@article{AleksicAnsoldiAntonellietal.2015,
  author    = {Aleksic, J. and Ansoldi, S. and Antonelli, L. A. and Antoranz, P. and Babic, A. and Bangale, P. and de Almeida, U. Barres and Barrio, J. A. and Gonzalez, J. Becerra and Bednarek, W. and Bernardini, E. and Biasuzzi, B. and Biland, A. and Blanch Bigas, O. and Boller, A. and Bonnefoy, S. and Bonnoli, G. and Borracci, F. and Bretz, T. and Carmona, E. and Carosi, A. and Colin, P. and Colombo, E. and Contreras, J. L. and Cortina, J. and Covino, S. and Da Vela, P. and Dazzi, F. and De Angelis, A. and De Caneva, G. and De Lotto, B. and Wilhelmi, E. de Ona and Mendez, C. Delgado and Prester, Dijana Dominis and Dorner, D. and Doro, M. and Einecke, S. and Eisenacher, D. and Elsaesser, D. and Fonseca, M. V. and Font, L. and Frantzen, K. and Fruck, C. and Galindo, D. and Lopez, R. J. Garcia and Garczarczyk, M. and Terrats, D. Garrido and Gaug, M. and Godinovic, N. and Munoz, A. Gonzalez and Gozzini, S. R. and Hadasch, D. and Hanabata, Y. and Hayashida, M. and Herrera, J. and Hildebrand, D. and Hose, J. and Hrupec, D. and Hughes, G. and Idec, W. and Kadenius, V. and Kellermann, H. and Knoetig, M. L. and Kodani, K. and Konno, Y. and Krause, J. and Kubo, H. and Kushida, J. and La Barbera, A. and Lelas, D. and Lewandowska, N. and Lindfors, E. and Lombardi, S. and Lopez, M. and Lopez-Coto, R. and Lopez-Oramas, A. and Lorenz, E. and Lozano, I. and Makariev, M. and Mallot, K. and Maneva, G. and Mankuzhiyil, N. and Mannheim, K. and Maraschi, L. and Marcote, B. and Mariotti, M. and Martinez, M. and Mazin, D. and Menzel, U. and Miranda, J. M. and Mirzoyan, R. and Moralejo, A. and Munar-Adrover, P. and Nakajima, D. and Niedzwiecki, A. and Nilsson, K. and Nishijima, K. and Noda, K. and Orito, R. and Overkemping, A. and Paiano, S. and Palatiello, M. and Paneque, D. and Paoletti, R. and Paredes, J. M. and Paredes-Fortuny, X. and Persic, M. and Moroni, P. G. Prada and Prandini, E. and Puljak, I. and Reinthal, R. and Rhode, W. and Ribo, M. and Rico, J. and Garcia, J. Rodriguez and Rugamer, S. and Saito, T. and Saito, K. and Satalecka, K. and Scalzotto, V. and Scapin, V. and Schultz, C. and Schweizer, T. and Sun, S. and Shore, S. N. and Sillanpaa, A. and Sitarek, J. and Snidaric, I. and Sobczynska, D. and Spanier, F. and Stamatescu, V. and Stamerra, A. and Steinbring, T. and Steinke, B. and Storz, J. and Strzys, M. and Takalo, L. and Takami, H. and Tavecchio, F. and Temnikov, P. and Terzic, T. and Tescaro, D. and Teshima, M. and Thaele, J. and Tibolla, O. and Torres, D. F. and Toyama, T. and Treves, A. and Uellenbeck, M. and Vogler, P. and Zanin, R. and Archambault, S. and Archer, A. and Beilicke, M. and Benbow, W. and Berger, K. and Bird, R. and Biteau, Jonathan and Buckley, J. H. and Bugaev, V. and Cerruti, M. and Chen, Xiaoming and Ciupik, L. and Collins-Hughes, E. and Cui, W. and Eisch, J. D. and Falcone, A. and Feng, Q. and Finley, J. P. and Fortin, P. and Fortson, L. and Furniss, A. and Galante, N. and Gillanders, G. H. and Griffin, S. and Gyuk, G. and Hakansson, Nils and Holder, J. and Johnson, C. A. and Kaaret, P. and Kar, P. and Kertzman, M. and Kieda, D. and Lang, M. J. and McArthur, S. and McCann, A. and Meagher, K. and Millis, J. and Moriarty, P. and Ong, R. A. and Otte, A. N. and Perkins, J. S. and Pichel, A. and Pohl, Manuela and Popkow, A. and Prokoph, H. and Pueschel, Elisa and Ragan, K. and Reyes, L. C. and Reynolds, P. T. and Richards, G. T. and Roache, E. and Rovero, A. C. and Sembroski, G. H. and Shahinyan, K. and Staszak, D. and Telezhinsky, Igor O. and Tucci, J. V. and Tyler, J. and Varlotta, A. and Wakely, S. P. and Welsing, R. and Wilhelm, Alina and Williams, D. A. and Buson, S. and Finke, J. and Villata, M. and Raiteri, C. and Aller, H. D. and Aller, M. F. and Cesarini, A. and Chen, W. P. and Gurwell, M. A. and Jorstad, S. G. and Kimeridze, G. N. and Koptelova, E. and Kurtanidze, O. M. and Kurtanidze, S. O. and Lahteenmaki, A. and Larionov, V. M. and Larionova, E. G. and Lin, H. C. and McBreen, B. and Moody, J. W. and Morozova, D. A. and Marscher, A. P. and Max-Moerbeck, W. and Nikolashvili, M. G. and Perri, M. and Readhead, A. C. S. and Richards, J. L. and Ros, J. A. and Sadun, A. C. and Sakamoto, T. and Sigua, L. A. and Smith, P. S. and Tornikoski, M. and Troitsky, I. S. and Wehrle, A. E. and Jordan, B.},
  title     = {Unprecedented study of the broadband emission of Mrk 421 during flaring activity in March 2010},
  series = {Astronomy and astrophysics : an international weekly journal},
  volume    = {578},
  journal   = {Astronomy and astrophysics : an international weekly journal},
  publisher = {EDP Sciences},
  address   = {Les Ulis},
  organization    = {MAGIC Collaboration, VERITAS Collaboration},
  issn      = {0004-6361},
  doi       = {10.1051/0004-6361/201424811},
  pages     = {26},
  year      = {2015},
  abstract  = {Context. Because of its proximity, Mrk 421 is one of the best sources on which to study the nature of BL Lac objects. Its proximity allows us to characterize its broadband spectral energy distribution (SED). Aims. The goal is to better understand the mechanisms responsible for the broadband emission and the temporal evolution of Mrk 421. These mechanisms may also apply to more distant blazars that cannot be studied with the same level of detail. Methods. A flare occurring in March 2010 was observed for 13 consecutive days (from MJD 55 265 to MJD 55 277) with unprecedented wavelength coverage from radio to very high energy (VHE; E > 100 GeV) gamma-rays with MAGIC, VERITAS, Whipple, Fermi-LAT, MAXI, RXTE, Swift, GASP-WEBT, and several optical and radio telescopes. We modeled the day-scale SEDs with one-zone and two-zone synchrotron self-Compton (SSC) models, investigated the physical parameters, and evaluated whether the observed broadband SED variability can be associated with variations in the relativistic particle population. Results. The activity of Mrk 421 initially was high and then slowly decreased during the 13-day period. The flux variability was remarkable at the X-ray and VHE bands, but it was minor or not significant at the other bands. The variability in optical polarization was also minor. These observations revealed an almost linear correlation between the X-ray flux at the 2-10 keV band and the VHE gamma-ray flux above 200 GeV, consistent with the gamma-rays being produced by inverse-Compton scattering in the Klein-Nishina regime in the framework of SSC models. The one-zone SSC model can describe the SED of each day for the 13 consecutive days reasonably well, which once more shows the success of this standard theoretical scenario to describe the SEDs of VHE BL Lacs such as Mrk 421. This flaring activity is also very well described by a two-zone SSC model, where one zone is responsible for the quiescent emission, while the other smaller zone, which is spatially separated from the first, contributes to the daily variable emission occurring at X-rays and VHE gamma-rays. The second blob is assumed to have a smaller volume and a narrow electron energy distribution with 3 x 10(4) < gamma < 6 x 10(5), where. is the Lorentz factor of the electrons. Such a two-zone scenario would naturally lead to the correlated variability at the X-ray and VHE bands without variability at the optical/UV band, as well as to shorter timescales for the variability at the X-ray and VHE bands with respect to the variability at the other bands. Conclusions. Both the one-zone and the two-zone SSC models can describe the daily SEDs via the variation of only four or five model parameters, under the hypothesis that the variability is associated mostly with the underlying particle population. This shows that the particle acceleration and cooling mechanism that produces the radiating particles might be the main mechanism responsible for the broadband SED variations during the flaring episodes in blazars. The two-zone SSC model provides a better agreement with the observed SED at the narrow peaks of the low-and high-energy bumps during the highest activity, although the reported one-zone SSC model could be further improved by varying the parameters related to the emitting region itself (delta, B and R), in addition to the parameters related to the particle population.},
  language  = {en}
}
@article{AbdallaAbramowskiAharonianetal.2018,
  author    = {Abdalla, Hassan E. and Abramowski, A. and Aharonian, Felix A. and Benkhali, F. Ait and Ang{\"u}ner, Ekrem Oǧuzhan and Arakawa, M. and Armand, C. and Arrieta, M. and Backes, M. and Balzer, A. and Barnard, M. and Becherini, Y. and Tjus, J. Becker and Berge, D. and Bernhard, S. and Bernloehr, K. and Blackwell, R. and Bottcher, M. and Boisson, C. and Bolmont, J. and Bonnefoy, S. and Bordas, Pol and Bregeon, J. and Brun, F. and Brun, P. and Bryan, M. and Buechele, M. and Bulik, T. and Capasso, M. and Caroff, S. and Carosi, A. and Casanova, Sabrina and Cerruti, M. and Chakraborty, N. and Chaves, R. C. G. and Chen, A. and Chevalier, J. and Colafrancesco, S. and Condon, B. and Conrad, J. and Davids, I. D. and Decock, J. and Deil, C. and Devin, J. and deWilt, P. and Dirson, L. and Djannati-Atai, A. and Donath, A. and Dyks, J. and Edwards, T. and Egberts, Kathrin and Emery, G. and Ernenwein, J-P and Eschbach, S. and Farnier, C. and Fegan, S. and Fernandes, M. and Fiasson, A. and Fontaine, G. and Funk, S. and Fuessling, M. and Gabici, S. and Gallant, Y. A. and Garrigoux, T. and Gate, F. and Giavitto, G. and Glawion, D. and Glicenstein, J. F. and Gottschall, D. and Grondin, M-H and Hahn, J. and Haupt, M. and Hawkes, J. and Heinzelmann, G. and Henri, G. and Hermann, G. and Hinton, J. A. and Hofmann, W. and Hoischen, Clemens and Holch, T. L. and Holler, M. and Horns, D. and Ivascenko, A. and Iwasaki, H. and Jacholkowska, A. and Jamrozy, M. and Jankowsky, D. and Jankowsky, F. and Jingo, M. and Jouvin, L. and Jung-Richardt, I and Kastendieck, M. A. and Katarzynski, K. and Katsuragawa, M. and Katz, U. and Kerszberg, D. and Khangulyan, D. and Khelifi, B. and King, J. and Klepser, S. and Klochkov, D. and Kluzniak, W. and Komin, Nu and Kosack, K. and Krakau, S. and Kraus, M. and Kruger, P. P. and Laffon, H. and Lamanna, G. and Lau, J. and Lefaucheur, J. and Lemiere, A. and Lemoine-Goumard, M. and Lenain, J-P and Leser, Eva and Lohse, T. and Lorentz, M. and Liu, R. and Lopez-Coto, R. and Lypova, I and Malyshev, D. and Marandon, V and Marcowith, A. and Mariaud, C. and Marx, R. and Maurin, G. and Maxted, N. and Mayer, M. and Meintjes, P. J. and Meyer, M. and Mitchell, A. M. W. and Moderski, R. and Mohamed, M. and Mohrmann, L. and Mora, K. and Moulin, E. and Murach, T. and Nakashima, S. and de Naurois, M. and Ndiyavala, H. and Niederwanger, F. and Niemiec, J. and Oakes, L. and Odaka, H. and Ohm, S. and Ostrowski, M. and Oya, I and Padovani, M. and Panter, M. and Parsons, R. D. and Pekeur, N. W. and Pelletier, G. and Perennes, C. and Petrucci, P-O and Peyaud, B. and Piel, Q. and Pita, S. and Poireau, V and Prokhorov, D. A. and Prokoph, H. and Puehlhofer, G. and Punch, M. and Quirrenbach, A. and Raab, S. and Rauth, R. and Reimer, A. and Reimer, O. and Renaud, M. and de los Reyes, R. and Rieger, F. and Rinchiuso, L. and Romoli, C. and Rowell, G. and Rudak, B. and Rulten, C. B. and Sahakian, V and Saito, S. and Sanchez, D. A. and Santangelo, A. and Sasaki, M. and Schlickeiser, R. and Schussler, F. and Schulz, A. and Schwanke, U. and Schwemmer, S. and Seglar-Arroyo, M. and Seyffert, A. S. and Shafi, N. and Shilon, I and Shiningayamwe, K. and Simoni, R. and Sol, H. and Spanier, F. and Spir-Jacob, M. and Stawarz, L. and Steenkamp, R. and Stegmann, Christian and Steppa, Constantin Beverly and Sushch, Iurii and Takahashi, T. and Tavernet, J-P and Tavernier, T. and Taylor, A. M. and Terrier, R. and Tibaldo, L. and Tiziani, D. and Tluczykont, M. and Trichard, C. and Tsirou, M. and Tsuji, N. and Tuffs, R. and Uchiyama, Y. and van der Walt, D. J. and van Eldik, C. and van Rensburg, C. and van Soelen, B. and Vasileiadis, G. and Veh, J. and Venter, C. and Viana, A. and Vincent, P. and Vink, J. and Voisin, F. and Voelk, H. J. and Vuillaume, T. and Wadiasingh, Z. and Wagner, S. J. and Wagner, P. and Wagner, R. M. and White, R. and Wierzcholska, A. and Willmann, P. and Woernlein, A. and Wouters, D. and Yang, R. and Zaborov, D. and Zacharias, M. and Zanin, R. and Zdziarski, A. A. and Zech, Alraune and Zefi, F. and Ziegler, A. and Zorn, J. and Zywucka, N. and Magill, J. D. and Buson, S. and Cheung, C. C. and Perkins, J. S. and Tanaka, Y.},
  title     = {The gamma-ray spectrum of the core of Centaurus A as observed with HESS and Fermi-LAT},
  series = {Astronomy and astrophysics : an international weekly journal},
  volume    = {619},
  journal   = {Astronomy and astrophysics : an international weekly journal},
  publisher = {EDP Sciences},
  address   = {Les Ulis},
  organization    = {HESS Collaboration Fermi LAT Collaborators},
  issn      = {1432-0746},
  doi       = {10.1051/0004-6361/201832640},
  pages     = {10},
  year      = {2018},
  abstract  = {Centaurus A (Cen A) is the nearest radio galaxy discovered as a very-high-energy (VHE; 100 GeV-100 TeV) gamma-ray source by the High Energy Stereoscopic System (H.E.S.S.). It is a faint VHE gamma-ray emitter, though its VHE flux exceeds both the extrapolation from early Fermi-LAT observations as well as expectations from a (misaligned) single-zone synchrotron-self Compton (SSC) description. The latter satisfactorily reproduces the emission from Cen A at lower energies up to a few GeV. New observations with H.E.S.S., comparable in exposure time to those previously reported, were performed and eight years of Fermi-LAT data were accumulated to clarify the spectral characteristics of the gamma-ray emission from the core of Cen A. The results allow us for the first time to achieve the goal of constructing a representative, contemporaneous gamma-ray core spectrum of Cen A over almost five orders of magnitude in energy. Advanced analysis methods, including the template fitting method, allow detection in the VHE range of the core with a statistical significance of 12 sigma on the basis of 213 hours of total exposure time. The spectrum in the energy range of 250 GeV-6 TeV is compatible with a power-law function with a photon index Gamma = 2.52 +/- 0.13(stat) +/- 0.20(sys). An updated Fermi-LAT analysis provides evidence for spectral hardening by Delta Gamma similar or equal to 0.4 +/- 0.1 at gamma-ray energies above 2.8(-0.6)(+1.0) GeV at a level of 4.0 sigma. The fact that the spectrum hardens at GeV energies and extends into the VHE regime disfavour a single-zone SSC interpretation for the overall spectral energy distribution (SED) of the core and is suggestive of a new gamma-ray emitting component connecting the high-energy emission above the break energy to the one observed at VHE energies. The absence of significant variability at both GeV and TeV energies does not yet allow disentanglement of the physical nature of this component, though a jet-related origin is possible and a simple two-zone SED model fit is provided to this end.},
  language  = {en}
}
@article{ArchambaultAuneBeheraetal.2014,
  author    = {Archambault, S. and Aune, T. and Behera, B. and Beilicke, M. and Benbow, W. and Berger, K. and Bird, R. and Biteau, Jonathan and Bugaev, V. and Byrum, K. and Cardenzana, J. V. and Cerruti, M. and Chen, Xuhui and Ciupik, L. and Connolly, M. P. and Cui, Wei and Dumm, J. and Errando, M. and Falcone, A. and Federici, Simone and Feng, Q. and Finley, J. P. and Fleischhack, H. and Fortson, L. and Furniss, A. and Galante, N. and Gillanders, G. H. and Griffin, S. and Griffiths, S. T. and Grube, J. and Gyuk, G. and Hanna, D. and Holder, J. and Hughes, G. and Humensky, T. B. and Johnson, C. A. and Kaaret, P. and Kertzman, M. and Khassen, Y. and Kieda, D. and Krawczynski, H. and Krennrich, F. and Kumar, S. and Lang, M. J. and Madhavan, A. S. and Maier, G. and McCann, A. and Meagher, K. and Moriarty, P. and Mukherjee, R. and Nieto, Daniel and Ong, R. A. and Otte, A. N. and Park, N. and Pohl, Martin and Popkow, A. and Prokoph, H. and Quinn, J. and Ragan, K. and Rajotte, J. and Reyes, L. C. and Reynolds, P. T. and Richards, G. T. and Roache, E. and Sembroski, G. H. and Shahinyan, K. and Staszak, D. and Telezhinsky, Igor O. and Tucci, J. V. and Tyler, J. and Varlotta, A. and Vassiliev, V. V. and Vincent, S. and Wakely, S. P. and Weinstein, A. and Welsing, R. and Wilhelm, Alina and Williams, D. A. and Ackermann, Margit and Ajello, M. and Albert, A. and Baldini, L. and Bastieri, D. and Bellazzini, R. and Bissaldi, E. and Bregeon, Johan and Buehler, R. and Buson, S. and Caliandro, G. A. and Cameron, R. A. and Caraveo, P. A. and Cavazzuti, E. and Charles, E. and Chiang, J. and Ciprini, S. and Claus, R. and Cutini, S. and de Angelis, A. and de Palma, F. and Dermer, C. D. and Digel, S. W. and Di Venere, L. and Drell, P. S. and Favuzzi, C. and Franckowiak, A. and Fusco, P. and Gargano, F. and Gasparrini, D. and Giglietto, N. and Giordano, F. and Giroletti, M. and Grenier, I. A. and Guiriec, S. and Jogler, T. and Kuss, M. and Larsson, S. and Latronico, L. and Longo, F. and Loparco, F. and Lubrano, P. and Madejski, G. M. and Mayer, M. and Mazziotta, Mario Nicola and Michelson, P. F. and Mizuno, T. and Monzani, M. E. and Morselli, Aldo and Murgia, S. and Nuss, E. and Ohsugi, T. and Ormes, J. F. and Paneque, D. and Perkins, J. S. and Piron, F. and Pivato, G. and Raino, S. and Razzano, M. and Reimer, A. and Reimer, Olaf and Ritz, S. and Schaal, M. and Sgro, C. and Siskind, E. J. and Spinelli, P. and Takahashi, H. and Tibaldo, L. and Tinivella, M. and Troja, E. and Vianello, G. and Werner, M. and Wood, M.},
  title     = {Deep broadband observations of the distant gamma-ray blazar PKS 1424+240},
  series = {The astrophysical journal : an international review of spectroscopy and astronomical physics ; Part 2, Letters},
  volume    = {785},
  journal   = {The astrophysical journal : an international review of spectroscopy and astronomical physics ; Part 2, Letters},
  number    = {1},
  publisher = {IOP Publ. Ltd.},
  address   = {Bristol},
  organization    = {VERITAS Collaboration, Fermi LAT Collaboration},
  issn      = {2041-8205},
  doi       = {10.1088/2041-8205/785/1/L16},
  pages     = {8},
  year      = {2014},
  abstract  = {We present deep VERITAS observations of the blazar PKS 1424+240, along with contemporaneous Fermi Large Area Telescope, Swift X-ray Telescope, and Swift UV Optical Telescope data between 2009 February 19 and 2013 June 8. This blazar resides at a redshift of z >= 0.6035, displaying a significantly attenuated gamma-ray flux above 100 GeV due to photon absorption via pair-production with the extragalactic background light. We present more than 100 hr of VERITAS observations over three years, a multiwavelength light curve, and the contemporaneous spectral energy distributions. The source shows a higher flux of (2.1 +/- 0.3) x 10(-7) photons m(-2) s(-1) above 120 GeV in 2009 and 2011 as compared to the flux measured in 2013, corresponding to (1.02 +/- 0.08) x 10-7 photons m(-2) s(-1) above 120 GeV. The measured differential very high energy (VHE; E >= 100 GeV) spectral indices are Gamma = 3.8 +/- 0.3, 4.3 +/- 0.6 and 4.5 +/- 0.2 in 2009, 2011, and 2013, respectively. No significant spectral change across the observation epochs is detected. We find no evidence for variability at gamma-ray opacities of greater than tau = 2, where it is postulated that any variability would be small and occur on timescales longer than a year if hadronic cosmic-ray interactions with extragalactic photon fields provide a secondary VHE photon flux. The data cannot rule out such variability due to low statistics.},
  language  = {en}
}