TY - JOUR
A1 - Abramowski, Attila
A1 - Aharonian, Felix
A1 - Benkhali, F. Ait
A1 - Akhperjanian, A. G.
A1 - Anguener, E. O.
A1 - Anton, Gisela
A1 - Backes, M.
A1 - Balenderan, S.
A1 - Balzer, A.
A1 - Barnacka, A.
A1 - Becherini, Y.
A1 - Tjus, J. Becker
A1 - Bernloehr, K.
A1 - Birsin, E.
A1 - Bissaldi, E.
A1 - Biteau, J.
A1 - Boettcher, M.
A1 - Boisson, C.
A1 - Bolmont, J.
A1 - Bordas, P.
A1 - Brucker, J.
A1 - Brun, F.
A1 - Brun, P.
A1 - Bulik, T.
A1 - Carrigan, S.
A1 - Casanova, S.
A1 - Chadwick, P. M.
A1 - Chalme-Calvet, R.
A1 - Chaves, R. C. G.
A1 - Cheesebrough, A.
A1 - Chretien, M.
A1 - Colafrancesco, S.
A1 - Cologna, G.
A1 - Conrad, J.
A1 - Couturier, C.
A1 - Cui, Y.
A1 - Djannati-Ataï, A.
A1 - Domainko, W.
A1 - Dubus, G.
A1 - Dutson, K.
A1 - Dyks, J.
A1 - Dyrda, M.
A1 - Edwards, T.
A1 - Egberts, K.
A1 - Eger, P.
A1 - Espigat, P.
A1 - Farnier, C.
A1 - Fegan, S.
A1 - Feinstein, F.
A1 - Fernandes, M. V.
A1 - Fernandez, D.
A1 - Fiasson, A.
A1 - Fontaine, G.
A1 - Foerster, A.
A1 - Fussling, M.
A1 - Gajdus, M.
A1 - Gallant, Y. A.
A1 - Garrigoux, T.
A1 - Giavitto, G.
A1 - Giebels, B.
A1 - Glicenstein, J. F.
A1 - Grondin, M. -H.
A1 - Grudzinska, M.
A1 - Haeffner, S.
A1 - Hahn, J.
A1 - Harris, J.
A1 - Heinzelmann, G.
A1 - Henri, G.
A1 - Hermann, G.
A1 - Hervet, O.
A1 - Hillert, A.
A1 - Hinton, J. A.
A1 - Hofmann, W.
A1 - Hofverberg, P.
A1 - Holler, M.
A1 - Horns, D.
A1 - Jacholkowska, A.
A1 - Jahn, C.
A1 - Jamrozy, M.
A1 - Janiak, M.
A1 - Jankowsky, F.
A1 - Jung, I.
A1 - Kastendieck, M. A.
A1 - Katarzynski, K.
A1 - Katz, U.
A1 - Kaufmann, S.
A1 - Khelifi, B.
A1 - Kieffer, M.
A1 - Klepser, S.
A1 - Klochkov, D.
A1 - Kluzniak, W.
A1 - Kneiske, T.
A1 - Kolitzus, D.
A1 - Komin, Nu.
A1 - Kosack, K.
A1 - Krakau, S.
A1 - Krayzel, F.
A1 - Krueger, P. P.
A1 - Laffon, H.
A1 - Lamanna, G.
A1 - Lefaucheur, J.
A1 - Lemiere, A.
A1 - Lemoine-Goumard, M.
A1 - Lenain, J. -P.
A1 - Lohse, T.
A1 - Lopatin, A.
A1 - Lu, C. -C.
A1 - Marandon, V.
A1 - Marcowith, A.
A1 - Marx, R.
A1 - Maurin, G.
A1 - Maxted, N.
A1 - Mayer, M.
A1 - McComb, T. J. L.
A1 - Mehault, J.
A1 - Meintjes, P. J.
A1 - Menzler, U.
A1 - Meyer, M.
A1 - Moderski, R.
A1 - Mohamed, M.
A1 - Moulin, E.
A1 - Murach, T.
A1 - Naumann, C. L.
A1 - de Naurois, M.
A1 - Niemiec, J.
A1 - Nolan, S. J.
A1 - Oakes, L.
A1 - Odaka, H.
A1 - Ohm, S.
A1 - Wilhelmi, E. de Ona
A1 - Opitz, B.
A1 - Ostrowski, M.
A1 - Oya, I.
A1 - Panter, M.
A1 - Parsons, R. D.
A1 - Arribas, M. Paz
A1 - Pekeur, N. W.
A1 - Pelletier, G.
A1 - Perez, J.
A1 - Petrucci, P. -O.
A1 - Peyaud, B.
A1 - Pita, S.
A1 - Poon, H.
A1 - Puehlhofer, G.
A1 - Punch, M.
A1 - Quirrenbach, A.
A1 - Raab, S.
A1 - Raue, M.
A1 - Reichardt, I.
A1 - Reimer, A.
A1 - Reimer, O.
A1 - Renaud, M.
A1 - Reyes, R. de los
A1 - Rieger, F.
A1 - Rob, L.
A1 - Romoli, C.
A1 - Rosier-Lees, S.
A1 - Rowell, G.
A1 - Rudak, B.
A1 - Rulten, C. B.
A1 - Sahakian, V.
A1 - Sanchez, D. A.
A1 - Santangelo, A.
A1 - Schlickeiser, R.
A1 - Schuessler, F.
A1 - Schulz, A.
A1 - Schwanke, U.
A1 - Schwarzburg, S.
A1 - Schwemmer, S.
A1 - Sol, H.
A1 - Spengler, G.
A1 - Spies, F.
A1 - Stawarz, L.
A1 - Steenkamp, R.
A1 - Stegmann, Christian
A1 - Stinzing, F.
A1 - Stycz, K.
A1 - Sushch, I.
A1 - Tavernet, J. -P.
A1 - Tavernier, T.
A1 - Taylor, A. M.
A1 - Terrier, R.
A1 - Tluczykont, M.
A1 - Trichard, C.
A1 - Valerius, K.
A1 - van Eldik, C.
A1 - van Soelen, B.
A1 - Vasileiadis, G.
A1 - Venter, C.
A1 - Viana, A.
A1 - Vincent, P.
A1 - Voelk, H. J.
A1 - Volpe, F.
A1 - Vorster, M.
A1 - Vuillaume, T.
A1 - Wagner, S. J.
A1 - Wagner, P.
A1 - Wagner, R. M.
A1 - Ward, M.
A1 - Weidinger, M.
A1 - Weitzel, Q.
A1 - White, R.
A1 - Wierzcholska, A.
A1 - Willmann, P.
A1 - Woernlein, A.
A1 - Wouters, D.
A1 - Yang, R.
A1 - Zabalza, V.
A1 - Zacharias, M.
A1 - Zdziarski, A. A.
A1 - Zech, A.
A1 - Zechlin, H. -S.
A1 - Malyshev, D.
T1 - Search for extended gamma-ray emission around AGN with HESS and Fermi-LAT
JF - Astronomy and astrophysics : an international weekly journal
N2 - Context. Very-high-energy (VHE; E > 100 GeV) gamma-ray emission from blazars inevitably gives rise to electron-positron pair production through the interaction of these gamma-rays with the extragalactic background light (EBL). Depending on the magnetic fields in the proximity of the source, the cascade initiated from pair production can result in either an isotropic halo around an initially- beamed source or a magnetically- broadened cascade :aux.
Aims. Both extended pair-halo (PH) and magnetically broadened cascade (MBC) emission from regions surrounding the blazars 1ES 1101-232, IRS 0229+200, and PKS 2155-304 were searched for using VHE y-ray data taken with the High Energy Stereoscopic System (HESS.) and high-energy (HE; 100 MeV < E < 100 GeV) gamma-ray data with the Fermi Large Area Telescope (LAT).
Methods. By comparing the angular distributions of the reconstructed gamma-ray events to the angular profiles calculated from detailed theoretical models, the presence of PH and MBC was investigated.
Results. Upper limits on the extended emission around lES 1101-232, lES 0229+200, and PKS 2155-304 are found to be at a level of a few per cent of the Crab nebula flux above 1 TeV, depending on the assumed photon index of the cascade emission. Assuming strong extra-Galactic magnetic field (EGME) values, >10(-12) G, this limits the production of pair haloes developing from electromagnetic cascades. For weaker magnetic fields, in which electromagnetic cascades would result in MBCs. EGMF strengths in the range (0.3-3) x 10(-15) G were excluded for PKS 2155-304 at the 99% confidence level, under the assumption of a 1 Mpc coherence length.
KW - gamma rays: galaxies
KW - galaxies: magnetic fields
KW - intergalactic medium
KW - BL Lacertae objects: individual: PKS 2155-304
KW - BL Lacertae objects: individual: lES 1101-232
KW - BL Lacertae objects: individual: lES 0229+200
Y1 - 2014
U6 - http://dx.doi.org/10.1051/0004-6361/201322510
SN - 0004-6361 (print)
SN - 1432-0746 (online)
VL - 562
PB - EDP Sciences
CY - Les Ulis
ER -
TY - JOUR
A1 - Abramowski, Attila
A1 - Aharonian, Felix
A1 - Benkhali, F. Ait
A1 - Akhperjanian, A. G.
A1 - Anguener, E. O.
A1 - Anton, Gisela
A1 - Balenderan, S.
A1 - Balzer, Arnim
A1 - Barnacka, A.
A1 - Becherini, Y.
A1 - Tjus, J. Becker
A1 - Bernloehr, K.
A1 - Birsin, E.
A1 - Bissaldi, E.
A1 - Biteau, J.
A1 - Boettcher, M.
A1 - Boisson, C.
A1 - Bolmont, J.
A1 - Bordas, P.
A1 - Brucker, J.
A1 - Brun, F.
A1 - Brun, P.
A1 - Bulik, T.
A1 - Carrigan, S.
A1 - Casanova, S.
A1 - Cerruti, M.
A1 - Chadwick, P. M.
A1 - Chalme-Calvet, R.
A1 - Chaves, R. C. G.
A1 - Cheesebrough, A.
A1 - Chretien, M.
A1 - Colafrancesco, S.
A1 - Cologna, G.
A1 - Conrad, J.
A1 - Couturier, C.
A1 - Cui, Y.
A1 - Dalton, M.
A1 - Daniel, M. K.
A1 - Davids, I. D.
A1 - Degrange, B.
A1 - Deil, C.
A1 - dewilt, P.
A1 - Dicldnson, H. J.
A1 - Djannati-Ataï, A.
A1 - Domainko, W.
A1 - Dubus, G.
A1 - Dutson, K.
A1 - Dyks, J.
A1 - Dyrda, M.
A1 - Edwards, T.
A1 - Egberts, K.
A1 - Eger, P.
A1 - Espigat, P.
A1 - Farnier, C.
A1 - Fegan, S.
A1 - Feinstein, F.
A1 - Fernandes, M. V.
A1 - Fernandez, D.
A1 - Fiasson, A.
A1 - Fontaine, G.
A1 - Foerster, A.
A1 - Fuessling, M.
A1 - Gajdus, M.
A1 - Gallant, Y. A.
A1 - Garrigoux, T.
A1 - Giavitto, G.
A1 - Giebels, B.
A1 - Glicenstein, J. F.
A1 - Grondin, M. -H.
A1 - Grudzinska, M.
A1 - Haeffner, S.
A1 - Hahn, J.
A1 - Harris, J.
A1 - Heinzelmann, G.
A1 - Henri, G.
A1 - Hermann, G.
A1 - Hervet, O.
A1 - Hillert, A.
A1 - Hinton, J. A.
A1 - Hofmann, W.
A1 - Hofverberg, P.
A1 - Holler, M.
A1 - Horns, D.
A1 - Jacholkowska, A.
A1 - Jahn, C.
A1 - Jamrozy, M.
A1 - Janiak, M.
A1 - Jankowsky, F.
A1 - Jung, I.
A1 - Kastendieck, M. A.
A1 - Katarzynski, K.
A1 - Katz, U.
A1 - Kaufmann, S.
A1 - Khelifi, B.
A1 - Kieffer, M.
A1 - Klepser, S.
A1 - Klochkov, D.
A1 - Kluzniak, W.
A1 - Kneiske, T.
A1 - Kolitzus, D.
A1 - Komin, Nu.
A1 - Kosack, K.
A1 - Krakau, S.
A1 - Krayzel, F.
A1 - Krueger, P. P.
A1 - Laffon, H.
A1 - Lamanna, G.
A1 - Lefaucheur, J.
A1 - Lemiere, A.
A1 - Lemoine-Goumard, M.
A1 - Lenain, J. -P.
A1 - Lennarz, D.
A1 - Lohse, T.
A1 - Lopatin, A.
A1 - Lu, C. -C.
A1 - Marandon, V.
A1 - Marcowith, A.
A1 - Marx, R.
A1 - Maurin, G.
A1 - Maxted, N.
A1 - Mayer, M.
A1 - McComb, T. J. L.
A1 - Mehault, J.
A1 - Meintjes, P. J.
A1 - Menzler, U.
A1 - Meyer, M.
A1 - Moderski, R.
A1 - Mohamed, M.
A1 - Moulin, E.
A1 - Murach, T.
A1 - Naumann, C. L.
A1 - de Naurois, M.
A1 - Niemiec, J.
A1 - Nolan, S. J.
A1 - Oakes, L.
A1 - Ohm, S.
A1 - Wilhelmi, E. de Ona
A1 - Opitz, B.
A1 - Ostrowski, M.
A1 - Oya, I.
A1 - Panter, M.
A1 - Parsons, R. D.
A1 - Arribas, M. Paz
A1 - Pekeur, N. W.
A1 - Pelletier, G.
A1 - Perez, J.
A1 - Petrucci, P. -O.
A1 - Peyaud, B.
A1 - Pita, S.
A1 - Poon, H.
A1 - Puehlhofer, G.
A1 - Punch, M.
A1 - Quirrenbach, A.
A1 - Raab, S.
A1 - Raue, M.
A1 - Reimer, A.
A1 - Reimer, O.
A1 - Renaud, M.
A1 - Reyes, R. de Los
A1 - Rieger, F.
A1 - Rob, L.
A1 - Romoli, C.
A1 - Rosier-Lees, S.
A1 - Rowell, G.
A1 - Rudak, B.
A1 - Rulten, C. B.
A1 - Sahakian, V.
A1 - Sanchez, D. A.
A1 - Santangelo, A.
A1 - Schlickeiser, R.
A1 - Schuessler, F.
A1 - Schulz, A.
A1 - Schwanke, U.
A1 - Schwarzburg, S.
A1 - Schwemmer, S.
A1 - Sol, H.
A1 - Spengler, G.
A1 - Spies, F.
A1 - Stawarz, L.
A1 - Steenkamp, R.
A1 - Stegmann, Christian
A1 - Stinzing, F.
A1 - Stycz, K.
A1 - Sushch, I.
A1 - Szostek, A.
A1 - Tavernet, J. -P.
A1 - Tavernier, T.
A1 - Taylor, A. M.
A1 - Terrier, R.
A1 - Tluczykont, M.
A1 - Trichard, C.
A1 - Valerius, K.
A1 - van Eldik, C.
A1 - van Soelen, B.
A1 - Vasileiadis, G.
A1 - Venter, C.
A1 - Viana, A.
A1 - Vincent, P.
A1 - Voelk, H. J.
A1 - Volpe, F.
A1 - Vorster, M.
A1 - Vuillaume, T.
A1 - Wagner, S. J.
A1 - Wagner, P.
A1 - Ward, M.
A1 - Weidinger, M.
A1 - Weitzel, Q.
A1 - White, R.
A1 - Wierzcholska, A.
A1 - Willmann, P.
A1 - Woernlein, A.
A1 - Wouters, D.
A1 - Zabalza, V.
A1 - Zacharias, M.
A1 - Zajczyk, A.
A1 - Zdziarski, A. A.
A1 - Zech, A.
A1 - Zechlin, H. -S.
T1 - Flux upper limits for 47 AGN observed with HESS in 2004-2011
JF - Astronomy and astrophysics : an international weekly journal
N2 - Context. About 40% of the observation time of the High Energy Stereoscopic System (H.E.S.S.) is dedicated to studying active galactic nuclei (AGN), with the aim of increasing the sample of known extragalactic very-high-energy (VHE, E > 100 GeV) sources and constraining the physical processes at play in potential emitters.
Aims. H.E.S.S. observations of AGN, spanning a period from April 2004 to December 2011, are investigated to constrain their gamma-ray fluxes. Only the 47 sources without significant excess detected at the position of the targets are presented.
Methods. Upper limits on VHE fluxes of the targets were computed and a search for variability was performed on the nightly time scale.
Results. For 41 objects, the flux upper limits we derived are the most constraining reported to date. These constraints at VHE are compared with the flux level expected from extrapolations of Fermi-LAT measurements in the two-year catalog of AGN. The H.E.S.S. upper limits are at least a factor of two lower than the extrapolated Fermi-LAT fluxes for 11 objects Taking into account the attenuation by the extragalactic background light reduces the tension for all but two of them, suggesting intrinsic curvature in the high-energy spectra of these two AGN.
Conclusions. Compilation efforts led by current VHE instruments are of critical importance for target-selection strategies before the advent of the Cherenkov Telescope Array (CTA).
KW - gamma rays: galaxies
KW - galaxies: active
Y1 - 2014
U6 - http://dx.doi.org/10.1051/0004-6361/201322897
SN - 0004-6361 (print)
SN - 1432-0746 (online)
VL - 564
PB - EDP Sciences
CY - Les Ulis
ER -
TY - JOUR
A1 - Archambault, S.
A1 - Aune, T.
A1 - Behera, B.
A1 - Beilicke, M.
A1 - Benbow, W.
A1 - Berger, K.
A1 - Bird, R.
A1 - Biteau, J.
A1 - Bugaev, V.
A1 - Byrum, K.
A1 - Cardenzana, J. V.
A1 - Cerruti, M.
A1 - Chen, Xuhui
A1 - Ciupik, L.
A1 - Connolly, M. P.
A1 - Cui, Wei
A1 - Dumm, J.
A1 - Errando, M.
A1 - Falcone, A.
A1 - Federici, Simone
A1 - Feng, Q.
A1 - Finley, J. P.
A1 - Fleischhack, H.
A1 - Fortson, L.
A1 - Furniss, A.
A1 - Galante, N.
A1 - Gillanders, G. H.
A1 - Griffin, S.
A1 - Griffiths, S. T.
A1 - Grube, J.
A1 - Gyuk, G.
A1 - Hanna, D.
A1 - Holder, J.
A1 - Hughes, G.
A1 - Humensky, T. B.
A1 - Johnson, C. A.
A1 - Kaaret, P.
A1 - Kertzman, M.
A1 - Khassen, Y.
A1 - Kieda, D.
A1 - Krawczynski, H.
A1 - Krennrich, F.
A1 - Kumar, S.
A1 - Lang, M. J.
A1 - Madhavan, A. S.
A1 - Maier, G.
A1 - McCann, A.
A1 - Meagher, K.
A1 - Moriarty, P.
A1 - Mukherjee, R.
A1 - Nieto, Daniel
A1 - Ong, R. A.
A1 - Otte, A. N.
A1 - Park, N.
A1 - Pohl, Martin
A1 - Popkow, A.
A1 - Prokoph, H.
A1 - Quinn, J.
A1 - Ragan, K.
A1 - Rajotte, J.
A1 - Reyes, L. C.
A1 - Reynolds, P. T.
A1 - Richards, G. T.
A1 - Roache, E.
A1 - Sembroski, G. H.
A1 - Shahinyan, K.
A1 - Staszak, D.
A1 - Telezhinsky, Igor
A1 - Tucci, J. V.
A1 - Tyler, J.
A1 - Varlotta, A.
A1 - Vassiliev, V. V.
A1 - Vincent, S.
A1 - Wakely, S. P.
A1 - Weinstein, A.
A1 - Welsing, R.
A1 - Wilhelm, Alina
A1 - Williams, D. A.
A1 - Ackermann, Margit
A1 - Ajello, M.
A1 - Albert, A.
A1 - Baldini, L.
A1 - Bastieri, D.
A1 - Bellazzini, R.
A1 - Bissaldi, E.
A1 - Bregeon, J.
A1 - Buehler, R.
A1 - Buson, S.
A1 - Caliandro, G. A.
A1 - Cameron, R. A.
A1 - Caraveo, P. A.
A1 - Cavazzuti, E.
A1 - Charles, E.
A1 - Chiang, J.
A1 - Ciprini, S.
A1 - Claus, R.
A1 - Cutini, S.
A1 - de Angelis, A.
A1 - de Palma, F.
A1 - Dermer, C. D.
A1 - Digel, S. W.
A1 - Di Venere, L.
A1 - Drell, P. S.
A1 - Favuzzi, C.
A1 - Franckowiak, A.
A1 - Fusco, P.
A1 - Gargano, F.
A1 - Gasparrini, D.
A1 - Giglietto, N.
A1 - Giordano, F.
A1 - Giroletti, M.
A1 - Grenier, I. A.
A1 - Guiriec, S.
A1 - Jogler, T.
A1 - Kuss, M.
A1 - Larsson, S.
A1 - Latronico, L.
A1 - Longo, F.
A1 - Loparco, F.
A1 - Lubrano, P.
A1 - Madejski, G. M.
A1 - Mayer, M.
A1 - Mazziotta, M. N.
A1 - Michelson, P. F.
A1 - Mizuno, T.
A1 - Monzani, M. E.
A1 - Morselli, Aldo
A1 - Murgia, S.
A1 - Nuss, E.
A1 - Ohsugi, T.
A1 - Ormes, J. F.
A1 - Paneque, D.
A1 - Perkins, J. S.
A1 - Piron, F.
A1 - Pivato, G.
A1 - Raino, S.
A1 - Razzano, M.
A1 - Reimer, A.
A1 - Reimer, Olaf
A1 - Ritz, S.
A1 - Schaal, M.
A1 - Sgro, C.
A1 - Siskind, E. J.
A1 - Spinelli, P.
A1 - Takahashi, H.
A1 - Tibaldo, L.
A1 - Tinivella, M.
A1 - Troja, E.
A1 - Vianello, G.
A1 - Werner, M.
A1 - Wood, M.
T1 - Deep broadband observations of the distant gamma-ray blazar PKS 1424+240
JF - The astrophysical journal : an international review of spectroscopy and astronomical physics ; Part 2, Letters
N2 - 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.
KW - BL Lacertae objects: individual (PKS 1424+240)-cosmic background radiation
KW - gamma rays: galaxies
Y1 - 2014
U6 - http://dx.doi.org/10.1088/2041-8205/785/1/L16
SN - 2041-8205 (print)
SN - 2041-8213 (online)
VL - 785
IS - 1
PB - IOP Publ. Ltd.
CY - Bristol
ER -
TY - JOUR
A1 - Archambault, S.
A1 - Arlen, T.
A1 - Aune, T.
A1 - Beilicke, M.
A1 - Benbow, W.
A1 - Bird, R.
A1 - Boettcher, M.
A1 - Bouvier, A.
A1 - Buckley, J. H.
A1 - Bugaev, V.
A1 - Ciupik, L.
A1 - Collins-Hughes, E.
A1 - Connolly, M. P.
A1 - Cui, W.
A1 - Dickherber, R.
A1 - Dumm, J.
A1 - Errando, M.
A1 - Falcone, A.
A1 - Federici, Simone
A1 - Feng, Q.
A1 - Finley, J. P.
A1 - Fortson, L.
A1 - Furniss, A.
A1 - Galante, N.
A1 - Gall, D.
A1 - Garson, A. III.
A1 - Gillanders, G. H.
A1 - Griffin, S.
A1 - Grube, J.
A1 - Gusbar, C.
A1 - Gyuk, G.
A1 - Hanna, D.
A1 - Holder, J.
A1 - Hughes, G.
A1 - Kaaret, P.
A1 - Kertzman, M.
A1 - Khassen, Y.
A1 - Kieda, D.
A1 - Krawczynski, H.
A1 - Lamerato, A.
A1 - Lang, M. J.
A1 - Li, K.
A1 - Madhavan, A. S.
A1 - Maier, G.
A1 - Majumdar, P.
A1 - McArthur, S.
A1 - McCann, A.
A1 - Millis, J.
A1 - Moriarty, P.
A1 - Mukherjee, R.
A1 - Nieto, D.
A1 - Ong, R. A.
A1 - Orr, M.
A1 - Otte, A. N.
A1 - Park, N.
A1 - Perkins, J. S.
A1 - Pohl, Martin
A1 - Popkow, A.
A1 - Prokoph, H.
A1 - Quinn, J.
A1 - Ragan, K.
A1 - Reynolds, P. T.
A1 - Richards, G. T.
A1 - Roache, E.
A1 - Roustazadeh, P.
A1 - Saxon, D. B.
A1 - Sembroski, G. H.
A1 - Senturk, G. D.
A1 - Skole, C.
A1 - Staszak, D.
A1 - Telezhinsky, Igor
A1 - Tesic, G.
A1 - Theiling, M.
A1 - Varlotta, A.
A1 - Vassiliev, V. V.
A1 - Vincent, S.
A1 - Wakely, S. P.
A1 - Weinstein, A.
A1 - Welsing, R.
A1 - Williams, D. A.
A1 - Zitzer, B.
T1 - Test of models of the cosmic infrared background with multiwavelength observations of the blazar 1ES 1218+30.4 IN 2009
JF - The astrophysical journal : an international review of spectroscopy and astronomical physics
N2 - We present the results of a multi-wavelength campaign targeting the blazar 1ES 1218+30.4 with observations with the 1.3 m McGraw-Hill optical telescope, the Rossi X-ray Timing Explorer (RXTE), the Fermi Gamma-Ray Space Telescope, and the Very Energetic Radiation Imaging Telescope Array System (VERITAS). The RXTE and VERITAS observations were spread over a 13 day period and revealed clear evidence for flux variability, and a strong X-ray and gamma-ray flare on 2009 February 26 (MJD 54888). The campaign delivered a well-sampled broadband energy spectrum with simultaneous RXTE and VERITAS very high energy (VHE, > 100 GeV) observations, as well as contemporaneous optical and Fermi observations. The 1ES 1218+30.4 broadband energy spectrum-the first with simultaneous X-ray and VHE gamma-ray energy spectra-is of particular interest as the source is located at a high cosmological redshift for a VHE source (z = 0.182), leading to strong absorption of VHE gamma rays by photons from the optical/infrared extragalactic background light (EBL) via gamma VHE +gamma EBL -> e(+) e(-)pair-creation processes. We model the data with a one-zone synchrotron self-Compton (SSC) emission model and with the extragalactic absorption predicted by several recent EBL models. We find that the observations are consistent with the SSC scenario and all the EBL models considered in this work. We discuss observational and theoretical avenues to improve on the EBL constraints.
KW - BL Lacertae objects: general
KW - BL Lacertae objects: individual (1ES1218+30.4)
KW - cosmic background radiation
KW - diffuse radiation
KW - galaxies: jets
KW - gamma rays: galaxies
Y1 - 2014
U6 - http://dx.doi.org/10.1088/0004-637X/788/2/158
SN - 0004-637X (print)
SN - 1538-4357 (online)
VL - 788
IS - 2
PB - IOP Publ. Ltd.
CY - Bristol
ER -
TY - JOUR
A1 - Zhang, Haocheng
A1 - Chen, Xuhui
A1 - Boettcher, Markus
T1 - Synchrotron polarization in blazars
JF - The astrophysical journal : an international review of spectroscopy and astronomical physics
N2 - We present a detailed analysis of time-and energy-dependent synchrotron polarization signatures in a shock-in-jet model for gamma-ray blazars. Our calculations employ a full three-dimensional radiation transfer code, assuming a helical magnetic field throughout the jet. The code considers synchrotron emission from an ordered magnetic field, and takes into account all light-travel-time and other relevant geometric effects, while the relevant synchrotron self-Compton and external Compton effects are handled with the two-dimensional Monte-Carlo/Fokker-Planck (MCFP) code. We consider several possible mechanisms through which a relativistic shock propagating through the jet may affect the jet plasma to produce a synchrotron and high-energy flare. Most plausibly, the shock is expected to lead to a compression of the magnetic field, increasing the toroidal field component and thereby changing the direction of the magnetic field in the region affected by the shock. We find that such a scenario leads to correlated synchrotron + synchrotron-self-Compton flaring, associated with substantial variability in the synchrotron polarization percentage and position angle. Most importantly, this scenario naturally explains large polarization angle rotations by greater than or similar to 180 degrees, as observed in connection with gamma-ray flares in several blazars, without the need for bent or helical jet trajectories or other nonaxisymmetric jet features.
KW - galaxies: active
KW - galaxies: jets
KW - gamma rays: galaxies
KW - radiation mechanisms: non-thermal
KW - relativistic processes
Y1 - 2014
U6 - http://dx.doi.org/10.1088/0004-637X/789/1/66
SN - 0004-637X (print)
SN - 1538-4357 (online)
VL - 789
IS - 1
PB - IOP Publ. Ltd.
CY - Bristol
ER -
TY - JOUR
A1 - Archer, A.
A1 - Barnacka, A.
A1 - Beilicke, M.
A1 - Benbow, W.
A1 - Berger, K.
A1 - Bird, R.
A1 - Biteau, J.
A1 - Buckley, J. H.
A1 - Bugaev, V.
A1 - Byrum, K.
A1 - Cardenzana, J. V.
A1 - Cerruti, M.
A1 - Chen, W.
A1 - Chen, Xiaoming
A1 - Ciupik, L.
A1 - Connolly, M. P.
A1 - Cui, W.
A1 - Dickinson, H. J.
A1 - Dumm, J.
A1 - Eisch, J. D.
A1 - Falcone, A.
A1 - Federici, Simone
A1 - Feng, Q.
A1 - Finley, J. P.
A1 - Fleischhack, H.
A1 - Fortson, L.
A1 - Furniss, A.
A1 - Galante, N.
A1 - Griffin, S.
A1 - Griffiths, S. T.
A1 - Grube, J.
A1 - Gyuk, G.
A1 - Hakansson, Nils
A1 - Hanna, D.
A1 - Holder, J.
A1 - Hughes, G.
A1 - Johnson, C. A.
A1 - Kaaret, P.
A1 - Kar, P.
A1 - Kertzman, M.
A1 - Khassen, Y.
A1 - Kieda, D.
A1 - Krawczynski, H.
A1 - Kumar, S.
A1 - Lang, M. J.
A1 - Maier, G.
A1 - McArthur, S.
A1 - McCann, A.
A1 - Meagher, K.
A1 - Moriarty, P.
A1 - Mukherjee, R.
A1 - Nieto, D.
A1 - Ong, R. A.
A1 - Otte, A. N.
A1 - Park, N.
A1 - Perkins, J. S.
A1 - Pohl, Manuela
A1 - Popkow, A.
A1 - Prokoph, H.
A1 - Pueschel, E.
A1 - Quinn, J.
A1 - Ragan, K.
A1 - Rajotte, J.
A1 - Reyes, L. C.
A1 - Reynolds, P. T.
A1 - Richards, G. T.
A1 - Roache, E.
A1 - Sembroski, G. H.
A1 - Shahinyan, K.
A1 - Smith, A. W.
A1 - Staszak, D.
A1 - Telezhinsky, Igor
A1 - Tucci, J. V.
A1 - Tyler, J.
A1 - Varlotta, A.
A1 - Vincent, S.
A1 - Wakely, S. P.
A1 - Weinstein, A.
A1 - Welsing, R.
A1 - Wilhelm, A.
A1 - Williams, D. A.
A1 - Zajczyk, A.
A1 - Zitzer, B.
T1 - Very-high energy observations of the galactic center region by veritas IN 2010-2012
JF - The astrophysical journal : an international review of spectroscopy and astronomical physics
N2 - The Galactic center is an interesting region for high-energy (0.1-100 GeV) and very-high-energy (E > 100 GeV) gamma-ray observations. Potential sources of GeV/TeV gamma-ray emission have been suggested, e.g., the accretion of matter onto the supermassive black hole, cosmic rays from a nearby supernova remnant (e.g., Sgr A East), particle acceleration in a plerion, or the annihilation of dark matter particles. The Galactic center has been detected by EGRET and by Fermi/LAT in the MeV/GeV energy band. At TeV energies, the Galactic center was detected with moderate significance by the CANGAROO and Whipple 10 m telescopes and with high significance by H.E.S.S., MAGIC, and VERITAS. We present the results from three years of VERITAS observations conducted at large zenith angles resulting in a detection of the Galactic center on the level of 18 standard deviations at energies above similar to 2.5 TeV. The energy spectrum is derived and is found to be compatible with hadronic, leptonic, and hybrid emission models discussed in the literature. Future, more detailed measurements of the high-energy cutoff and better constraints on the high-energy flux variability will help to refine and/or disentangle the individual models.
KW - astroparticle physics
KW - black hole physics
KW - Galaxy: center
KW - gamma rays: galaxies
KW - methods: data analysis
KW - radiation mechanisms: non-thermal
Y1 - 2014
U6 - http://dx.doi.org/10.1088/0004-637X/790/2/149
SN - 0004-637X (print)
SN - 1538-4357 (online)
VL - 790
IS - 2
PB - IOP Publ. Ltd.
CY - Bristol
ER -
TY - JOUR
A1 - Abramowski, Attila
A1 - Aharonian, Felix
A1 - Benkhali, F. Ait
A1 - Akhperjanian, A. G.
A1 - Angüner, E. O.
A1 - Backes, M.
A1 - Balenderan, S.
A1 - Balzer, A.
A1 - Barnacka, A.
A1 - Becherini, Y.
A1 - Tjus, J. Becker
A1 - Berge, D.
A1 - Bernhard, S.
A1 - Bernlohr, K.
A1 - Birsin, E.
A1 - Biteau, J.
A1 - Bottcher, M.
A1 - Boisson, C.
A1 - Bolmont, J.
A1 - Bordas, P.
A1 - Bregeon, J.
A1 - Brun, F.
A1 - Brun, P.
A1 - Bryan, M.
A1 - Bulik, T.
A1 - Carrigan, S.
A1 - Casanova, S.
A1 - Chadwick, P. M.
A1 - Chakraborty, N.
A1 - Chalme-Calvet, R.
A1 - Chaves, R. C. G.
A1 - Chretien, M.
A1 - Colafrancesco, S.
A1 - Cologna, G.
A1 - Conrad, J.
A1 - Couturier, C.
A1 - Cui, Y.
A1 - Dalton, M.
A1 - Davids, I. D.
A1 - Degrange, B.
A1 - Deil, C.
A1 - dewilt, P.
A1 - Djannati-Ataï, A.
A1 - Domainko, W.
A1 - Donath, A.
A1 - Dubus, G.
A1 - Dutson, K.
A1 - Dyks, J.
A1 - Dyrda, M.
A1 - Edwards, T.
A1 - Egberts, Kathrin
A1 - Eger, P.
A1 - Espigat, P.
A1 - Farnier, C.
A1 - Fegan, S.
A1 - Feinstein, F.
A1 - Fernandes, M. V.
A1 - Fernandez, D.
A1 - Fiasson, A.
A1 - Fontaine, G.
A1 - Forster, A.
A1 - Fuling, M.
A1 - Gabici, S.
A1 - Gajdus, M.
A1 - Gallant, Y. A.
A1 - Garrigoux, T.
A1 - Giavitto, G.
A1 - Giebels, B.
A1 - Glicenstein, J. F.
A1 - Gottschall, D.
A1 - Grondin, M. -H.
A1 - Grudzinska, M.
A1 - Hadsch, D.
A1 - Haeffner, S.
A1 - Hahn, J.
A1 - Harris, J.
A1 - Heinzelmann, G.
A1 - Henri, G.
A1 - Hermann, G.
A1 - Hervet, O.
A1 - Hillert, A.
A1 - Hinton, J. A.
A1 - Hofmann, W.
A1 - Hofverberg, P.
A1 - Holler, Markus
A1 - Horns, D.
A1 - Ivascenko, A.
A1 - Jacholkowska, A.
A1 - Jahn, C.
A1 - Jamrozy, M.
A1 - Janiak, M.
A1 - Jankowsky, F.
A1 - Jung, I.
A1 - Kastendieck, M. A.
A1 - Katarzynski, K.
A1 - Katz, U.
A1 - Kaufmann, S.
A1 - Khelifi, B.
A1 - Kiefeer, M.
A1 - Klepser, S.
A1 - Klochkov, D.
A1 - Kluzniak, W.
A1 - Kolitzus, D.
A1 - Komin, Nu.
A1 - Kosack, K.
A1 - Krakau, S.
A1 - Krayzel, F.
A1 - Kruger, P. P.
A1 - Laffon, H.
A1 - Lamanna, G.
A1 - Lefaucheur, J.
A1 - Lefranc, V.
A1 - Lemiere, A.
A1 - Lemoine-Goumard, M.
A1 - Lenain, J. -P.
A1 - Lohse, T.
A1 - Lopatin, A.
A1 - Lu, C. -C.
A1 - Marandon, V.
A1 - Marcowith, A.
A1 - Marx, R.
A1 - Maurin, G.
A1 - Maxted, N.
A1 - Mayer, M.
A1 - McComb, T. J. L.
A1 - Mehault, J.
A1 - Meintjes, P. J.
A1 - Menzler, U.
A1 - Meyer, M.
A1 - Mitchell, A. M. W.
A1 - Moderski, R.
A1 - Mohamed, M.
A1 - Mora, K.
A1 - Moulin, E.
A1 - Murach, T.
A1 - de Naurois, M.
A1 - Niemiec, J.
A1 - Nolan, S. J.
A1 - Oakes, L.
A1 - Odaka, H.
A1 - Ohm, S.
A1 - Opitz, B.
A1 - Ostrowski, M.
A1 - Oya, I.
A1 - Panter, M.
A1 - Parsons, R. D.
A1 - Arribas, M. Paz
A1 - Pekeur, N. W.
A1 - Pelletier, G.
A1 - Perez, J.
A1 - Petrucci, P. -O.
A1 - Peyaud, B.
A1 - Pita, S.
A1 - Poon, H.
A1 - Puhlhofer, G.
A1 - Punch, M.
A1 - Quirrenbach, A.
A1 - Raab, S.
A1 - Reichardt, I.
A1 - Reimer, A.
A1 - Reimer, O.
A1 - Renaud, M.
A1 - de los Reyes, R.
A1 - Rieger, F.
A1 - Rob, L.
A1 - Romoli, C.
A1 - Rosier-Lees, S.
A1 - Rowell, G.
A1 - Rudak, B.
A1 - Rulten, C. B.
A1 - Sahakian, V.
A1 - Salek, D.
A1 - Sanchez, D. A.
A1 - Santangelo, A.
A1 - Schlickeiser, R.
A1 - Schussler, F.
A1 - Schulz, A.
A1 - Schwanke, U.
A1 - Schwarzburg, S.
A1 - Schwemmer, S.
A1 - Sol, H.
A1 - Spanier, F.
A1 - Spengler, G.
A1 - Spies, F.
A1 - Stawarz, L.
A1 - Steenkamp, R.
A1 - Stegmann, Christian
A1 - Stinzing, F.
A1 - Stycz, K.
A1 - Sushch, I.
A1 - Tavernet, J. -P.
A1 - Tavernier, T.
A1 - Taylor, A. M.
A1 - Terrier, R.
A1 - Tluczykont, M.
A1 - Trichard, C.
A1 - Valerius, K.
A1 - Van Eldik, C.
A1 - Van Soelen, B.
A1 - Vasileiadis, G.
A1 - Veh, J.
A1 - Venter, C.
A1 - Viana, A.
A1 - Vincent, P.
A1 - Vink, J.
A1 - Volk, H. J.
A1 - Volpe, F.
A1 - Vorster, M.
A1 - Vuillaume, T.
A1 - Wagner, S. J.
A1 - Wagner, P.
A1 - Wagner, R. M.
A1 - Ward, M.
A1 - Weidinger, M.
A1 - Weitzel, Q.
A1 - White, R.
A1 - Wierzcholska, A.
A1 - Willmann, P.
A1 - Wornlein, A.
A1 - Wouters, D.
A1 - Yang, R.
A1 - Zabalza, V.
A1 - Zaborov, D.
A1 - Zacharias, M.
A1 - Zdziarski, A. A.
A1 - Zech, A.
A1 - Zechlin, H. -S.
T1 - Long-term monitoring of PKS2155-304 with ATOM and HESS:investigation of optical/gamma-ray correlations in different spectral states
JF - Astronomy and astrophysics : an international weekly journal
N2 - In this paper we report on the analysis of all the available optical and very high-energy gamma-ray (> 200 GeV) data for the BL Lac object PKS 2155-304, collected simultaneously with the ATOM and H.E.S.S. telescopes from 2007 until 2009. This study also includes X-ray (RXTE, Swift) and high-energy gamma-ray (Fermi-LAT) data. During the period analysed, the source was transitioning from its flaring to quiescent optical states, and was characterized by only moderate flux changes at different wavelengths on the timescales of days and months. A flattening of the optical continuum with an increasing optical flux can be noted in the collected dataset, but only occasionally and only at higher flux levels. We did not find any universal relation between the very high-energy gamma-ray and optical flux changes on the timescales from days and weeks up to several years. On the other hand, we noted that at higher flux levels the source can follow two distinct tracks in the optical flux-colour diagrams, which seem to be related to distinct gamma-ray states of the blazar. The obtained results therefore indicate a complex scaling between the optical and gamma-ray emission of PKS 2155 304, with different correlation patterns holding at different epochs, and a gamma-ray flux depending on the combination of an optical flux and colour rather than a flux alone.
KW - radiation mechanisms: non-thermal
KW - galaxies: active
KW - black hole physics
KW - BL Lacertae objects: individual: PKS 2155-304
KW - galaxies: jets
KW - gamma rays: galaxies
Y1 - 2014
U6 - http://dx.doi.org/10.1051/0004-6361/201424142
SN - 0004-6361 (print)
SN - 1432-0746 (online)
VL - 571
PB - EDP Sciences
CY - Les Ulis
ER -
TY - JOUR
A1 - Aliu, E.
A1 - Archambault, S.
A1 - Arlen, T.
A1 - Aune, T.
A1 - Barnacka, A.
A1 - Beilicke, M.
A1 - Benbow, W.
A1 - Berger, K.
A1 - Bird, R.
A1 - Bouvier, A.
A1 - Buckley, J. H.
A1 - Bugaev, V.
A1 - Cerruti, M.
A1 - Chen, X.
A1 - Ciupik, L.
A1 - Collins-Hughes, E.
A1 - Connolly, M. P.
A1 - Cui, W.
A1 - Dumm, J.
A1 - Eisch, J. D.
A1 - Falcone, A.
A1 - Federici, S.
A1 - Feng, Q.
A1 - Finley, J. P.
A1 - Fleischhack, H.
A1 - Fortin, P.
A1 - Fortson, L.
A1 - Furniss, A.
A1 - Galante, N.
A1 - Gillanders, G. H.
A1 - Griffin, S.
A1 - Griffiths, S. T.
A1 - Grube, J.
A1 - Gyuk, G.
A1 - Hakansson, N.
A1 - Hanna, D.
A1 - Holder, J.
A1 - Hughes, G.
A1 - Hughes, Z.
A1 - Humensky, T. B.
A1 - Johnson, C. A.
A1 - Kaaret, P.
A1 - Kar, P.
A1 - Kertzman, M.
A1 - Khassen, Y.
A1 - Kieda, D.
A1 - Krawczynski, H.
A1 - Krennrich, F.
A1 - Lang, M. J.
A1 - Madhavan, A. S.
A1 - Majumdar, P.
A1 - McArthur, S.
A1 - McCann, A.
A1 - Meagher, K.
A1 - Millis, J.
A1 - Moriarty, P.
A1 - Mukherjee, R.
A1 - Nelson, T.
A1 - Nieto, D.
A1 - Ong, R. A.
A1 - Otte, A. N.
A1 - Park, N.
A1 - Perkins, J. S.
A1 - Pohl, M.
A1 - Popkow, A.
A1 - Prokoph, H.
A1 - Quinn, J.
A1 - Ragan, K.
A1 - Rajotte, J.
A1 - Reyes, L. C.
A1 - Reynolds, P. T.
A1 - Richards, G. T.
A1 - Roache, E.
A1 - Sadun, A.
A1 - Santander, M.
A1 - Sembroski, G. H.
A1 - Shahinyan, K.
A1 - Sheidaei, F.
A1 - Smith, A. W.
A1 - Staszak, D.
A1 - Telezhinsky, I.
A1 - Theiling, M.
A1 - Tyler, J.
A1 - Varlotta, A.
A1 - Vassiliev, V. V.
A1 - Vincent, S.
A1 - Wakely, S. P.
A1 - Weekes, T. C.
A1 - Weinstein, A.
A1 - Welsing, R.
A1 - Wilhelm, A.
A1 - Williams, D. A.
A1 - Zitzer, B.
A1 - Boettcher, M.
A1 - Fumagalli, M.
T1 - Investigating broadband variability of the TeV blazar 1ES 1959+650
JF - The astrophysical journal : an international review of spectroscopy and astronomical physics
N2 - We summarize broadband observations of the TeV-emitting blazar 1ES 1959+650, including optical R-band observations by the robotic telescopes Super-LOTIS and iTelescope, UV observations by Swift Ultraviolet and Optical Telescope, X-ray observations by the Swift X-ray Telescope, high-energy gamma-ray observations with the Fermi Large Area Telescope, and very-high-energy (VHE) gamma-ray observations by VERITAS above 315 GeV, all taken between 2012 April 17 and 2012 June 1 (MJD 56034 and 56079). The contemporaneous variability of the broadband spectral energy distribution is explored in the context of a simple synchrotron self Compton (SSC) model. In the SSC emission scenario, we find that the parameters required to represent the high state are significantly different than those in the low state. Motivated by possible evidence of gas in the vicinity of the blazar, we also investigate a reflected emission model to describe the observed variability pattern. This model assumes that the non-thermal emission from the jet is reflected by a nearby cloud of gas, allowing the reflected emission to re-enter the blob and produce an elevated gamma-ray state with no simultaneous elevated synchrotron flux. The model applied here, although not required to explain the observed variability pattern, represents one possible scenario which can describe the observations. As applied to an elevated VHE state of 66% of the Crab Nebula flux, observed on a single night during the observation period, the reflected emission scenario does not support a purely leptonic non-thermal emission mechanism. The reflected emission model does, however, predict a reflected photon field with sufficient energy to enable elevated gamma-ray emission via pion production with protons of energies between 10 and 100 TeV.
KW - BL Lacertae objects: individual (1ES 1959+650)
KW - gamma rays: galaxies
Y1 - 2014
U6 - http://dx.doi.org/10.1088/0004-637X/797/2/89
SN - 0004-637X (print)
SN - 1538-4357 (online)
VL - 797
IS - 2
PB - IOP Publ. Ltd.
CY - Bristol
ER -