Moskalenko, I. V., Negro, M., Nuss, E., Ohsugi, T., Omodei, N., Orienti, M., Orlando, E., Paliya, V. S., Paneque, D., Perkins, J. S., Persic, M., Pesce-Rollins, M., Petrosian, V., Piron, F., Porter, T. A., Principe, G., Rainò, S., Rando, R., Razzano, M., Razzaque, S., Reimer, A., Reimer, O., Sgrò, C., Simone, D., Siskind, E. J., Spada, F., Spandre, G., Spinelli, P., Stawarz, L., Suson, D. J., Takahashi, M., Tanaka, K., Thayer, J. B., Thompson, D. J., Torres, D. F., Torresi, E., Tosti, G., Troja, E., Vianello, G., and Wood, K. S.
Subjects: Astrophysics - High Energy Astrophysical Phenomena
Abstract: We present the second catalog of flaring gamma-ray sources (2FAV) detected with the Fermi All-sky Variability Analysis (FAVA), a tool that blindly searches for transients over the entire sky observed by the Large Area Telescope (LAT) on board the \textit{Fermi} Gamma-ray Space Telescope. With respect to the first FAVA catalog, this catalog benefits from a larger data set, the latest LAT data release (Pass 8), as well as from an improved analysis that includes likelihood techniques for a more precise localization of the transients. Applying this analysis on the first 7.4 years of \textit{Fermi} observations, and in two separate energy bands 0.1$-$0.8 GeV and 0.8$-$300 GeV, a total of 4547 flares has been detected with a significance greater than $6\sigma$ (before trials), on the time scale of one week. Through spatial clustering of these flares, 518 variable gamma-ray sources are identified. Likely counterparts, based on positional coincidence, have been found for 441 sources, mostly among the blazar class of active galactic nuclei. For 77 2FAV sources, no likely gamma-ray counterpart has been found. For each source in the catalog, we provide the time, location, and spectrum of each flaring episode. Studying the spectra of the flares, we observe a harder-when-brighter behavior for flares associated with blazars, with the exception of BL Lac flares detected in the low-energy band. The photon indexes of the flares are never significantly smaller than 1.5. For a leptonic model, and under the assumption of isotropy, this limit suggests that the spectrum of the freshly accelerated electrons is never harder than $p\sim$2., Comment: Accepted for publication by The Astrophysical Journal Supplement. Online analysis results available at http://fermi.gsfc.nasa.gov/ssc/data/access/lat/FAVA/index.php . Corresponding authors: M. Giomi, R. Buehler, D. Kocevski, and M. Ajello
Published: 2016
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27. First NuSTAR observations of the BL Lac - type blazar PKS~2155-304: constraints on the jet content and distribution of radiating particles

Author: Madejski, G. M., Nalewajko, K., Madsen, K. K., Chiang, J., Baloković, M., Paneque, D., Furniss, A. K., Hayashida, M., Urry, C. M., Sikora, M., Ajello, M., Blandford, R. D., Harrison, F. A., Sanchez, D., Giebels, B., Stern, D., Alexander, D. M., Barret, D., Boggs, S. E., Christensen, F. E., Craig, W. W., Forster, K., Giommi, P., Grefenstette, B., Hailey, C., Hornstrup, A., Kitaguchi, T., Koglin, J. E., Mao, P. H., Miyasaka, H., Mori, K., Perri, M., Pivovaroff, M. J., Puccetti, S., Rana, V., Westergaard, N. J., Zhang, W. W., and Zoglauer, A.
Subjects: Astrophysics - High Energy Astrophysical Phenomena
Abstract: We report the first hard X-ray observations with NuSTAR of the BL Lac type blazar PKS 2155-304, augmented with soft X-ray data from XMM-Newton and gamma-ray data from the Fermi Large Area Telescope, obtained in April 2013 when the source was in a very low flux state. A joint NuSTAR and XMM spectrum, covering the energy range 0.5 - 60 keV, is best described by a model consisting of a log-parabola component with curvature beta = 0.3(+0.2,-0.1) and a (local) photon index 3.04 +/- 0.15 at photon energy of 2 keV, and a hard power-law tail with photon index 2.2 +/- 0.4. The hard X-ray tail can be smoothly joined to the quasi-simultaneous gamma-ray spectrum by a synchrotron self-Compton component produced by an electron distribution with index p = 2.2. Assuming that the power-law electron distribution extends down to the minimum electron Lorentz factor gamma_min = 1 and that there is one proton per electron, an unrealistically high total jet power L_p of roughly 10^47 erg/s is inferred. This can be reduced by two orders of magnitude either by considering a significant presence of electron-positron pairs with lepton-to-proton ratio of at least 30, or by introducing an additional, low-energy break in the electron energy distribution at the electron Lorentz factor gamma_br1 of roughly 100. In either case, the jet composition is expected to be strongly matter-dominated., Comment: Astrophysical Journal, in press
Published: 2016
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28. H0LiCOW I. $H_0$ Lenses in COSMOGRAIL's Wellspring: Program Overview

Author: Suyu, S. H., Bonvin, V., Courbin, F., Fassnacht, C. D., Rusu, C. E., Sluse, D., Treu, T., Wong, K. C., Auger, M. W., Ding, X., Hilbert, S., Marshall, P. J., Rumbaugh, N., Sonnenfeld, A., Tewes, M., Tihhonova, O., Agnello, A., Blandford, R. D., Chen, G. C. -F., Collett, T., Koopmans, L. V. E., Liao, K., Meylan, G., and Spiniello, C.
Subjects: Astrophysics - Cosmology and Nongalactic Astrophysics, Astrophysics - Astrophysics of Galaxies
Abstract: Strong gravitational lens systems with time delays between the multiple images allow measurements of time-delay distances, which are primarily sensitive to the Hubble constant that is key to probing dark energy, neutrino physics, and the spatial curvature of the Universe, as well as discovering new physics. We present H0LiCOW ($H_0$ Lenses in COSMOGRAIL's Wellspring), a program that aims to measure $H_0$ with $<3.5\%$ uncertainty from five lens systems (B1608+656, RXJ1131-1231, HE0435-1223, WFI2033-4723 and HE1104-1805). We have been acquiring (1) time delays through COSMOGRAIL and Very Large Array monitoring, (2) high-resolution Hubble Space Telescope imaging for the lens mass modeling, (3) wide-field imaging and spectroscopy to characterize the lens environment, and (4) moderate-resolution spectroscopy to obtain the stellar velocity dispersion of the lenses for mass modeling. In cosmological models with one-parameter extension to flat $\Lambda$CDM, we expect to measure $H_0$ to $<3.5\%$ in most models, spatial curvature $\Omega_{\rm k}$ to 0.004, $w$ to 0.14, and the effective number of neutrino species to 0.2 (1$\sigma$ uncertainties) when combined with current CMB experiments. These are, respectively, a factor of $\sim15$, $\sim2$, and $\sim1.5$ tighter than CMB alone. Our data set will further enable us to study the stellar initial mass function of the lens galaxies, and the co-evolution of supermassive black holes and their host galaxies. This program will provide a foundation for extracting cosmological distances from the hundreds of time-delay lenses that are expected to be discovered in current and future surveys., Comment: 16 pages, 3 figures, submitted to MNRAS and revised based on referee's comments
Published: 2016
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29. Searching the Gamma-ray Sky for Counterparts to Gravitational Wave Sources: Fermi GBM and LAT Observations of LVT151012 and GW151226

Author: Racusin, J. L., Burns, E., Goldstein, A., Connaughton, V., Wilson-Hodge, C. A., Jenke, P., Blackburn, L., Briggs, M. S., Broida, J., Camp, J., Christensen, N., Hui, C. M., Littenberg, T., Shawhan, P., Singer, L., Veitch, J., Bhat, P. N., Cleveland, W., Fitzpatrick, G., Gibby, M. H., von Kienlin, A., McBreen, S., Mailyan, B., Meegan, C. A., Paciesas, W. S., Preece, R. D., Roberts, O. J., Stanbro, M., Veres, P., Zhang, B. -B., Ackermann, M., Albert, A., Atwood, W. B., Axelsson, M., Baldini, L., Ballet, J., Barbiellini, G., Baring, M. G., Bastieri, D., Bellazzini, R., Bissaldi, E., Blandford, R. D., Bloom, E. D., Bonino, R., Bregeon, J., Bruel, P., Buson, S., Caliandro, G. A., Cameron, R. A., Caputo, R., Caragiulo, M., Caraveo, P. A., Cavazzuti, E., Charles, E., Chiang, J., Ciprini, S., Costanza, F., Cuoco, A., Cutini, S., D'Ammando, F., de Palma, F., Desiante, R., Digel, S. W., Di Lalla, N., Di Mauro, M., Di Venere, L., Drell, P. S., Favuzzi, C., Ferrara, E. C., Focke, W. B., Fukazawa, Y., Funk, S., Fusco, P., Gargano, F., Gasparrini, D., Giglietto, N., Gill, R., Giroletti, M., Glanzman, T., Granot, J., Green, D., Grove, J. E., Guillemot, L., Guiriec, S., Harding, A. K., Jogler, T., Johannesson, G., Kamae, T., Kensei, S., Kocevski, D., Kuss, M., Larsson, S., Latronico, L., Li, J., Longo, F., Loparco, F., Lubrano, P., Magill, J. D., Maldera, S., Malyshev, D., McEnery, J. E., Michelson, P. F., Mizuno, T., Morselli, A., Moskalenko, I. V., Negro, M., Nuss, E., Omodei, N., Orienti, M., Orlando, E., Ormes, J. F., Paneque, D., Perkins, J. S., Pesce-Rollins, M., Piron, F., Pivato, G., Porter, T. A., Principe, G., Raino, S., Rando, R., Razzano, M., Razzaque, S., Reimer, A., Reimer, O., Parkinson, P. M. Saz, Scargle, J. D., Sgro, C., Simone, D., Siskind, E. J., Smith, D. A., Spada, F., Spinelli, P., Suson, D. J., Tajima, H., Thayer, J. B., Torres, D. F., Troja, E., Uchiyama, Y., Vianello, G., Wood, K. S., and Wood, M.
Subjects: Astrophysics - High Energy Astrophysical Phenomena
Abstract: We present the Fermi Gamma-ray Burst Monitor (GBM) and Large Area Telescope (LAT) observations of the LIGO binary black hole merger event GW151226 and candi- date LVT151012. No candidate electromagnetic counterparts were detected by either the GBM or LAT. We present a detailed analysis of the GBM and LAT data over a range of timescales from seconds to years, using automated pipelines and new techniques for char- acterizing the upper limits across a large area of the sky. Due to the partial GBM and LAT coverage of the large LIGO localization regions at the trigger times for both events, dif- ferences in source distances and masses, as well as the uncertain degree to which emission from these sources could be beamed, these non-detections cannot be used to constrain the variety of theoretical models recently applied to explain the candidate GBM counterpart to GW150914., Comment: 27 pages, 1 table, 11 figures, Submitted to ApJ
Published: 2016
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30. Supplement: Localization and broadband follow-up of the gravitational-wave transient GW150914

Author: Abbott, B. P., Abbott, R., Abbott, T. D., Abernathy, M. R., Acernese, F., Ackley, K., Adams, C., Adams, T., Addesso, P., Adhikari, R. X., Adya, V. B., Affeldt, C., Agathos, M., Agatsuma, K., Aggarwal, N., Aguiar, O. D., Aiello, L., Ain, A., Ajith, P., Allen, B., Allocca, A., Altin, P. A., Anderson, S. B., Anderson, W. G., Arai, K., Araya, M. C., Arceneaux, C. C., Areeda, J. S., Arnaud, N., Arun, K. G., Ascenzi, S., Ashton, G., Ast, M., Aston, S. M., Astone, P., Aufmuth, P., Aulbert, C., Babak, S., Bacon, P., Bader, M. K. M., Baker, P. T., Baldaccini, F., Ballardin, G., Ballmer, S. W., Barayoga, J. C., Barclay, S. E., Barish, B. C., Barker, D., Barone, F., Barr, B., Barsotti, L., Barsuglia, M., Barta, D., Barthelmy, S., Bartlett, J., Bartos, I., Bassiri, R., Basti, A., Batch, J. C., Baune, C., Bavigadda, V., Bazzan, M., Behnke, B., Bejger, M., Bell, A. S., Bell, C. J., Berger, B. K., Bergman, J., Bergmann, G., Berry, C. P. L., Bersanetti, D., Bertolini, A., Betzwieser, J., Bhagwat, S., Bhandare, R., Bilenko, I. A., Billingsley, G., Birch, J., Birney, R., Biscans, S., Bisht, A., Bitossi, M., Biwer, C., Bizouard, M. A., Blackburn, J. K., Blair, C. D., Blair, D. G., Blair, R. M., Bloemen, S., Bock, O., Bodiya, T. P., Boer, M., Bogaert, G., Bogan, C., Bohe, A., Bojtos, P., Bond, C., Bondu, F., Bonnand, R., Boom, B. A., Bork, R., Boschi, V., Bose, S., Bouffanais, Y., Bozzi, A., Bradaschia, C., Brady, P. R., Braginsky, V. B., Branchesi, M., Brau, J. E., Briant, T., Brillet, A., Brinkmann, M., Brisson, V., Brockill, P., Brooks, A. F., Brown, D. A., Brown, D. D., Brown, N. M., Buchanan, C. C., Buikema, A., Bulik, T., Bulten, H. J., Buonanno, A., Buskulic, D., Buy, C., Byer, R. L., Cadonati, L., Cagnoli, G., Cahillane, C., Bustillo, J. C., Callister, T., Calloni, E., Camp, J. B., Cannon, K. C., Cao, J., Capano, C. D., Capocasa, E., Carbognani, F., Caride, S., Diaz, J. C., Casentini, C., Caudill, S., Cavaglià, M., Cavalier, F., Cavalieri, R., Cella, G., Cepeda, C. B., Baiardi, L. C., Cerretani, G., Cesarini, E., Chakraborty, R., Chalermsongsak, T., Chamberlin, S. J., Chan, M., Chao, S., Charlton, P., Chassande-Mottin, E., Chen, H. Y., Chen, Y., Cheng, C., Chincarini, A., Chiummo, A., Cho, H. S., Cho, M., Chow, J. H., Christensen, N., Chu, Q., Chua, S., Chung, S., Ciani, G., Clara, F., Clark, J. A., Cleva, F., Coccia, E., Cohadon, P. -F., Colla, A., Collette, C. G., Cominsky, L., Constancio Jr., M., Conte, A., Conti, L., Cook, D., Corbitt, T. R., Cornish, N., Corsi, A., Cortese, S., Costa, C. A., Coughlin, M. W., Coughlin, S. B., Coulon, J. -P., Countryman, S. T., Couvares, P., Cowan, E. E., Coward, D. M., Cowart, M. J., Coyne, D. C., Coyne, R., Craig, K., Creighton, J. D. E., Cripe, J., Crowder, S. G., Cumming, A., Cunningham, L., Cuoco, E., Canton, T. Dal, Danilishin, S. L., D'Antonio, S., Danzmann, K., Darman, N. S., Dattilo, V., Dave, I., Daveloza, H. P., Davier, M., Davies, G. S., Daw, E. J., Day, R., DeBra, D., Debreczeni, G., Degallaix, J., De Laurentis, M., Deléglise, S., Del Pozzo, W., Denker, T., Dent, T., Dereli, H., Dergachev, V., DeRosa, R. T., De Rosa, R., DeSalvo, R., Dhurandhar, S., Díaz, M. C., Di Fiore, L., Di Giovanni, M., Di Lieto, A., Di Pace, S., Di Palma, I., Di Virgilio, A., Dojcinoski, G., Dolique, V., Donovan, F., Dooley, K. L., Doravari, S., Douglas, R., Downes, T. P., Drago, M., Drever, R. W. P., Driggers, J. C., Du, Z., Ducrot, M., Dwyer, S. E., Edo, T. B., Edwards, M. C., Effler, A., Eggenstein, H. -B., Ehrens, P., Eichholz, J., Eikenberry, S. S., Engels, W., Essick, R. C., Etzel, T., Evans, M., Evans, T. M., Everett, R., Factourovich, M., Fafone, V., Fair, H., Fairhurst, S., Fan, X., Fang, Q., Farinon, S., Farr, B., Farr, W. M., Favata, M., Fays, M., Fehrmann, H., Fejer, M. M., Ferrante, I., Ferreira, E. C., Ferrini, F., Fidecaro, F., Fiori, I., Fiorucci, D., Fisher, R. P., Flaminio, R., Fletcher, M., Fournier, J. -D., Franco, S., Frasca, S., Frasconi, F., Frei, Z., Freise, A., Frey, R., Frey, V., Fricke, T. T., Fritschel, P., Frolov, V. V., Fulda, P., Fyffe, M., Gabbard, H. A. G., Gair, J. R., Gammaitoni, L., Gaonkar, S. G., Garufi, F., Gatto, A., Gaur, G., Gehrels, N., Gemme, G., Gendre, B., Genin, E., Gennai, A., George, J., Gergely, L., Germain, V., Ghosh, A., Ghosh, S., Giaime, J. A., Giardina, K. D., Giazotto, A., Gill, K., Glaefke, A., Goetz, E., Goetz, R., Gondan, L., González, G., Castro, J. M. G., Gopakumar, A., Gordon, N. A., Gorodetsky, M. L., Gossan, S. E., Gosselin, M., Gouaty, R., Graef, C., Graff, P. B., Granata, M., Grant, A., Gras, S., Gray, C., Greco, G., Green, A. C., Groot, P., Grote, H., Grunewald, S., Guidi, G. M., Guo, X., Gupta, A., Gupta, M. K., Gushwa, K. E., Gustafson, E. K., Gustafson, R., Hacker, J. J., Hall, B. R., Hall, E. D., Hammond, G., Haney, M., Hanke, M. M., Hanks, J., Hanna, C., Hannam, M. D., Hanson, J., Hardwick, T., Haris, K., Harms, J., Harry, G. M., Harry, I. W., Hart, M. J., Hartman, M. T., Haster, C. -J., Haughian, K., Heidmann, A., Heintze, M. C., Heitmann, H., Hello, P., Hemming, G., Hendry, M., Heng, I. S., Hennig, J., Heptonstall, A. W., Heurs, M., Hild, S., Hoak, D., Hodge, K. A., Hofman, D., Hollitt, S. E., Holt, K., Holz, D. E., Hopkins, P., Hosken, D. J., Hough, J., Houston, E. A., Howell, E. J., Hu, Y. M., Huang, S., Huerta, E. A., Huet, D., Hughey, B., Husa, S., Huttner, S. H., Huynh-Dinh, T., Idrisy, A., Indik, N., Ingram, D. R., Inta, R., Isa, H. N., Isac, J. -M., Isi, M., Islas, G., Isogai, T., Iyer, B. R., Izumi, K., Jacqmin, T., Jang, H., Jani, K., Jaranowski, P., Jawahar, S., Jiménez-Forteza, F., Johnson, W. W., Jones, D. I., Jones, R., Jonker, R. J. G., Ju, L., Kalaghatgi, C. V., Kalogera, V., Kandhasamy, S., Kang, G., Kanner, J. B., Karki, S., Kasprzack, M., Katsavounidis, E., Katzman, W., Kaufer, S., Kaur, T., Kawabe, K., Kawazoe, F., Kéfélian, F., Kehl, M. S., Keitel, D., Kelley, D. B., Kells, W., Kennedy, R., Key, J. S., Khalaidovski, A., Khalili, F. Y., Khan, I., Khan, S., Khan, Z., Khazanov, E. A., Kijbunchoo, N., Kim, C., Kim, J., Kim, K., Kim, N., Kim, Y. -M., King, E. J., King, P. J., Kinzel, D. L., Kissel, J. S., Kleybolte, L., Klimenko, S., Koehlenbeck, S. M., Kokeyama, K., Koley, S., Kondrashov, V., Kontos, A., Korobko, M., Korth, W. Z., Kowalska, I., Kozak, D. B., Kringel, V., Królak, A., Krueger, C., Kuehn, G., Kumar, P., Kuo, L., Kutynia, A., Lackey, B. D., Landry, M., Lange, J., Lantz, B., Lasky, P. D., Lazzarini, A., Lazzaro, C., Leaci, P., Leavey, S., Lebigot, E. O., Lee, C. H., Lee, H. K., Lee, H. M., Lee, K., Lenon, A., Leonardi, M., Leong, J. R., Leroy, N., Letendre, N., Levin, Y., Levine, B. M., Li, T. G. F., Libson, A., Littenberg, T. B., Lockerbie, N. A., Logue, J., Lombardi, A. L., Lord, J. E., Lorenzini, M., Loriette, V., Lormand, M., Losurdo, G., Lough, J. D., Lück, H., Lundgren, A. P., Luo, J., Lynch, R., Ma, Y., MacDonald, T., Machenschalk, B., MacInnis, M., Macleod, D. M., Magaña-Sandoval, F., Magee, R. M., Mageswaran, M., Majorana, E., Maksimovic, I., Malvezzi, V., Man, N., Mandel, I., Mandic, V., Mangano, V., Mansell, G. L., Manske, M., Mantovani, M., Marchesoni, F., Marion, F., Márka, S., Márka, Z., Markosyan, A. S., Maros, E., Martelli, F., Martellini, L., Martin, I. W., Martin, R. M., Martynov, D. V., Marx, J. N., Mason, K., Masserot, A., Massinger, T. J., Masso-Reid, M., Matichard, F., Matone, L., Mavalvala, N., Mazumder, N., Mazzolo, G., McCarthy, R., McClelland, D. E., McCormick, S., McGuire, S. C., McIntyre, G., McIver, J., McManus, D. J., McWilliams, S. T., Meacher, D., Meadors, G. D., Meidam, J., Melatos, A., Mendell, G., Mendoza-Gandara, D., Mercer, R. A., Merilh, E., Merzougui, M., Meshkov, S., Messenger, C., Messick, C., Meyers, P. M., Mezzani, F., Miao, H., Michel, C., Middleton, H., Mikhailov, E. E., Milano, L., Miller, J., Millhouse, M., Minenkov, Y., Ming, J., Mirshekari, S., Mishra, C., Mitra, S., Mitrofanov, V. P., Mitselmakher, G., Mittleman, R., Moggi, A., Mohan, M., Mohapatra, S. R. P., Montani, M., Moore, B. C., Moore, C. J., Moraru, D., Moreno, G., Morriss, S. R., Mossavi, K., Mours, B., Mow-Lowry, C. M., Mueller, C. L., Mueller, G., Muir, A. W., Mukherjee, A., Mukherjee, D., Mukherjee, S., Mukund, N., Mullavey, A., Munch, J., Murphy, D. J., Murray, P. G., Mytidis, A., Nardecchia, I., Naticchioni, L., Nayak, R. K., Necula, V., Nedkova, K., Nelemans, G., Neri, M., Neunzert, A., Newton, G., Nguyen, T. T., Nielsen, A. B., Nissanke, S., Nitz, A., Nocera, F., Nolting, D., Normandin, M. E. N., Nuttall, L. K., Oberling, J., Ochsner, E., O'Dell, J., Oelker, E., Ogin, G. H., Oh, J. J., Oh, S. H., Ohme, F., Oliver, M., Oppermann, P., Oram, R. J., O'Reilly, B., O'Shaughnessy, R., Ottaway, D. J., Ottens, R. S., Overmier, H., Owen, B. J., Pai, A., Pai, S. A., Palamos, J. R., Palashov, O., Palliyaguru, N., Palomba, C., Pal-Singh, A., Pan, H., Pankow, C., Pannarale, F., Pant, B. C., Paoletti, F., Paoli, A., Papa, M. A., Paris, H. R., Parker, W., Pascucci, D., Pasqualetti, A., Passaquieti, R., Passuello, D., Patricelli, B., Patrick, Z., Pearlstone, B. L., Pedraza, M., Pedurand, R., Pekowsky, L., Pele, A., Penn, S., Perreca, A., Phelps, M., Piccinni, O., Pichot, M., Piergiovanni, F., Pierro, V., Pillant, G., Pinard, L., Pinto, I. M., Pitkin, M., Poggiani, R., Popolizio, P., Post, A., Powell, J., Prasad, J., Predoi, V., Premachandra, S. S., Prestegard, T., Price, L. R., Prijatelj, M., Principe, M., Privitera, S., Prodi, G. A., Prokhorov, L., Puncken, O., Punturo, M., Puppo, P., Pürrer, M., Qi, H., Qin, J., Quetschke, V., Quintero, E. A., Quitzow-James, R., Raab, F. J., Rabeling, D. S., Radkins, H., Raffai, P., Raja, S., Rakhmanov, M., Rapagnani, P., Raymond, V., Razzano, M., Re, V., Read, J., Reed, C. M., Regimbau, T., Rei, L., Reid, S., Reitze, D. H., Rew, H., Reyes, S. D., Ricci, F., Riles, K., Robertson, N. A., Robie, R., Robinet, F., Rocchi, A., Rolland, L., Rollins, J. G., Roma, V. J., Romano, R., Romanov, G., Romie, J. H., Rosińska, D., Rowan, S., Rüdiger, A., Ruggi, P., Ryan, K., Sachdev, S., Sadecki, T., Sadeghian, L., Salconi, L., Saleem, M., Salemi, F., Samajdar, A., Sammut, L., Sanchez, E. J., Sandberg, V., Sandeen, B., Sanders, J. R., Sassolas, B., Sathyaprakash, B. S., Saulson, P. R., Sauter, O., Savage, R. L., Sawadsky, A., Schale, P., Schilling, R., Schmidt, J., Schmidt, P., Schnabel, R., Schofield, R. M. S., Schönbeck, A., Schreiber, E., Schuette, D., Schutz, B. F., Scott, J., Scott, S. M., Sellers, D., Sentenac, D., Sequino, V., Sergeev, A., Serna, G., Setyawati, Y., Sevigny, A., Shaddock, D. A., Shah, S., Shahriar, M. S., Shaltev, M., Shao, Z., Shapiro, B., Shawhan, P., Sheperd, A., Shoemaker, D. H., Shoemaker, D. M., Siellez, K., Siemens, X., Sigg, D., Silva, A. D., Simakov, D., Singer, A., Singh, A., Singh, R., Singhal, A., Sintes, A. M., Slagmolen, B. J. J., Smith, J. R., Smith, N. D., Smith, R. J. E., Son, E. J., Sorazu, B., Sorrentino, F., Souradeep, T., Srivastava, A. K., Staley, A., Steinke, M., Steinlechner, J., Steinlechner, S., Steinmeyer, D., Stephens, B. C., Stone, R., Strain, K. A., Straniero, N., Stratta, G., Strauss, N. A., Strigin, S., Sturani, R., Stuver, A. L., Summerscales, T. Z., Sun, L., Sutton, P. J., Swinkels, B. L., Szczepańczyk, M. J., Tacca, M., Talukder, D., Tanner, D. B., Tápai, M., Tarabrin, S. P., Taracchini, A., Taylor, R., Theeg, T., Thirugnanasambandam, M. P., Thomas, E. G., Thomas, M., Thomas, P., Thorne, K. A., Thorne, K. S., Thrane, E., Tiwari, S., Tiwari, V., Tokmakov, K. V., Tomlinson, C., Tonelli, M., Torres, C. V., Torrie, C. I., Töyrä, D., Travasso, F., Traylor, G., Trifirò, D., Tringali, M. C., Trozzo, L., Tse, M., Turconi, M., Tuyenbayev, D., Ugolini, D., Unnikrishnan, C. S., Urban, A. L., Usman, S. A., Vahlbruch, H., Vajente, G., Valdes, G., van Bakel, N., van Beuzekom, M., Brand, J. F. J. van den, Broeck, C. Van Den, Vander-Hyde, D. C., van der Schaaf, L., van Heijningen, J. V., van Veggel, A. A., Vardaro, M., Vass, S., Vasúth, M., Vaulin, R., Vecchio, A., Vedovato, G., Veitch, J., Veitch, P. J., Venkateswara, K., Verkindt, D., Vetrano, F., Viceré, A., Vinciguerra, S., Vine, D. J., Vinet, J. -Y., Vitale, S., Vo, T., Vocca, H., Vorvick, C., Voss, D., Vousden, W. D., Vyatchanin, S. P., Wade, A. R., Wade, L. E., Wade, M., Walker, M., Wallace, L., Walsh, S., Wang, G., Wang, H., Wang, M., Wang, X., Wang, Y., Ward, R. L., Warner, J., Was, M., Weaver, B., Wei, L. -W., Weinert, M., Weinstein, A. J., Weiss, R., Welborn, T., Wen, L., Weßels, P., Westphal, T., Wette, K., Whelan, J. T., White, D. J., Whiting, B. F., Williams, R. D., Williamson, A. R., Willis, J. L., Willke, B., Wimmer, M. H., Winkler, W., Wipf, C. C., Wittel, H., Woan, G., Worden, J., Wright, J. L., Wu, G., Yablon, J., Yam, W., Yamamoto, H., Yancey, C. C., Yap, M. J., Yu, H., Yvert, M., Zadrożny, A., Zangrando, L., Zanolin, M., Zendri, J. -P., Zevin, M., Zhang, F., Zhang, L., Zhang, M., Zhang, Y., Zhao, C., Zhou, M., Zhou, Z., Zhu, X. J., Zucker, M. E., Zuraw, S. E., Zweizig, J., Allison, J., Bannister, K., Bell, M. E., Chatterjee, S., Chippendale, A. P., Edwards, P. G., Harvey-Smith, L., Heywood, Ian, Hotan, A., Indermuehle, B., Marvil, J., McConnell, D., Murphy, T., Popping, A., Reynolds, J., Sault, R. J., Voronkov, M. A., Whiting, M. T., Castro-Tirado, A. J., Cunniffe, R., Jelínek, M., Tello, J. C., Oates, S. R., Hu, Y. -D., Kubánek, P., Guziy, S., Castellón, A., García-Cerezo, A., Muñoz, V. F., del Pulgar, C. Pérez, Castillo-Carrión, S., Cerón, J. M. Castro, Hudec, R., Caballero-García, M. 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L., Rainò, S., Rando, R., Razzaque, S., Reimer, A., Reimer, O., Salvetti, D., Parkinson, P. M. Saz, Sgrò, C., Simone, D., Siskind, E. J., Spada, F., Spandre, G., Spinelli, P., Suson, D. J., Tajima, H., Thayer, J. B., Thompson, D. J., Tibaldo, L., Torres, D. F., Troja, E., Uchiyama, Y., Venters, T. M., Vianello, G., Wood, K. S., Wood, M., Zhu, S., Zimmer, S., Brocato, E., Cappellaro, E., Covino, S., Grado, A., Nicastro, L., Palazzi, E., Pian, E., Amati, L., Antonelli, L. A., Capaccioli, M., D'Avanzo, P., D'Elia, V., Getman, F., Giuffrida, G., Iannicola, G., Limatola, L., Lisi, M., Marinoni, S., Marrese, P., Melandri, A., Piranomonte, S., Possenti, A., Pulone, L., Rossi, A., Stamerra, A., Stella, L., Testa, V., Tomasella, L., Yang, S., Bazzano, A., Bozzo, E., Brandt, S., Courvoisier, T. J. -L., Ferrigno, C., Hanlon, L., Kuulkers, E., Laurent, P., Mereghetti, S., Roques, J. P., Savchenko, V., Ubertini, P., Kasliwal, M. M., Singer, L. P., Cao, Y., Duggan, G., Kulkarni, S. 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J., Lipunov, V., Gorbovskoy, E., Tyurina, N., Kornilov, V., Balanutsa, P., Kuznetsov, A., Buckley, D., Rebolo, R., Serra-Ricart, M., Israelian, G., Budnev, N. M., Gress, O., Ivanov, K., Poleshuk, V., Tlatov, A., Yurkov, V., Kawai, N., Serino, M., Negoro, H., Nakahira, S., Mihara, T., Tomida, H., Ueno, S., Tsunemi, H., Matsuoka, M., Croft, S., Feng, L., Franzen, T. M. O., Gaensler, B. M., Johnston-Hollitt, M., Kaplan, D. L., Morales, M. F., Tingay, S. J., Wayth, R. B., Williams, A., Smartt, S. J., Chambers, K. C., Smith, K. W., Huber, M. E., Young, D. R., Wright, D. E., Schultz, A., Denneau, L., Flewelling, H., Magnier, E. A., Primak, N., Rest, A., Sherstyuk, A., Stalder, B., Stubbs, C. W., Tonry, J., Waters, C., Willman, M., E., F. Olivares, Campbell, H., Kotak, R., Sollerman, J., Smith, M., Dennefeld, M., Anderson, J. P., Botticella, M. T., Chen, T. -W., Valle, M. D., Elias-Rosa, N., Fraser, M., Inserra, C., Kankare, E., Kupfer, T., Harmanen, J., Galbany, L., Guillou, L. Le, Lyman, J. D., Maguire, K., Mitra, A., Nicholl, M., Razza, A., Terreran, G., Valenti, S., Gal-Yam, A., Ćwiek, A., Ćwiok, M., Mankiewicz, L., Opiela, R., Zaremba, M., Żarnecki, A. F., Onken, C. A., Scalzo, R. A., Schmidt, B. P., Wolf, C., Yuan, F., Evans, P. A., Kennea, J. A., Burrows, D. N., Campana, S., Cenko, S. B., Marshall, F. E., Nousek, J., O'Brien, P., Osborne, J. P., Palmer, D., Perri, M., Siegel, M., Tagliaferri, G., Klotz, A., Turpin, D., Laugier, R., Beroiz, M., Peñuela, T., Macri, L. M., Oelkers, R. J., Lambas, D. G., Vrech, R., Cabral, J., Colazo, C., Dominguez, M., Sanchez, B., Gurovich, S., Lares, M., Marshall, J. L., DePoy, D. L., Padilla, N., Pereyra, N. A., Benacquista, M., Tanvir, N. R., Wiersema, K., Levan, A. J., Steeghs, D., Hjorth, J., Fynbo, J. P. U., Malesani, D., Milvang-Jensen, B., Watson, D., Irwin, M., Fernandez, C. G., McMahon, R. G., Banerji, M., Gonzalez-Solares, E., Schulze, S., Postigo, A. de U., Thoene, C. C., Cano, Z., and Rosswog, S.
Subjects: Astrophysics - High Energy Astrophysical Phenomena, General Relativity and Quantum Cosmology
Abstract: This Supplement provides supporting material for arXiv:1602.08492 . We briefly summarize past electromagnetic (EM) follow-up efforts as well as the organization and policy of the current EM follow-up program. We compare the four probability sky maps produced for the gravitational-wave transient GW150914, and provide additional details of the EM follow-up observations that were performed in the different bands., Comment: For the main Letter, see arXiv:1602.08492
Published: 2016
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31. Measurement of the high-energy gamma-ray emission from the Moon with the Fermi Large Area Telescope

Author: Ackermann, M., Ajello, M., Albert, A., Atwood, W. B., Baldini, L., Barbiellini, G., Bastieri, D., Bellazzini, R., Bissaldi, E., Blandford, R. D., Bonino, R., Bottacini, E., Bregeon, J., Bruel, P., Buehler, R., Caliandro, G. A., Cameron, R. A., Caragiulo, M., Caraveo, P. A., Cavazzuti, E., Cecchi, C., Chekhtman, A., Chiang, J., Chiaro, G., Ciprini, S., Claus, R., Cohen-Tanugi, J., Costanza, F., Cuoco, A., Cutini, S., D'Ammando, F., de Angelis, A., de Palma, F., Desiante, R., Digel, S. W., Di Venere, L., Drell, P. S., Favuzzi, C., Fegan, S. J., Focke, W. B., Franckowiak, A., Funk, S., Fusco, P., Gargano, F., Gasparrini, D., Giglietto, N., Giordano, F., Giroletti, M., Glanzman, T., Godfrey, G., Grenier, I. A., Grove, J. E., Guiriec, S., Harding, A. K., Hewitt, J. W., Horan, D., Hou, X., Iafrate, G., Johannesson, G., Kamae, T., Kuss, M., Larsson, S., Latronico, L., Li, J., Li, L., Longo, F., Loparco, F., Lovellette, M. N., Lubrano, P., Magill, J., Maldera, S., Manfreda, A., Mayer, M., Mazziotta, M. N., Michelson, P. F., Mitthumsiri, W., Mizuno, T., Monzani, M. E., Morselli, A., Murgia, S., Nuss, E., Omodei, N., Orlando, E., Ormes, J. F., Paneque, D., Perkins, J. S., Pesce-Rollins, M., Petrosian, V., Piron, F., Pivato, G., Rainò, S., Rando, R., Razzano, M., Reimer, A., Reimer, O., Reposeur, T., Sgrò, C., Siskind, E. J., Spada, F., Spandre, G., Spinelli, P., Takahashi, H., Thayer, J. B., Thompson, D. J., Tibaldo, L., Torres, D. F., Tosti, G., Troja, E., Vianello, G., Winer, B. L., Wood, K. S., Yassine, M., Cerutti, F., Ferrari, A., and Sala, P. R.
Subjects: Astrophysics - High Energy Astrophysical Phenomena, High Energy Physics - Experiment
Abstract: We have measured the gamma-ray emission spectrum of the Moon using the data collected by the Large Area Telescope onboard the Fermi satellite during its first 7 years of operation, in the energy range from 30 MeV up to a few GeV. We have also studied the time evolution of the flux, finding a correlation with the solar activity. We have developed a full Monte Carlo simulation describing the interactions of cosmic rays with the lunar surface. The results of the present analysis can be explained in the framework of this model, where the production of gamma rays is due to the interactions of cosmic-ray proton and helium nuclei with the surface of the Moon. Finally, we have used our simulation to derive the cosmic-ray proton and helium spectra near Earth from the Moon gamma-ray data., Comment: Published by PRD, 16 pages, 11 figures, corresponding authors: F. Loparco and M. N. Mazziotta
Published: 2016
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32. Localization and broadband follow-up of the gravitational-wave transient GW150914

Author: Abbott, B. P., Abbott, R., Abbott, T. D., Abernathy, M. R., Acernese, F., Ackley, K., Adams, C., Adams, T., Addesso, P., Adhikari, R. X., Adya, V. B., Affeldt, C., Agathos, M., Agatsuma, K., Aggarwal, N., Aguiar, O. D., Aiello, L., Ain, A., Ajith, P., Allen, B., Allocca, A., Altin, P. A., Anderson, S. B., Anderson, W. G., Arai, K., Araya, M. C., Arceneaux, C. C., Areeda, J. S., Arnaud, N., Arun, K. G., Ascenzi, S., Ashton, G., Ast, M., Aston, S. M., Astone, P., Aufmuth, P., Aulbert, C., Babak, S., Bacon, P., Bader, M. K. M., Baker, P. T., Baldaccini, F., Ballardin, G., Ballmer, S. W., Barayoga, J. C., Barclay, S. E., Barish, B. C., Barker, D., Barone, F., Barr, B., Barsotti, L., Barsuglia, M., Barta, D., Barthelmy, S., Bartlett, J., Bartos, I., Bassiri, R., Basti, A., Batch, J. C., Baune, C., Bavigadda, V., Bazzan, M., Behnke, B., Bejger, M., Bell, A. S., Bell, C. J., Berger, B. K., Bergman, J., Bergmann, G., Berry, C. P. L., Bersanetti, D., Bertolini, A., Betzwieser, J., Bhagwat, S., Bhandare, R., Bilenko, I. A., Billingsley, G., Birch, J., Birney, R., Biscans, S., Bisht, A., Bitossi, M., Biwer, C., Bizouard, M. A., Blackburn, J. K., Blair, C. D., Blair, D. G., Blair, R. M., Bloemen, S., Bock, O., Bodiya, T. P., Boer, M., Bogaert, G., Bogan, C., Bohe, A., Bojtos, P., Bond, C., Bondu, F., Bonnand, R., Boom, B. A., Bork, R., Boschi, V., Bose, S., Bouffanais, Y., Bozzi, A., Bradaschia, C., Brady, P. R., Braginsky, V. B., Branchesi, M., Brau, J. E., Briant, T., Brillet, A., Brinkmann, M., Brisson, V., Brockill, P., Brooks, A. F., Brown, D. A., Brown, D. D., Brown, N. M., Buchanan, C. C., Buikema, A., Bulik, T., Bulten, H. J., Buonanno, A., Buskulic, D., Buy, C., Byer, R. L., Cadonati, L., Cagnoli, G., Cahillane, C., Bustillo, J. C., Callister, T., Calloni, E., Camp, J. B., Cannon, K. C., Cao, J., Capano, C. D., Capocasa, E., Carbognani, F., Caride, S., Diaz, J. C., Casentini, C., Caudill, S., Cavaglià, M., Cavalier, F., Cavalieri, R., Cella, G., Cepeda, C. B., Baiardi, L. C., Cerretani, G., Cesarini, E., Chakraborty, R., Chalermsongsak, T., Chamberlin, S. J., Chan, M., Chao, S., Charlton, P., Chassande-Mottin, E., Chen, H. Y., Chen, Y., Cheng, C., Chincarini, A., Chiummo, A., Cho, H. S., Cho, M., Chow, J. H., Christensen, N., Chu, Q., Chua, S., Chung, S., Ciani, G., Clara, F., Clark, J. A., Cleva, F., Coccia, E., Cohadon, P. -F., Colla, A., Collette, C. G., Cominsky, L., Constancio Jr., M., Conte, A., Conti, L., Cook, D., Corbitt, T. R., Cornish, N., Corsi, A., Cortese, S., Costa, C. A., Coughlin, M. W., Coughlin, S. B., Coulon, J. -P., Countryman, S. T., Couvares, P., Cowan, E. E., Coward, D. M., Cowart, M. J., Coyne, D. C., Coyne, R., Craig, K., Creighton, J. D. E., Cripe, J., Crowder, S. G., Cumming, A., Cunningham, L., Cuoco, E., Canton, T. Dal, Danilishin, S. L., D'Antonio, S., Danzmann, K., Darman, N. S., Dattilo, V., Dave, I., Daveloza, H. P., Davier, M., Davies, G. S., Daw, E. J., Day, R., DeBra, D., Debreczeni, G., Degallaix, J., De Laurentis, M., Deléglise, S., Del Pozzo, W., Denker, T., Dent, T., Dereli, H., Dergachev, V., DeRosa, R. T., De Rosa, R., DeSalvo, R., Dhurandhar, S., Díaz, M. C., Di Fiore, L., Di Giovanni, M., Di Lieto, A., Di Pace, S., Di Palma, I., Di Virgilio, A., Dojcinoski, G., Dolique, V., Donovan, F., Dooley, K. L., Doravari, S., Douglas, R., Downes, T. P., Drago, M., Drever, R. W. P., Driggers, J. C., Du, Z., Ducrot, M., Dwyer, S. E., Edo, T. B., Edwards, M. C., Effler, A., Eggenstein, H. -B., Ehrens, P., Eichholz, J., Eikenberry, S. S., Engels, W., Essick, R. C., Etzel, T., Evans, M., Evans, T. M., Everett, R., Factourovich, M., Fafone, V., Fair, H., Fairhurst, S., Fan, X., Fang, Q., Farinon, S., Farr, B., Farr, W. M., Favata, M., Fays, M., Fehrmann, H., Fejer, M. M., Ferrante, I., Ferreira, E. C., Ferrini, F., Fidecaro, F., Fiori, I., Fiorucci, D., Fisher, R. P., Flaminio, R., Fletcher, M., Fournier, J. -D., Franco, S., Frasca, S., Frasconi, F., Frei, Z., Freise, A., Frey, R., Frey, V., Fricke, T. T., Fritschel, P., Frolov, V. V., Fulda, P., Fyffe, M., Gabbard, H. A. G., Gair, J. R., Gammaitoni, L., Gaonkar, S. G., Garufi, F., Gatto, A., Gaur, G., Gehrels, N., Gemme, G., Gendre, B., Genin, E., Gennai, A., George, J., Gergely, L., Germain, V., Ghosh, A., Ghosh, S., Giaime, J. A., Giardina, K. D., Giazotto, A., Gill, K., Glaefke, A., Goetz, E., Goetz, R., Gondan, L., González, G., Castro, J. M. G., Gopakumar, A., Gordon, N. A., Gorodetsky, M. L., Gossan, S. E., Gosselin, M., Gouaty, R., Graef, C., Graff, P. B., Granata, M., Grant, A., Gras, S., Gray, C., Greco, G., Green, A. C., Groot, P., Grote, H., Grunewald, S., Guidi, G. M., Guo, X., Gupta, A., Gupta, M. K., Gushwa, K. E., Gustafson, E. K., Gustafson, R., Hacker, J. J., Hall, B. R., Hall, E. D., Hammond, G., Haney, M., Hanke, M. M., Hanks, J., Hanna, C., Hannam, M. D., Hanson, J., Hardwick, T., Haris, K., Harms, J., Harry, G. M., Harry, I. W., Hart, M. J., Hartman, M. T., Haster, C. -J., Haughian, K., Heidmann, A., Heintze, M. C., Heitmann, H., Hello, P., Hemming, G., Hendry, M., Heng, I. S., Hennig, J., Heptonstall, A. W., Heurs, M., Hild, S., Hoak, D., Hodge, K. A., Hofman, D., Hollitt, S. E., Holt, K., Holz, D. E., Hopkins, P., Hosken, D. J., Hough, J., Houston, E. A., Howell, E. J., Hu, Y. M., Huang, S., Huerta, E. A., Huet, D., Hughey, B., Husa, S., Huttner, S. H., Huynh-Dinh, T., Idrisy, A., Indik, N., Ingram, D. R., Inta, R., Isa, H. N., Isac, J. -M., Isi, M., Islas, G., Isogai, T., Iyer, B. R., Izumi, K., Jacqmin, T., Jang, H., Jani, K., Jaranowski, P., Jawahar, S., Jiménez-Forteza, F., Johnson, W. W., Jones, D. I., Jones, R., Jonker, R. J. G., Ju, L., Kalaghatgi, C. V., Kalogera, V., Kandhasamy, S., Kang, G., Kanner, J. 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L., Lord, J. E., Lorenzini, M., Loriette, V., Lormand, M., Losurdo, G., Lough, J. D., Lück, H., Lundgren, A. P., Luo, J., Lynch, R., Ma, Y., MacDonald, T., Machenschalk, B., MacInnis, M., Macleod, D. M., Magaña-Sandoval, F., Magee, R. M., Mageswaran, M., Majorana, E., Maksimovic, I., Malvezzi, V., Man, N., Mandel, I., Mandic, V., Mangano, V., Mansell, G. L., Manske, M., Mantovani, M., Marchesoni, F., Marion, F., Márka, S., Márka, Z., Markosyan, A. S., Maros, E., Martelli, F., Martellini, L., Martin, I. W., Martin, R. M., Martynov, D. V., Marx, J. N., Mason, K., Masserot, A., Massinger, T. J., Masso-Reid, M., Matichard, F., Matone, L., Mavalvala, N., Mazumder, N., Mazzolo, G., McCarthy, R., McClelland, D. E., McCormick, S., McGuire, S. C., McIntyre, G., McIver, J., McManus, D. J., McWilliams, S. T., Meacher, D., Meadors, G. D., Meidam, J., Melatos, A., Mendell, G., Mendoza-Gandara, D., Mercer, R. A., Merilh, E., Merzougui, M., Meshkov, S., Messenger, C., Messick, C., Meyers, P. 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S., Shaltev, M., Shao, Z., Shapiro, B., Shawhan, P., Sheperd, A., Shoemaker, D. H., Shoemaker, D. M., Siellez, K., Siemens, X., Sigg, D., Silva, A. D., Simakov, D., Singer, A., Singh, A., Singh, R., Singhal, A., Sintes, A. M., Slagmolen, B. J. J., Smith, J. R., Smith, N. D., Smith, R. J. E., Son, E. J., Sorazu, B., Sorrentino, F., Souradeep, T., Srivastava, A. K., Staley, A., Steinke, M., Steinlechner, J., Steinlechner, S., Steinmeyer, D., Stephens, B. C., Stone, R., Strain, K. A., Straniero, N., Stratta, G., Strauss, N. A., Strigin, S., Sturani, R., Stuver, A. L., Summerscales, T. Z., Sun, L., Sutton, P. J., Swinkels, B. L., Szczepańczyk, M. J., Tacca, M., Talukder, D., Tanner, D. B., Tápai, M., Tarabrin, S. P., Taracchini, A., Taylor, R., Theeg, T., Thirugnanasambandam, M. P., Thomas, E. G., Thomas, M., Thomas, P., Thorne, K. A., Thorne, K. S., Thrane, E., Tiwari, S., Tiwari, V., Tokmakov, K. V., Tomlinson, C., Tonelli, M., Torres, C. V., Torrie, C. I., Töyrä, D., Travasso, F., Traylor, G., Trifirò, D., Tringali, M. C., Trozzo, L., Tse, M., Turconi, M., Tuyenbayev, D., Ugolini, D., Unnikrishnan, C. S., Urban, A. L., Usman, S. A., Vahlbruch, H., Vajente, G., Valdes, G., van Bakel, N., van Beuzekom, M., Brand, J. F. J. van den, Broeck, C. Van Den, Vander-Hyde, D. C., van der Schaaf, L., van Heijningen, J. V., van Veggel, A. A., Vardaro, M., Vass, S., Vasúth, M., Vaulin, R., Vecchio, A., Vedovato, G., Veitch, J., Veitch, P. J., Venkateswara, K., Verkindt, D., Vetrano, F., Viceré, A., Vinciguerra, S., Vine, D. J., Vinet, J. -Y., Vitale, S., Vo, T., Vocca, H., Vorvick, C., Voss, D., Vousden, W. D., Vyatchanin, S. P., Wade, A. R., Wade, L. E., Wade, M., Walker, M., Wallace, L., Walsh, S., Wang, G., Wang, H., Wang, M., Wang, X., Wang, Y., Ward, R. L., Warner, J., Was, M., Weaver, B., Wei, L. -W., Weinert, M., Weinstein, A. J., Weiss, R., Welborn, T., Wen, L., Weßels, P., Westphal, T., Wette, K., Whelan, J. T., White, D. J., Whiting, B. F., Williams, R. D., Williamson, A. R., Willis, J. L., Willke, B., Wimmer, M. H., Winkler, W., Wipf, C. C., Wittel, H., Woan, G., Worden, J., Wright, J. L., Wu, G., Yablon, J., Yam, W., Yamamoto, H., Yancey, C. C., Yap, M. J., Yu, H., Yvert, M., Zadrożny, A., Zangrando, L., Zanolin, M., Zendri, J. -P., Zevin, M., Zhang, F., Zhang, L., Zhang, M., Zhang, Y., Zhao, C., Zhou, M., Zhou, Z., Zhu, X. J., Zucker, M. E., Zuraw, S. E., Zweizig, J., Allison, J., Bannister, K., Bell, M. E., Chatterjee, S., Chippendale, A. P., Edwards, P. G., Harvey-Smith, L., Heywood, Ian, Hotan, A., Indermuehle, B., Marvil, J., McConnell, D., Murphy, T., Popping, A., Reynolds, J., Sault, R. J., Voronkov, M. A., Whiting, M. T., Castro-Tirado, A. J., Cunniffe, R., Jelínek, M., Tello, J. C., Oates, S. R., Hu, Y. -D., Kubánek, P., Guziy, S., Castellón, A., García-Cerezo, A., Muñoz, V. F., del Pulgar, C. Pérez, Castillo-Carrión, S., Cerón, J. M. Castro, Hudec, R., Caballero-García, M. D., Páta, P., Vitek, S., Adame, J. A., Konig, S., Rendón, F., Sanguino, T. de J. Mateo, Fernández-Muñoz, R., Yock, P. C., Rattenbury, N., Allen, W. H., Querel, R., Jeong, S., Park, I. H., Bai, J., Cui, Ch., Fan, Y., Wang, Ch., Hiriart, D., Lee, W. H., Claret, A., Sánchez-Ramírez, R., Pandey, S. B., Mediavilla, T., Sabau-Graziati, L., Abbott, T. M. C., Abdalla, F. B., Allam, S., Annis, J., Armstrong, R., Benoit-Lévy, A., Berger, E., Bernstein, R. A., Bertin, E., Brout, D., Buckley-Geer, E., Burke, D. L., Capozzi, D., Carretero, J., Castander, F. J., Chornock, R., Cowperthwaite, P. S., Crocce, M., Cunha, C. E., D'Andrea, C. B., da Costa, L. N., Desai, S., Diehl, H. T., Dietrich, J. P., Doctor, Z., Drlica-Wagner, A., Drout, M. R., Eifler, T. F., Estrada, J., Evrard, A. E., Fernandez, E., Finley, D. A., Flaugher, B., Foley, R. J., Fong, W. -F., Fosalba, P., Fox, D. B., Frieman, J., Fryer, C. L., Gaztanaga, E., Gerdes, D. W., Goldstein, D. A., Gruen, D., Gruendl, R. A., Gutierrez, G., Herner, K., Honscheid, K., James, D. J., Johnson, M. D., Johnson, M. W. G., Karliner, I., Kasen, D., Kent, S., Kessler, R., Kim, A. G., Kind, M. C., Kuehn, K., Kuropatkin, N., Lahav, O., Li, T. S., Lima, M., Lin, H., Maia, M. A. G., Margutti, R., Marriner, J., Martini, P., Matheson, T., Melchior, P., Metzger, B. D., Miller, C. J., Miquel, R., Neilsen, E., Nichol, R. C., Nord, B., Nugent, P., Ogando, R., Petravick, D., Plazas, A. A., Quataert, E., Roe, N., Romer, A. K., Roodman, A., Rosell, A. C., Rykoff, E. S., Sako, M., Sanchez, E., Scarpine, V., Schindler, R., Schubnell, M., Scolnic, D., Sevilla-Noarbe, I., Sheldon, E., Smith, N., Smith, R. C., Soares-Santos, M., Sobreira, F., Stebbins, A., Suchyta, E., Swanson, M. E. C., Tarle, G., Thaler, J., Thomas, D., Thomas, R. C., Tucker, D. L., Vikram, V., Walker, A. R., Wechsler, R. H., Wester, W., Yanny, B., Zuntz, J., Connaughton, V., Burns, E., Goldstein, A., Briggs, M. S., Zhang, B. -B., Hui, C. M., Jenke, P., Wilson-Hodge, C. A., Bhat, P. N., Bissaldi, E., Cleveland, W., Fitzpatrick, G., Giles, M. M., Gibby, M. H., Greiner, J., von Kienlin, A., Kippen, R. M., McBreen, S., Mailyan, B., Meegan, C. A., Paciesas, W. S., Preece, R. D., Roberts, O., Sparke, L., Stanbro, M., Toelge, K., Veres, P., Yu, H. -F., Blackburn, L., Ackermann, M., Ajello, M., Albert, A., Anderson, B., Atwood, W. B., Axelsson, M., Baldini, L., Barbiellini, G., Bastieri, D., Bellazzini, R., Blandford, R. D., Bloom, E. D., Bonino, R., Bottacini, E., Brandt, T. J., Bruel, P., Buson, S., Caliandro, G. A., Cameron, R. A., Caragiulo, M., Caraveo, P. A., Cavazzuti, E., Charles, E., Chekhtman, A., Chiang, J., Chiaro, G., Ciprini, S., Cohen-Tanugi, J., Cominsky, L. R., Costanza, F., Cuoco, A., D'Ammando, F., de Palma, F., Desiante, R., Digel, S. W., Di Lalla, N., Di Mauro, M., Di Venere, L., Domínguez, A., Drell, P. S., Dubois, R., Favuzzi, C., Ferrara, E. C., Franckowiak, A., Fukazawa, Y., Funk, S., Fusco, P., Gargano, F., Gasparrini, D., Giglietto, N., Giommi, P., Giordano, F., Giroletti, M., Glanzman, T., Godfrey, G., Gomez-Vargas, G. A., Green, D., Grenier, I. A., Grove, J. E., Guiriec, S., Hadasch, D., Harding, A. K., Hays, E., Hewitt, J. W., Hill, A. B., Horan, D., Jogler, T., Jóhannesson, G., Johnson, A. S., Kensei, S., Kocevski, D., Kuss, M., La Mura, G., Larsson, S., Latronico, L., Li, J., Li, L., Longo, F., Loparco, F., Lovellette, M. N., Lubrano, P., Magill, J., Maldera, S., Manfreda, A., Marelli, M., Mayer, M., Mazziotta, M. N., McEnery, J. E., Meyer, M., Michelson, P. F., Mirabal, N., Mizuno, T., Moiseev, A. A., Monzani, M. E., Moretti, E., Morselli, A., Moskalenko, I. V., Negro, M., Nuss, E., Ohsugi, T., Omodei, N., Orienti, M., Orlando, E., Ormes, J. F., Paneque, D., Perkins, J. S., Pesce-Rollins, M., Piron, F., Pivato, G., Porter, T. A., Racusin, J. L., Rainò, S., Rando, R., Razzaque, S., Reimer, A., Reimer, O., Salvetti, D., Parkinson, P. M. Saz, Sgrò, C., Simone, D., Siskind, E. J., Spada, F., Spandre, G., Spinelli, P., Suson, D. J., Tajima, H., Thayer, J. B., Thompson, D. J., Tibaldo, L., Torres, D. F., Troja, E., Uchiyama, Y., Venters, T. M., Vianello, G., Wood, K. S., Wood, M., Zhu, S., Zimmer, S., Brocato, E., Cappellaro, E., Covino, S., Grado, A., Nicastro, L., Palazzi, E., Pian, E., Amati, L., Antonelli, L. A., Capaccioli, M., D'Avanzo, P., D'Elia, V., Getman, F., Giuffrida, G., Iannicola, G., Limatola, L., Lisi, M., Marinoni, S., Marrese, P., Melandri, A., Piranomonte, S., Possenti, A., Pulone, L., Rossi, A., Stamerra, A., Stella, L., Testa, V., Tomasella, L., Yang, S., Bazzano, A., Bozzo, E., Brandt, S., Courvoisier, T. J. -L., Ferrigno, C., Hanlon, L., Kuulkers, E., Laurent, P., Mereghetti, S., Roques, J. P., Savchenko, V., Ubertini, P., Kasliwal, M. M., Singer, L. P., Cao, Y., Duggan, G., Kulkarni, S. R., Bhalerao, V., Miller, A. A., Barlow, T., Bellm, E., Manulis, I., Rana, J., Laher, R., Masci, F., Surace, J., Rebbapragada, U., Van Sistine, A., Sesar, B., Perley, D., Ferreti, R., Prince, T., Kendrick, R., Horesh, A., Hurley, K., Golenetskii, S. V., Aptekar, R. L., Frederiks, D. D., Svinkin, D. S., Rau, A., Zhang, X., Smith, D. M., Cline, T., Krimm, H., Abe, F., Doi, M., Fujisawa, K., Kawabata, K. S., Morokuma, T., Motohara, K., Tanaka, M., Ohta, K., Yanagisawa, K., Yoshida, M., Baltay, C., Rabinowitz, D., Ellman, N., Rostami, S., Bersier, D. F., Bode, M. F., Collins, C. A., Copperwheat, C. M., Darnley, M. J., Galloway, D. K., Gomboc, A., Kobayashi, S., Mazzali, P., Mundell, C. G., Piascik, A. S., Pollacco, Don, Steele, I. A., Ulaczyk, K., Broderick, J. W., Fender, R. P., Jonker, P. G., Rowlinson, A., Stappers, B. W., Wijers, R. A. M. J., Lipunov, V., Gorbovskoy, E., Tyurina, N., Kornilov, V., Balanutsa, P., Kuznetsov, A., Buckley, D., Rebolo, R., Serra-Ricart, M., Israelian, G., Budnev, N. M., Gress, O., Ivanov, K., Poleshuk, V., Tlatov, A., Yurkov, V., Kawai, N., Serino, M., Negoro, H., Nakahira, S., Mihara, T., Tomida, H., Ueno, S., Tsunemi, H., Matsuoka, M., Croft, S., Feng, L., Franzen, T. M. O., Gaensler, B. M., Johnston-Hollitt, M., Kaplan, D. L., Morales, M. F., Tingay, S. J., Wayth, R. B., Williams, A., Smartt, S. J., Chambers, K. C., Smith, K. W., Huber, M. E., Young, D. R., Wright, D. E., Schultz, A., Denneau, L., Flewelling, H., Magnier, E. A., Primak, N., Rest, A., Sherstyuk, A., Stalder, B., Stubbs, C. W., Tonry, J., Waters, C., Willman, M., E., F. Olivares, Campbell, H., Kotak, R., Sollerman, J., Smith, M., Dennefeld, M., Anderson, J. P., Botticella, M. T., Chen, T. -W., Valle, M. D., Elias-Rosa, N., Fraser, M., Inserra, C., Kankare, E., Kupfer, T., Harmanen, J., Galbany, L., Guillou, L. Le, Lyman, J. D., Maguire, K., Mitra, A., Nicholl, M., Razza, A., Terreran, G., Valenti, S., Gal-Yam, A., Ćwiek, A., Ćwiok, M., Mankiewicz, L., Opiela, R., Zaremba, M., Żarnecki, A. F., Onken, C. A., Scalzo, R. A., Schmidt, B. P., Wolf, C., Yuan, F., Evans, P. A., Kennea, J. A., Burrows, D. N., Campana, S., Cenko, S. B., Marshall, F. E., Nousek, J., O'Brien, P., Osborne, J. P., Palmer, D., Perri, M., Siegel, M., Tagliaferri, G., Klotz, A., Turpin, D., Laugier, R., Beroiz, M., Peñuela, T., Macri, L. M., Oelkers, R. J., Lambas, D. G., Vrech, R., Cabral, J., Colazo, C., Dominguez, M., Sanchez, B., Gurovich, S., Lares, M., Marshall, J. L., DePoy, D. L., Padilla, N., Pereyra, N. A., Benacquista, M., Tanvir, N. R., Wiersema, K., Levan, A. J., Steeghs, D., Hjorth, J., Fynbo, J. P. U., Malesani, D., Milvang-Jensen, B., Watson, D., Irwin, M., Fernandez, C. G., McMahon, R. G., Banerji, M., Gonzalez-Solares, E., Schulze, S., Postigo, A. de U., Thoene, C. C., Cano, Z., and Rosswog, S.
Subjects: Astrophysics - High Energy Astrophysical Phenomena, General Relativity and Quantum Cosmology
Abstract: A gravitational-wave (GW) transient was identified in data recorded by the Advanced Laser Interferometer Gravitational-wave Observatory (LIGO) detectors on 2015 September 14. The event, initially designated G184098 and later given the name GW150914, is described in detail elsewhere. By prior arrangement, preliminary estimates of the time, significance, and sky location of the event were shared with 63 teams of observers covering radio, optical, near-infrared, X-ray, and gamma-ray wavelengths with ground- and space-based facilities. In this Letter we describe the low-latency analysis of the GW data and present the sky localization of the first observed compact binary merger. We summarize the follow-up observations reported by 25 teams via private Gamma-ray Coordinates Network circulars, giving an overview of the participating facilities, the GW sky localization coverage, the timeline and depth of the observations. As this event turned out to be a binary black hole merger, there is little expectation of a detectable electromagnetic (EM) signature. Nevertheless, this first broadband campaign to search for a counterpart of an Advanced LIGO source represents a milestone and highlights the broad capabilities of the transient astronomy community and the observing strategies that have been developed to pursue neutron star binary merger events. Detailed investigations of the EM data and results of the EM follow-up campaign are being disseminated in papers by the individual teams., Comment: For Supplement, see https://arxiv.org/abs/1604.07864
Published: 2016
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33. Very-high-energy gamma-rays from the Universe's middle age: detection of the z=0.940 blazar PKS 1441+25 with MAGIC

Author: MAGIC Collaboration, Ahnen, M. L., Ansoldi, S., Antonelli, A., Antoranz, P., Babic, A., Banerjee, B., Bangale, P., de Almeida, U. Barres, Barrio, J. A., Bednarek, W., Bernardini, E., Biassuzzi, B., Biland, A., Blanch, O., Bonnefoy, S., Bonnoli, G., Borracci, F., Bretz, T., Carmona, E., Carosi, A., Chatterjee, A., Clavero, R., Colin, P., Colombo, E., Contreras, J. L., Cortina, J., Covino, S., Da Vela, P., Dazzi, F., De Angelis, A., De Lotto, B., Wilhelmi, E. de Oña, Mendez, C. Delgado, Di Pierro, F., Prester, D. Dominis, Dorner, D., Doro, M., Einecke, S., Glawion, D. Eisenacher, Elsaesser, D., Fernández-Barral, A., Fidalgo, D., Fonseca, M. V., Font, L., Frantzen, K., Fruck, C., Galindo, D., López, R. J. García, Garczarczyk, M., Terrats, D. Garrido, Gaug, M., Giammaria, P., Godinović, N., Muñoz, A. González, Guberman, D., Hahn, A., Hanabata, Y., Hayashida, M., Herrera, J., Hose, J., Hrupec, D., Hughes, G., Idec, W., Kodani, K., Konno, Y., Kubo, H., Kushida, J., La Barbera, A., Lelas, D., Lindfors, E., Lombardi, S., López, M., López-Coto, R., López-Oramas, A., Lorenz, E., Majumdar, P., Makariev, M., Mallot, K., Maneva, G., Manganaro, M., Mannheim, K., Maraschi, L., Marcote, B., Mariotti, M., Martínez, M., Mazin, D., Menzel, U., Miranda, J. M., Mirzoyan, R., Moralejo, A., Moretti, E., Nakajima, D., Neustroev, V., Niedzwiecki, A., Rosillo, M. Nievas, Nilsson, K., Nishijima, K., Noda, K., Orito, R., Overkemping, A., Paiano, S., Palacio, J., Palatiello, M., Paneque, D., Paoletti, R., Paredes, J. M., Paredes-Fortuny, X., Persic, M., Poutanen, J., Moroni, P. G. Prada, Prandini, E., Puljak, I., Rhode, W., Ribó, M., Rico, J., Garcia, J. Rodriguez, Saito, T., Satalecka, K., Schultz, C., Schweizer, T., Shore, S. N., Sillanpää, A., Sitarek, J., Snidaric, I., Sobczynska, D., Stamerra, A., Steinbring, T., Strzys, M., Takalo, L., Takami, H., Tavecchio, F., Temnikov, P., Terzić, T., Tescaro, D., Teshima, M., Thaele, J., Torres, D. F., Toyama, T., Treves, A., Verguilov, V., Vovk, I., Ward, J. E., Will, M., Wu, M. H., Zanin, R., Collaboration, FERMI-LAT, Ajello, M., Baldini, L., Barbiellini, G., Bastieri, D., González, J. Becerra, Bellazzini, R., Bissaldi, E., Blandford, R. D., Bonino, R., Bregeon, J., Bruel, P., Buson, S., Caliandro, G. A., Cameron, R. A., Caragiulo, M., Caraveo, P. A., Cavazzuti, E., Chiang, J., Chiaro, G., Ciprini, S., D'Ammando, F., de Palma, F., Desiante, R., Di Venere, L., Domínguez, A., Fusco, P., Gargano, F., Gasparrini, D., Giglietto, N., Giordano, F., Giroletti, M., Grenier, I. A., Guiriec, S., Hays, E., Hewitt, J. W., Jogler, T., Kuss, M., Larsson, S., Li, J., Li, L., Longo, F., Loparco, F., Lovellette, M. N., Lubrano, P., Maldera, S., Mayer, M., Mazziotta, M. N., McEnery, J. E., Mirabal, N., Mizuno, T., Monzani, M. E., Morselli, A., Moskalenko, I. V., Nuss, E., Ojha, R., Ohsugi, T., Omodei, N., Orlando, E., Perkins, J. S., Pesce-Rollins, M., Piron, F., Pivato, G., Porter, T. A., Rainò, S., Rando, R., Razzano, M., Reimer, A., Reimer, O., Sgrò, C., Siskind, E. J., Spada, F., Spandre, G., Spinelli, P., Tajima, H., Takahashi, H., Thayer, J. B., Thompson, D. J., Troja, E., Wood, K. S., Balokovic, M., Berdyugin, A., Carraminana, A., Carrasco, L., Chavushyan, V., Ramazani, V. Fallah, Feige, M., Haarto, S., Haeusner, P., Hovatta, T., Kania, J., Klamt, J., Lähteenmäki, A., Leon-Tavares, J., Lorey, C., Pacciani, L., Porras, A., Recillas, E., Reinthal, R., Tornikoski, M., Wolfert, D., and Zottmann, N.
Subjects: Astrophysics - Astrophysics of Galaxies, Astrophysics - High Energy Astrophysical Phenomena
Abstract: The flat-spectrum radio quasar PKS 1441+25 at a redshift of z = 0.940 is detected between 40 and 250 GeV with a significance of 25.5 {\sigma} using the MAGIC telescopes. Together with the gravitationally lensed blazar QSO B0218+357 (z = 0.944), PKS 1441+25 is the most distant very high energy (VHE) blazar detected to date. The observations were triggered by an outburst in 2015 April seen at GeV energies with the Large Area Telescope on board Fermi. Multi-wavelength observations suggest a subdivision of the high state into two distinct flux states. In the band covered by MAGIC, the variability time scale is estimated to be 6.4 +/- 1.9 days. Modeling the broadband spectral energy distribution with an external Compton model, the location of the emitting region is understood as originating in the jet outside the broad line region (BLR) during the period of high activity, while being partially within the BLR during the period of low (typical) activity. The observed VHE spectrum during the highest activity is used to probe the extragalactic background light at an unprecedented distance scale for ground-based gamma-ray astronomy., Comment: Corresponding Authors: J. Becerra (josefa.becerra@nasa.gov), M. Nievas Rosillo (mnievas@ucm.es), M. Manganaro (manganaro@iac.es), F. Tavecchio (fabrizio.tavecchio@brera.inaf.it) Published in The Astrophysical Journal Letters (ApJL), 2015ApJ...815L..23A, DOI: 10.1088/2041-8205/815/2/L23
Published: 2015
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34. Multiwavelength Study of Quiescent States of Mrk 421 with Unprecedented Hard X-Ray Coverage Provided by NuSTAR in 2013

Author: Baloković, M., Paneque, D., Madejski, G., Furniss, A., Chiang, J., team, the NuSTAR, Ajello, M., Alexander, D. M., Barret, D., Blandford, R., Boggs, S. E., Christensen, F. E., Craig, W. W., Forster, K., Giommi, P., Grefenstette, B. W., Hailey, C. J., Harrison, F. A., Hornstrup, A., Kitaguchi, T., Koglin, J. E., Madsen, K. K., Mao, P. H., Miyasaka, H., Mori, K., Perri, M., Pivovaroff, M. J., Puccetti, S., Rana, V., Stern, D., Tagliaferri, G., Urry, C. M., Westergaard, N. J., Zhang, W. W., Zoglauer, A., collaboration, the VERITAS, Archambault, S., Archer, A. A., Barnacka, A., Benbow, W., Bird, R., Buckley, J., Bugaev, V., Cerruti, M., Chen, X., Ciupik, L., Connolly, M. P., Cui, W., Dickinson, H. J., Dumm, J., Eisch, J. D., Falcone, A., Feng, Q., Finley, J. P., Fleischhack, H., Fortson, L., Griffin, S., Griffiths, S. T., Grube, J., Gyuk, G., Huetten, M., Haakansson, N., Holder, J., Humensky, T. B., Johnson, C. A., Kaaret, P., Kertzman, M., Khassen, Y., Kieda, D., Krause, M., Krennrich, F., Lang, M. J., Maier, G., McArthur, S., Meagher, K., Moriarty, P., Nelson, T., Nieto, D., Ong, R. A., Park, N., Pohl, M., Popkow, A., Pueschel, E., Reynolds, P. T., Richards, G. T., Roache, E., Santander, M., Sembroski, G. H., Shahinyan, K., Smith, A. W., Staszak, D., Telezhinsky, I., Todd, N. W., Tucci, J. V., Tyler, J., Vincent, S., Weinstein, A., Wilhelm, A., Williams, D. A., Zitzer, B., collaboration, the MAGIC, Ahnen, M. L., Ansoldi, S., Antonelli, L. A., Antoranz, P., Babic, A., Banerjee, B., Bangale, P., de Almeida, U. Barres, Barrio, J., González, J. Becerra, Bednarek, W., Bernardini, E., Biasuzzi, B., Biland, A., Blanch, O., Bonnefoy, S., Bonnoli, G., Borracci, F., Bretz, T., Carmona, E., Carosi, A., Chatterjee, A., Clavero, R., Colin, P., Colombo, E., Contreras, J. L., Cortina, J., Covino, S., Da Vela, P., Dazzi, F., de Angelis, A., De Lotto, B., Wilhelmi, E. D. de Oña, Mendez, C. Delgado, Di Pierro, F., Prester, D. Dominis, Dorner, D., Doro, M., Einecke, S., Elsaesser, D., Fernández-Barral, A., Fidalgo, D., Fonseca, M. V., Font, L., Frantzen, K., Fruck, C., Galindo, D., López, R. J. García, Garczarczyk, M., Terrats, D. Garrido, Gaug, M., Giammaria, P., Eisenacher, D., Godinović, N., Muñoz, A. González, Guberman, D., Hahn, A., Hanabata, Y., Hayashida, M., Herrera, J., Hose, J., Hrupec, D., Hughes, G., Idec, W., Kodani, K., Konno, Y., Kubo, H., Kushida, J., La Barbera, A., Lelas, D., Lindfors, E., Lombardi, S., Longo, F., López, M., López-Coto, R., López-Oramas, A., Lorenz, E., Majumdar, P., Makariev, M., Mallot, K., Maneva, G., Manganaro, M., Mannheim, K., Maraschi, L., Marcote, B., Mariotti, M., Martínez, M., Mazin, D., Menzel, U., Miranda, J. M., Mirzoyan, R., Moralejo, A., Moretti, E., Nakajima, D., Neustroev, V., Niedzwiecki, A., Nievas-Rosillo, M., Nilsson, K., Nishijima, K., Noda, K., Orito, R., Overkemping, A., Paiano, S., Palacio, S., Palatiello, M., Paoletti, R., Paredes, J. M., Paredes-Fortuny, X., Persic, M., Poutanen, J., Moroni, P. G. Prada, Prandini, E., Puljak, I., Rhode, W., Ribó, M., Rico, J., Garcia, J. Rodriguez, Saito, T., Satalecka, K., Scapin, V., Schultz, C., Schweizer, T., Shore, S. N., Sillanpää, A., Sitarek, J., Snidaric, I., Sobczynska, D., Stamerra, A., Steinbring, T., Strzys, M., Takalo, L. O., Takami, H., Tavecchio, F., Temnikov, P., Terzić, T., Tescaro, D., Teshima, M., Thaele, J., Torres, D. F., Toyama, T., Treves, A., Verguilov, V., Vovk, I., Ward, J. E., Will, M., Wu, M. H., Zanin, R., collaborators, external, Perkins, J., Verrecchia, F., Leto, C., Böttcher, M., Villata, M., Raiteri, C. M., Acosta-Pulido, J. A., Bachev, R., Berdyugin, A., Blinov, D. A., Carnerero, M. I., Chen, W. P., Chinchilla, P., Damljanovic, G., Eswaraiah, C., Grishina, T. S., Ibryamov, S., Jordan, B., Jorstad, S. G., Joshi, M., Kopatskaya, E. N., Kurtanidze, O. M., Kurtanidze, S. O., Larionova, E. G., Larionova, L. V., Larionov, V. M., Latev, G., Lin, H. C., Marscher, A. P., Mokrushina, A. A., Morozova, D. A., Nikolashvili, M. G., Semkov, E., Strigachev, A., Troitskaya, Yu. V., Troitsky, I. S., Vince, O., Barnes, J., Güver, T., Moody, J. W., Sadun, A. C., Sun, S., Hovatta, T., Richards, J. L., Max-Moerbeck, W., Readhead, A. C., Lähteenmäki, A., Tornikoski, M., Tammi, J., Ramakrishnan, V., Reinthal, R., Angelakis, E., Fuhrmann, L., Myserlis, I., Karamanavis, V., Sievers, A., Ungerechts, H., and Zensus, J. A.
Subjects: Astrophysics - High Energy Astrophysical Phenomena
Abstract: We present coordinated multiwavelength observations of the bright, nearby BL Lac object Mrk 421 taken in 2013 January-March, involving GASP-WEBT, Swift, NuSTAR, Fermi-LAT, MAGIC, VERITAS, and other collaborations and instruments, providing data from radio to very-high-energy (VHE) gamma-ray bands. NuSTAR yielded previously unattainable sensitivity in the 3-79 keV range, revealing that the spectrum softens when the source is dimmer until the X-ray spectral shape saturates into a steep power law with a photon index of approximately 3, with no evidence for an exponential cutoff or additional hard components up to about 80 keV. For the first time, we observed both the synchrotron and the inverse-Compton peaks of the spectral energy distribution (SED) simultaneously shifted to frequencies below the typical quiescent state by an order of magnitude. The fractional variability as a function of photon energy shows a double-bump structure which relates to the two bumps of the broadband SED. In each bump, the variability increases with energy which, in the framework of the synchrotron self-Compton model, implies that the electrons with higher energies are more variable. The measured multi-band variability, the significant X-ray-to-VHE correlation down to some of the lowest fluxes ever observed in both bands, the lack of correlation between optical/UV and X-ray flux, the low degree of polarization and its significant (random) variations, the short estimated electron cooling time, and the significantly longer variability timescale observed in the NuSTAR light curves point toward in-situ electron acceleration, and suggest that there are multiple compact regions contributing to the broadband emission of Mrk 421 during low-activity states., Comment: 32 pages, 14 figures; accepted for publication in ApJ
Published: 2015
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35. Active Galactic Nuclei: The TeV Challenge

Author: Blandford, R., East, W., Nalewajko, K., Yuan, Y., and Zrake, J.
Subjects: Astrophysics - High Energy Astrophysical Phenomena, Astrophysics - Astrophysics of Galaxies
Abstract: Jets associated with Active Galactic Nuclei (AGN) have been observed for almost a century, initially at optical and radio wavelengths. They are now widely accepted as "exhausts" produced electromagnetically by the central, spinning, massive black hole and its orbiting, accreting gas. Observations at X-ray and, especially, gamma-ray energies have transformed our understanding of how these jets evolve dynamically, accelerate electrons (and positrons) and radiate throughout the entire electromagnetic spectrum. Some new approaches to modeling the powerful and rapidly variable TeV emission observed from many blazars are sketched. Observations at the highest TeV energies, to which the High Altitude Water Cherenkov Gamma-Ray Observatory (HAWC) will contribute, promise crucial discrimination between rival models of AGN jets., Comment: Invited talk at the HAWC inauguration conference, Puebla, Mexico, March 19, 2015. To appear in Pubs. Academia Mexicana de Ciencias, Eds. Alberto Carrami\~nana, Daniel Rosa, Stefan Westerhoff and Omar Tibolla
Published: 2015

36. Multiwavelength Evidence for Quasi-periodic Modulation in the Gamma-ray Blazar PG 1553+113

Author: The Fermi LAT collaboration, Ackermann, M., Ajello, M., Albert, A., Atwood, W. B., Baldini, L., Ballet, J., Barbiellini, G., Bastieri, D., Gonzalez, J. Becerra, Bellazzini, R., Bissaldi, E., Blandford, R. D., Bloom, E. D., Bonino, R., Bottacini, E., Bregeon, J., Bruel, P., Buehler, R., Buson, S., Caliandro, G. A., Cameron, R. A., Caputo, R., Caragiulo, M., Caraveo, P. A., Cavazzuti, E., Cecchi, C., Chekhtman, A., Chiang, J., Chiaro, G., Ciprini, S., Cohen-Tanugi, J., Conrad, J., Cutini, S., D'Ammando, F., De Angelis, A., De Palma, F., Desiante, R., Di Venere, L., Dominguez, A., Drell, P. S., Favuzzi, C., Fegan, S. J., Ferrara, E. C., Focke, W. B., Fuhrmann, L., Fukazawa, Y., Fusco, P., Gargano, F., Gasparrini, D., Giglietto, N., Giommi, P., Giordano, F., Giroletti, M., Godfrey, G., Green, D., Grenier, I. A., Grove, J. E., Guiriec, S., Harding, A. K., Hays, E., Hewitt, J. W., Hill, A. B., Horan, D., Jogler, T., Johannesson, G., Johnson, A. S., Kamae, T., Kuss, M., Larsson, S., Latronico, L., Li, J., Li, L., Longo, F., Loparco, F., Lott, B., Lovellette, M. N., Lubrano, P., Magill, J., Maldera, S., Manfreda, A., Max-Moerbeck, W., Mayer, M., Mazziotta, M. N., Mcenery, J. E., Michelson, P. F., Mizuno, T., Monzani, M. E., Morselli, A., Moskalenko, I. V., Murgia, S., Nuss, E., Ohno, M., Ohsugi, T., Ojha, R., Omodei, N., Orlando, E., Ormes, J. F., Paneque, D., Pearson, T. J., Perkins, J. S., Perri, M., Pesce-Rollins, M., Petrosian, V., Piron, F., Pivato, G., Porter, T. A., Raino', S., Rando, R., Razzano, M., Readhead, A., Reimer, A., Reimer, O., Schulz, A., Sgro', C., Siskind, E. J., Spada, F., Spandre, G., Spinelli, P., Suson, D. J., Takahashi, H., Thayer, J. B., Thompson, D. J., Tibaldo, L., Torres, D. F., Tosti, G., Troja, E., Uchiyama, Y., Vianello, G., Wood, K. S., Wood, M., Zimmer, S., Berdyugin, A., Corbet, R. H. D., Hovatta, T., Lindfors, E., Nilsson, K., Reinthal, R., Sillanpaa, A., Stamerra, A., Takalo, L. O., and Valtonen, M. J.
Subjects: Astrophysics - High Energy Astrophysical Phenomena
Abstract: We report for the first time a gamma-ray and multi-wavelength nearly-periodic oscillation in an active galactic nucleus. Using the Fermi Large Area Telescope (LAT) we have discovered an apparent quasi-periodicity in the gamma-ray flux (E >100 MeV) from the GeV/TeV BL Lac object PG 1553+113. The marginal significance of the 2.18 +/-0.08 year-period gamma-ray cycle is strengthened by correlated oscillations observed in radio and optical fluxes, through data collected in the OVRO, Tuorla, KAIT, and CSS monitoring programs and Swift UVOT. The optical cycle appearing in ~10 years of data has a similar period, while the 15 GHz oscillation is less regular than seen in the other bands. Further long-term multi-wavelength monitoring of this blazar may discriminate among the possible explanations for this quasi-periodicity., Comment: 8 pages, 5 figures. Accepted to The Astrophysical Journal Letters. Corresponding authors: S. Ciprini (ASDC/INFN), S. Cutini (ASDC/INFN), S. Larsson (Stockholm Univ/KTH), A. Stamerra (INAF/SNS), D. J. Thompson (NASA GSFC)
Published: 2015
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37. Search for Early Gamma-ray Production in Supernovae Located in a Dense Circumstellar Medium with the Fermi LAT

Author: Ackermann, M., Arcavi, I., Baldini, L., Ballet, J., Barbiellini, G., Bastieri, D., Bellazzini, R., Bissaldi, E., Blandford, R. D., Bonino, R., Bottacini, E., Brandt, T. J., Bregeon, J., Bruel, P., Buehler, R., Buson, S., Caliandro, G. A., Cameron, R. A., Caragiulo, M., Caraveo, P. A., Cavazzuti, E., Cecchi, C., Charles, E., Chekhtman, A., Chiang, J., Chiaro, G., Ciprini, S., Claus, R., Cohen-Tanugi, J., Cutini, S., D'Ammando, F., de Angelis, A., de Palma, F., Desiante, R., Di Venere, L., Drell, P. S., Favuzzi, C., Fegan, S. J., Franckowiak, A., Funk, S., Fusco, P., Gal-Yam, A., Gargano, F., Gasparrini, D., Giglietto, N., Giordano, F., Giroletti, M., Glanzman, T., Godfrey, G., Grenier, I. A., Grove, J. E., Guiriec, S., Harding, A. K., Hayashi, K., Hewitt, J. W., Hill, A. B., Horan, D., Jogler, T., Jóhannesson, G., Kocevski, D., Kuss, M., Larsson, S., Lashner, J., Latronico, L., Li, J., Li, L., Longo, F., Loparco, F., Lovellette, M. N., Lubrano, P., Malyshev, D., Mayer, M., Mazziotta, M. N., McEnery, J. E., Michelson, P. F., Mizuno, T., Monzani, M. E., Morselli, A., Murase, K., Nugent, P., Nuss, E., Ofek, E., Ohsugi, T., Orienti, M., Orlando, E., Ormes, J. F., Paneque, D., Pesce-Rollins, M., Piron, F., Pivato, G., Rainò, S., Rando, R., Razzano, M., Reimer, A., Reimer, O., Schulz, A., Sgrò, C., Siskind, E. J., Spada, F., Spandre, G., Spinelli, P., Suson, D. J., Takahashi, H., Thayer, J. B., Tibaldo, L., Torres, D. F., Troja, E., Vianello, G., Werner, M., Wood, K. S., and Wood, M.
Subjects: Astrophysics - High Energy Astrophysical Phenomena
Abstract: Supernovae (SNe) exploding in a dense circumstellar medium (CSM) are hypothesized to accelerate cosmic rays in collisionless shocks and emit GeV gamma rays and TeV neutrinos on a time scale of several months. We perform the first systematic search for gamma-ray emission in Fermi LAT data in the energy range from 100 MeV to 300 GeV from the ensemble of 147 SNe Type IIn exploding in dense CSM. We search for a gamma-ray excess at each SNe location in a one year time window. In order to enhance a possible weak signal, we simultaneously study the closest and optically brightest sources of our sample in a joint-likelihood analysis in three different time windows (1 year, 6 months and 3 months). For the most promising source of the sample, SN 2010jl (PTF10aaxf), we repeat the analysis with an extended time window lasting 4.5 years. We do not find a significant excess in gamma rays for any individual source nor for the combined sources and provide model-independent flux upper limits for both cases. In addition, we derive limits on the gamma-ray luminosity and the ratio of gamma-ray-to-optical luminosity ratio as a function of the index of the proton injection spectrum assuming a generic gamma-ray production model. Furthermore, we present detailed flux predictions based on multi-wavelength observations and the corresponding flux upper limit at 95% confidence level (CL) for the source SN 2010jl (PTF10aaxf)., Comment: Accepted for publication in ApJ. Corresponding author: A. Franckowiak (afrancko@slac.stanford.edu), updated author list and acknowledgements
Published: 2015
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38. Characterization of the Inner Knot of the Crab: The Site of the Gamma-ray Flares?

Author: Rudy, A., Horns, D., DeLuca, A., Kolodziejczak, J., Tennant, A., Yuan, Y., Buehler, R., Arons, J., Blandford, R., Caraveo, P., Costa, E., Funk, S., Hays, E., Lobanov, A., Max, C., Mayer, M., Mignani, R., O'Dell, S. L., Romani, R., Tavani, M., and Weisskopf, M. C.
Subjects: Astrophysics - High Energy Astrophysical Phenomena
Abstract: One of the most intriguing results from the gamma-ray instruments in orbit has been the detection of powerful flares from the Crab Nebula. These flares challenge our understanding of pulsar wind nebulae and models for particle acceleration. We report on the portion of a multiwavelength campaign using Keck, HST, and Chandra concentrating on a small emitting region, the Crab's inner knot, located a fraction of an arcsecond from the pulsar. We find that the knot's radial size, tangential size, peak flux, and the ratio of the flux to that of the pulsar are correlated with the projected distance of the knot from the pulsar. A new approach, using singular value decomposition for analyzing time series of images, was introduced yielding results consistent with the more traditional methods while some uncertainties were substantially reduced. We exploit the characterization of the knot to discuss constraints on standard shock-model parameters that may be inferred from our observations assuming the inner knot lies near to the shocked surface. These include inferences as to wind magnetization, shock shape parameters such as incident angle and poloidal radius of curvature, as well as the IR/optical emitting particle enthalpy fraction. We find that while the standard shock model gives good agreement with observation in many respects, there remain two puzzles: (a) The observed angular size of the knot relative to the pulsar--knot separation is much smaller than expected; (b) The variable, yet high degree of polarization reported is difficult to reconcile with a highly relativistic downstream flow., Comment: 46 pages, 14 figures, submitted to the Astrophysical Journal
Published: 2015
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39. Rapid Variability of Blazar 3C 279 during Flaring States in 2013-2014 with Joint Fermi-LAT, NuSTAR, Swift, and Ground-Based Multi-wavelength Observations

Author: Hayashida, M., Nalewajko, K., Madejski, G. M., Sikora, M., Itoh, R., Ajello, M., Blandford, R. D., Buson, S., Chiang, J., Fukazawa, Y., Furniss, A. K., Urry, C. M., Hasan, I., Harrison, F. A., Alexander, D. M., Baloković, M., Barret, D., Boggs, S. E., Christensen, F. E., Craig, W. W., Forster, K., Giommi, P., Grefenstette, B., Hailey, C., Hornstrup, A., Kitaguchi, T., Koglin, J. E., Madsen, K. K., Mao, P. H., Miyasaka, H., Mori, K., Perri, M., Pivovaroff, M. J., Puccetti, S., Rana, V., Stern, D., Tagliaferri, G., Westergaard, N. J., Zhang, W. W., Zoglauer, A., Gurwell, M. A., Uemura, M., Akitaya, H., Kawabata, K. S., Kawaguch, K., Kanda, Y., Moritani, Y., Takaki, K., Ui, T., Yoshida, M., Agarwal, A., and Gupta, A. C.
Subjects: Astrophysics - High Energy Astrophysical Phenomena, Astrophysics - Astrophysics of Galaxies
Abstract: We report the results of a multi-band observing campaign on the famous blazar 3C 279 conducted during a phase of increased activity from 2013 December to 2014 April, including first observations of it with NuSTAR. The $\gamma$-ray emission of the source measured by Fermi-LAT showed multiple distinct flares reaching the highest flux level measured in this object since the beginning of the Fermi mission, with $F(E > 100\,{\rm MeV})$ of $10^{-5}$ photons cm$^{-2}$ s$^{-1}$, and with a flux doubling time scale as short as 2 hours. The $\gamma$-ray spectrum during one of the flares was very hard, with an index of $\Gamma_\gamma = 1.7 \pm 0.1$, which is rarely seen in flat spectrum radio quasars. The lack of concurrent optical variability implies a very high Compton dominance parameter $L_\gamma/L_{\rm syn} > 300$. Two 1-day NuSTAR observations with accompanying Swift pointings were separated by 2 weeks, probing different levels of source activity. While the 0.5$-$70 keV X-ray spectrum obtained during the first pointing, and fitted jointly with Swift-XRT is well-described by a simple power law, the second joint observation showed an unusual spectral structure: the spectrum softens by $\Delta\Gamma_{\rm X} \simeq 0.4$ at $\sim$4 keV. Modeling the broad-band SED during this flare with the standard synchrotron plus inverse Compton model requires: (1) the location of the $\gamma$-ray emitting region is comparable with the broad line region radius, (2) a very hard electron energy distribution index $p \simeq 1$, (3) total jet power significantly exceeding the accretion disk luminosity $L_{\rm j}/L_{\rm d} \gtrsim 10$, and (4) extremely low jet magnetization with $L_{\rm B}/L_{\rm j} \lesssim 10^{-4}$. We also find that single-zone models that match the observed $\gamma$-ray and optical spectra cannot satisfactorily explain the production of X-ray emission., Comment: 17 pages, 10 figures, accepted for publication in The Astrophysical Journal
Published: 2015
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40. The Third Catalog of Active Galactic Nuclei Detected by the Fermi Large Area Telescope

Author: Ackermann, M., Ajello, M., Atwood, W., Baldini, L., Ballet, J., Barbiellini, G., Bastieri, D., Gonzalez, J., Bellazzini, R., Bissaldi, E., Blandford, R., Bloom, E., Bonino, R., Bottacini, E., Brandt, T., Bregeon, J., Britto, R., Bruel, P., Buehler, R., Buson, S., Caliandro, G., Cameron, R., Caragiulo, M., Caraveo, P., Casandjian, J., Cavazzuti, E., Cecchi, C., Charles, E., Chekhtman, A., Cheung, C., Chiang, J., Chiaro, G., Ciprini, S., Claus, R., Cohen-Tanugi, J., Cominsky, L., Conrad, J., Cutini, S., D'Abrusco, R., D'Ammando, F., Angelis, A., Desiante, R., Digel, S., Venere, L., Drell, P., Favuzzi, C., Fegan, S., Ferrara, E., Finke, J., Focke, W., Franckowiak, A., Fuhrmann, L., Furniss, A., Fusco, P., Gargano, F., Gasparrini, D., Giglietto, N., Giommi, P., Giordano, F., Giroletti, M., Glanzman, T., Godfrey, G., Grenier, I., Grove, J., Guiriec, S., Hewitt, J. W., Hill, A., Horan, D., J'ohannesson, G., Johnson, A., Johnson, W., Kataoka, J., Kuss, M., Mura, G., Larsson, S., Latronico, L., Leto, C., Li, J., Li, L., Longo, F., Loparco, F., Lott, B., Lovellette, M., Lubrano, P., Madejski, G., Mayer, M., Mazziotta, M., McEnery, J., Michelson, P., Mizuno, T., Moiseev, A., Monzani, M., Morselli, A., Moskalenko, I., Murgia, S., Nuss, E., Ohno, M., Ohsugi, T., Ojha, R., Omodei, N., Orienti, M., Orlando, E., Paggi, A., Paneque, D., Perkins, J., Pesce-Rollins, M., Piron, F., Pivato, G., Porter, T., Rain`o, S., Rando, R., Razzano, M., Razzaque, S., Reimer, A., Reimer, O., Romani, R., Salvetti, D., Schaal, M., Schinzel, F., Schulz, A., Sgr`o, C., Siskind, E., Sokolovsky, K., Spada, F., Spandre, G., Spinelli, P., Stawarz, L., Suson, D., Takahashi, H., Takahashi, T., Tanaka, Y., Thayer, J., Tibaldo, L., Torres, D., Torresi, E., Tosti, G., Troja, E., Uchiyama, Y., Vianello, G., Winer, B., Wood, K., and Zimmer, S.
Subjects: Astrophysics - High Energy Astrophysical Phenomena
Abstract: The third catalog of active galactic nuclei (AGNs) detected by the Fermi-LAT (3LAC) is presented. It is based on the third Fermi-LAT catalog (3FGL) of sources detected between 100 MeV and 300 GeV with a Test Statistic (TS) greater than 25, between 2008 August 4 and 2012 July 31. The 3LAC includes 1591 AGNs located at high Galactic latitudes (|b|>10{\deg}), a 71% increase over the second catalog based on 2 years of data. There are 28 duplicate associations, thus 1563 of the 2192 high-latitude gamma-ray sources of the 3FGL catalog are AGNs. Most of them (98%) are blazars. About half of the newly detected blazars are of unknown type, i.e., they lack spectroscopic information of sufficient quality to determine the strength of their emission lines. Based on their gamma-ray spectral properties, these sources are evenly split between flat-spectrum radio quasars (FSRQs) and BL~Lacs. The most abundant detected BL~Lacs are of the high-synchrotron-peaked (HSP) type. About 50% of the BL~Lacs have no measured redshifts. A few new rare outliers (HSP-FSRQs and high-luminosity HSP BL~Lacs) are reported. The general properties of the 3LAC sample confirm previous findings from earlier catalogs. The fraction of 3LAC blazars in the total population of blazars listed in BZCAT remains non-negligible even at the faint ends of the BZCAT-blazar radio, optical and X-ray flux distributions, which is a clue that even the faintest known blazars could eventually shine in gamma rays at LAT-detection levels. The energy-flux distributions of the different blazar populations are in good agreement with extrapolation from earlier catalogs., Comment: Accepted by ApJ. Updated to published version
Published: 2015
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41. Compact Symmetric Objects. III. Evolution of the High-luminosity Branch and a Possible Connection with Tidal Disruption Events

Author: Readhead, A. C. S, primary, Ravi, V., additional, Blandford, R. D., additional, Sullivan, A. G., additional, Somalwar, J., additional, Begelman, M. C., additional, Birkinshaw, M., additional, Liodakis, I., additional, Lister, M. L., additional, Pearson, T. J., additional, Taylor, G. B., additional, Wilkinson, P. N., additional, Globus, N., additional, Kiehlmann, S., additional, Lawrence, C. R., additional, Murphy, D., additional, O’Neill, S., additional, Pavlidou, V., additional, Sheldahl, E., additional, Siemiginowska, A., additional, and Tassis, K., additional
Published: 2024
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42. Gamma-ray flaring activity from the gravitationally lensed blazar PKS 1830-211 observed by Fermi LAT

Author: The Fermi LAT Collaboration, Abdo, A. A., Ackermann, M., Ajello, M., Allafort, A., Amin, M. A., Baldini, L., Barbiellini, G., Bastieri, D., Bechtol, K., Bellazzini, R., Blandford, R. D., Bonamente, E., Borgland, A. W., Bregeon, J., Brigida, M., Buehler, R., Bulmash, D., Buson, S., Caliandro, G. A., Cameron, R. A., Caraveo, P. A., Cavazzuti, E., Cecchi, C., Charles, E., Cheung, C. C., Chiang, J., Chiaro, G., Ciprini, S., Claus, R., Cohen-Tanugi, J., Conrad, J., Corbet, R. H. D., Cutini, S., D'Ammando, F., de Angelis, A., de Palma, F., Dermer, C. D., Drell, P. S., Drlica-Wagner, A., Favuzzi, C., Finke, J., Focke, W. B., Fukazawa, Y., Fusco, P., Gargano, F., Gasparrini, D., Gehrels, N., Giglietto, N., Giordano, F., Giroletti, M., Glanzman, T., Grenier, I. A., Grove, J. E., Guiriec, S., Hadasch, D., Hayashida, M., Hays, E., Hughes, R. E., Inoue, Y., Jackson, M. S., Jogler, T., Jòhannesson, G., Johnson, A. S., Kamae, T., Knödlseder, J., Kuss, M., Lande, J., Larsson, S., Latronico, L., Longo, F., Loparco, F., Lott, B., Lovellette, M. N., Lubrano, P., Madejski, G. M., Mazziotta, M. N., Mehault, J., Michelson, P. F., Mizuno, T., Monzani, M. E., Morselli, A., Moskalenko, I. V., Murgia, S., Nemmen, R., Nuss, E., Ohno, M., Ohsugi, T., Paneque, D., Perkins, J. S., Pesce-Rollins, M., Piron, F., Pivato, G., Porter, T. A., Rainò, S., Rando, R., Razzano, M., Reimer, A., Reimer, O., Reyes, L. C., Ritz, S., Romoli, C., Roth, M., Parkinson, P. M. Saz, Sgrò, C., Siskind, E. J., Spandre, G., Spinelli, P., Takahashi, H., Takeuchi, Y., Tanaka, T., Thayer, J. G., Thayer, J. B., Thompson, D. J., Tibaldo, L., Tinivella, M., Torres, D. F., Tosti, G., Troja, E., Tronconi, V., Usher, T. L., Vandenbroucke, J., Vasileiou, V., Vianello, G., Vitale, V., Waite, A. P., Werner, M., Winer, B. L., and Wood, K. S.
Subjects: Astrophysics - High Energy Astrophysical Phenomena
Abstract: The Large Area Telescope (LAT) on board the Fermi Gamma-ray Space Telescope routinely detects the highly dust-absorbed, reddened, and MeV-peaked flat spectrum radio quasar PKS 1830-211 (z=2.507). Its apparent isotropic gamma-ray luminosity (E>100 MeV) averaged over $\sim$ 3 years of observations and peaking on 2010 October 14/15 at 2.9 X 10^{50} erg s^{-1}, makes it among the brightest high-redshift Fermi blazars. No published model with a single lens can account for all of the observed characteristics of this complex system. Based on radio observations, one expects time delayed variability to follow about 25 days after a primary flare, with flux about a factor 1.5 less. Two large gamma-ray flares of PKS 1830-211 have been detected by the LAT in the considered period and no substantial evidence for such a delayed activity was found. This allows us to place a lower limit of about 6 on the gamma rays flux ratio between the two lensed images. Swift XRT observations from a dedicated Target of Opportunity program indicate a hard spectrum and with no significant correlation of X-ray flux with the gamma-ray variability. The spectral energy distribution can be modeled with inverse Compton scattering of thermal photons from the dusty torus. The implications of the LAT data in terms of variability, the lack of evident delayed flare events, and different radio and gamma-ray flux ratios are discussed. Microlensing effects, absorption, size and location of the emitting regions, the complex mass distribution of the system, an energy-dependent inner structure of the source, and flux suppression by the lens galaxy for one image path may be considered as hypotheses for understanding our results., Comment: 14 pages, 6 figures, 2 tables. Accepted by the The Astrophysical Journal. Corresponding authors: S. Ciprini (ASI ASDC & INAF OAR, Rome, Italy), S. Buson (INAF Padova & Univ. of Padova, Padova, Italy), J. Finke (NRL, Washington, DC, USA), F. D'Ammando (INAF IRA, Bologna, Italy)
Published: 2014
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43. The spectrum of isotropic diffuse gamma-ray emission between 100 MeV and 820 GeV

Author: The Fermi LAT collaboration, Ackermann, M., Ajello, M., Albert, A., Atwood, W. B., Baldini, L., Ballet, J., Barbiellini, G., Bastieri, D., Bechtol, K., Bellazzini, R., Bissaldi, E., Blandford, R. D., Bloom, E. D., Bottacini, E., Brandt, T. J., Bregeon, J., Bruel, P., Buehler, R., Buson, S., Caliandro, G. A., Cameron, R. A., Caragiulo, M., Caraveo, P. A., Cavazzuti, E., Cecchi, C., Charles, E., Chekhtman, A., Chiang, J., Chiaro, G., Ciprini, S., Claus, R., Cohen-Tanugi, J., Conrad, J., Cuoco, A., Cutini, S., D'Ammando, F., de Angelis, A., de Palma, F., Dermer, C. D., Digel, S. W., Silva, E. do Couto e, Drell, P. S., Favuzzi, C., Ferrara, E. C., Focke, W. B., Franckowiak, A., Fukazawa, Y., Funk, S., Fusco, P., Gargano, F., Gasparrini, D., Germani, S., Giglietto, N., Giommi, P., Giordano, F., Giroletti, M., Godfrey, G., Gomez-Vargas, G. A., Grenier, I. A., Guiriec, S., Gustafsson, M., Hadasch, D., Hayashi, K., Hays, E., Hewitt, J. W., Ippoliti, P., Jogler, T., Jóhannesson, G., Johnson, A. S., Johnson, W. N., Kamae, T., Kataoka, J., Knödlseder, J., Kuss, M., Larsson, S., Latronico, L., Li, J., Li, L., Longo, F., Loparco, F., Lott, B., Lovellette, M. N., Lubrano, P., Madejski, G. M., Manfreda, A., Massaro, F., Mayer, M., Mazziotta, M. N., McEnery, J. E., Michelson, P. F., Mitthumsiri, W., Mizuno, T., Moiseev, A. A., Monzani, M. E., Morselli, A., Moskalenko, I. V., Murgia, S., Nemmen, R., Nuss, E., Ohsugi, T., Omodei, N., Orlando, E., Ormes, J. F., Paneque, D., Panetta, J. H., Perkins, J. S., Pesce-Rollins, M., Piron, F., Pivato, G., Porter, T. A., Rainò, S., Rando, R., Razzano, M., Razzaque, S., Reimer, A., Reimer, O., Reposeur, T., Ritz, S., Romani, R. W., Sánchez-Conde, M., Schaal, M., Schulz, A., Sgrò, C., Siskind, E. J., Spandre, G., Spinelli, P., Strong, A. W., Suson, D. J., Takahashi, H., Thayer, J. G., Thayer, J. B., Tibaldo, L., Tinivella, M., Torres, D. F., Tosti, G., Troja, E., Uchiyama, Y., Vianello, G., Werner, M., Winer, B. L., Wood, K. S., Wood, M., Zaharijas, G., and Zimmer, S.
Subjects: Astrophysics - High Energy Astrophysical Phenomena
Abstract: The {\gamma}-ray sky can be decomposed into individually detected sources, diffuse emission attributed to the interactions of Galactic cosmic rays with gas and radiation fields, and a residual all-sky emission component commonly called the isotropic diffuse {\gamma}-ray background (IGRB). The IGRB comprises all extragalactic emissions too faint or too diffuse to be resolved in a given survey, as well as any residual Galactic foregrounds that are approximately isotropic. The first IGRB measurement with the Large Area Telescope (LAT) on board the Fermi Gamma-ray Space Telescope (Fermi) used 10 months of sky-survey data and considered an energy range between 200 MeV and 100 GeV. Improvements in event selection and characterization of cosmic-ray backgrounds, better understanding of the diffuse Galactic emission, and a longer data accumulation of 50 months, allow for a refinement and extension of the IGRB measurement with the LAT, now covering the energy range from 100 MeV to 820 GeV. The IGRB spectrum shows a significant high-energy cutoff feature, and can be well described over nearly four decades in energy by a power law with exponential cutoff having a spectral index of $2.32\pm0.02$ and a break energy of $(279\pm52)$ GeV using our baseline diffuse Galactic emission model. The total intensity attributed to the IGRB is $(7.2\pm0.6) \times 10^{-6}$ cm$^{-2}$ s$^{-1}$ sr$^{-1}$ above 100 MeV, with an additional $+15$%/$-30$% systematic uncertainty due to the Galactic diffuse foregrounds., Comment: Accepted by The Astrophysical Journal
Published: 2014
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44. The variability of the Crab Nebula in radio: No radio counterpart to gamma-ray flares

Author: Bietenholz, Michael F., Yuan, Y., Buehler, R., Lobanov, A. P., and Blandford, R.
Subjects: Astrophysics - Solar and Stellar Astrophysics, Astrophysics - High Energy Astrophysical Phenomena
Abstract: We present new Jansky Very Large Array (VLA) radio images of the Crab Nebula at 5.5 GHz, taken at two epochs separated by 6 days about two months after a gamma-ray flare in 2012 July. We find no significant change in the Crab's radio emission localized to a region of <2 light-months in radius, either over the 6-day interval between our present observations or between the present observations and ones from 2001. Any radio counterpart to the flare has a radio luminosity of <~ $2 \times 10^{-4}$ times that of the nebula. Comparing our images to one from 2001, we do however find changes in radio brightness, up to 10% in amplitude, which occur on decade timescales throughout the nebula. The morphology of the changes is complex suggesting both filamentary and knotty structures. The variability is stronger, and the timescales likely somewhat shorter, nearer the centre of the nebula. We further find that even with the excellent uv~coverage and signal-to-noise of the VLA, deconvolution errors are much larger than the noise, being up to 1.2% of peak brightness of the nebula in this particular case., Comment: Accepted to MNRAS; 13 pages, 6 figures
Published: 2014
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45. Inferred cosmic-ray spectrum from ${\it Fermi}$-LAT $\gamma$-ray observations of the Earth's limb

Author: Collaboration, Fermi-LAT, Ackermann, M., Ajello, M., Albert, A., Allafort, A., Baldini, L., Barbiellini, G., Bastieri, D., Bechtol, K., Bellazzini, R., Blandford, R. D., Bloom, E. D., Bonamente, E., Bottacini, E., Bouvier, A., Brandt, T. J., Brigida, M., Bruel, P., Buehler, R., Buson, S., Caliandro, G. A., Cameron, R. A., Caraveo, P. A., Cecchi, C., Charles, E., Chaves, R. C. G., Chekhtman, A., Chiang, J., Chiaro, G., Ciprini, S., Claus, R., Cohen-Tanugi, J., Conrad, J., Cutini, S., Dalton, M., D'Ammando, F., de Angelis, A., de Palma, F., Dermer, C. D., Digel, S. W., Di Venere, L., Silva, E. do Couto e, Drell, P. S., Drlica-Wagner, A., Favuzzi, C., Fegan, S. J., Ferrara, E. C., Focke, W. B., Franckowiak, A., Fukazawa, Y., Funk, S., Fusco, P., Gargano, F., Gasparrini, D., Germani, S., Giglietto, N., Giordano, F., Giroletti, M., Glanzman, T., Godfrey, G., Gomez-Vargas, G. A., Grenier, I. A., Grove, J. E., Guiriec, S., Gustafsson, M., Hadasch, D., Hanabata, Y., Harding, A. K., Hayashida, M., Hayashi, K., Hewitt, J. W., Horan, D., Hou, X., Hughes, R. E., Inoue, Y., Jackson, M. S., Jogler, T., Jóhannesson, G., Johnson, A. S., Kamae, T., Kawano, T., Knödlseder, J., Kuss, M., Lande, J., Larsson, S., Latronico, L., Longo, F., Loparco, F., Lovellette, M. N., Lubrano, P., Mayer, M., Mazziotta, M. N., McEnery, J. E., Mehault, J., Michelson, P. F., Mitthumsiri, W., Mizuno, T., Moiseev, A. A., Monte, C., Monzani, M. E., Morselli, A., Moskalenko, I. V., Murgia, S., Nemmen, R., Nuss, E., Ohsugi, T., Okumura, A., Orienti, M., Orlando, E., Ormes, J. F., Paneque, D., Panetta, J. H., Perkins, J. S., Pesce-Rollins, M., Piron, F., Pivato, G., Porter, T. A., Rainò, S., Rando, R., Razzano, M., Razzaque, S., Reimer, A., Reimer, O., Ritz, S., Roth, M., Schaal, M., Schulz, A., Sgrò, C., Siskind, E. J., Spandre, G., Spinelli, P., Strong, A. W., Takahashi, H., Takeuchi, Y., Thayer, J. G., Thayer, J. B., Thompson, D. J., Tibaldo, L., Tinivella, M., Torres, D. F., Tosti, G., Troja, E., Tronconi, V., Usher, T. L., Vandenbroucke, J., Vasileiou, V., Vianello, G., Vitale, V., Werner, M., Winer, B. L., Wood, K. S., Wood, M., and Yang, Z.
Subjects: Astrophysics - High Energy Astrophysical Phenomena
Abstract: Recent accurate measurements of cosmic-ray (CR) species by ATIC-2, CREAM, and PAMELA reveal an unexpected hardening in the proton and He spectra above a few hundred GeV, a gradual softening of the spectra just below a few hundred GeV, and a harder spectrum of He compared to that of protons. These newly-discovered features may offer a clue to the origin of high-energy CRs. We use the ${\it Fermi}$ Large Area Telescope observations of the $\gamma$-ray emission from the Earth's limb for an indirect measurement of the local spectrum of CR protons in the energy range $\sim 90~$GeV-$6~$TeV (derived from a photon energy range $15~$GeV-$1~$TeV). Our analysis shows that single power law and broken power law spectra fit the data equally well and yield a proton spectrum with index $2.68 \pm 0.04$ and $2.61 \pm 0.08$ above $\sim 200~$GeV, respectively., Comment: Accepted by PRL for publication; Contact authors: Stefan Funk, Warit Mitthumsiri, Igor Moskalenko; 2 figures
Published: 2014

46. Fermi-LAT Detection of Gravitational Lens Delayed Gamma-ray Flares from Blazar B0218+357

Author: Cheung, C. C., Larsson, S., Scargle, J. D., Amin, M. A., Blandford, R. D., Bulmash, D., Chiang, J., Ciprini, S., Corbet, R. H. D., Falco, E. E., Marshall, P. J., Wood, D. L., Ajello, M., Bastieri, D., Chekhtman, A., D'Ammando, F., Giroletti, M., Grove, J. E., Lott, B., Ojha, R., Orienti, M., Perkins, J. S., Razzano, M., Smith, A. W., Thompson, D. J., and Wood, K. S.
Subjects: Astrophysics - High Energy Astrophysical Phenomena
Abstract: Using data from the Fermi Large Area Telescope (LAT), we report the first clear gamma-ray measurement of a delay between flares from the gravitationally lensed images of a blazar. The delay was detected in B0218+357, a known double-image lensed system, during a period of enhanced gamma-ray activity with peak fluxes consistently observed to reach >20-50 times its previous average flux. An auto-correlation function analysis identified a delay in the gamma-ray data of 11.46 +/- 0.16 days (1 sigma) that is ~1 day greater than previous radio measurements. Considering that it is beyond the capabilities of the LAT to spatially resolve the two images, we nevertheless decomposed individual sequences of superposing gamma-ray flares/delayed emissions. In three such ~8-10 day-long sequences within a ~4-month span, considering confusion due to overlapping flaring emission and flux measurement uncertainties, we found flux ratios consistent with ~1, thus systematically smaller than those from radio observations. During the first, best-defined flare, the delayed emission was detailed with a Fermi pointing, and we observed flux doubling timescales of ~3-6 hrs implying as well extremely compact gamma-ray emitting regions., Comment: ApJL, accepted for publication, 7 pages, 4 figures
Published: 2014
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47. First Results from NuSTAR Observations of Mkn 421

Author: Baloković, M., Ajello, M., Blandford, R. D., Boggs, S. E., Borracci, F., Chiang, J., Christensen, F. E., Craig, W. W., Forster, K., Furniss, A., Fuerst, F., Ghisellini, G., Giebels, B., Giommi, P., Grefenstette, B. W., Hailey, C. J., Harrison, F. A., Hayashida, M., Humensky, B., Inoue, Y., Koglin, J. E., Krawczynski, H., Madejski, G. M., Madsen, K. K., Meier, D. L., Nelson, T., Ogle, P., Paneque, D., Perri, M., Puccetti, S., Reynolds, C. S., Sbarrato, T., Stern, D., Tagliaferri, G., Urry, C. M., Wehrle, A. E., and Zhang, W. W.
Subjects: Astrophysics - High Energy Astrophysical Phenomena
Abstract: Mkn 421 is a nearby active galactic nucleus dominated at all wavelengths by a very broad non-thermal continuum thought to arise from a relativistic jet seen at a small angle to the line of sight. Its spectral energy distribution peaks in the X-ray and TeV gamma-ray bands, where the energy output is dominated by cooling of high-energy electrons in the jet. In order to study the electron distribution and its evolution, we carried out a dedicated multi-wavelength campaign, including extensive observations by the recently launched highly sensitive hard X-ray telescope NuSTAR, between December 2012 and May 2013. Here we present some initial results based on NuSTAR data from January through March 2013, as well as calibration observations conducted in 2012. Although the observations cover some of the faintest hard X-ray flux states ever observed for Mkn 421, the sensitivity is high enough to resolve intra-day spectral variability. We find that in this low state the dominant flux variations are smooth on timescales of hours, with typical intra-hour variations of less than 5%. We do not find evidence for either a cutoff in the hard X-ray spectrum, or a rise towards a high-energy component, but rather that at low flux the spectrum assumes a power law shape with a photon index of approximately 3. The spectrum is found to harden with increasing brightness., Comment: 4 pages, 4 figures; to appear in "The Innermost Regions of Relativistic Jets and Their Magnetic Fields" conference proceedings; updated with minor corrections
Published: 2013
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48. Constraints on the Galactic Population of TEV Pulsar Wind Nebulae Using Fermi Large Area Telescope Observations

Author: Acero, F., Ackermann, M., Ajello, M., Allafort, A., Baldini, L., Ballet, J., Barbiellini, G., Bastieri, D., Bechtol, K., Bellazzini, R., Blandford, R. D., Bloom, E. D., Bonamente, E., Bottacini, E., Brandt, T. J., Bregeon, J., Brigida, M., Bruel, P., Buehler, R., Buson, S., Caliandro, G. A., Cameron, R. A., Caraveo, P. A., Cecchi, C., Charles, E., Chaves, R. C. G., Chekhtman, A., Chiang, J., Chiaro, G., Ciprini, S., Claus, R., Cohen-Tanugi, J., Conrad, J., Cutini, S., Dalton, M., D'Ammando, F., de Palma, F., Dermer, C. D., Di Venere, L., Silva, E. do Couto e, Drell, P. S., Drlica-Wagner, A., Falletti, L., Favuzzi, C., Fegan, S. J., Ferrara, E. C., Focke, W. B., Franckowiak, A., Fukazawa, Y., Funk, S., Fusco, P., Gargano, F., Gasparrini, D., Giglietto, N., Giordano, F., Giroletti, M., Glanzman, T., Godfrey, G., Grégoire, T., Grenier, I. A., Grondin, M. -H., Grove, J. E., Guiriec, S., Hadasch, D., Hanabata, Y., Harding, A. K., Hayashida, M., Hayashi, K., Hays, E., Hewitt, J., Hill, A. B., Horan, D., Hou, X., Hughes, R. E., Inoue, Y., Jackson, M. S., Jogler, T., Jóhannesson, G., Johnson, A. S., Kamae, T., Kawano, T., Kerr, M., Knödlseder, J., Kuss, M., Lande, J., Larsson, S., Latronico, L., Lemoine-Goumard, M., Longo, F., Loparco, F., Lovellette, M. N., Lubrano, P., Marelli, M., Massaro, F., Mayer, M., Mazziotta, M. N., McEnery, J. E., Mehault, J., Michelson, P. F., Mitthumsiri, W., Mizuno, T., Monte, C., Monzani, M. E., Morselli, A., Moskalenko, I. V., Murgia, S., Nakamori, T., Nemmen, R., Nuss, E., Ohsugi, T., Okumura, A., Orienti, M., Orlando, E., Ormes, J. F., Paneque, D., Panetta, J. H., Perkins, J. S., Pesce-Rollins, M., Piron, F., Pivato, G., Porter, T. A., Rainò, S., Rando, R., Razzano, M., Reimer, A., Reimer, O., Reposeur, T., Ritz, S., Roth, M., Rousseau, R., Parkinson, P. M. Saz, Schulz, A., Sgrò, C., Siskind, E. J., Smith, D. A., Spandre, G., Spinelli, P., Suson, D. J., Takahashi, H., Takeuchi, Y., Thayer, J. G., Thayer, J. B., Thompson, D. J., Tibaldo, L., Tibolla, O., Tinivella, M., Torres, D. F., Tosti, G., Troja, E., Uchiyama, Y., Vandenbroucke, J., Vasileiou, V., Vianello, G., Vitale, V., Werner, M., Winer, B. L., Wood, K. S., and Yang, Z.
Subjects: Astrophysics - High Energy Astrophysical Phenomena
Abstract: Pulsar wind nebulae (PWNe) have been established as the most populous class of TeV gamma-ray emitters. Since launch, the Fermi Large Area Telescope (LAT)identified five high-energy (100MeV
Published: 2013
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49. Cosmology from gravitational lens time delays and Planck data

Author: Suyu, S. H., Treu, T., Hilbert, S., Sonnenfeld, A., Auger, M. W., Blandford, R. D., Collett, T., Courbin, F., Fassnacht, C. D., Koopmans, L. V. E., Marshall, P. J., Meylan, G., Spiniello, C., and Tewes, M.
Subjects: Astrophysics - Cosmology and Nongalactic Astrophysics
Abstract: Under the assumption of a flat Lambda-CDM cosmology, recent data from the Planck satellite point toward a Hubble constant that is in tension with that measured by gravitational lens time delays and by the local distance ladder. Prosaically, this difference could arise from unknown systematic uncertainties in some of the measurements. More interestingly -- if systematics were ruled out -- resolving the tension would require a departure from the flat Lambda-CDM cosmology, introducing for example a modest amount of spatial curvature, or a non-trivial dark energy equation of state. To begin to address these issues, we present here an analysis of the gravitational lens RXJ1131-1231 that is improved in one particular regard: we examine the issue of systematic error introduced by an assumed lens model density profile. We use more flexible gravitational lens models with baryonic and dark matter components, and find that the exquisite Hubble Space Telescope image with thousands of intensity pixels in the Einstein ring and the stellar velocity dispersion of the lens contain sufficient information to constrain these more flexible models. The total uncertainty on the time-delay distance is 6.6% for a single system. We proceed to combine our improved time-delay distance measurements with the WMAP9 and Planck posteriors. In an open Lambda-CDM model, the data for RXJ1131-1231 in combination with Planck favor a flat universe with Omega_k = 0.00+0.01/-0.02 (68% CI). In a flat wCDM model, the combination of RXJ1131-1231 and Planck yields w = -1.52+0.19/-0.20 (68% CI)., Comment: 6 pages, 5 figures, accepted for publication in ApJL
Published: 2013
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50. Detection of the Characteristic Pion-Decay Signature in Supernova Remnants

Author: collaboration, The Fermi-LAT, Ackermann, M., Ajello, M., Allafort, A., Baldini, L., Ballet, J., Barbiellini, G., Baring, M. G., Bastieri, D., Bechtol, K., Bellazzini, R., Blandford, R. D., Bloom, E. D., Bonamente, E., Borgland, A. W., Bottacini, E., Brandt, T. J., Bregeon, J., Brigida, M., Bruel, P., Buehler, R., Busetto, G., Buson, S., Caliandro, G. A., Cameron, R. A., Caraveo, P. A., Casandjian, J. M., Cecchi, C., Çelik, Ö., Charles, E., Chaty, S., Chaves, R. C. G., Chekhtman, A., Cheung, C. C., Chiang, J., Chiaro, G., Cillis, A. N., Ciprini, S., Claus, R., Cohen-Tanugi, J., Cominsky, L. R., Conrad, J., Corbel, S., Cutini, S., D'Ammando, F., de Angelis, A., de Palma, F., Dermer, C. D., Silva, E. do Couto e, Drell, P. S., Drlica-Wagner, A., Falletti, L., Favuzzi, C., Ferrara, E. C., Franckowiak, A., Fukazawa, Y., Funk, S., Fusco, P., Gargano, F., Germani, S., Giglietto, N., Giommi, P., Giordano, F., Giroletti, M., Glanzman, T., Godfrey, G., Grenier, I. A., Grondin, M. -H., Grove, J. E., Guiriec, S., Hadasch, D., Hanabata, Y., Harding, A. K., Hayashida, M., Hayashi, K., Hays, E., Hewitt, J., Hill, A. B., Hughes, R. E., Jackson, M. S., Jogler, T., Jóhannesson, G., Johnson, A. S., Kamae, T., Kataoka, J., Katsuta, J., Knödlseder, J., Kuss, M., Lande, J., Larsson, S., Latronico, L., Lemoine-Goumard, M., Longo, F., Loparco, F., Lovellette, M. N., Lubrano, P., Madejski, G. M., Massaro, F., Mayer, M., Mazziotta, M. N., McEnery, J. E., Mehault, J., Michelson, P. F., Mignani, R. P., Mitthumsiri, W., Mizuno, T., Moiseev, A. A., Monzani, M. E., Morselli, A., Moskalenko, I. V., Murgia, S., Nakamori, T., Nemmen, R., Nuss, E., Ohno, M., Ohsugi, T., Omodei, N., Orienti, M., Orlando, E., Ormes, J. F., Paneque, D., Perkins, J. S., Pesce-Rollins, M., Piron, F., Pivato, G., Rainò, S., Rando, R., Razzano, M., Razzaque, S., Reimer, A., Reimer, O., Ritz, S., Romoli, C., Sánchez-Conde, M., Schulz, A., Sgrò, C., Simeon, P. E., Siskind, E. J., Smith, D. A., Spandre, G., Spinelli, P., Stecker, F. W., Strong, A. W., Suson, D. J., Tajima, H., Takahashi, H., Takahashi, T., Tanaka, T., Thayer, J. G., Thayer, J. B., Thompson, D. J., Thorsett, S. E., Tibaldo, L., Tibolla, O., Tinivella, M., Troja, E., Uchiyama, Y., Usher, T. L., Vandenbroucke, J., Vasileiou, V., Vianello, G., Vitale, V., Waite, A. P., Werner, M., Winer, B. L., Wood, K. S., Wood, M., Yamazaki, R., Yang, Z., and Zimmer, S.
Subjects: Astrophysics - High Energy Astrophysical Phenomena, Astrophysics - Galaxy Astrophysics
Abstract: Cosmic rays are particles (mostly protons) accelerated to relativistic speeds. Despite wide agreement that supernova remnants (SNRs) are the sources of galactic cosmic rays, unequivocal evidence for the acceleration of protons in these objects is still lacking. When accelerated protons encounter interstellar material, they produce neutral pions, which in turn decay into gamma rays. This offers a compelling way to detect the acceleration sites of protons. The identification of pion-decay gamma rays has been difficult because high-energy electrons also produce gamma rays via bremsstrahlung and inverse Compton scattering. We detected the characteristic pion-decay feature in the gamma-ray spectra of two SNRs, IC 443 and W44, with the Fermi Large Area Telescope. This detection provides direct evidence that cosmic-ray protons are accelerated in SNRs., Comment: To appear in Science Magazine on February 15th; contact authors: Stefan Funk, Takaaki Tanaka, Yasunobu Uchiyama
Published: 2013
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