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Archer, A. ; Benbow, W. ; Bird, R. ; Brose, Robert ; Buchovecky, M. ; Buckley, J. H. ; Bugaev, V. ; Connolly, M. P. ; Cui, W. ; Daniel, M. K. ; Feng, Q. ; Finley, J. P. ; Fortson, L. ; Furniss, A. ; Gillanders, G. ; Huetten, M. ; 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. ; Lin, T. T. Y. ; Maier, G. ; McArthur, S. ; Moriarty, P. ; Mukherjee, R. ; Ong, R. A. ; Otte, A. N. ; Petrashyk, A. ; Pohl, M. ; Pueschel, Elisa ; Quinn, J. ; Ragan, K. ; Reynolds, P. T. ; Richards, G. T. ; Roache, E. ; Rulten, C. ; Sadeh, I. ; Santander, M. ; Sembroski, G. H. ; Staszak, D. ; Sushch, I. ; Wakely, S. P. ; Wells, R. M. ; Wilcox, P. ; Wilhelm, Alina ; Williams, D. A. ; Williamson, T. J. ; Zitzer, B.
Cosmic-ray electrons and positrons (CREs) at GeV-TeV energies are a unique probe of our local Galactic neighborhood. CREs lose energy rapidly via synchrotron radiation and inverse-Compton scattering processes while propagating within the Galaxy, and these losses limit their propagation distance. For electrons with TeV energies, the limit is on the order of a kiloparsec. Within that distance, there are only a few known astrophysical objects capable of accelerating electrons to such high energies. It is also possible that the CREs are the products of the annihilation or decay of heavy dark matter (DM) particles. VERITAS, an array of imaging air Cherenkov telescopes in southern Arizona, is primarily utilized for gamma-ray astronomy but also simultaneously collects CREs during all observations. We describe our methods of identifying CREs in VERITAS data and present an energy spectrum, extending from 300 GeV to 5 TeV, obtained from approximately 300 hours of observations. A single power-law fit is ruled out in VERITAS data. We find that the spectrum of CREs is consistent with a broken power law, with a break energy at 710 +/- 40(stat) +/- 140(syst) GeV.
VERITAS and Fermi-LAT Observations of TeV Gamma-Ray Sources Discovered by HAWC in the 2HWC Catalog
(2018)
Abeysekara, A. U. ; Archer, A. ; Benbow, Wystan ; Bird, Ralph ; Brose, Robert ; Buchovecky, M. ; Buckley, J. H. ; Bugaev, V. ; Chromey, A. J. ; Connolly, M. P. ; Cui, Wei ; Daniel, M. K. ; Falcone, A. ; Feng, Qi ; Finley, John P. ; Fortson, L. ; Furniss, Amy ; Huetten, M. ; Hanna, David ; Hervet, O. ; Holder, J. ; Hughes, G. ; Humensky, T. B. ; Johnson, Caitlin A. ; Kaaret, Philip ; Kar, P. ; Kertzman, M. ; Kieda, David ; Krause, M. ; Krennrich, F. ; Kumar, S. ; Lang, M. J. ; Lin, T. T. Y. ; McArthur, S. ; Moriarty, P. ; Mukherjee, Reshmi ; Ong, R. A. ; Otte, Adam Nepomuk ; Park, Nahee ; Petrashyk, A. ; Pohl, Martin ; Pueschel, Elisa ; Quinn, J. ; Ragan, K. ; Reynolds, P. T. ; Richards, Gregory T. ; Roache, E. ; Rulten, C. ; Sadeh, I. ; Santander, Marcos ; Sembroski, G. H. ; Shahinyan, Karlen ; Sushch, I. ; Tyler, J. ; Wakely, S. P. ; Weinstein, A. ; Wells, R. M. ; Wilcox, P. ; Wilhelm, Alina ; Williams, D. A. ; Williamson, T. J. ; Zitzer, B. ; Abdollahi, S. ; Ajello, Marco ; Baldini, Luca ; Barbiellini, G. ; Bastieri, Denis ; Bellazzini, Ronaldo ; Berenji, B. ; Bissaldi, Elisabetta ; Blandford, R. D. ; Bonino, R. ; Bottacini, E. ; Brandt, Terri J. ; Bruel, P. ; Buehler, R. ; Cameron, R. A. ; Caputo, R. ; Caraveo, P. A. ; Castro, D. ; Cavazzuti, E. ; Charles, Eric ; Chiaro, G. ; Ciprini, S. ; Cohen-Tanugi, Johann ; Costantin, D. ; Cutini, S. ; de Palma, F. ; Di Lalla, N. ; Di Mauro, M. ; Di Venere, L. ; Dominguez, A. ; Favuzzi, C. ; Fegan, S. J. ; Franckowiak, Anna ; Fukazawa, Yasushi ; Funk, Stefan ; Fusco, Piergiorgio ; Gargano, Fabio ; Gasparrini, Dario ; Giglietto, Nicola ; Giordano, F. ; Giroletti, Marcello ; Green, D. ; Grenier, I. A. ; Guillemot, L. ; Guiriec, Sylvain ; Hays, Elizabeth ; Hewitt, John W. ; Horan, D. ; Johannesson, G. ; Kensei, S. ; Kuss, M. ; Larsson, Stefan ; Latronico, L. ; Lemoine-Goumard, Marianne ; Li, J. ; Longo, Francesco ; Loparco, Francesco ; Lovellette, M. N. ; Lubrano, Pasquale ; Magill, Jeffrey D. ; Maldera, Simone ; Mazziotta, Mario Nicola ; McEnery, J. E. ; Michelson, P. F. ; Mitthumsiri, W. ; Mizuno, Tsunefumi ; Monzani, Maria Elena ; Morselli, Aldo ; Moskalenko, Igor V. ; Negro, M. ; Nuss, E. ; Ojha, R. ; Omodei, Nicola ; Orienti, M. ; Orlando, E. ; Palatiello, M. ; Paliya, Vaidehi S. ; Paneque, D. ; Perkins, Jeremy S. ; Persic, M. ; Pesce-Rollins, Melissa ; Petrosian, Vahe' ; Piron, F. ; Porter, Troy A. ; Principe, G. ; Raino, S. ; Rando, Riccardo ; Rani, B. ; Razzano, Massimilano ; Razzaque, Soebur ; Reimer, A. ; Reimer, Olaf ; Reposeur, T. ; Sgro, C. ; Siskind, E. J. ; Spandre, Gloria ; Spinelli, P. ; Suson, D. J. ; Tajima, Hiroyasu ; Thayer, J. B. ; Thompson, David J. ; Torres, Diego F. ; Tosti, Gino ; Troja, Eleonora ; Valverde, J. ; Vianello, Giacomo ; Vogel, M. ; Wood, K. ; Yassine, M. ; Alfaro, R. ; Alvarez, C. ; Alvarez, J. D. ; Arceo, R. ; Arteaga-Velazquez, J. C. ; Rojas, D. Avila ; Ayala Solares, H. A. ; Becerril, A. ; Belmont-Moreno, E. ; BenZvi, S. Y. ; Bernal, A. ; Braun, J. ; Brisbois, C. ; Caballero-Mora, K. S. ; Capistran, T. ; Carraminana, A. ; Casanova, Sabrina ; Castillo, M. ; Cotti, U. ; Cotzomi, J. ; Coutino de Leon, S. ; De Leon, C. ; De la Fuente, E. ; Dichiara, S. ; Dingus, B. L. ; DuVernois, M. A. ; Diaz-Velez, J. C. ; Engel, K. ; Enriquez-Rivera, O. ; Fiorino, D. W. ; Fleischhack, H. ; Fraija, N. ; Garcia-Gonzalez, J. A. ; Garfias, F. ; Gonzalez Munoz, A. ; Gonzalez, M. M. ; Goodman, J. A. ; Hampel-Arias, Z. ; Harding, J. P. ; Hernandez, S. ; Hernandez-Almada, A. ; Hona, B. ; Hueyotl-Zahuantitla, F. ; Hui, C. M. ; Huntemeyer, P. ; Iriarte, A. ; Jardin-Blicq, A. ; Joshi, V. ; Kaufmann, S. ; Lara, A. ; Lauer, R. J. ; Lee, W. H. ; Lennarz, D. ; Leon Vargas, H. ; Linnemann, J. T. ; Longinotti, A. L. ; Luis-Raya, G. ; Luna-Garcia, R. ; Lopez-Coto, R. ; Malone, K. ; Marinelli, S. S. ; Martinez, O. ; Martinez-Castellanos, I. ; Martinez-Castro, J. ; Martinez-Huerta, H. ; Matthews, J. A. ; Miranda-Romagnoli, P. ; Moreno, E. ; Mostafa, M. ; Nayerhoda, A. ; Nellen, L. ; Newbold, M. ; Nisa, M. U. ; Noriega-Papaqui, R. ; Pelayo, R. ; Pretz, J. ; Perez-Perez, E. G. ; Ren, Z. ; Rho, C. D. ; Riviere, C. ; Rosa-Gonzalez, D. ; Rosenberg, M. ; Ruiz-Velasco, E. ; Salazar, H. ; Greus, F. Salesa ; Sandoval, A. ; Schneider, M. ; Arroyo, M. Seglar ; Sinnis, G. ; Smith, A. J. ; Springer, R. W. ; Surajbali, P. ; Taboada, Ignacio ; Tibolla, O. ; Tollefson, K. ; Torres, I. ; Ukwatta, Tilan N. ; Villasenor, L. ; Weisgarber, T. ; Westerhoff, Stefan ; Wisher, I. G. ; Wood, J. ; Yapici, Tolga ; Yodh, G. ; Zepeda, A. ; Zhou, H.
The High Altitude Water Cherenkov (HAWC) collaboration recently published their 2HWC catalog, listing 39 very high energy (VHE; >100 GeV) gamma-ray sources based on 507 days of observation. Among these, 19 sources are not associated with previously known teraelectronvolt (TeV) gamma-ray sources. We have studied 14 of these sources without known counterparts with VERITAS and Fermi-LAT. VERITAS detected weak gamma-ray emission in the 1 TeV-30 TeV band in the region of DA 495, a pulsar wind nebula coinciding with 2HWC J1953+294, confirming the discovery of the source by HAWC. We did not find any counterpart for the selected 14 new HAWC sources from our analysis of Fermi-LAT data for energies higher than 10 GeV. During the search, we detected gigaelectronvolt (GeV) gamma-ray emission coincident with a known TeV pulsar wind nebula, SNR G54.1+0.3 (VER J1930+188), and a 2HWC source, 2HWC J1930+188. The fluxes for isolated, steady sources in the 2HWC catalog are generally in good agreement with those measured by imaging atmospheric Cherenkov telescopes. However, the VERITAS fluxes for SNR G54.1+0.3, DA 495, and TeV J2032+4130 are lower than those measured by HAWC, and several new HAWC sources are not detected by VERITAS. This is likely due to a change in spectral shape, source extension, or the influence of diffuse emission in the source region.
Abeysekara, A. U. ; Benbow, Wystan ; Bird, Ralph ; Brill, A. ; Brose, Robert ; Buckley, J. H. ; Chromey, A. J. ; Daniel, M. K. ; Falcone, A. ; Finley, J. P. ; Fortson, L. ; Furniss, Amy ; Gent, A. ; Gillanders, Gerald H. ; Hanna, David ; Hassan, T. ; Hervet, O. ; Holder, J. ; Hughes, G. ; Humensky, T. B. ; Kaaret, Philip ; Kar, P. ; Kertzman, M. ; Kieda, David ; Krause, Maria ; Krennrich, F. ; Kumar, S. ; Lang, M. J. ; Lin, T. T. Y. ; Maier, Gernot ; Moriarty, P. ; Mukherjee, Reshmi ; Ong, R. A. ; Otte, Adam Nepomuk ; Park, Nahee ; Petrashyk, A. ; Pohl, Martin ; Pueschel, Elisa ; Quinn, J. ; Ragan, K. ; Richards, Gregory T. ; Roache, E. ; Sadeh, I. ; Santander, Marcos ; Schlenstedt, S. ; Sembroski, G. H. ; Sushch, Iurii ; Tyler, J. ; Vassiliev, V. V. ; Wakely, S. P. ; Weinstein, A. ; Wells, R. M. ; Wilcox, P. ; Wilhelm, Alina ; Williams, David A. ; Williamson, T. J. ; Zitzer, B. ; Acciari, V. A. ; Ansoldi, S. ; Antonelli, L. A. ; Engels, A. Arbet ; Baack, D. ; Babic, A. ; Banerjee, B. ; de Almeida, U. Barres ; Barrio, J. A. ; Becerra Gonzalez, Josefa ; Bednarek, Wlodek ; Bernardini, Elisa ; Berti, A. ; Besenrieder, J. ; Bhattacharyya, W. ; Bigongiari, C. ; Biland, A. ; Blanch, O. ; Bonnoli, G. ; Busetto, G. ; Carosi, R. ; Ceribella, G. ; Cikota, S. ; Colak, S. M. ; Colin, P. ; Colombo, E. ; Contreras, J. L. ; Cortina, J. ; Covino, S. ; Da Vela, P. ; Dazzi, F. ; De Angelis, A. ; De Lotto, B. ; Delfino, M. ; Delgado, J. ; Di Pierro, F. ; Do Souto Espinera, E. ; Dominguez, A. ; Prester, D. Dominis ; Dorner, D. ; Doro, M. ; Einecke, S. ; Elsaesser, D. ; Ramazani, V. Fallah ; Fattorini, A. ; Fernandez-Barral, A. ; Ferrara, G. ; Fidalgo, D. ; Foffano, L. ; Fonseca, M. V. ; Font, L. ; Fruck, C. ; Galindo, D. ; Gallozzi, S. ; Lopez, R. J. Garcia ; Garczarczyk, M. ; Gasparyan, S. ; Gaug, Markus ; Giammaria, P. ; Godinovic, N. ; Guberman, D. ; Hadasch, D. ; Hahn, A. ; Herrera, J. ; Hoang, J. ; Hrupec, D. ; Inoue, S. ; Ishio, K. ; Iwamura, Y. ; Kubo, H. ; Kushida, J. ; Kuvezdic, D. ; Lamastra, A. ; Lelas, D. ; Leone, Francesco ; Lindfors, E. ; Lombardi, S. ; Longo, Francesco ; Lopez, M. ; Lopez-Oramas, A. ; Machado de Oliveira Fraga, B. ; Maggio, C. ; Majumdar, P. ; Makariev, M. ; Mallamaci, M. ; Maneva, G. ; Manganaro, M. ; Mannheim, K. ; Maraschi, L. ; Mariotti, M. ; Martinez, M. ; Masuda, S. ; Mazin, D. ; Minev, M. ; Miranda, J. M. ; Mirzoyan, R. ; Molina, E. ; Moralejo, A. ; Moreno, V. ; Moretti, E. ; Munar-Adrover, Pere ; Neustroev, V. ; Niedzwiecki, Andrzej ; Rosillo, Mireia Nievas ; Nigro, C. ; Nilsson, Kari ; Ninci, D. ; Nishijima, K. ; Noda, K. ; Nogues, L. ; Noethe, M. ; Paiano, Simona ; Palacio, J. ; Paneque, D. ; Paoletti, R. ; Paredes, J. M. ; Pedaletti, G. ; Penil, P. ; Peresano, M. ; Persic, M. ; Moroni, P. G. Prada ; Prandini, E. ; Puljak, I. ; Garcia, J. R. ; Rhode, W. ; Ribo, Marc ; Rico, J. ; Righi, C. ; Rugliancich, A. ; Saha, Lab ; Sahakyan, Narek ; Saito, T. ; Satalecka, K. ; Schweizer, T. ; Sitarek, J. ; Snidaric, I. ; Sobczynska, D. ; Somero, A. ; Stamerra, A. ; Strzys, M. ; Suric, T. ; Tavecchio, Fabrizio ; Temnikov, P. ; Terzic, T. ; Teshima, M. ; Torres-Alba, N. ; Tsujimoto, S. ; van Scherpenberg, J. ; Vanzo, G. ; Vazquez Acosta, M. ; Vovk, I. ; Will, M. ; Zaric, D.
We report on observations of the pulsar/Be star binary system PSR J2032+4127/MT91 213 in the energy range between 100 GeV and 20 TeV with the Very Energetic Radiation Imaging Telescope Array and Major Atmospheric Gamma Imaging Cherenkov telescope arrays. The binary orbit has a period of approximately 50 years, with the most recent periastron occurring on 2017 November 13. Our observations span from 18 months prior to periastron to one month after. A new point-like gamma-ray source is detected, coincident with the location of PSR J2032+4127/MT91 213. The gamma-ray light curve and spectrum are well characterized over the periastron passage. The flux is variable over at least an order of magnitude, peaking at periastron, thus providing a firm association of the TeV source with the pulsar/Be star system. Observations prior to periastron show a cutoff in the spectrum at an energy around 0.5 TeV. This result adds a new member to the small population of known TeV binaries, and it identifies only the second source of this class in which the nature and properties of the compact object are firmly established. We compare the gamma-ray results with the light curve measured with the X-ray Telescope on board the Neil Gehrels Swift Observatory and with the predictions of recent theoretical models of the system. We conclude that significant revision of the models is required to explain the details of the emission that we have observed, and we discuss the relationship between the binary system and the overlapping steady extended source, TeV J2032+4130.
A Search for Pulsed Very High-energy Gamma-Rays from 13 Young Pulsars in Archival VERITAS Data
(2019)
Archer, A. ; Benbow, Wystan ; Bird, Ralph ; Brose, Robert ; Buchovecky, M. ; Buckley, J. H. ; Chromey, A. J. ; Cui, Wei ; Falcone, A. ; Feng, Qi ; Finley, J. P. ; Fortson, Lucy ; Furniss, Amy ; Gent, A. ; Gueta, O. ; Hanna, David ; Hassan, T. ; Hervet, Olivier ; Holder, J. ; Hughes, G. ; Humensky, T. B. ; Johnson, Caitlin A. ; Kaaret, Philip ; Kar, P. ; Kelley-Hoskins, N. ; Kertzman, M. ; Kieda, David ; Krennrich, F. ; Kumar, S. ; Lang, M. J. ; Lin, T. T. Y. ; McCann, A. ; Moriarty, P. ; Mukherjee, Reshmi ; Ong, R. A. ; Otte, Adam Nepomuk ; Pandel, D. ; Park, N. ; Petrashyk, A. ; Pohl, Martin ; Pueschel, Elisa ; Quinn, J. ; Ragan, K. ; Richards, Gregory T. ; Roache, E. ; Sadeh, I ; Santander, Marcos ; Scott, S. S. ; Sembroski, G. H. ; Shahinyan, Karlen ; Sushch, Iurii ; Tyler, J. ; Wakely, S. P. ; Weinstein, A. ; Wells, R. M. ; Wilcox, P. ; Wilhelm, Alina ; Williams, D. A. ; Williamson, T. J. ; Zitzer, B.
We conduct a search for periodic emission in the very high-energy (VHE) gamma-ray band (E > 100 GeV) from a total of 13 pulsars in an archival VERITAS data set with a total exposure of over 450 hr. The set of pulsars includes many of the brightest young gamma-ray pulsars visible in the Northern Hemisphere. The data analysis resulted in nondetections of pulsed VHE gamma-rays from each pulsar. Upper limits on a potential VHE gamma-ray flux are derived at the 95% confidence level above three energy thresholds using two methods. These are the first such searches for pulsed VHE emission from each of the pulsars, and the obtained limits constrain a possible flux component manifesting at VHEs as is seen for the Crab pulsar.
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.
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.
Discovery of Very-high-energy Emission from RGB J2243+203 and Derivation of Its Redshift Upper Limit
(2017)
Abeysekara, A. U. ; Archambault, S. ; Archer, A. ; Benbow, W. ; Bird, R. ; Brose, Robert ; Buchovecky, M. ; Buckley, J. H. ; Bugaev, V. ; Cerruti, M. ; Connolly, M. P. ; Cui, W. ; Falcone, A. ; Feng, Q. ; Finley, J. P. ; Fleischhack, H. ; Fortson, L. ; Furniss, A. ; Gillanders, G. H. ; Griffin, S. ; Grube, J. ; Huetten, M. ; Hanna, D. ; Hervet, O. ; 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. ; 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. ; Santander, M. ; Sembroski, G. H. ; Shahinyan, K. ; Staszak, D. ; Telezhinsky, Igor O. ; Tyler, J. ; Vassiliev, V. V. ; Wakely, S. P. ; Weiner, O. M. ; Weinstein, A. ; Wilcox, P. ; Wilhelm, Alina ; Williams, D. A. ; Zitzer, B.
Very-high-energy (VHE; > 100 GeV) gamma-ray emission from the blazar RGB J2243+203 was discovered with the VERITAS Cherenkov telescope array, during the period between 2014 December 21 and 24. The VERITAS energy spectrum from this source can be fitted by a power law with a photon index of 4.6 +/- 0.5, and a flux normalization at 0.15 TeV of (6.3 +/- 1.1) x 10(-10) cm(-2) s(-1) TeV-1. The integrated Fermi-LAT flux from 1 to 100 GeV during the VERITAS detection is (4.1 +/- 0.8) x 10(-8) cm(-2) s(-1), which is an order of magnitude larger than the four-year-averaged flux in the same energy range reported in the 3FGL catalog, (4.0 +/- 0.1 x 10(-9) cm(-2) s(-1)). The detection with VERITAS triggered observations in the X-ray band with the Swift-XRT. However, due to scheduling constraints Swift-XRT observations were performed 67 hr after the VERITAS detection, rather than simultaneously with the VERITAS observations. The observed X-ray energy spectrum between 2 and 10 keV can be fitted with a power law with a spectral index of 2.7 +/- 0.2, and the integrated photon flux in the same energy band is (3.6 +/- 0.6) x 10(-13) cm(-2) s(-1). EBL-model-dependent upper limits of the blazar redshift have been derived. Depending on the EBL model used, the upper limit varies in the range from z < 0.9 to z < 1.1.
Archambault, S. ; Archer, A. ; Aune, T. ; Barnacka, Anna ; Benbow, W. ; Bird, R. ; Buchovecky, M. ; Buckley, J. H. ; Bugaev, V. ; Byrum, K. ; Cardenzana, J. V. ; Cerruti, M. ; Chen, Xuhui ; Ciupik, L. ; Collins-Hughes, E. ; Connolly, M. P. ; Cui, W. ; Dickinson, H. J. ; Dumm, J. ; Eisch, J. D. ; Falcone, A. ; Feng, Q. ; Finley, J. P. ; Fleischhack, H. ; Flinders, A. ; 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. ; Khassen, Y. ; Kieda, D. ; Krause, M. ; Krennrich, F. ; Kumar, S. ; Lang, M. J. ; Maier, G. ; McArthur, S. ; McCann, A. ; Meagher, K. ; Millis, J. ; Moriarty, P. ; Mukherjee, R. ; Nieto, D. ; Ong, R. A. ; Otte, A. N. ; Pandel, D. ; Park, N. ; Pelassa, V. ; Pohl, Martin ; Popkow, A. ; Pueschel, Elisa ; Quinn, J. ; Ragan, K. ; Reynolds, P. T. ; Richards, G. T. ; Roache, E. ; Rousselle, J. ; Rulten, 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. ; Wilhelm, Alina ; Williams, D. A. ; Zitzer, B.
The TeV binary system LS I +61 degrees 303 is known for its regular, non-thermal emission pattern that traces the orbital period of the compact object in its 26.5 day orbit around its B0 Ve star companion. The system typically presents elevated TeV emission around apastron passage with flux levels between 5% and 15% of the steady flux from the Crab Nebula (> 300 GeV). In this article, VERITAS observations of LS I + 61 degrees. 303 taken in late 2014 are presented, during which bright TeV flares around apastron at flux levels peaking above 30% of the Crab Nebula flux were detected. This is the brightest such activity from this source ever seen in the TeV regime. The strong outbursts have rise and fall times of less than a day. The short timescale of the flares, in conjunction with the observation of 10 TeV photons from LS I + 61 degrees 303 during the flares, provides constraints on the properties of the accelerator in the source.
Abeysekara, A. U. ; Archambault, S. ; Archer, A. ; Benbow, W. ; Bird, R. ; Buchovecky, M. ; Buckley, J. H. ; Byrum, K. ; Cardenzana, J. V. ; Cerruti, M. ; Chen, Xuhui ; Christiansen, J. L. ; Ciupik, L. ; Cui, W. ; Dickinson, H. J. ; Eisch, J. D. ; Errando, M. ; Falcone, A. ; Fegan, D. J. ; 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. ; Lin, T. T. Y. ; Maier, G. ; McArthur, S. ; McCann, A. ; Meagher, K. ; Moriarty, P. ; Mukherjee, R. ; Nieto, D. ; Ong, R. A. ; Otte, A. N. ; Park, N. ; Perkins, J. S. ; Petrashyk, A. ; Pohl, Martin ; Popkow, A. ; Pueschel, Elisa ; Quinn, J. ; Ragan, K. ; Ratliff, G. ; Reynolds, P. T. ; Richards, G. T. ; Roache, E. ; Santander, M. ; Sembroski, G. H. ; Shahinyan, K. ; 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.
The F-type star KIC. 8462852 has recently been identified as an exceptional target for search for extraterrestrial intelligence (SETI) observations. We describe an analysis methodology for optical SETI, which we have used to analyze nine hours of serendipitous archival observations of KIC. 8462852 made with the VERITAS gamma-ray observatory between 2009 and 2015. No evidence of pulsed optical beacons, above a pulse intensity at the Earth of approximately 1 photon m(-2), is found. We also discuss the potential use of imaging atmospheric Cherenkov telescope arrays in searching for extremely short duration optical transients in general.
Archer, A. ; Benbow, W. ; Bird, R. ; Buchovecky, M. ; Buckley, J. H. ; Bugaev, V. ; Byrum, K. ; Cardenzana, J. V. ; Cerruti, M. ; Chen, Xuhui ; Ciupik, L. ; Collins-Hughes, E. ; Connolly, M. P. ; Eisch, J. D. ; Falcone, A. ; Feng, Q. ; Finley, J. P. ; Fleischhack, H. ; Flinders, A. ; Fortson, L. ; Furniss, A. ; Gillanders, G. H. ; Griffin, S. ; Grube, J. ; Gyuk, G. ; Hakansson, Nils ; Hanna, D. ; Holder, J. ; Humensky, T. B. ; Huetten, M. ; Johnson, C. A. ; Kaaret, P. ; Kar, P. ; Kelley-Hoskins, N. ; Kertzman, M. ; Kieda, D. ; Krause, M. ; Krennrich, F. ; Kumar, S. ; Lang, M. J. ; McArthur, S. ; McCann, A. ; Meagher, K. ; Millis, J. ; Moriarty, P. ; Mukherjee, R. ; Nieto, D. ; Ong, R. A. ; Park, N. ; Pelassa, V. ; Pohl, Martin ; Popkow, A. ; Pueschel, Elisa ; Quinn, J. ; Ragan, K. ; Ratliff, G. ; Reynolds, P. T. ; Richards, G. T. ; Roache, E. ; Rousselle, J. ; Santander, M. ; Sembroski, G. H. ; Shahinyan, K. ; Smith, A. W. ; Staszak, D. ; Telezhinsky, Igor O. ; Tucci, J. V. ; Tyler, J. ; Vassiliev, V. V. ; Wakely, S. P. ; Weiner, O. M. ; Weinstein, A. ; Wilhelm, Alina ; Williams, D. A. ; Zitzer, B. ; Yusef-Zadeh, F.
The Galactic Center ridge has been observed extensively in the past by both GeV and TeV gamma-ray instruments revealing a wealth of structure, including a diffuse component and the point sources G0.9+0.1 (a composite supernova remnant) and Sgr A* (believed to be associated with the supermassive black hole located at the center of our Galaxy). Previous very high energy (VHE) gamma-ray observations with the H.E.S.S.. experiment have also detected an extended TeV gamma-ray component along the Galactic plane in the >300 GeV gamma-ray regime. Here we report on observations of the Galactic Center ridge from 2010 to 2014 by the VERITAS telescope array in the >2 TeV energy range. From these observations we (1) provide improved measurements of the differential energy spectrum for Sgr A* in the >2 TeV gamma-ray regime, (2) provide a detection in the >2 TeV gamma-ray emission from the composite SNR G0.9+0.1 and an improved determination of its multi-TeV gamma-ray energy spectrum, and. (3) report on the detection of VER J1746-289, a localized enhancement of >2 TeV gamma-ray emission along the Galactic plane.