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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, Wystan ; Bird, Ralph ; Bourbeau, E. ; Buchovecky, M. ; Buckley, J. H. ; Bugaev, V. ; Cerruti, M. ; Connolly, M. P. ; Cui, W. ; Dwarkadas, Vikram V. ; Errando, M. ; Falcone, A. ; Feng, Q. ; Finley, J. P. ; Fleischhack, H. ; Fortson, L. ; Furniss, A. ; Griffin, S. ; Huetten, M. ; Hanna, D. ; Holder, J. ; Johnson, C. A. ; Kaaret, P. ; Kar, P. ; Kelley-Hoskins, N. ; Kertzman, M. ; Kieda, D. ; Krause, M. ; Kumar, S. ; Lang, M. J. ; Maier, G. ; McArthur, S. ; McCann, A. ; Moriarty, P. ; Mukherjee, R. ; Nieto, D. ; Ong, R. A. ; Otte, A. N. ; Park, Nahee ; Pohl, Martin ; Popkow, A. ; Pueschel, Elisa ; Quinn, J. ; Ragan, K. ; Reynolds, P. T. ; Richards, G. T. ; Roache, E. ; Sadeh, I. ; Santander, M. ; Sembroski, G. H. ; Shahinyan, K. ; Slane, P. ; Staszak, D. ; Telezhinsky, Igor O. ; Trepanier, S. ; Tyler, J. ; Wakely, S. P. ; Weinstein, A. ; Weisgarber, T. ; Wilcox, P. ; Wilhelm, Alina ; Williams, D. A. ; Zitzer, B.
Abeysekara, A. U. ; Archambault, S. ; Archer, A. ; Benbow, Wystan ; Bird, Ralph ; Buchovecky, M. ; Buckley, J. H. ; Bugaev, V. ; Byrum, K. ; Cerruti, M. ; Chen, X. ; Ciupik, L. ; Cui, W. ; Dickinson, H. J. ; Eisch, J. D. ; Errando, M. ; Falcone, A. ; Feng, Q. ; Finley, J. P. ; Fleischhack, H. ; Fortson, L. ; Furniss, A. ; Gillanders, G. H. ; Griffin, S. ; Grube, J. ; Hutten, M. ; Hakansson, N. ; Hanna, D. ; Holder, J. ; Humensky, T. B. ; Johnson, C. A. ; Kaaret, P. ; Kar, P. ; 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. ; Pelassa, V. ; Pohl, Martin ; Popkow, A. ; Pueschel, Elisa ; Quinn, J. ; Ragan, K. ; Reynolds, P. T. ; Richards, G. T. ; Roache, E. ; Rulten, C. ; Santander, M. ; Sembroski, G. H. ; Shahinyan, K. ; Staszak, D. ; Telezhinsky, Igor O. ; Tucci, J. V. ; Tyler, J. ; Wakely, S. P. ; Weiner, O. M. ; Weinstein, A. ; Wilhelm, Alina ; Williams, D. A. ; Fegan, S. ; Giebels, B. ; Horan, D. ; Berdyugin, A. ; Kuan, J. ; Lindfors, E. ; Nilsson, K. ; Oksanen, A. ; Prokoph, H. ; Reinthal, R. ; Takalo, L. ; Zefi, F.
B2 1215+30 is a BL-Lac-type blazar that was first detected at TeV energies by the MAGIC atmospheric Cherenkov telescopes and subsequently confirmed by the Very Energetic Radiation Imaging Telescope Array System (VERITAS) observatory with data collected between 2009 and 2012. In 2014 February 08, VERITAS detected a large-amplitude flare from B2. 1215+30 during routine monitoring observations of the blazar 1ES. 1218+304, located in the same field of view. The TeV flux reached 2.4 times the Crab Nebula flux with a variability timescale of <3.6 hr. Multiwavelength observations with Fermi-LAT, Swift, and the Tuorla Observatory revealed a correlated high GeV flux state and no significant optical counterpart to the flare, with a spectral energy distribution where the gamma-ray luminosity exceeds the synchrotron luminosity. When interpreted in the framework of a onezone leptonic model, the observed emission implies a high degree of beaming, with Doppler factor delta > 10, and an electron population with spectral index p < 2.3.
Dark matter constraints from a joint analysis of dwarf Spheroidal galaxy observations with VERITAS
(2017)
Archambault, S. ; Archer, A. ; Benbow, W. ; Bird, R. ; Bourbeau, E. ; Brantseg, T. ; Buchovecky, M. ; Buckley, J. H. ; Bugaev, V. ; Byrum, K. ; Cerruti, M. ; Christiansen, J. L. ; Connolly, M. P. ; Cui, W. ; Daniel, M. K. ; Feng, Q. ; Finley, J. P. ; Fleischhack, H. ; Fortson, L. ; Furniss, A. ; Geringer-Sameth, A. ; Griffin, S. ; Grube, J. ; Hütten, M. ; Hakansson, N. ; Hanna, D. ; Hervet, O. ; Holder, J. ; Hughes, G. ; Hummensky, B. ; Johnson, C. A. ; Kaaret, P. ; Kar, P. ; Kelley-Hoskins, N. ; Kertzman, M. ; Kieda, D. ; Koushiappas, S. ; Krause, M. ; Krennrich, F. ; Lang, M. J. ; Lin, T. T. Y. ; McArthur, S. ; Moriarty, P. ; Mukherjee, R. ; Nieto, D. ; Ong, R. A. ; Otte, A. N. ; Park, N. ; Pohl, M. ; Popkow, A. ; Pueschel, Elisa ; Quinn, J. ; Ragan, K. ; Reynolds, P. T. ; Richards, G. T. ; Roache, E. ; Rulten, C. ; Sadeh, I. ; Santander, M. ; Sembroski, G. H. ; Shahinyan, K. ; Smith, A. W. ; Staszak, D. ; Telezhinsky, Igor O. ; Trepanier, S. ; Tucci, J. V. ; Tyler, J. ; Wakely, S. P. ; Weinstein, A. ; Wilcox, P. ; Williams, D. A. ; Zitzer, B.
We present constraints on the annihilation cross section of weakly interacting massive particles dark matter based on the joint statistical analysis of four dwarf galaxies with VERITAS. These results are derived from an optimized photon weighting statistical technique that improves on standard imaging atmospheric Cherenkov telescope (IACT) analyses by utilizing the spectral and spatial properties of individual photon events. We report on the results of similar to 230 hours of observations of five dwarf galaxies and the joint statistical analysis of four of the dwarf galaxies. We find no evidence of gamma-ray emission from any individual dwarf nor in the joint analysis. The derived upper limit on the dark matter annihilation cross section from the joint analysis is 1.35 x 10(-23) cm(3) s(-1) at 1 TeV for the bottom quark (b (b) over bar) final state, 2.85 x 10(-24) cm(3) s(-1) at 1 TeV for the tau lepton (tau+tau(-)) final state and 1.32 x 10-25 cm(3) s(-1) at 1 TeV for the gauge boson (gamma gamma) final state.
Archambault, S. ; Archer, A. ; Benbow, W. ; Bird, Ralph ; Bourbeau, E. ; Bouvier, A. ; Buchovecky, M. ; Bugaev, V. ; Cardenzana, J. V. ; Cerruti, M. ; Ciupik, L. ; Connolly, M. P. ; Cui, W. ; Daniel, M. K. ; Errando, M. ; Falcone, A. ; Feng, Q. ; Finley, J. P. ; Fleischhack, H. ; Fortson, L. ; Furniss, A. ; Gillanders, G. H. ; Griffin, S. ; Hanna, D. ; Hervet, O. ; Holder, J. ; Hughes, G. ; Humensky, T. B. ; Hutten, M. ; Johnson, C. A. ; Kaaret, P. ; Kar, P. ; Kertzman, M. ; Kieda, D. ; Krause, M. ; Lang, M. J. ; Lin, T. T. Y. ; Maier, G. ; McArthur, S. ; Moriarty, P. ; Mukherjee, R. ; Nieto, D. ; Ong, R. A. ; Otte, A. N. ; Park, N. ; Pohl, Martin ; Popkow, A. ; Pueschel, Elisa ; Quinn, J. ; Ragan, K. ; Reynolds, P. T. ; Richards, G. T. ; Roache, E. ; Rulten, C. ; Sadeh, I. ; Sembroski, G. H. ; Shahinyan, K. ; Staszak, D. ; Telezhinsky, Igor O. ; Trepanier, S. ; Wakely, S. P. ; Weinstein, A. ; Wilcox, P. ; Williams, D. A. ; Zitzer, B.
Imaging atmospheric Cherenkov telescopes (IACTs) are equipped with sensitive photomultiplier tube (PMT) cameras. Exposure to high levels of background illumination degrades the efficiency of and potentially destroys these photo-detectors over time, so IACTs cannot be operated in the same configuration in the presence of bright moonlight as under dark skies. Since September 2012, observations have been carried out with the VERITAS IACTs under bright moonlight (defined as about three times the night-sky-background (NSB) of a dark extragalactic field, typically occurring when Moon illumination > 35%) in two observing modes, firstly by reducing the voltage applied to the PMTs and, secondly, with the addition of ultra-violet (UV) bandpass filters to the cameras. This has allowed observations at up to about 30 times previous NSB levels (around 80% Moon illumination), resulting in 30% more observing time between the two modes over the course of a year. These additional observations have already allowed for the detection of a flare from the 1ES 1727 + 502 and for an observing program targeting a measurement of the cosmic-ray positron fraction. We provide details of these new observing modes and their performance relative to the standard VERITAS observations. (C) 2017 Elsevier B.V. All rights reserved.
Prospects for Cherenkov Telescope Array Observations of the Young Supernova Remnant RX J1713.7-3946
(2017)
Acero, F. ; Aloisio, R. ; Amans, J. ; Amato, Elena ; Antonelli, L. A. ; Aramo, C. ; Armstrong, T. ; Arqueros, F. ; Asano, Katsuaki ; Ashley, M. ; Backes, M. ; Balazs, C. ; Balzer, A. ; Bamba, Aya ; Barkov, Maxim ; Barrio, J. A. ; Benbow, Wystan ; Bernloehr, K. ; Beshley, V. ; Bigongiari, C. ; Biland, A. ; Bilinsky, A. ; Bissaldi, Elisabetta ; Biteau, J. ; Blanch, O. ; Blasi, P. ; Blazek, J. ; Boisson, C. ; Bonanno, G. ; Bonardi, A. ; Bonavolonta, C. ; Bonnoli, G. ; Braiding, C. ; Brau-Nogue, S. ; Bregeon, J. ; Brown, A. M. ; Bugaev, V. ; Bulgarelli, A. ; Bulik, T. ; Burton, Michael ; Burtovoi, A. ; Busetto, G. ; Bottcher, M. ; Cameron, R. ; Capalbi, M. ; Caproni, Anderson ; Caraveo, P. ; Carosi, R. ; Cascone, E. ; Cerruti, M. ; Chaty, Sylvain ; Chen, A. ; Chen, X. ; Chernyakova, M. ; Chikawa, M. ; Chudoba, J. ; Cohen-Tanugi, J. ; Colafrancesco, S. ; Conforti, V. ; Contreras, J. L. ; Costa, A. ; Cotter, G. ; Covino, Stefano ; Covone, G. ; Cumani, P. ; Cusumano, G. ; Daniel, M. ; Dazzi, F. ; De Angelis, A. ; De Cesare, G. ; De Franco, A. ; De Frondat, F. ; Dal Pino, E. M. de Gouveia ; De Lisio, C. ; Lopez, R. de los Reyes ; De Lotto, B. ; de Naurois, M. ; De Palma, F. ; Del Santo, M. ; Delgado, C. ; della Volpe, D. ; Di Girolamo, T. ; Di Giulio, C. ; Di Pierro, F. ; Di Venere, L. ; Doro, M. ; Dournaux, J. ; Dumas, D. ; Dwarkadas, Vikram V. ; Diaz, C. ; Ebr, J. ; Egberts, Kathrin ; Einecke, S. ; Elsaesser, D. ; Eschbach, S. ; Falceta-Goncalves, D. ; Fasola, G. ; Fedorova, E. ; Fernandez-Barral, A. ; Ferrand, Gilles ; Fesquet, M. ; Fiandrini, E. ; Fiasson, A. ; Filipovic, Miroslav D. ; Fioretti, V. ; Font, L. ; Fontaine, Gilles ; Franco, F. J. ; Freixas Coromina, L. ; Fujita, Yutaka ; Fukui, Y. ; Funk, S. ; Forster, A. ; Gadola, A. ; Lopez, R. Garcia ; Garczarczyk, M. ; Giglietto, N. ; Giordano, F. ; Giuliani, A. ; Glicenstein, J. ; Gnatyk, R. ; Goldoni, P. ; Grabarczyk, T. ; Graciani, R. ; Graham, J. ; Grandi, P. ; Granot, Jonathan ; Green, A. J. ; Griffiths, S. ; Gunji, S. ; Hakobyan, H. ; Hara, S. ; Hassan, T. ; Hayashida, M. ; Heller, M. ; Helo, J. C. ; Hinton, J. ; Hnatyk, B. ; Huet, J. ; Huetten, M. ; Humensky, T. B. ; Hussein, M. ; Horandel, J. ; Ikeno, Y. ; Inada, T. ; Inome, Y. ; Inoue, S. ; Inoue, T. ; Inoue, Y. ; Ioka, K. ; Iori, Maurizio ; Jacquemier, J. ; Janecek, P. ; Jankowsky, D. ; Jung, I. ; Kaaret, P. ; Katagiri, H. ; Kimeswenger, S. ; Kimura, Shigeo S. ; Knodlseder, J. ; Koch, B. ; Kocot, J. ; Kohri, K. ; Komin, N. ; Konno, Y. ; Kosack, K. ; Koyama, S. ; Kraus, Michaela ; Kubo, Hidetoshi ; Mezek, G. Kukec ; Kushida, J. ; La Palombara, N. ; Lalik, K. ; Lamanna, G. ; Landt, H. ; Lapington, J. ; Laporte, P. ; Lee, S. ; Lees, J. ; Lefaucheur, J. ; Lenain, J. -P. ; Leto, Giuseppe ; Lindfors, E. ; Lohse, T. ; Lombardi, S. ; Longo, F. ; Lopez, M. ; Lucarelli, F. ; Luque-Escamilla, Pedro Luis ; Lopez-Coto, R. ; Maccarone, M. C. ; Maier, G. ; Malaguti, G. ; Mandat, D. ; Maneva, G. ; Mangano, S. ; Marcowith, Alexandre ; Marti, J. ; Martinez, M. ; Martinez, G. ; Masuda, S. ; Maurin, G. ; Maxted, N. ; Melioli, Claudio ; Mineo, T. ; Mirabal, N. ; Mizuno, T. ; Moderski, R. ; Mohammed, M. ; Montaruli, T. ; Moralejo, A. ; Mori, K. ; Morlino, G. ; Morselli, A. ; Moulin, Emmanuel ; Mukherjee, R. ; Mundell, C. ; Muraishi, H. ; Murase, Kohta ; Nagataki, Shigehiro ; Nagayoshi, T. ; Naito, T. ; Nakajima, D. ; Nakamori, T. ; Nemmen, R. ; Niemiec, Jacek ; Nieto, D. ; Nievas-Rosillo, M. ; Nikolajuk, M. ; Nishijima, K. ; Noda, K. ; Nogues, L. ; Nosek, D. ; Novosyadlyj, B. ; Nozaki, S. ; Ohira, Yutaka ; Ohishi, M. ; Ohm, S. ; Okumura, A. ; Ong, R. A. ; Orito, R. ; Orlati, A. ; Ostrowski, M. ; Oya, I. ; Padovani, Marco ; Palacio, J. ; Palatka, M. ; Paredes, Josep M. ; Pavy, S. ; Persic, M. ; Petrucci, P. ; Petruk, Oleh ; Pisarski, A. ; Pohl, Martin ; Porcelli, A. ; Prandini, E. ; Prast, J. ; Principe, G. ; Prouza, M. ; Pueschel, Elisa ; Puelhofer, G. ; Quirrenbach, A. ; Rameez, M. ; Reimer, O. ; Renaud, M. ; Ribo, M. ; Rico, J. ; Rizi, V. ; Rodriguez, J. ; Fernandez, G. Rodriguez ; Rodriguez Vazquez, J. J. ; Romano, Patrizia ; Romeo, G. ; Rosado, J. ; Rousselle, J. ; Rowell, G. ; Rudak, B. ; Sadeh, I. ; Safi-Harb, S. ; Saito, T. ; Sakaki, N. ; Sanchez, D. ; Sangiorgi, P. ; Sano, H. ; Santander, M. ; Sarkar, S. ; Sawada, M. ; Schioppa, E. J. ; Schoorlemmer, H. ; Schovanek, P. ; Schussler, F. ; Sergijenko, O. ; Servillat, M. ; Shalchi, A. ; Shellard, R. C. ; Siejkowski, H. ; Sillanpaa, A. ; Simone, D. ; Sliusar, V. ; Sol, H. ; Stanic, S. ; Starling, R. ; Stawarz, L. ; Stefanik, S. ; Stephan, M. ; Stolarczyk, T. ; Szanecki, M. ; Szepieniec, T. ; Tagliaferri, G. ; Tajima, H. ; Takahashi, M. ; Takeda, J. ; Tanaka, M. ; Tanaka, S. ; Tejedor, L. A. ; Telezhinsky, Igor O. ; Temnikov, P. ; Terada, Y. ; Tescaro, D. ; Teshima, M. ; Testa, V. ; Thoudam, S. ; Tokanai, F. ; Torres, D. F. ; Torresi, E. ; Tosti, G. ; Townsley, C. ; Travnicek, P. ; Trichard, C. ; Trifoglio, M. ; Tsujimoto, S. ; Vagelli, V. ; Vallania, P. ; Valore, L. ; van Driel, W. ; van Eldik, C. ; Vandenbroucke, Justin ; Vassiliev, V. ; Vecchi, M. ; Vercellone, Stefano ; Vergani, S. ; Vigorito, C. ; Vorobiov, S. ; Vrastil, M. ; Vazquez Acosta, M. L. ; Wagner, S. J. ; Wagner, R. ; Wakely, S. P. ; Walter, R. ; Ward, J. E. ; Watson, J. J. ; Weinstein, A. ; White, M. ; White, R. ; Wierzcholska, A. ; Wilcox, P. ; Williams, D. A. ; Wischnewski, R. ; Wojcik, P. ; Yamamoto, T. ; Yamamoto, H. ; Yamazaki, Ryo ; Yanagita, S. ; Yang, L. ; Yoshida, T. ; Yoshida, M. ; Yoshiike, S. ; Yoshikoshi, T. ; Zacharias, M. ; Zampieri, L. ; Zanin, R. ; Zavrtanik, M. ; Zavrtanik, D. ; Zdziarski, A. ; Zech, Alraune ; Zechlin, Hannes ; Zhdanov, V. ; Ziegler, A. ; Zorn, J.
We perform simulations for future Cherenkov Telescope Array (CTA) observations of RX J1713.7-3946, a young supernova remnant (SNR) and one of the brightest sources ever discovered in very high energy (VHE) gamma rays. Special attention is paid to exploring possible spatial (anti) correlations of gamma rays with emission at other wavelengths, in particular X-rays and CO/H I emission. We present a series of simulated images of RX J1713.7-3946 for CTA based on a set of observationally motivated models for the gamma-ray emission. In these models, VHE gamma rays produced by high-energy electrons are assumed to trace the nonthermal X-ray emission observed by XMM-Newton, whereas those originating from relativistic protons delineate the local gas distributions. The local atomic and molecular gas distributions are deduced by the NANTEN team from CO and H I observations. Our primary goal is to show how one can distinguish the emission mechanism(s) of the gamma rays (i.e., hadronic versus leptonic, or a mixture of the two) through information provided by their spatial distribution, spectra, and time variation. This work is the first attempt to quantitatively evaluate the capabilities of CTA to achieve various proposed scientific goals by observing this important cosmic particle accelerator.
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.
Archer, A. ; Benbow, W. ; Bird, R. ; Brose, Robert ; Buchovecky, M. ; Bugaev, V. ; Connolly, M. P. ; Cui, W. ; Daniel, M. K. ; Falcone, A. ; Feng, Q. ; Finley, J. P. ; Fleischhack, H. ; Fortson, L. ; Furniss, A. ; Hanna, D. ; Hervet, O. ; Holder, J. ; Hughes, G. ; Humensky, T. B. ; Hutten, M. ; Johnson, C. A. ; Kaaret, P. ; Kelley-Hoskins, N. ; Kieda, D. ; Krause, M. ; Krennrich, F. ; Kumar, S. ; Lang, M. J. ; Maier, G. ; McArthur, S. ; Moriarty, P. ; Mukherjee, R. ; Nieto, D. ; Ong, R. A. ; Otte, A. N. ; Park, N. ; Petrashyk, A. ; Pohl, Martin ; Popkow, A. ; Pueschel, Elisa ; Quinn, J. ; Ragan, K. ; Reynolds, P. T. ; Richards, G. T. ; Roache, E. ; Rulten, C. ; Sadeh, I. ; Tyler, J. ; Wakely, S. P. ; Weiner, O. M. ; Wilcox, P. ; Wilhelm, Alina ; Williams, D. A. ; Wissel, S. A. ; Zitzer, B.
We present a new measurement of the energy spectrum of iron nuclei in cosmic rays from 20 TeV to 500 TeV; The measurement makes use of a template-based analysis method, which, for the first time, is applied to the energy reconstruction of iron-induced air showers recorded by the VERITAS array of imaging atmospheric Cherenkov telescopes. The event selection makes use of the direct Cherenkov light which is emitted by charged particles before the first interaction, as well as other parameters related to the shape of the recorded air shower images. The measured spectrum is well described by a power law dF/dE = f(0) center dot (E/E-0)(-gamma) over the full energy range, with gamma = 2.82 +/- 0.30(stat)(-0.27)(+0.24)(syst) and f(0) = (4.82 +/- 0.98(stat)(-2.70)(+2.12)(syst)) x 10(-7) m(-2) s(-1) TeV-1 sr(-1) at E-0 = 50 TeV, with no indication of a cutoff or spectral break. The measured differential flux is compatible with previous results, with improved statistical uncertainty at the highest energies.
De Angelis, A. ; Tatischeff, V. ; Grenier, I. A. ; McEnery, J. ; Mallamaci, Manuela ; Tavani, M. ; Oberlack, U. ; Hanlon, L. ; Walter, R. ; Argan, A. ; Von Ballmoos, P. ; Bulgarelli, A. ; Bykov, A. ; Hernanz, M. ; Kanbach, G. ; Kuvvetli, I. ; Pearce, M. ; Zdziarski, A. ; Conrad, J. ; Ghisellini, G. ; Harding, A. ; Isern, J. ; Leising, M. ; Longo, F. ; Madejski, G. ; Martinez, M. ; Mazziotta, Mario Nicola ; Paredes, J. M. ; Pohl, Martin ; Rando, R. ; Razzano, M. ; Aboudan, A. ; Ackermann, M. ; Addazi, A. ; Ajello, M. ; Albertus, C. ; Alvarez, J. M. ; Ambrosi, G. ; Anton, S. ; Antonelli, L. A. ; Babic, A. ; Baibussinov, B. ; Balbom, M. ; Baldini, L. ; Balman, S. ; Bambi, C. ; Barres de Almeida, U. ; Barrio, J. A. ; Bartels, R. ; Bastieri, D. ; Bednarek, W. ; Bernard, D. ; Bernardini, E. ; Bernasconi, T. ; Bertucci, B. ; Biland, A. ; Bissaldi, E. ; Boettcher, M. ; Bonvicini, V. ; Bosch-Ramon, V. ; Bottacini, E. ; Bozhilov, V. ; Bretz, T. ; Branchesi, M. ; Brdar, V. ; Bringmann, T. ; Brogna, A. ; Jorgensen, C. Budtz ; Busetto, G. ; Buson, S. ; Busso, M. ; Caccianiga, A. ; Camera, S. ; Campana, R. ; Caraveo, P. ; Cardillo, M. ; Carlson, P. ; Celestin, S. ; Cermeno, M. ; Chen, A. ; Cheung, C. C. ; Churazov, E. ; Ciprini, S. ; Coc, A. ; Colafrancesco, S. ; Coleiro, A. ; Collmar, W. ; Coppi, P. ; Curado da Silva, R. ; Cutini, S. ; De Lotto, B. ; de Martino, D. ; De Rosa, A. ; Del Santo, M. ; Delgado, L. ; Diehl, R. ; Dietrich, S. ; Dolgov, A. D. ; Dominguez, A. ; Prester, D. Dominis ; Donnarumma, I. ; Dorner, D. ; Doro, M. ; Dutra, M. ; Elsaesser, D. ; Fabrizio, M. ; Fernandez-Barral, A. ; Fioretti, V. ; Foffano, L. ; Formato, V. ; Fornengo, N. ; Foschini, L. ; Franceschini, A. ; Franckowiak, A. ; Funk, S. ; Fuschino, F. ; Gaggero, D. ; Galanti, G. ; Gargano, F. ; Gasparrini, D. ; Gehrz, R. ; Giammaria, P. ; Giglietto, N. ; Giommi, P. ; Giordano, F. ; Giroletti, M. ; Ghirlanda, G. ; Godinovic, N. ; Gouiffes, C. ; Grove, J. E. ; Hamadache, C. ; Hartmann, D. H. ; Hayashida, M. ; Hryczuk, A. ; Jean, P. ; Johnson, T. ; Jose, J. ; Kaufmann, S. ; Khelifi, B. ; Kiener, J. ; Knodlseder, J. ; Kolem, M. ; Kopp, J. ; Kozhuharov, V. ; Labanti, C. ; Lalkovski, S. ; Laurent, P. ; Limousin, O. ; Linares, M. ; Lindfors, E. ; Lindner, M. ; Liu, J. ; Lombardi, S. ; Loparco, F. ; Lopez-Coto, R. ; Lopez Moya, M. ; Lott, B. ; Lubrano, P. ; Malyshev, D. ; Mankuzhiyil, N. ; Mannheim, K. ; Marcha, M. J. ; Marciano, A. ; Marcote, B. ; Mariotti, M. ; Marisaldi, M. ; McBreen, S. ; Mereghetti, S. ; Merle, A. ; Mignani, R. ; Minervini, G. ; Moiseev, A. ; Morselli, A. ; Moura, F. ; Nakazawa, K. ; Nava, L. ; Nieto, D. ; Orienti, M. ; Orio, M. ; Orlando, E. ; Orleanski, P. ; Paiano, S. ; Paoletti, R. ; Papitto, A. ; Pasquato, M. ; Patricelli, B. ; Perez-Garcia, M. A. ; Persic, M. ; Piano, G. ; Pichel, A. ; Pimenta, M. ; Pittori, C. ; Porter, T. ; Poutanen, J. ; Prandini, E. ; Prantzos, N. ; Produit, N. ; Profumo, S. ; Queiroz, F. S. ; Raino, S. ; Raklev, A. ; Regis, M. ; Reichardt, I. ; Rephaeli, Y. ; Rico, J. ; Rodejohann, W. ; Fernandez, G. Rodriguez ; Roncadelli, M. ; Roso, L. ; Rovero, A. ; Ruffini, R. ; Sala, G. ; Sanchez-Conde, M. A. ; Santangelo, Andrea ; Parkinson, P. Saz ; Sbarrato, T. ; Shearer, A. ; Shellard, R. ; Short, K. ; Siegert, T. ; Siqueira, C. ; Spinelli, P. ; Stamerra, A. ; Starrfield, S. ; Strong, A. ; Strumke, I. ; Tavecchio, F. ; Taverna, R. ; Terzic, T. ; Thompson, D. J. ; Tibolla, O. ; Torres, D. F. ; Turolla, R. ; Ulyanov, A. ; Ursi, A. ; Vacchi, A. ; Van den Abeele, J. ; Vankova-Kirilovai, G. ; Venter, C. ; Verrecchia, F. ; Vincent, P. ; Wang, X. ; Weniger, C. ; Wu, X. ; Zaharijas, G. ; Zampieri, L. ; Zane, S. ; Zimmer, S. ; Zoglauer, A.
Benbow, W. ; Bird, R. ; Brill, A. ; Brose, Robert ; Chromey, A. J. ; Daniel, M. K. ; Feng, Q. ; Finley, J. P. ; Fortson, L. ; Furniss, A. ; Gillanders, G. H. ; Giuri, C. ; Gueta, O. ; Hanna, D. ; Halpern, J. P. ; Hassan, Tarek ; Holder, J. ; Hughes, G. ; Humensky, T. B. ; Joyce, Amy M. ; Kaaret, P. ; Kar, P. ; Kelley-Hoskins, N. ; Kertzman, M. ; Kieda, D. ; Krause, M. ; Lang, M. J. ; Lin, T. T. Y. ; Maier, Gernot ; Matthews, N. ; Moriarty, P. ; Mukherjee, R. ; Nieto, D. ; Nievas-Rosillos, M. ; Ong, R. A. ; Park, N. ; Petrashyk, A. ; Pohl, Martin ; Pueschel, Elisa ; Quinn, John ; Ragan, K. ; Reynolds, P. T. ; Richards, G. T. ; Roache, E. ; Rulten, C. ; Sadeh, Iftach ; Santander, M. ; Sembroski, G. H. ; Shahinyan, K. ; Sushch, Iurii ; Wakely, S. P. ; Wells, R. M. ; Wilcox, P. ; Wilhelm, Alina ; Williams, David A. ; Williamson, T. J.
The angular size of a star is a critical factor in determining its basic properties1. Direct measurement of stellar angular diameters is difficult: at interstellar distances stars are generally too small to resolve by any individual imaging telescope. This fundamental limitation can be overcome by studying the diffraction pattern in the shadow cast when an asteroid occults a star2, but only when the photometric uncertainty is smaller than the noise added by atmospheric scintillation3. Atmospheric Cherenkov telescopes used for particle astrophysics observations have not generally been exploited for optical astronomy due to the modest optical quality of the mirror surface. However, their large mirror area makes them well suited for such high-time-resolution precision photometry measurements4. Here we report two occultations of stars observed by the Very Energetic Radiation Imaging Telescope Array System (VERITAS)5 Cherenkov telescopes with millisecond sampling, from which we are able to provide a direct measurement of the occulted stars’ angular diameter at the ≤0.1 mas scale. This is a resolution never achieved before with optical measurements and represents an order of magnitude improvement over the equivalent lunar occultation method6. We compare the resulting stellar radius with empirically derived estimates from temperature and brightness measurements, confirming the latter can be biased for stars with ambiguous stellar classifications.