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- astroparticle physics (4)
- gamma rays: general (4)
- galaxies: active (3)
- gamma rays: galaxies (3)
- binaries: general (2)
- galaxies: jets (2)
- galaxies: nuclei (2)
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- BL Lacertae objects: individual (B2 1215+30, VER J1217+301) (1)
- BL Lacertae objects: individual (BL Lacertae = VER J2202+422) (1)
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Introducing the CTA concept
(2013)
Acharya, B. S. ; Actis, M. ; Aghajani, T. ; Agnetta, G. ; Aguilar, J. ; Aharonian, Felix A. ; Ajello, M. ; Akhperjanian, A. G. ; Alcubierre, M. ; Aleksic, J. ; Alfaro, R. ; Aliu, E. ; Allafort, A. J. ; Allan, D. ; Allekotte, I. ; Amato, E. ; Anderson, J. ; Angüner, Ekrem Oǧuzhan ; Antonelli, L. A. ; Antoranz, P. ; Aravantinos, A. ; Arlen, T. ; Armstrong, T. ; Arnaldi, H. ; Arrabito, L. ; Asano, K. ; Ashton, T. ; Asorey, H. G. ; Awane, Y. ; Baba, H. ; Babic, A. ; Baby, N. ; Baehr, J. ; Bais, A. ; Baixeras, C. ; Bajtlik, S. ; Balbo, M. ; Balis, D. ; Balkowski, C. ; Bamba, A. ; Bandiera, R. ; Barber, A. ; Barbier, C. ; Barcelo, M. ; Barnacka, Anna ; Barnstedt, Jürgen ; Barres de Almeida, U. ; Barrio, J. A. ; Basili, A. ; Basso, S. ; Bastieri, D. ; Bauer, C. ; Baushev, Anton N. ; Becerra Gonzalez, J. ; Becherini, Yvonne ; Bechtol, K. C. ; Tjus, J. Becker ; Beckmann, Volker ; Bednarek, W. ; Behera, B. ; Belluso, M. ; Benbow, W. ; Berdugo, J. ; Berger, K. ; Bernard, F. ; Bernardino, T. ; Bernlöhr, K. ; Bhat, N. ; Bhattacharyya, S. ; Bigongiari, C. ; Biland, A. ; Billotta, S. ; Bird, T. ; Birsin, E. ; Bissaldi, E. ; Biteau, Jonathan ; Bitossi, M. ; Blake, S. ; Blanch Bigas, O. ; Blasi, P. ; Bobkov, A. A. ; Boccone, V. ; Boettcher, Markus ; Bogacz, L. ; Bogart, J. ; Bogdan, M. ; Boisson, Catherine ; Boix Gargallo, J. ; Bolmont, J. ; Bonanno, G. ; Bonardi, A. ; Bonev, T. ; Bonifacio, P. ; Bonnoli, G. ; Bordas, Pol ; Borgland, A. W. ; Borkowski, Janett ; Bose, R. ; Botner, O. ; Bottani, A. ; Bouchet, L. ; Bourgeat, M. ; Boutonnet, C. ; Bouvier, A. ; Brau-Nogue, S. ; Braun, I. ; Bretz, T. ; Briggs, M. S. ; Bringmann, T. ; Brook, P. ; Brun, Pierre ; Brunetti, L. ; Buanes, T. ; Buckley, J. H. ; Buehler, R. ; Bugaev, V. ; Bulgarelli, A. ; Bulik, Tomasz ; Busetto, G. ; Buson, S. ; Byrum, K. ; Cailles, M. ; Cameron, R. A. ; Camprecios, J. ; Canestrari, R. ; Cantu, S. ; Capalbi, M. ; Caraveo, P. A. ; Carmona, E. ; Carosi, A. ; Carr, John ; Carton, P. H. ; Casanova, Sabrina ; Casiraghi, M. ; Catalano, O. ; Cavazzani, S. ; Cazaux, S. ; Cerruti, M. ; Chabanne, E. ; Chadwick, Paula M. ; Champion, C. ; Chen, Andrew ; Chiang, J. ; Chiappetti, L. ; Chikawa, M. ; Chitnis, V. R. ; Chollet, F. ; Chudoba, J. ; Cieslar, M. ; Cillis, A. N. ; Cohen-Tanugi, J. ; Colafrancesco, Sergio ; Colin, P. ; Calome, J. ; Colonges, S. ; Compin, M. ; Conconi, P. ; Conforti, V. ; Connaughton, V. ; Conrad, Jan ; Contreras, J. L. ; Coppi, P. ; Corona, P. ; Corti, D. ; Cortina, J. ; Cossio, L. ; Costantini, H. ; Cotter, G. ; Courty, B. ; Couturier, S. ; Covino, S. ; Crimi, G. ; Criswell, S. J. ; Croston, J. ; Cusumano, G. ; Dafonseca, M. ; Dale, O. ; Daniel, M. ; Darling, J. ; Davids, I. ; Dazzi, F. ; De Angelis, A. ; De Caprio, V. ; De Frondat, F. ; de Gouveia Dal Pino, E. M. ; de la Calle, I. ; De La Vega, G. 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M. ; Impiombato, D. ; Incorvaia, S. ; Inoue, S. ; Inoue, Y. ; Ioka, K. ; Ismailova, E. ; Jablonski, C. ; Jacholkowska, A. ; Jamrozy, M. ; Janiak, M. ; Jean, P. ; Jeanney, C. ; Jimenez, J. J. ; Jogler, T. ; Johnson, T. ; Journet, L. ; Juffroy, C. ; Jung, I. ; Kaaret, P. ; Kabuki, S. ; Kagaya, M. ; Kakuwa, J. ; Kalkuhl, C. ; Kankanyan, R. ; Karastergiou, A. ; Kaercher, K. ; Karczewski, M. ; Karkar, S. ; Kasperek, Aci. ; Kastana, D. ; Katagiri, H. ; Kataoka, J. ; Katarzynski, K. ; Katz, U. ; Kawanaka, N. ; Kellner-Leidel, B. ; Kelly, H. ; Kendziorra, E. ; Khelifi, B. ; Kieda, D. 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G. ; Wagner, S. ; Wakely, S. P. ; Walter, R. ; Walther, T. ; Warda, K. ; Warwick, R. ; Wawer, P. ; Wawrzaszek, R. ; Webb, N. ; Wegner, P. ; Weinstein, A. ; Weitzel, Q. ; Welsing, R. ; Werner, M. ; Wetteskind, H. ; White, R. ; Wierzcholska, A. ; Wiesand, S. ; Wilkinson, M. ; Williams, D. A. ; Willingale, R. ; Winiarski, K. ; Wischnewski, R. ; Wisniewski, L. ; Wood, M. ; Woernlein, A. ; Xiong, Q. ; Yadav, K. K. ; Yamamoto, H. ; Yamamoto, T. ; Yamazaki, R. ; Yanagita, S. ; Yebras, J. M. ; Yelos, D. ; Yoshida, A. ; Yoshida, T. ; Yoshikoshi, T. ; Zabalza, V. ; Zacharias, M. ; Zajczyk, A. ; Zanin, R. ; Zdziarski, A. ; Zech, Alraune ; Zhao, A. ; Zhou, X. ; Zietara, K. ; Ziolkowski, J. ; Ziolkowski, P. ; Zitelli, V. ; Zurbach, C. ; Zychowski, P.
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.
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.
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. ; Archambault, S. ; Archer, A. ; Benbow, W. ; Bird, R. ; Biteau, Jonathan ; Buchovecky, M. ; Buckley, J. H. ; Bugaev, V. ; Byrum, K. ; Cardenzana, J. V. ; Cerruti, M. ; Chen, Xuhui ; Christiansen, J. L. ; Ciupik, L. ; Connolly, M. P. ; Cui, W. ; Dickinson, H. J. ; Dumm, J. ; Eisch, J. D. ; Errando, M. ; 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. ; 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. ; Lang, M. J. ; Maier, G. ; McArthur, S. ; McCann, A. ; Meagher, K. ; Moriarty, P. ; Mukherjee, R. ; Nieto, D. ; Ong, R. A. ; Otte, A. N. ; Park, N. ; Pelassa, V. ; Petrashyk, A. ; Petry, D. ; Pohl, Martin ; Popkow, A. ; Pueschel, Elisa ; Quinn, J. ; Ragan, K. ; Ratliff, G. ; Reyes, L. C. ; Reynolds, P. T. ; Reynolds, K. ; Richards, G. T. ; Roache, E. ; 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.
We present results from multiwavelength observations of the BL Lacertae object 1ES 1741 + 196, including results in the very high energy gamma-ray regime using the Very Energetic Radiation Imaging Telescope Array System (VERITAS). The VERITAS time-averaged spectrum, measured above 180 GeV, is well modelled by a power law with a spectral index of 2.7 +/- 0.7(stat) +/- 0.2(syst). The integral flux above 180 GeV is (3.9 +/- 0.8(stat) +/- 1.0(syst)) x 10(-8) m(-2) s(-1), corresponding to 1.6 per cent of the Crab nebula flux on average. The multiwavelength spectral energy distribution of the source suggests that 1ES 1741+196 is an extreme-high-frequency-peaked BL Lacertae object. The observations analysed in this paper extend over a period of six years, during which time no strong flares were observed in any band. This analysis is therefore one of the few characterizations of a blazar in a non-flaring state.
Abeysekara, A. U. ; Benbow, Wystan ; Bird, Ralph ; Brantseg, T. ; Brose, Robert ; Buchovecky, M. ; Buckley, J. H. ; Bugaev, V. ; Connolly, M. P. ; Cui, Wei ; Daniel, M. K. ; Falcone, A. ; Feng, Qi ; Finley, John P. ; Fortson, L. ; Furniss, Amy ; Gillanders, Gerard H. ; Gunawardhana, Isuru ; Huetten, M. ; Hanna, David ; Hervet, O. ; Holder, J. ; Hughes, G. ; Humensky, T. B. ; Johnson, Caitlin A. ; Kaaret, Philip ; Kar, P. ; Kertzman, M. ; Krennrich, F. ; Lang, M. J. ; Lin, T. T. Y. ; McArthur, S. ; Moriarty, P. ; Mukherjee, Reshmi ; Ong, R. A. ; Otte, Adam Nepomuk ; Park, N. ; Petrashyk, A. ; Pohl, Martin ; Pueschel, Elisa ; Quinn, J. ; Ragan, K. ; Reynolds, P. T. ; Richards, Gregory T. ; Roache, E. ; Rulten, C. ; Sadeh, I. ; Santander, M. ; Sembroski, G. H. ; Shahinyan, Karlen ; Wakely, S. P. ; Weinstein, A. ; Wells, R. M. ; Wilcox, P. ; Williams, D. A. ; Zitzer, B. ; Jorstad, Svetlana G. ; Marscher, Alan P. ; Lister, Matthew L. ; Kovalev, Yuri Y. ; Pushkarev, A. B. ; Savolainen, Tuomas ; Agudo, I. ; Molina, S. N. ; Gomez, J. L. ; Larionov, Valeri M. ; Borman, G. A. ; Mokrushina, A. A. ; Tornikoski, Merja ; Lahteenmaki, A. ; Chamani, W. ; Enestam, S. ; Kiehlmann, S. ; Hovatta, Talvikki ; Smith, P. S. ; Pontrelli, P.
Combined with measurements made by very-long-baseline interferometry, the observations of fast TeV gamma-ray flares probe the structure and emission mechanism of blazar jets. However, only a handful of such flares have been detected to date, and only within the last few years have these flares been observed from lower-frequency-peaked BL. Lac objects and flat-spectrum radio quasars. We report on a fast TeV gamma-ray flare from the blazar BL. Lacertae observed by the Very Energetic Radiation Imaging Telescope Array System (VERITAS). with a rise time of similar to 2.3 hr and a decay time of similar to 36 min. The peak flux above 200 GeV is (4.2 +/- 0.6) x 10(-6) photon m(-2) s(-1) measured with a 4-minute-binned light curve, corresponding to similar to 180% of the flux that is observed from the Crab Nebula above the same energy threshold. Variability contemporaneous with the TeV gamma-ray flare was observed in GeV gamma-ray, X-ray, and optical flux, as well as in optical and radio polarization. Additionally, a possible moving emission feature with superluminal apparent velocity was identified in Very Long Baseline Array observations at 43 GHz, potentially passing the radio core of the jet around the time of the gamma-ray flare. We discuss the constraints on the size, Lorentz factor, and location of the emitting region of the flare, and the interpretations with several theoretical models that invoke relativistic plasma passing stationary shocks.
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.
A SEARCH FOR VERY HIGH ENERGY GAMMA RAYS FROM THE MISSING LINK BINARY PULSAR J1023+0038 WITH VERITAS
(2016)
Aliu, E. ; Archambault, S. ; Archer, A. ; Benbow, W. ; Bird, R. ; Biteau, Jonathan ; Buchovecky, M. ; Buckley, J. H. ; Bugaev, V. ; Byrum, K. ; Cardenzana, J. V. ; Cerruti, M. ; Chen, Xuhui ; Ciupik, L. ; Connolly, M. P. ; Cui, W. ; Dickinson, H. 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 ; Holder, J. ; Humensky, T. B. ; Johnson, C. A. ; Kaaret, P. ; Kar, P. ; Kelley-Hoskins, N. ; Kertzman, M. ; Kieda, D. ; Krause, M. ; Lang, M. J. ; Loo, A. ; Maier, G. ; McArthur, S. ; McCann, A. ; Meagher, K. ; Moriarty, P. ; Mukherjee, R. ; Nguyen, T. ; Nieto, D. ; Ong, R. A. ; Otte, A. N. ; Pandel, D. ; Park, N. ; Pelassa, V. ; Petrashyk, A. ; Pohl, M. ; 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. ; Smith, A. W. ; Staszak, D. ; Telezhinsky, Igor O. ; Tucci, J. V. ; Tyler, J. ; Varlotta, A. ; Vincent, S. ; Wakely, S. P. ; Weiner, O. M. ; Weinstein, A. ; Wilhelm, Alina ; Williams, D. A. ; Zitzer, B. ; Chernyakova, M. ; Roberts, M. S. E.
The binary millisecond radio pulsar PSR J1023+0038 exhibits many characteristics similar to the gamma-ray binary system PSR B1259-63/LS 2883, making it an ideal candidate for the study of high-energy nonthermal emission. It has been the subject of multiwavelength campaigns following the disappearance of the pulsed radio emission in 2013 June, which revealed the appearance of an accretion disk around the neutron star. We present the results of very high energy (VHE) gamma-ray observations carried out by the Very Energetic Radiation Imaging Telescope Array System before and after this change of state. Searches for steady and pulsed emission of both data sets yield no significant gamma-ray signal above 100 GeV, and upper limits are given for both a steady and pulsed gamma-ray flux. These upper limits are used to constrain the magnetic field strength in the shock region of the PSR J1023+0038 system. Assuming that VHE gamma rays are produced via an inverse Compton mechanism in the shock region, we constrain the shock magnetic field to be greater than similar to 2 G before the disappearance of the radio pulsar and greater than similar to 10 G afterward.
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.
Abeysekara, A. U. ; Archer, A. ; Benbow, Wystan ; Bird, Ralph ; Brill, A. ; Brose, Robert ; Buckley, J. H. ; Christiansen, Jessie L. ; Chromey, A. J. ; Daniel, M. K. ; Falcone, A. ; Feng, Qi ; Finley, John P. ; Fortson, L. ; Furniss, Amy ; Gillanders, Gerard H. ; Gueta, O. ; Hanna, David ; Hervet, O. ; Holder, J. ; Hughes, G. ; Humensky, T. B. ; Johnson, Caitlin A. ; Kaaret, Philip ; Kar, P. ; Kelley-Hoskins, N. ; Kertzman, M. ; Kieda, David ; Krause, Maria ; Krennrich, F. ; Lang, M. J. ; Moriarty, P. ; Mukherjee, Reshmi ; Ong, R. A. ; Otte, A. N. ; Park, N. ; Petrashyk, A. ; Pohl, Martin ; Pueschel, Elisa ; Quinn, J. ; Ragan, K. ; Reynolds, P. T. ; Richards, Gregory T. ; Roache, E. ; Rulten, C. ; Sadeh, I. ; Santander, Marcos ; Scott, S. S. ; Sembroski, G. H. ; Shahinyan, Karlen ; Tyler, J. ; Wakely, S. P. ; Weinstein, A. ; Wells, R. M. ; Wilcox, P. ; Wilhelm, Alina ; Williams, D. A. ; Williamson, T. J. ; Zitzer, B. ; Kaur, A.
On 2017 September 22, the IceCube Neutrino Observatory reported the detection of the high-energy neutrino event IC 170922A, of potential astrophysical origin. It was soon determined that the neutrino direction was consistent with the location of the gamma-ray blazar TXS 0506+056. (3FGL J0509.4+ 0541), which was in an elevated gamma-ray emission state as measured by the Fermi satellite. Very Energetic Radiation Imaging Telescope Array System (VERITAS) observations of the neutrino/blazar region started on 2017 September 23 in response to the neutrino alert and continued through 2018 February 6. While no significant very-high-energy (VHE; E > 100 GeV) emission was observed from the blazar by VERITAS in the two-week period immediately following the IceCube alert, TXS 0506+ 056 was detected by VERITAS with a significance of 5.8 standard deviations (sigma) in the full 35 hr data set. The average photon flux of the source during this period was (8.9 +/- 1.6). x. 10(-12) cm(-2) s(-1), or 1.6% of the Crab Nebula flux, above an energy threshold of 110 GeV, with a soft spectral index of 4.8. +/-. 1.3.