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Archambault, S. ; Archer, A. ; Benbow, W. ; Buchovecky, M. ; Bugaev, V. ; Cerruti, M. ; Connolly, M. P. ; Cui, W. ; Falcone, A. ; Alonso, M. Fernandez ; Finley, J. P. ; Fleischhack, H. ; Fortson, L. ; Furniss, A. ; Griffin, S. ; Hutten, M. ; Hervet, O. ; Holder, J. ; Humensky, T. B. ; Johnson, C. A. ; Kaaret, P. ; Kar, P. ; Kieda, D. ; Krause, M. ; Krennrich, F. ; Lang, M. J. ; Lin, T. T. Y. ; Maier, G. ; McArthur, S. ; Moriarty, P. ; Nieto, D. ; Ong, R. A. ; Otte, A. N. ; Pohl, M. ; Popkow, A. ; Pueschel, Elisa ; Quinn, J. ; Ragan, K. ; Reynolds, P. T. ; Richards, G. T. ; Roache, E. ; Rovero, A. C. ; Sadeh, I. ; Shahinyan, K. ; Staszak, D. ; Telezhinsky, Igor O. ; Tyler, J. ; Wakely, S. P. ; Weinstein, A. ; Weisgarber, T. ; Wilcox, P. ; Wilhelm, Alina ; Williams, D. A. ; Zitzer, B.
We present a search for magnetically broadened gamma-ray emission around active galactic nuclei (AGNs), using VERITAS observations of seven hard-spectrum blazars. A cascade process occurs when multi-TeV gamma-rays from an AGN interact with extragalactic background light (EBL) photons to produce electron-positron pairs, which then interact with cosmic microwave background photons via inverse-Compton scattering to produce gamma-rays. Due to the deflection of the electron- positron pairs, a non-zero intergalactic magnetic field (IGMF) would potentially produce detectable effects on the angular distribution of the cascade emission. In particular, an angular broadening compared to the unscattered emission could occur. Through non-detection of angularly broadened emission from 1ES 1218 vertical bar 304, the source with the largest predicted cascade fraction, we exclude a range of IGMF strengths around 10(-14) G at the 95% confidence level. The extent of the exclusion range varies with the assumptions made about the intrinsic spectrum of 1ES. 1218+304 and the EBL model used in the simulation of the cascade process. All of the sources are used to set limits on the flux due to extended emission.
Archambault, S. ; Archer, A. ; Benbow, W. ; Bird, R. ; Biteau, Jonathan ; Buchovecky, M. ; Buckley, J. H. ; Bugaev, V. ; Byrum, K. ; Cerruti, M. ; Chen, Xuhui ; Ciupik, L. ; Connolly, M. P. ; Cui, W. ; Eisch, J. D. ; Errando, M. ; Falcone, A. ; Feng, Q. ; Finley, J. P. ; Fleischhack, H. ; Fortin, P. ; Fortson, L. ; Furniss, A. ; Gillanders, G. H. ; Griffin, S. ; Grube, J. ; Gyuk, G. ; Huetten, M. ; Hakansson, Nils ; Hanna, D. ; Holder, J. ; Humensky, T. B. ; Johnson, C. A. ; Kaaret, P. ; Kar, P. ; Kelley-Hoskins, N. ; Kertzman, M. ; Kieda, D. ; Krause, M. ; Krennrich, F. ; Kumar, S. ; Lang, M. J. ; Maier, G. ; McArthur, S. ; McCann, A. ; Meagher, K. ; Moriarty, P. ; Mukherjee, R. ; Nguyen, T. ; Nieto, D. ; Ong, R. A. ; Otte, A. N. ; Park, N. ; Perkins, J. S. ; Pichel, A. ; Pohl, Martin ; Popkow, A. ; Pueschel, Elisa ; Quinn, J. ; Ragan, K. ; Reynolds, P. T. ; Richards, G. T. ; Roache, E. ; Rovero, A. C. ; Santander, M. ; Sembroski, G. H. ; Shahinyan, K. ; Smith, A. W. ; Staszak, D. ; Telezhinsky, Igor O. ; Tucci, J. V. ; Tyler, J. ; Vincent, S. ; Wakely, S. P. ; Weiner, O. M. ; Weinstein, A. ; Williams, D. A. ; Zitzer, B. ; Fumagalli, M. ; Prochaska, J. X.
Between the beginning of its full-scale scientific operations in 2007 and 2012, the VERITAS Cherenkov telescope array observed more than 130 blazars; of these, 26 were detected as very-high-energy (VHE; E > 100 GeV) gamma-ray sources. In this work, we present the analysis results of a sample of 114 undetected objects. The observations constitute a total live-time of similar to 570 hr. The sample includes several unidentified Fermi-Large Area Telescope (LAT) sources (located at high Galactic latitude) as well as all the sources from the second Fermi-LAT catalog that are contained within the field of view of the VERITAS observations. We have also performed optical spectroscopy measurements in order to estimate the redshift of some of these blazars that do not have spectroscopic distance estimates. We present new optical spectra from the Kast instrument on the Shane telescope at the Lick observatory for 18 blazars included in this work, which allowed for the successful measurement or constraint on the redshift of four of them. For each of the blazars included in our sample, we provide the flux upper limit in the VERITAS energy band. We also study the properties of the significance distributions and we present the result of a stacked analysis of the data set, which shows a 4s excess.
Allen, C. ; Archambault, S. ; Archer, A. ; Benbow, W. ; Bird, R. ; Bourbeau, E. ; Brose, Robert ; Buchovecky, M. ; Buckley, J. H. ; Bugaev, V. ; Cardenzana, J. V. ; Cerruti, M. ; Chen, Xuhui ; Christiansen, J. L. ; Connolly, M. P. ; Cui, W. ; Daniel, M. K. ; Eisch, J. D. ; Falcone, Abe ; Feng, Q. ; Fernandez-Alonso, M. ; Finley, J. P. ; Fleischhack, H. ; Flinders, A. ; Fortson, L. ; Furniss, A. ; Gillanders, G. H. ; Griffin, S. ; Grube, J. ; Huetten, M. ; Hakansson, N. ; Hanna, D. ; Hervet, O. ; Holder, J. ; Hughes, G. ; Humensky, T. B. ; Johnson, C. A. ; Kaaret, P. ; Kar, P. ; Kelley-Hoskins, N. ; Kertzman, M. ; Kieda, D. ; Krause, M. ; Krennrich, F. ; Kumar, S. ; Lang, M. J. ; Maier, G. ; McArthur, S. ; McCann, A. ; Meagher, K. ; Moriarty, P. ; Mukherjee, R. ; Nguyen, T. ; Nieto, D. ; Ong, R. A. ; Otte, A. N. ; Park, N. ; Petrashyk, A. ; Pichel, A. ; Pohl, Martin ; Popkow, A. ; Pueschel, Elisa ; Quinn, J. ; Ragan, K. ; Reynolds, P. T. ; Richards, G. T. ; Roache, E. ; Rovero, A. C. ; Rulten, C. ; Sadeh, I. ; Santander, Marcos ; Sembroski, G. H. ; Shahinyan, K. ; Telezhinsky, Igor O. ; Tucci, J. V. ; Tyler, J. ; Wakely, S. P. ; Weinstein, A. ; Wilhelm, Alina ; Williams, D. A.
We present very-high-energy gamma-ray observations of the BL Lac object 1ES 2344+514 taken by the Very Energetic Radiation Imaging Telescope Array System between 2007 and 2015. 1ES 2344+514 is detected with a statistical significance above the background of 20.8 sigma in 47.2 h (livetime) of observations, making this the most comprehensive very-high-energy study of 1ES 2344+514 to date. Using these observations, the temporal properties of 1ES 2344+514 are studied on short and long times-scales. We fit a constant-flux model to nightly and seasonally binned light curves and apply a fractional variability test to determine the stability of the source on different time-scales. We reject the constant-flux model for the 2007-2008 and 2014-2015 nightly binned light curves and for the long-term seasonally binned light curve at the > 3 sigma level. The spectra of the time-averaged emission before and after correction for attenuation by the extragalactic background light are obtained. The observed time-averaged spectrum above 200 GeV is satisfactorily fitted (x(2)/NDF = 7.89/6) by a power-law function with an index Gamma = 2.46 +/- 0.06(stat) +/- 0.20(sys) and extends to at least 8 TeV. The extragalactic-backgroundlight-deabsorbed spectrum is adequately fit (x(2)/NDF = 6.73/6) by a power-law function with an index Gamma = 2.15 +/- 0.06(stat) +/- 0.20(sys) while an F-test indicates that the power law with an exponential cut-off function provides a marginally better fit (x(2)/NDF = 2.56/5) at the 2.1 sigma level. The source location is found to be consistent with the published radio location and its spatial extent is consistent with a point source.
Aliu, E. ; Archambault, S. ; Archer, A. ; Arlen, T. ; Aune, T. ; Barnacka, Anna ; Behera, B. ; Beilicke, M. ; Benbow, W. ; Berger, K. ; Bird, R. ; Böttcher, Markus ; Bouvier, A. ; Buchovecky, M. ; Buckley, J. H. ; Bugaev, V. ; Cardenzana, J. V. ; Cerruti, M. ; Cesarini, A. ; Chen, Xuhui ; Ciupik, L. ; Collins-Hughes, E. ; Connolly, M. P. ; Cui, W. ; Dumm, J. ; Eisch, J. D. ; Falcone, A. ; Federici, Simone ; Feng, Q. ; Finley, J. P. ; Fleischhack, H. ; Fortin, P. ; Fortson, L. ; Furniss, A. ; Galante, N. ; Gall, D. ; Gillanders, G. H. ; Griffin, S. ; Griffiths, S. T. ; Grube, J. ; Gyuk, G. ; Hütten, M. ; Hakansson, Nils ; Holder, J. ; Hughes, G. ; Humensky, T. B. ; Johnson, C. A. ; Kaaret, P. ; Kar, P. ; Kelley-Hoskins, N. ; Kertzman, M. ; Khassen, Y. ; Kieda, D. ; Krause, M. ; Krawczynski, H. ; Krennrich, F. ; Lang, M. J. ; Madhavan, A. S. ; Maier, G. ; McArthur, S. ; McCann, A. ; Meagher, K. ; Millis, J. ; Moriarty, P. ; Mukherjee, R. ; Nieto, D. ; Ong, R. A. ; Orr, M. ; Otte, A. N. ; Pandel, D. ; Park, N. ; Pelassa, V. ; Perkins, J. S. ; Pichel, A. ; Pohl, Martin ; Popkow, A. ; Quinn, J. ; Ragan, K. ; Reyes, L. C. ; Reynolds, P. T. ; Roache, E. ; Rousselle, J. ; Rovero, A. C. ; Saxon, D. B. ; Sembroski, G. H. ; Shahinyan, K. ; Sheidaei, F. ; Skole, C. ; Smith, A. W. ; Staszak, D. ; Telezhinsky, Igor O. ; Theiling, M. ; Todd, N. W. ; Tucci, J. V. ; Tyler, J. ; Varlotta, A. ; Vassiliev, V. V. ; Vincent, S. ; Wakely, S. P. ; Weiner, O. M. ; Weinstein, A. ; Welsing, R. ; Wilhelm, Alina ; Williams, D. A. ; Zitzer, B. ; Baring, M. G. ; Gonzalez, J. Becerra ; Cillis, A. N. ; Horan, D. ; Paneque, D.
The very high energy (VHE; E > 100 GeV) blazar Markarian 501 was observed between April 17 and May 5 (MJD 54 938-54 956), 2009, as part of an extensive multiwavelength campaign from radio to VHE. Strong VHE yray activity was detected on May 1st with Whipple and VERITAS, when the flux (E > 400 GeV) increased to 10 times the preflare baseline flux (3.9 x 10(-11) ph cm(-2) s(-1)), reaching five times the flux of the Crab Nebula. This coincided with a decrease in the optical polarization and a rotation of the polarization angle by 15. This VHE flare showed a fast flux variation with an increase of a factor similar to 4 in 25 min, and a falling time of similar to 50 min. We present the observations of the quiescent state previous to the flare and of the high state after the flare, focusing on the flux and spectral variability from Whipple, VERITAS, Fermi-LAT, RXTE, and Swift combined with optical and radio data.
Unprecedented study of the broadband emission of Mrk 421 during flaring activity in March 2010
(2015)
Aleksic, J. ; Ansoldi, S. ; Antonelli, L. A. ; Antoranz, P. ; Babic, A. ; Bangale, P. ; de Almeida, U. Barres ; Barrio, J. A. ; Gonzalez, J. Becerra ; Bednarek, W. ; Bernardini, E. ; Biasuzzi, B. ; Biland, A. ; Blanch Bigas, O. ; Boller, A. ; Bonnefoy, S. ; Bonnoli, G. ; Borracci, F. ; Bretz, T. ; Carmona, E. ; Carosi, A. ; Colin, P. ; Colombo, E. ; Contreras, J. L. ; Cortina, J. ; Covino, S. ; Da Vela, P. ; Dazzi, F. ; De Angelis, A. ; De Caneva, G. ; De Lotto, B. ; Wilhelmi, E. de Ona ; Mendez, C. Delgado ; Prester, Dijana Dominis ; Dorner, D. ; Doro, M. ; Einecke, S. ; Eisenacher, D. ; Elsaesser, D. ; Fonseca, M. V. ; Font, L. ; Frantzen, K. ; Fruck, C. ; Galindo, D. ; Lopez, R. J. Garcia ; Garczarczyk, M. ; Terrats, D. Garrido ; Gaug, M. ; Godinovic, N. ; Munoz, A. Gonzalez ; Gozzini, S. R. ; Hadasch, D. ; Hanabata, Y. ; Hayashida, M. ; Herrera, J. ; Hildebrand, D. ; Hose, J. ; Hrupec, D. ; Hughes, G. ; Idec, W. ; Kadenius, V. ; Kellermann, H. ; Knoetig, M. L. ; Kodani, K. ; Konno, Y. ; Krause, J. ; Kubo, H. ; Kushida, J. ; La Barbera, A. ; Lelas, D. ; Lewandowska, N. ; Lindfors, E. ; Lombardi, S. ; Lopez, M. ; Lopez-Coto, R. ; Lopez-Oramas, A. ; Lorenz, E. ; Lozano, I. ; Makariev, M. ; Mallot, K. ; Maneva, G. ; Mankuzhiyil, N. ; Mannheim, K. ; Maraschi, L. ; Marcote, B. ; Mariotti, M. ; Martinez, M. ; Mazin, D. ; Menzel, U. ; Miranda, J. M. ; Mirzoyan, R. ; Moralejo, A. ; Munar-Adrover, P. ; Nakajima, D. ; Niedzwiecki, A. ; Nilsson, K. ; Nishijima, K. ; Noda, K. ; Orito, R. ; Overkemping, A. ; Paiano, S. ; Palatiello, M. ; Paneque, D. ; Paoletti, R. ; Paredes, J. M. ; Paredes-Fortuny, X. ; Persic, M. ; Moroni, P. G. Prada ; Prandini, E. ; Puljak, I. ; Reinthal, R. ; Rhode, W. ; Ribo, M. ; Rico, J. ; Garcia, J. Rodriguez ; Rugamer, S. ; Saito, T. ; Saito, K. ; Satalecka, K. ; Scalzotto, V. ; Scapin, V. ; Schultz, C. ; Schweizer, T. ; Sun, S. ; Shore, S. N. ; Sillanpaa, A. ; Sitarek, J. ; Snidaric, I. ; Sobczynska, D. ; Spanier, F. ; Stamatescu, V. ; Stamerra, A. ; Steinbring, T. ; Steinke, B. ; Storz, J. ; Strzys, M. ; Takalo, L. ; Takami, H. ; Tavecchio, F. ; Temnikov, P. ; Terzic, T. ; Tescaro, D. ; Teshima, M. ; Thaele, J. ; Tibolla, O. ; Torres, D. F. ; Toyama, T. ; Treves, A. ; Uellenbeck, M. ; Vogler, P. ; Zanin, R. ; Archambault, S. ; Archer, A. ; Beilicke, M. ; Benbow, W. ; Berger, K. ; Bird, R. ; Biteau, Jonathan ; Buckley, J. H. ; Bugaev, V. ; Cerruti, M. ; Chen, Xiaoming ; Ciupik, L. ; Collins-Hughes, E. ; Cui, W. ; Eisch, J. D. ; Falcone, A. ; Feng, Q. ; Finley, J. P. ; Fortin, P. ; Fortson, L. ; Furniss, A. ; Galante, N. ; Gillanders, G. H. ; Griffin, S. ; Gyuk, G. ; Hakansson, Nils ; Holder, J. ; Johnson, C. A. ; Kaaret, P. ; Kar, P. ; Kertzman, M. ; Kieda, D. ; Lang, M. J. ; McArthur, S. ; McCann, A. ; Meagher, K. ; Millis, J. ; Moriarty, P. ; Ong, R. A. ; Otte, A. N. ; Perkins, J. S. ; Pichel, A. ; Pohl, Manuela ; Popkow, A. ; Prokoph, H. ; Pueschel, Elisa ; Ragan, K. ; Reyes, L. C. ; Reynolds, P. T. ; Richards, G. T. ; Roache, E. ; Rovero, A. C. ; Sembroski, G. H. ; Shahinyan, K. ; Staszak, D. ; Telezhinsky, Igor O. ; Tucci, J. V. ; Tyler, J. ; Varlotta, A. ; Wakely, S. P. ; Welsing, R. ; Wilhelm, Alina ; Williams, D. A. ; Buson, S. ; Finke, J. ; Villata, M. ; Raiteri, C. ; Aller, H. D. ; Aller, M. F. ; Cesarini, A. ; Chen, W. P. ; Gurwell, M. A. ; Jorstad, S. G. ; Kimeridze, G. N. ; Koptelova, E. ; Kurtanidze, O. M. ; Kurtanidze, S. O. ; Lahteenmaki, A. ; Larionov, V. M. ; Larionova, E. G. ; Lin, H. C. ; McBreen, B. ; Moody, J. W. ; Morozova, D. A. ; Marscher, A. P. ; Max-Moerbeck, W. ; Nikolashvili, M. G. ; Perri, M. ; Readhead, A. C. S. ; Richards, J. L. ; Ros, J. A. ; Sadun, A. C. ; Sakamoto, T. ; Sigua, L. A. ; Smith, P. S. ; Tornikoski, M. ; Troitsky, I. S. ; Wehrle, A. E. ; Jordan, B.
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.
Aleksic, J. ; Ansoldi, S. ; Antonelli, L. A. ; Antoranz, P. ; Babic, A. ; Bangale, P. ; de Almeida, U. Barres ; Barrio, J. A. ; Gonzalez, J. Becerra ; Bednarek, W. ; Berger, K. ; Bernardini, E. ; Bilandli, A. ; Bianch, O. ; Bock, R. K. ; Bonnefoy, S. ; Bonnoli, G. ; Borracci, F. ; Bretz, T. ; Carmona, E. ; Carosi, A. ; Fidalgo, D. Carreto ; Colin, P. ; Colombo, E. ; Contreras, J. L. ; Cortina, J. ; Covino, S. ; Da Vela, P. ; Dazzi, F. ; De Angelis, A. ; De Caneva, G. ; De Lotto, B. ; Delgado Mendez, C. ; Doert, M. ; Dominguez, A. ; Prester, Dijana Dominis ; Dorner, D. ; Doro, M. ; Einecke, S. ; Eisenacher, D. ; Elsaesser, D. ; Farina, E. ; Ferenc, D. ; Fonseca, M. V. ; Font, L. ; Frantzen, K. ; Fruck, C. ; Garcia Lopez, R. J. ; Garczarczyki, M. ; Garrido Terrats, D. ; Gaug, M. ; Giavitto, G. ; Godinovic, N. ; Gonzalez Munoz, A. ; Gozzini, S. R. ; Hadamek, A. ; Hadasch, D. ; Herrero, A. ; Hildebrand, D. ; Hose, J. ; Hrupec, D. ; Idec, W. ; Kadenius, V. ; Kellermann, H. ; Knoetig, M. L. ; Krause, J. ; Kushida, J. ; La Barbera, A. ; Lelas, D. ; Lewandowska, N. ; Lindfors, E. ; Longo, F. ; Lombardi, S. ; Lopez, M. ; Lopez-Coto, R. ; Lopez-Oramas, A. ; Lorenz, E. ; Lozano, I. ; Makariev, M. ; Mallot, K. ; Maneva, G. ; Mankuzhiyil, N. ; Mannheim, K. ; Maraschi, L. ; Marcote, B. ; Mariotti, M. ; Martinez, M. ; Mazin, D. ; Menzel, U. ; Meucci, M. ; Miranda, J. M. ; Mirzoyan, R. ; Moralejo, A. ; Munar-Adrover, P. ; Nakajima, D. ; Niedzwiecki, A. ; Nilsson, K. ; Nowak, N. ; Orito, R. ; Overkemping, A. ; Paiano, S. ; Palatiello, M. ; Paneque, D. ; Paoletti, R. ; Paredes, J. M. ; Paredes-Fortuny, X. ; Partini, S. ; Persic, M. ; Prada, F. ; Moroni, P. G. Prada ; Prandini, E. ; Preziuso, S. ; Puljak, I. ; Reinthal, R. ; Rhode, W. ; Ribo, M. ; Rico, J. ; Garcia, J. Rodriguez ; Ruegamer, S. ; Saggion, A. ; Saito, K. ; Salvati, M. ; Satalecka, K. ; Scalzotto, V. ; Scapin, V. ; Schuliz, C. ; Schweizer, T. ; Shore, S. N. ; Sillanpaa, A. ; Sitarek, J. ; Snidaric, I. ; Sobczynska, D. ; Spanier, F. ; Stamatescu, V. ; Stamerra, A. ; Steinbring, T. ; Storz, J. ; Sun, S. ; Suric, T. ; Takalo, L. ; Tavecchio, F. ; Temnikov, P. ; Terzic, T. ; Tescaro, D. ; Teshima, M. ; Thaele, J. ; Tibolla, O. ; Torres, D. F. ; Toyama, T. ; Treves, A. ; Uellenbeck, M. ; Vogler, P. ; Wagner, R. M. ; Zandanel, F. ; Zanin, R. ; Archambault, S. ; Behera, B. ; Beilicke, M. ; Benbow, W. ; Bird, R. ; Buckley, J. H. ; Bugaev, V. ; Cerruti, M. ; Chen, X. ; Ciupik, L. ; Collins-Hughes, E. ; Cui, W. ; Dumm, J. ; Eisch, J. D. ; Falcone, A. ; Federici, S. ; Feng, Q. ; Finley, J. P. ; Fleischhack, H. ; Fortin, P. ; Fortson, L. ; Furniss, A. ; Griffin, S. ; Griffiths, S. T. ; Grube, J. ; Gyuk, G. ; Hanna, D. ; Holder, J. ; Hughes, G. ; Humensky, T. B. ; Johnson, C. A. ; Kaaret, P. ; Kertzman, M. ; Khassen, Y. ; Kieda, D. ; Krawczynski, H. ; Krennrich, F. ; Kumar, S. ; Lang, M. J. ; Maier, G. ; McArthur, S. ; Meagher, K. ; Moriarty, P. ; Mukherjee, R. ; Ong, R. A. ; Otte, A. N. ; Park, N. ; Pichel, A. ; Pohl, M. ; Popkow, A. ; Prokoph, H. ; Quinn, M. J. ; Ragan, K. ; Rajotte, J. ; Reynolds, P. T. ; Richards, G. T. ; Roache, E. ; Rovero, A. C. ; Sembroski, G. H. ; Shahinyan, K. ; Staszak, D. ; Telezhinsky, Igor O. ; Theiling, M. ; Tucci, J. V. ; Tyler, J. ; Varlotta, A. ; Wakely, S. P. ; Weekes, T. C. ; Weinstein, A. ; Welsing, R. ; Wilhelm, Alina ; Williams, D. A. ; Zitzer, B. ; Villata, M. ; Raiteri, C. ; Aller, H. D. ; Aller, M. F. ; Chen, W. P. ; Jordan, B. ; Koptelova, E. ; Kurtanidze, O. M. ; Lahteenmaki, A. ; McBreen, B. ; Larionov, V. M. ; Lin, C. S. ; Nikolashvili, M. G. ; Angelakis, E. ; Capalbi, M. ; Carraminana, A. ; Carrasco, L. ; Cassaro, P. ; Cesarini, A. ; Fuhrmann, L. ; Giroletti, M. ; Hovatta, T. ; Krichbaum, T. P. ; Krimm, H. A. ; Max-Moerbeck, W. ; Moody, J. W. ; Maccaferri, G. ; Mori, Y. ; Nestoras, I. ; Orlati, A. ; Pace, C. ; Pearson, R. ; Perri, M. ; Readhead, A. C. S. ; Richards, J. L. ; Sadun, A. C. ; Sakamoto, T. ; Tammi, J. ; Tornikoski, M. ; Yatsu, Y. ; Zook, A.
Aims. We perform an extensive characterization of the broadband emission of Mrk 421, as well as its temporal evolution, during the non-flaring (low) state. The high brightness and nearby location (z = 0.031) of Mrk 421 make it an excellent laboratory to study blazar emission. The goal is to learn about the physical processes responsible for the typical emission of Mrk 421, which might also be extended to other blazars that are located farther away and hence are more difficult to study.
Methods. We performed a 4.5-month multi-instrument campaign on Mrk 421 between January 2009 and June 2009, which included VLBA, F-GAMMA, GASP-WEBT, Swift, RXTE, Fermi-LAT, MAGIC, and Whipple, among other instruments and collaborations. This extensive radio to very-high-energy (VHE; E > 100 GeV) gamma-ray dataset provides excellent temporal and energy coverage, which allows detailed studies of the evolution of the broadband spectral energy distribution.
Results. Mrk421 was found in its typical (non-flaring) activity state, with a VHE flux of about half that of the Crab Nebula, yet the light curves show significant variability at all wavelengths, the highest variability being in the X-rays. We determined the power spectral densities (PSD) at most wavelengths and found that all PSDs can be described by power-laws without a break, and with indices consistent with pink/red-noise behavior. We observed a harder-when-brighter behavior in the X-ray spectra and measured a positive correlation between VHE and X-ray fluxes with zero time lag. Such characteristics have been reported many times during flaring activity, but here they are reported for the first time in the non-flaring state. We also observed an overall anti-correlation between optical /UV and X-rays extending over the duration of the campaign.
Conclusions. The harder-when-brighter behavior in the X-ray spectra and the measured positive X-ray/VHE correlation during the 2009 multiwavelength campaign suggests that the physical processes dominating the emission during non-flaring states have similarities with those occurring during flaring activity. In particular, this observation supports leptonic scenarios as being responsible for the emission of Mrk 421 during non-flaring activity. Such a temporally extended X-ray /VHE correlation is not driven by any single flaring event, and hence is difficult to explain within the standard hadronic scenarios. The highest variability is observed in the X-ray band, which, within the one-zone synchrotron self-Compton scenario, indicates that the electron energy distribution is most variable at the highest energies.
Ahnen, M. L. ; Ansoldi, S. ; Antonelli, L. A. ; Arcaro, C. ; Babic, A. ; Banerjee, B. ; Bangale, P. ; Barres de Almeida, U. ; Barrio, J. A. ; Gonzalez, J. Becerra ; Bednarek, W. ; Bernardini, E. ; Berti, A. ; Bhattacharyya, W. ; Blanch, O. ; Bonnoli, G. ; Carosi, R. ; Carosi, A. ; 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, Jose Miguel Martins ; Di Pierro, F. ; Doert, M. ; Dominguez, A. ; Prester, D. Dominis ; Doro, M. ; Glawion, D. Eisenacher ; Engelkemeier, M. ; Ramazani, V. Fallah ; Fernandez-Barral, A. ; Fidalgo, D. ; Fonseca, M. V. ; Font, L. ; Fruck, C. ; Galindo, D. ; Lopez, R. J. Garcia ; Garczarczyk, M. ; Gaug, M. ; Giammaria, P. ; Godinovic, 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. ; Kuvezdic, D. ; Lelas, D. ; Lindfors, E. ; Lombardi, S. ; Longo, F. ; Lopez, M. ; Maggio, C. ; Majumdar, P. ; Makariev, M. ; Maneva, G. ; Manganaro, M. ; Maraschi, L. ; Mariotti, M. ; Martinez, M. ; Mazin, D. ; Menzel, U. ; Minev, M. ; Miranda, J. M. ; Mirzoyan, R. ; Moralejo, A. ; Moreno, V. ; Moretti, E. ; Nagayoshi, T. ; Neustroev, V. ; Niedzwiecki, A. ; Nievas Rosillo, M. ; Nigro, C. ; Nilsson, K. ; Ninci, D. ; Nishijima, K. ; Noda, K. ; Nogues, L. ; Paiano, S. ; Palacio, J. ; Paneque, D. ; Paoletti, R. ; Paredes, J. M. ; Pedaletti, G. ; Peresano, M. ; Perri, L. ; Persic, M. ; Moroni, P. G. Prada ; Prandini, E. ; Puljak, I. ; Garcia, J. R. ; Reichardt, I. ; Ribo, M. ; Rico, J. ; Righi, C. ; Rugliancich, A. ; Saito, T. ; Satalecka, K. ; Schroeder, S. ; Schweizer, T. ; Shore, S. N. ; Sitarek, J. ; Snidaric, I. ; Sobczynska, D. ; Stamerra, A. ; Strzys, M. ; Suric, T. ; Takalo, L. ; Tavecchio, F. ; Temnikov, P. ; Terzic, T. ; Teshima, M. ; Torres-Alba, N. ; Treves, A. ; Tsujimoto, S. ; Vanzo, G. ; Vazquez Acosta, M. ; Vovk, I. ; Ward, J. E. ; Will, M. ; Zaric, D. ; Arbet-Engels, A. ; Baack, D. ; Balbo, M. ; Biland, A. ; Blank, M. ; Bretz, T. ; Bruegge, K. ; Bulinski, M. ; Buss, J. ; Dmytriiev, A. ; Dorner, D. ; Einecke, S. ; Elsaesser, D. ; Herbst, T. ; Hildebrand, D. ; Kortmann, L. ; Linhoff, L. ; Mahlke, M. ; Mannheim, K. ; Mueller, S. A. ; Neise, D. ; Neronov, A. ; Noethe, M. ; Oberkirch, J. ; Paravac, A. ; Rhode, W. ; Schleicher, B. ; Schulz, F. ; Sedlaczek, K. ; Shukla, A. ; Sliusar, V. ; Walter, R. ; Archer, A. ; Benbow, W. ; Bird, R. ; Brose, Robert ; Buckley, J. H. ; Bugaev, V. ; Christiansen, J. L. ; Cui, W. ; Daniel, M. K. ; Falcone, A. ; Feng, Q. ; Finley, J. P. ; Gillanders, G. H. ; Gueta, O. ; Hanna, D. ; Hervet, O. ; Holder, J. ; Hughes, G. ; Huetten, M. ; Humensky, T. B. ; Johnson, C. A. ; Kaaret, P. ; Kar, P. ; Kelley-Hoskins, N. ; Kertzman, M. ; Kieda, D. ; Krause, M. ; Krennrich, F. ; Kumar, S. ; Lang, M. J. ; Lin, T. T. Y. ; Maier, G. ; McArthur, S. ; Moriarty, P. ; Mukherjee, R. ; Ong, R. A. ; Otte, A. N. ; Park, N. ; Petrashyk, A. ; Pichel, A. ; Pohl, Martin ; Quinn, J. ; Ragan, K. ; Reynolds, P. T. ; Richards, G. T. ; Roache, E. ; Rovero, A. C. ; Rulten, C. ; Sadeh, I. ; Santander, M. ; Sembroski, G. H. ; Shahinyan, K. ; Sushch, Iurii ; Tyler, J. ; Wakely, S. P. ; Weinstein, A. ; Wells, R. M. ; Wilcox, P. ; Wilhel, A. ; Williams, D. A. ; Williamson, T. J. ; Zitzer, B. ; Perri, M. ; Verrecchia, F. ; Leto, C. ; Villata, M. ; Raiteri, C. M. ; Jorstad, S. G. ; Larionov, V. M. ; Blinov, D. A. ; Grishina, T. S. ; Kopatskaya, E. N. ; Larionova, E. G. ; Nikiforova, A. A. ; Morozova, D. A. ; Troitskaya, Yu. V. ; Troitsky, I. S. ; Kurtanidze, O. M. ; Nikolashvili, M. G. ; Kurtanidze, S. O. ; Kimeridze, G. N. ; Chigladze, R. A. ; Strigachev, A. ; Sadun, A. C.
Aims. We aim to characterize the multiwavelength emission from Markarian 501 (Mrk 501), quantify the energy-dependent variability, study the potential multiband correlations, and describe the temporal evolution of the broadband emission within leptonic theoretical scenarios. Methods. We organized a multiwavelength campaign to take place between March and July of 2012. Excellent temporal coverage was obtained with more than 25 instruments, including the MAGIC, FACT and VERITAS Cherenkov telescopes, the instruments on board the Swift and Fermi spacecraft, and the telescopes operated by the GASP-WEBT collaboration. Results. Mrk 501 showed a very high energy (VHE) gamma-ray flux above 0.2 TeV of similar to 0.5 times the Crab Nebula flux (CU) for most of the campaign. The highest activity occurred on 2012 June 9, when the VHE flux was similar to 3 CU, and the peak of the high-energy spectral component was found to be at similar to 2 TeV. Both the X-ray and VHE gamma-ray spectral slopes were measured to be extremely hard, with spectral indices <2 during most of the observing campaign, regardless of the X-ray and VHE flux. This study reports the hardest Mrk 501 VHE spectra measured to date. The fractional variability was found to increase with energy, with the highest variability occurring at VHE. Using the complete data set, we found correlation between the X-ray and VHE bands; however, if the June 9 flare is excluded, the correlation disappears (significance <3 sigma) despite the existence of substantial variability in the X-ray and VHE bands throughout the campaign. Conclusions. The unprecedentedly hard X-ray and VHE spectra measured imply that their low- and high-energy components peaked above 5 keV and 0.5 TeV, respectively, during a large fraction of the observing campaign, and hence that Mrk 501 behaved like an extreme high-frequency-peaked blazar (EHBL) throughout the 2012 observing season. This suggests that being an EHBL may not be a permanent characteristic of a blazar, but rather a state which may change over time. The data set acquired shows that the broadband spectral energy distribution (SED) of Mrk 501, and its transient evolution, is very complex, requiring, within the framework of synchrotron self-Compton (SSC) models, various emission regions for a satisfactory description. Nevertheless the one-zone SSC scenario can successfully describe the segments of the SED where most energy is emitted, with a significant correlation between the electron energy density and the VHE gamma-ray activity, suggesting that most of the variability may be explained by the injection of high-energy electrons. The one-zone SSC scenario used reproduces the behavior seen between the measured X-ray and VHE gamma-ray fluxes, and predicts that the correlation becomes stronger with increasing energy of the X-rays.
Ahnen, M. L. ; Ansoldi, S. ; Antonelli, L. A. ; Antoranz, P. ; Babic, A. ; Banerjee, B. ; Bangale, P. ; de Almeida, U. Barres ; Barrio, J. A. ; Gonzalez, J. Becerra ; Bednarek, W. ; Bernardini, E. ; Berti, A. ; Biasuzzi, B. ; Biland, A. ; Blanch, O. ; Bonnefoy, S. ; Bonnoli, G. ; Borracci, F. ; Bretz, T. ; Buson, S. ; 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 Ona ; Di Pierro, F. ; Doert, M. ; Dominguez, A. ; Prester, D. Dominis ; Dorner, D. ; Doro, M. ; Einecke, S. ; Glawion, D. Eisenacher ; Elsaesser, D. ; Engelkemeier, M. ; Ramazani, V. Fallah ; Fernandez-Barral, A. ; Fidalgo, D. ; Fonseca, M. V. ; Font, L. ; Frantzen, K. ; Fruck, C. ; Galindo, D. ; Lopez, R. J. Garcia ; Garczarczyk, M. ; Terrats, D. Garrido ; Gaug, M. ; Giammaria, P. ; Godinovic, N. ; Gonzalez Munoz, A. ; Gora, D. ; Guberman, D. ; Hadasch, 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. ; Lopez, M. ; Lopez-Coto, R. ; Majumdar, P. ; Makariev, M. ; Mallot, K. ; Maneva, G. ; Manganaro, M. ; Mannheim, K. ; Maraschi, L. ; Marcote, B. ; Mariotti, M. ; Martinez, 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. ; Nogues, L. ; Overkemping, A. ; Paiano, S. ; Palacio, J. ; Palatiello, M. ; Paneque, D. ; Paoletti, R. ; Paredes, J. M. ; Paredes-Fortuny, X. ; Pedaletti, G. ; Peresano, M. ; Perri, L. ; Persic, M. ; Poutanen, J. ; Moroni, P. G. Prada ; Prandini, E. ; Puljak, I. ; Reichardt, I. ; Rhode, W. ; Ribo, M. ; Rico, J. ; Rodriguez Garcia, J. ; Saito, T. ; Satalecka, K. ; Schroder, S. ; Schultz, C. ; Schweizer, T. ; Shore, S. N. ; Sillanpaa, A. ; Sitarek, J. ; Snidaric, I. ; Sobczynska, D. ; Stamerra, A. ; Steinbring, T. ; Strzys, M. ; Suric, T. ; Takalo, L. ; Tavecchio, F. ; Temnikov, P. ; Terzic, T. ; Tescaro, D. ; Teshima, M. ; Thaele, J. ; Torres, D. F. ; Toyama, T. ; Treves, A. ; Vanzo, G. ; Verguilov, V. ; Vovk, I. ; Ward, J. E. ; Will, M. ; Wu, M. H. ; Zanin, R. ; Abeysekara, A. U. ; Archambault, S. ; Archer, A. ; Benbow, W. ; Bird, R. ; Buchovecky, M. ; Buckley, J. H. ; Bugaev, V. ; Connolly, M. P. ; Cui, W. ; Dickinson, H. J. ; Falcone, A. ; Feng, Q. ; Finley, J. P. ; Fleischhack, H. ; Flinders, A. ; Fortson, L. ; Gillanders, G. H. ; Griffin, S. ; Grube, J. ; Huetten, M. ; Hanna, D. ; Holder, J. ; Humensky, T. B. ; Kaaret, P. ; Kar, P. ; Kelley-Hoskins, N. ; Kertzman, M. ; Kieda, D. ; Krause, M. ; Krennrich, F. ; Lang, M. J. ; Maier, G. ; McCann, A. ; Moriarty, P. ; Mukherjee, R. ; Nieto, D. ; Ong, R. A. ; Otte, N. ; Park, N. ; Perkins, J. ; Pichel, A. ; Pohl, M. ; Popkow, A. ; Pueschel, Elisa ; Quinn, J. ; Ragan, K. ; Reynolds, P. T. ; Richards, G. T. ; Roache, E. ; Rovero, A. C. ; Rulten, C. ; Sadeh, I. ; Santander, M. ; Sembroski, G. H. ; Shahinyan, K. ; Telezhinsky, Igor O. ; Tucci, J. V. ; Tyler, J. ; Wakely, S. P. ; Weinstein, A. ; Wilcox, P. ; Wilhelm, Alina ; Williams, D. A. ; Zitzer, B. ; Razzaque, S. ; Villata, M. ; Raiteri, C. M. ; Aller, H. D. ; Aller, M. F. ; Larionov, V. M. ; Arkharov, A. A. ; Blinov, D. A. ; Efimova, N. V. ; Grishina, T. S. ; Hagen-Thorn, V. A. ; Kopatskaya, E. N. ; Larionova, L. V. ; Larionova, E. G. ; Morozova, D. A. ; Troitsky, I. S. ; Ligustri, R. ; Calcidese, P. ; Berdyugin, A. ; Kurtanidze, O. M. ; Nikolashvili, M. G. ; Kimeridze, G. N. ; Sigua, L. A. ; Kurtanidze, S. O. ; Chigladze, R. A. ; Chen, W. P. ; Koptelova, E. ; Sakamoto, T. ; Sadun, A. C. ; Moody, J. W. ; Pace, C. ; Pearson, R. ; Yatsu, Y. ; Mori, Y. ; Carraminyana, A. ; Carrasco, L. ; de la Fuente, E. ; Norris, J. P. ; Smith, P. S. ; Wehrle, A. ; Gurwell, M. A. ; Zook, A. ; Pagani, C. ; Perri, M. ; Capalbi, M. ; Cesarini, A. ; Krimm, H. A. ; Kovalev, Y. Y. ; Kovalev, Yu. A. ; Ros, E. ; Pushkarev, A. B. ; Lister, M. L. ; Sokolovsky, K. V. ; Kadler, M. ; Piner, G. ; Lahteenmaki, A. ; Tornikoski, M. ; Angelakis, E. ; Krichbaum, T. P. ; Nestoras, I. ; Fuhrmann, L. ; Zensus, J. A. ; Cassaro, P. ; Orlati, A. ; Maccaferri, G. ; Leto, P. ; Giroletti, M. ; Richards, J. L. ; Max-Moerbeck, W. ; Readhead, A. C. S.
Aims. We present an extensive study of the BL Lac object Mrk 501 based on a data set collected during the multi-instrument campaign spanning from 2009 March 15 to 2009 August 1, which includes, among other instruments, MAGIC, VERITAS, Whipple 10 m, and Fermi-LAT to cover the gamma-ray range from 0.1 GeV to 20 TeV; RXTE and Swift to cover wavelengths from UV to hard X-rays; and GASP-WEBT, which provides coverage of radio and optical wavelengths. Optical polarization measurements were provided for a fraction of the campaign by the Steward and St. Petersburg observatories. We evaluate the variability of the source and interband correlations, the gamma-ray flaring activity occurring in May 2009, and interpret the results within two synchrotron self-Compton (SSC) scenarios. Methods. The multiband variability observed during the full campaign is addressed in terms of the fractional variability, and the possible correlations are studied by calculating the discrete correlation function for each pair of energy bands where the significance was evaluated with dedicated Monte Carlo simulations. The space of SSC model parameters is probed following a dedicated grid-scan strategy, allowing for a wide range of models to be tested and offering a study of the degeneracy of model-to-data agreement in the individual model parameters, hence providing a less biased interpretation than the "single-curve SSC model adjustment" typically reported in the literature. Results. We find an increase in the fractional variability with energy, while no significant interband correlations of flux changes are found on the basis of the acquired data set. The SSC model grid-scan shows that the flaring activity around May 22 cannot be modeled adequately with a one-zone SSC scenario (using an electron energy distribution with two breaks), while it can be suitably described within a two (independent) zone SSC scenario. Here, one zone is responsible for the quiescent emission from the averaged 4.5-month observing period, while the other one, which is spatially separated from the first, dominates the flaring emission occurring at X-rays and very-high-energy (> 100 GeV, VHE) gamma-rays. The flaring activity from May 1, which coincides with a rotation of the electric vector polarization angle (EVPA), cannot be satisfactorily reproduced by either a one-zone or a two-independent-zone SSC model, yet this is partially affected by the lack of strictly simultaneous observations and the presence of large flux changes on sub-hour timescales (detected at VHE gamma rays). Conclusions. The higher variability in the VHE emission and lack of correlation with the X-ray emission indicate that, at least during the 4.5-month observing campaign in 2009, the highest energy (and most variable) electrons that are responsible for the VHE gamma rays do not make a dominant contribution to the similar to 1 keV emission. Alternatively, there could be a very variable component contributing to the VHE gamma-ray emission in addition to that coming from the SSC scenario. The studies with our dedicated SSC grid-scan show that there is some degeneracy in both the one-zone and the two-zone SSC scenarios probed, with several combinations of model parameters yielding a similar model-to-data agreement, and some parameters better constrained than others. The observed gamma-ray flaring activity, with the EVPA rotation coincident with the first gamma-ray flare, resembles those reported previously for low frequency peaked blazars, hence suggesting that there are many similarities in the flaring mechanisms of blazars with different jet properties.
Actis, M. ; Agnetta, G. ; Aharonian, Felix A. ; Akhperjanian, A. G. ; Aleksic, J. ; Aliu, E. ; Allan, D. ; Allekotte, I. ; Antico, F. ; Antonelli, L. A. ; Antoranz, P. ; Aravantinos, A. ; Arlen, T. ; Arnaldi, H. ; Artmann, S. ; Asano, K. ; Asorey, H. G. ; Baehr, J. ; Bais, A. ; Baixeras, C. ; Bajtlik, S. ; Balis, D. ; Bamba, A. ; Barbier, C. ; Barcelo, M. ; Barnacka, Anna ; Barnstedt, Jürgen ; de Almeida, U. Barres ; Barrio, J. A. ; Basso, S. ; Bastieri, D. ; Bauer, C. ; Becerra Gonzalez, J. ; Becherini, Yvonne ; Bechtol, K. C. ; Becker, J. ; Beckmann, Volker ; Bednarek, W. ; Behera, B. ; Beilicke, M. ; Belluso, M. ; Benallou, M. ; Benbow, W. ; Berdugo, J. ; Berger, K. ; Bernardino, T. ; Bernlöhr, K. ; Biland, A. ; Billotta, S. ; Bird, T. ; Birsin, E. ; Bissaldi, E. ; Blake, S. ; Blanch Bigas, O. ; Bobkov, A. A. ; Bogacz, L. ; Bogdan, M. ; Boisson, Catherine ; Boix Gargallo, J. ; Bolmont, J. ; Bonanno, G. ; Bonardi, A. ; Bonev, T. ; Borkowski, Janett ; Botner, O. ; Bottani, A. ; Bourgeat, M. ; Boutonnet, C. ; Bouvier, A. ; Brau-Nogue, S. ; Braun, I. ; Bretz, T. ; Briggs, M. S. ; Brun, Pierre ; Brunetti, L. ; Buckley, H. ; Bugaev, V. ; Buehler, R. ; Bulik, Tomasz ; Busetto, G. ; Buson, S. ; Byrum, K. ; Cailles, M. ; Cameron, R. A. ; Canestrari, R. ; Cantu, S. ; Carmona, E. ; Carosi, A. ; Carr, John ; Carton, P. H. ; Casiraghi, M. ; Castarede, H. ; Catalano, O. ; Cavazzani, S. ; Cazaux, S. ; Cerruti, B. ; Cerruti, M. ; Chadwick, M. ; Chiang, J. ; Chikawa, M. ; Cieslar, M. ; Ciesielska, M. ; Cillis, A. N. ; Clerc, C. ; Colin, P. ; Colome, J. ; Compin, M. ; Conconi, P. ; Connaughton, V. ; Conrad, Jan ; Contreras, J. L. ; Coppi, P. ; Corlier, M. ; Corona, P. ; Corpace, O. ; Corti, D. ; Cortina, J. ; Costantini, H. ; Cotter, G. ; Courty, B. ; Couturier, S. ; Covino, S. ; Croston, J. ; Cusumano, G. ; Daniel, M. K. ; Dazzi, F. ; Deangelis, A. ; de Cea del Pozo, E. ; Dal Pino, E. M. de Gouveia ; de Jager, O. ; de la Calle Perez, I. ; De La Vega, G. ; De Lotto, B. ; de Naurois, M. ; Wilhelmi, E. de Ona ; de Souza, V. ; Decerprit, B. ; Deil, C. ; Delagnes, E. ; Deleglise, G. ; Delgado, C. ; Dettlaff, T. ; Di Paolo, A. ; Di Pierro, F. ; Diaz, C. ; Dick, J. ; Dickinson, H. ; Digel, S. W. ; Dimitrov, D. ; Disset, G. ; Djannati-Ataï, A. ; Doert, M. ; Domainko, W. ; Dorner, D. ; Doro, M. ; Dournaux, J. -L. ; Dravins, D. ; Drury, L. ; Dubois, F. ; Dubois, R. ; Dubus, G. ; Dufour, C. ; Durand, D. ; Dyks, J. ; Dyrda, M. ; Edy, E. ; Egberts, Kathrin ; Eleftheriadis, C. ; Elles, S. ; Emmanoulopoulos, D. ; Enomoto, R. ; Ernenwein, J. -P. ; Errando, M. ; Etchegoyen, A. ; Falcone, A. D. ; Farakos, K. ; Farnier, C. ; Federici, S. ; Feinstein, F. ; Ferenc, D. ; Fillin-Martino, E. ; Fink, D. ; Finley, C. ; Finley, J. P. ; Firpo, R. ; Florin, D. ; Foehr, C. ; Fokitis, E. ; Font, Ll. ; Fontaine, G. ; Fontana, A. ; Foerster, A. ; Fortson, L. ; Fouque, N. ; Fransson, C. ; Fraser, G. W. ; Fresnillo, L. ; Fruck, C. ; Fujita, Y. ; Fukazawa, Y. ; Funk, S. ; Gaebele, W. ; Gabici, S. ; Gadola, A. ; Galante, N. ; Gallant, Y. ; Garcia, B. ; Garcia Lopez, R. 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Ground-based gamma-ray astronomy has had a major breakthrough with the impressive results obtained using systems of imaging atmospheric Cherenkov telescopes. Ground-based gamma-ray astronomy has a huge potential in astrophysics, particle physics and cosmology. CTA is an international initiative to build the next generation instrument, with a factor of 5-10 improvement in sensitivity in the 100 GeV-10 TeV range and the extension to energies well below 100 GeV and above 100 TeV. CTA will consist of two arrays (one in the north, one in the south) for full sky coverage and will be operated as open observatory. The design of CTA is based on currently available technology. This document reports on the status and presents the major design concepts of CTA.
Acharya, B. S. ; Aramo, C. ; Babic, A. ; Barrio, J. A. ; Baushev, Anton N. ; Tjus, J. Becker ; Berge, David ; Bohacova, M. ; Bonardi, A. ; Brown, A. ; Bugaev, V. ; Bulik, Tomasz ; Burton, M. ; Busetto, G. ; Caraveo, P. A. ; Carosi, R. ; Carr, John ; Chadwick, Paula M. ; Chudoba, J. ; Conforti, V. ; Connaughton, V. ; Contreras, J. L. ; Cotter, G. ; Dazzi, F. ; De Franco, A. ; de la Calle, I. ; Lopez, R. de los Reyes ; De Lotto, B. ; De Palma, F. ; Di Girolamo, T. ; Di Giulio, C. ; Di Pierro, F. ; Dournaux, J. -L. ; Dwarkadas, Vikram V. ; Ebr, J. ; Egberts, Kathrin ; Fesquet, M. ; Fleischhack, H. ; Font, L. ; Fontaine, G. ; Foerster, A. ; Füßling, Matthias ; Garcia, B. ; Lopez, R. Garcia ; Garczarczyk, M. ; Gargano, F. ; Garrido, D. ; Gaug, M. ; Giglietto, N. ; Giordano, F. ; Giuliani, A. ; Godinovic, N. ; Gonzalez, M. M. ; Grabarczyk, T. ; Hassan, T. ; Hoerandel, J. ; Hrabovsky, M. ; Hrupec, D. ; Humensky, T. B. ; Huovelin, J. ; Jamrozy, M. ; Janecek, P. ; Kaaret, P. E. ; Katz, U. ; Kaufmann, S. ; Khelifi, B. ; Kluzniak, W. ; Kocot, J. ; Komin, N. ; Kubo, H. ; Kushida, J. ; Lamanna, G. ; Lee, W. H. ; Lenain, J. -P. ; Lohse, T. ; Lombardi, S. ; Lopez-Coto, R. ; Lopez-Oramas, A. ; Lucarelli, F. ; Maccarone, M. C. ; Maier, G. ; Majumdar, P. ; Malaguti, G. ; Mandat, D. ; Mazziotta, Mario Nicola ; Meagher, K. ; Mirabal, N. ; Morselli, A. ; Moulin, Emmanuel ; Niemiec, J. ; Nievas, M. ; Nishijima, K. ; Nosek, D. ; Nunio, F. ; Ohishi, M. ; Ohm, S. ; Ong, R. A. ; Orito, R. ; Otte, N. ; Palatka, M. ; Pareschi, G. ; Pech, M. ; Persic, M. ; Pohl, Manuela ; Prouza, M. ; Quirrenbach, A. ; Raino, S. ; Fernandez, G. Rodriguez ; Romano, Patrizia ; Rovero, A. C. ; Rudak, B. ; Schovanek, P. ; Shayduk, M. ; Siejkowski, H. ; Sillanpaa, A. ; Stefanik, S. ; Stolarczyk, T. ; Szanecki, M. ; Szepieniec, T. ; Tejedor, L. A. ; Telezhinsky, Igor O. ; Teshima, M. ; Tibaldo, L. ; Tibolla, O. ; Tovmassian, G. ; Travnicek, P. ; Trzeciak, M. ; Vallania, P. ; van Eldik, C. ; Vercellone, S. ; Vigorito, C. ; Wagner, S. J. ; Wakely, S. P. ; Weinstein, A. ; Wierzcholska, A. ; Wilhelm, Alina ; Wojcik, P. ; Yoshikoshi, T.
Supernova remnants (SNRs) are among the most important targets for gamma-ray observatories. Being prominent non-thermal sources, they are very likely responsible for the acceleration of the bulk of Galactic cosmic rays (CRS). To firmly establish the SNR paradigm for the origin of cosmic rays, it should be confirmed that protons are indeed accelerated in, and released from, SNRs with the appropriate flux and spectrum. This can be done by detailed theoretical models which account for microphysics of acceleration and various radiation processes of hadrons and leptons. The current generation of Cherenkov telescopes has insufficient sensitivity to constrain theoretical models. A new facility, the Cherenkov Telescope Array (CTA), will have superior capabilities and may finally resolve this long standing issue of high-energy astrophysics. We want to assess the capabilities of CTA to reveal the physics of various types of SNRs in the initial 2000 years of their evolution. During this time, the efficiency to accelerate cosmic rays is highest. We perform time-dependent simulations of the hydrodynamics, the magnetic fields, the cosmic-ray acceleration, and the non-thermal emission for type Ia, Ic and IIP SNRs. We calculate the CTA response to the y-ray emission from these SNRs for various ages and distances, and we perform a realistic analysis of the simulated data. We derive distance limits for the detectability and resolvability of these SNR types at several ages. We test the ability of CTA to reconstruct their morphological and spectral parameters as a function of their distance. Finally, we estimate how well CTA data will constrain the theoretical models. (C) 2014 Elsevier B.V. All rights reserved.
Introducing the CTA concept
(2013)
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The Cherenkov Telescope Array (CTA) is a new observatory for very high-energy (VHE) gamma rays. CTA has ambitions science goals, for which it is necessary to achieve full-sky coverage, to improve the sensitivity by about an order of magnitude, to span about four decades of energy, from a few tens of GeV to above 100 TeV with enhanced angular and energy resolutions over existing VHE gamma-ray observatories. An international collaboration has formed with more than 1000 members from 27 countries in Europe, Asia, Africa and North and South America. In 2010 the CTA Consortium completed a Design Study and started a three-year Preparatory Phase which leads to production readiness of CTA in 2014. In this paper we introduce the science goals and the concept of CTA, and provide an overview of the project.
Abeysekara, A. U. ; Archer, A. ; Benbow, Wystan ; Bird, Ralph ; Brill, A. ; Brose, Robert ; Buchovecky, M. ; Calderon-Madera, D. ; Christiansen, J. L. ; Cui, W. ; Daniel, M. K. ; Falcone, A. ; Feng, Q. ; Fernandez-Alonso, M. ; Finley, J. P. ; Fortson, Lucy ; Furniss, Amy ; Gent, A. ; Giuri, C. ; Gueta, O. ; Hanna, David ; Hassan, T. ; Hervet, Oliver ; Holder, J. ; Hughes, G. ; Humensky, T. B. ; Johnson, Caitlin A. ; Kaaret, P. ; Kertzman, M. ; Kieda, David ; Krause, Maria ; Krennrich, F. ; Kumar, S. ; Lang, M. J. ; Maier, Gernot ; Moriarty, P. ; Mukherjee, Reshmi ; Nievas-Rosillo, M. ; Ong, R. A. ; Pfrang, Konstantin Johannes ; Pohl, Martin ; Prado, R. R. ; Pueschel, Elisa ; Quinn, J. ; Ragan, K. ; Reynolds, P. T. ; Ribeiro, D. ; Richards, G. T. ; Roache, E. ; Rovero, A. C. ; Sadeh, Iftach ; Santander, M. ; Sembroski, G. H. ; Shahinyan, Karlen ; Sushch, Iurii ; Svraka, T. ; Weinstein, A. ; Wells, R. M. ; Wilcox, Patrick ; Wilhelm, Alina ; Williams, David Arnold ; Williamson, T. J. ; Zitzer, B.
The extragalactic background light (EBL), a diffuse photon field in the optical and infrared range, is a record of radiative processes over the universe?s history. Spectral measurements of blazars at very high energies (>100 GeV) enable the reconstruction of the spectral energy distribution (SED) of the EBL, as the blazar spectra are modified by redshift- and energy-dependent interactions of the gamma-ray photons with the EBL. The spectra of 14 VERITAS-detected blazars are included in a new measurement of the EBL SED that is independent of EBL SED models. The resulting SED covers an EBL wavelength range of 0.56?56 ?m, and is in good agreement with lower limits obtained by assuming that the EBL is entirely due to radiation from cataloged galaxies.
Abdo, A. A. ; Ackermann, Margit ; Ajello, M. ; Allafort, A. J. ; Baldini, L. ; Ballet, J. ; Barbiellini, G. ; Baring, M. G. ; Bastieri, D. ; Bechtol, K. C. ; Bellazzini, R. ; Berenji, B. ; Blandford, R. D. ; Bloom, E. D. ; Bonamente, E. ; Borgland, A. W. ; Bouvier, A. ; Brandt, T. J. ; Bregeon, Johan ; Brez, A. ; Brigida, M. ; Bruel, P. ; Buehler, R. ; Buson, S. ; Caliandro, G. A. ; Cameron, R. A. ; Cannon, A. ; Caraveo, P. A. ; Carrigan, Svenja ; Casandjian, J. M. ; Cavazzuti, E. ; Cecchi, C. ; Celik, O. ; Charles, E. ; Chekhtman, A. ; Cheung, C. C. ; Chiang, J. ; Ciprini, S. ; Claus, R. ; Cohen-Tanugi, J. ; Conrad, Jan ; Cutini, S. ; Dermer, C. D. ; de Palma, F. ; do Couto e Silva, E. ; Drell, P. S. ; Dubois, R. ; Dumora, D. ; Favuzzi, C. ; Fegan, S. J. ; Ferrara, E. C. ; Focke, W. B. ; Fortin, P. ; Frailis, M. ; Fuhrmann, L. ; Fukazawa, Y. ; Funk, S. ; Fusco, P. ; Gargano, F. ; Gasparrini, D. ; Gehrels, N. ; Germani, S. ; Giglietto, N. ; Giordano, F. ; Giroletti, M. ; Glanzman, T. ; Godfrey, G. ; Grenier, I. A. ; Guillemot, L. ; Guiriec, S. ; Hayashida, M. ; Hays, E. ; Horan, D. ; Hughes, R. E. ; Johannesson, G. ; Johnson, A. S. ; Johnson, W. N. ; Kadler, M. ; Kamae, T. ; Katagiri, H. ; Kataoka, J. ; Knoedlseder, J. ; Kuss, M. ; Lande, J. ; Latronico, L. ; Lee, S. -H. ; Lemoine-Goumard, M. ; Longo, F. ; Loparco, F. ; Lott, B. ; Lovellette, M. N. ; Lubrano, P. ; Madejski, G. M. ; Makeev, A. ; Max-Moerbeck, W. ; Mazziotta, Mario Nicola ; 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. ; Naumann-Godo, M. ; Nishino, S. ; Nolan, P. L. ; Norris, J. P. ; Nuss, E. ; Ohsugi, T. ; Okumura, A. ; Omodei, N. ; Orlando, E. ; Ormes, J. 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Y. ; Salvati, M. ; Sanchez-Conde, M. ; Satalecka, K. ; Scalzotto, V. ; Scapin, V. ; Schultz, C. ; Schweizer, T. ; Shayduk, M. ; Shore, S. N. ; Sierpowska-Bartosik, A. ; Sillanpaa, A. ; Sitarek, J. ; Sobczynska, D. ; Spanier, F. ; Spiro, S. ; Stamerra, A. ; Steinke, B. ; Storz, J. ; Strah, N. ; Struebig, J. C. ; Suric, T. ; Takalo, L. O. ; Tavecchio, F. ; Temnikov, P. ; Terzic, T. ; Tescaro, D. ; Teshima, M. ; Vankov, H. ; Wagner, R. M. ; Weitzel, Q. ; Zabalza, V. ; Zandanel, F. ; Zanin, R. ; Acciari, V. A. ; Arlen, T. ; Aune, T. ; Benbow, W. ; Boltuch, D. ; Bradbury, S. M. ; Buckley, J. H. ; Bugaev, V. ; Cannon, A. ; Cesarini, A. ; Ciupik, L. ; Cui, W. ; Dickherber, R. ; Errando, M. ; Falcone, A. ; Finley, J. P. ; Finnegan, G. ; Fortson, L. ; Furniss, A. ; Galante, N. ; Gall, D. ; Gillanders, G. H. ; Godambe, S. ; Grube, J. ; Guenette, R. ; Gyuk, G. ; Hanna, D. ; Holder, J. ; Huang, D. ; Hui, C. M. ; Humensky, T. B. ; Kaaret, P. ; Karlsson, N. ; Kertzman, M. ; Kieda, D. ; Konopelko, A. ; Krawczynski, H. ; Krennrich, F. ; Lang, M. J. ; Maier, G. ; McArthur, S. ; McCann, A. ; McCutcheon, M. ; Moriarty, P. ; Mukherjee, R. ; Ong, R. ; Otte, N. ; Pandel, D. ; Perkins, J. S. ; Pichel, A. ; Pohl, M. ; Quinn, J. ; Ragan, K. ; Reyes, L. C. ; Reynolds, P. T. ; Roache, E. ; Rose, H. J. ; Rovero, A. C. ; Schroedter, M. ; Sembroski, G. H. ; Senturk, G. D. ; Steele, D. ; Swordy, S. P. ; Tesic, G. ; Theiling, M. ; Thibadeau, S. ; Varlotta, A. ; Vincent, S. ; Wakely, S. P. ; Ward, J. E. ; Weekes, T. C. ; Weinstein, A. ; Weisgarber, T. ; Williams, D. A. ; Wood, M. ; Zitzer, B. ; Villata, M. ; Raiteri, C. M. ; Aller, H. D. ; Aller, M. F. ; Arkharov, A. A. ; Blinov, D. A. ; Calcidese, P. ; Chen, W. P. ; Efimova, N. V. ; Kimeridze, G. ; Konstantinova, T. S. ; Kopatskaya, E. N. ; Koptelova, E. ; Kurtanidze, O. M. ; Kurtanidze, S. O. ; Lahteenmaki, A. ; Larionov, V. M. ; Larionova, E. G. ; Larionova, L. V. ; Ligustri, R. ; Morozova, D. A. ; Nikolashvili, M. G. ; Sigua, L. A. ; Troitsky, I. S. ; Angelakis, E. ; Capalbi, M. ; Carraminana, A. ; Carrasco, L. ; Cassaro, P. ; de la Fuente, E. ; Gurwell, M. A. ; Kovalev, Y. Y. ; Kovalev, Yu. A. ; Krichbaum, T. P. ; Krimm, H. A. ; Leto, Paolo ; Lister, M. L. ; Maccaferri, G. ; Moody, J. W. ; Mori, Y. ; Nestoras, I. ; Orlati, A. ; Pagani, C. ; Pace, C. ; Pearson, R. ; Perri, M. ; Piner, B. G. ; Pushkarev, A. B. ; Ros, E. ; Sadun, A. C. ; Sakamoto, T. ; Tornikoski, M. ; Yatsu, Y. ; Zook, A.
We report on the gamma-ray activity of the blazar Mrk 501 during the first 480 days of Fermi operation. We find that the average Large Area Telescope (LAT) gamma-ray spectrum of Mrk 501 can be well described by a single power-law function with a photon index of 1.78 +/- 0.03. While we observe relatively mild flux variations with the Fermi-LAT (within less than a factor of two), we detect remarkable spectral variability where the hardest observed spectral index within the LAT energy range is 1.52 +/- 0.14, and the softest one is 2.51 +/- 0.20. These unexpected spectral changes do not correlate with the measured flux variations above 0.3 GeV. In this paper, we also present the first results from the 4.5 month long multifrequency campaign (2009 March 15-August 1) on Mrk 501, which included the Very Long Baseline Array (VLBA), Swift, RXTE, MAGIC, and VERITAS, the F-GAMMA, GASP-WEBT, and other collaborations and instruments which provided excellent temporal and energy coverage of the source throughout the entire campaign. The extensive radio to TeV data set from this campaign provides us with the most detailed spectral energy distribution yet collected for this source during its relatively low activity. The average spectral energy distribution of Mrk 501 is well described by the standard one-zone synchrotron self-Compton (SSC) model. In the framework of this model, we find that the dominant emission region is characterized by a size less than or similar to 0.1 pc (comparable within a factor of few to the size of the partially resolved VLBA core at 15-43 GHz), and that the total jet power (similar or equal to 10(44) erg s(-1)) constitutes only a small fraction (similar to 10(-3)) of the Eddington luminosity. The energy distribution of the freshly accelerated radiating electrons required to fit the time-averaged data has a broken power-law form in the energy range 0.3 GeV-10 TeV, with spectral indices 2.2 and 2.7 below and above the break energy of 20 GeV. We argue that such a form is consistent with a scenario in which the bulk of the energy dissipation within the dominant emission zone of Mrk 501 is due to relativistic, proton-mediated shocks. We find that the ultrarelativistic electrons and mildly relativistic protons within the blazar zone, if comparable in number, are in approximate energy equipartition, with their energy dominating the jet magnetic field energy by about two orders of magnitude.
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