Browsing by Author "Meyer, M."
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Item A Decade of Gamma-Ray Bursts Observed by Fermi-LAT: The Second GRB Catalog(The American Astronomical Society, 2019-06-10) Ajello, M.; Arimoto, M.; Axelsson, M.; Baldini, L.; Barbiellini, G.; Bastieri, D.; Bellazzini, R.; Bhat, P. N.; Bissaldi, E.; Blandford, R. D.; Bonino, R.; Bonnell, J.; Bottacini, E.; Bregeon, J.; Bruel, P.; Buehler, R.; Cameron, R. A.; Caputo, R.; Caraveo, P. A.; Cavazzuti, E.; Chen, S.; Cheung, C. C.; Chiaro, G.; Ciprini, S.; Costantin, D.; Crnogorcevic, M.; Cutini, S.; Dainotti, M.; D’Ammando, F.; Luque, P. de la Torre; Palma, F. de; Desai, A.; Desiante, R.; Lalla, N. Di; Venere, L. Di; Dirirsa, F. Fana; Fegan, S. J.; Franckowiak, A.; Fukazawa, Y.; Funk, S.; Fusco, P.; Gargano, F.; Gasparrini, D.; Giglietto, N.; Giordano, F.; Giroletti, M.; Green, D.; Grenier, I. A.; Grove, J. E.; Guiriec, S.; Hays, E.; Hewitt, J. W.; Horan, D.; Jóhannesson, G.; Kocevski, D.; Kuss, M.; Latronico, L.; Li, J.; Longo, F.; Loparco, F.; Lovellette, M. N.; Lubrano, P.; Maldera, S.; Manfreda, A.; Martí-Devesa, G.; Mazziotta, M. N.; Mereu, I.; Meyer, M.; Michelson, P. F.; Mirabal, N.; Mitthumsiri, W.; Mizuno, T.; Monzani, M. E.; Moretti, E.; Morselli, A.; Moskalenko, I. V.; Negro, M.; Nuss, E.; Ohno, M.; Omodei, N.; Orienti, M.; Orlando, E.; Palatiello, M.; Paliya, V. S.; Paneque, D.; Persic, M.; Pesce-Rollins, M.; Petrosian, V.; Piron, F.; Poolakkil, S.; Poon, H.; Porter, T. A.; Principe, G.; Racusin, J. L.; Rainò, S.; Rando, R.; Razzano, M.; Razzaque, S.; Reimer, A.; Reimer, O.; Reposeur, T.; Ryde, F.; Serini, D.; Sgrò, C.; Siskind, E. J.; Sonbas, E.; Spandre, G.; Spinelli, P.; Suson, D. J.; Tajima, H.; Takahashi, M.; Tak, D.; Thayer, J. B.; Torres, D. F.; Troja, E.; Valverde, J.; Veres, P.; Vianello, G.; Kienlin, A. von; Wood, K.; Yassine, M.; Zhu, S.; Zimmer, S.The Large Area Telescope (LAT) aboard the Fermi spacecraft routinely observes high-energy emission from gamma-ray bursts (GRBs). Here we present the second catalog of LAT-detected GRBs, covering the first 10 yr of operations, from 2008 to 2018 August 4. A total of 186 GRBs are found; of these, 91 show emission in the range 30–100 MeV (17 of which are seen only in this band) and 169 are detected above 100 MeV. Most of these sources were discovered by other instruments (Fermi/GBM, Swift/BAT, AGILE, INTEGRAL) or reported by the Interplanetary Network (IPN); the LAT has independently triggered on four GRBs. This catalog presents the results for all 186 GRBs. We study onset, duration, and temporal properties of each GRB, as well as spectral characteristics in the 100 MeV–100 GeV energy range. Particular attention is given to the photons with the highest energy. Compared with the first LAT GRB catalog, our rate of detection is significantly improved. The results generally confirm the main findings of the first catalog: the LAT primarily detects the brightest GBM bursts, and the high-energy emission shows delayed onset as well as longer duration. However, in this work we find delays exceeding 1 ks and several GRBs with durations over 10 ks. Furthermore, the larger number of LAT detections shows that these GRBs not only cover the high-fluence range of GBM-detected GRBs but also sample lower fluences. In addition, the greater number of detected GRBs with redshift estimates allows us to study their properties in both the observer and rest frames. Comparison of the observational results with theoretical predictions reveals that no model is currently able to explain all results, highlighting the role of LAT observations in driving theoretical models.Item Neutrinos, Cosmic Rays and the MeV Band(2019-03-13) Ojha, R.; Zhang, H.; Kadler, M.; Neilson, N. K.; Kreter, M.; McEnery, J.; Buson, S.; Caputo, R.; Coppi, P.; D'Ammando, F.; Angelis, A. De; Fang, K.; Giannios, D.; Guiriec, S.; Guo, F.; Kopp, J.; Krauss, F.; Li, H.; Meyer, M.; Moiseev, A.; Petropoulou, M.; Prescod-Weinstein, C.; Rani, B.; Shrader, C.; Venters, T.; Wadiasingh, Z.The possible association of the blazar TXS 0506+056 with a high-energy neutrino detected by IceCube holds the tantalizing potential to answer three astrophysical questions: 1. Where do high-energy neutrinos originate? 2. Where are cosmic rays produced and accelerated? 3. What radiation mechanisms produce the high-energy gamma-rays in blazars? The MeV gamma-ray band holds the key to these questions, because it is an excellent proxy for photo-hadronic processes in blazar jets, which also produce neutrino counterparts. Variability in MeV gamma-rays sheds light on the physical conditions and mechanisms that take place in the particle acceleration sites in blazar jets. In addition, hadronic blazar models also predict a high level of polarization fraction in the MeV band, which can unambiguously distinguish the radiation mechanism. Future MeV missions with a large field of view, high sensitivity, and polarization capabilities will play a central role in multi-messenger astronomy, since pointed, high-resolution telescopes will follow neutrino alerts only when triggered by an all-sky instrument.Item Sensitivity projections for dark matter searches with the Fermi large area telescope(Elsevier, 2016-05-20) Charles, E.; Sánchez-Conde, M.; Anderson, B.; Caputo, R.; Cuoco, A.; Mauro, M. Di; Drlica-Wagner, A.; Gomez-Vargas, G.A.; Meyer, M.; Tibaldo, L.; Wood, M.; Zaharijas, G.; Zimmer, S.; Ajello, M.; Albert, A.; Baldini, L.; Bechtol, K.; Bloom, E.D.; Ceraudo, F.; Cohen-Tanugi, J.; Digel, S.W.; Gaskins, J.; Gustafsson, M.; Mirabal, N.; Razzano, M.The nature of dark matter is a longstanding enigma of physics; it may consist of particles beyond the Standard Model that are still elusive to experiments. Among indirect search techniques, which look for stable products from the annihilation or decay of dark matter particles, or from axions coupling to high-energy photons, observations of the 𝛾-ray sky have come to prominence over the last few years, because of the excellent sensitivity of the Large Area Telescope (LAT) on the Fermi Gamma-ray Space Telescope mission. The LAT energy range from 20 meV to above 300 GeV is particularly well suited for searching for products of the interactions of dark matter particles. In this report we describe methods used to search for evidence of dark matter with the LAT, and review the status of searches performed with up to six years of LAT data. We also discuss the factors that determine the sensitivities of these searches, including the magnitudes of the signals and the relevant backgrounds, considering both statistical and systematic uncertainties. We project the expected sensitivities of each search method for 10 and 15 years of LAT data taking. In particular, we find that the sensitivity of searches targeting dwarf galaxies, which provide the best limits currently, will improve faster than the square root of observing time. Current LAT limits for dwarf galaxies using six years of data reach the thermal relic level for masses up to 120 GeV for the bb annihilation channel for reasonable dark matter density profiles. With projected discoveries of additional dwarfs, these limits could extend to about 250 GeV. With as much as 15 years of LAT data these searches would be sensitive to dark matter annihilations at the thermal relic cross section for masses to greater than 400 GeV (200 GeV) bb¯(τ +τ−) in the annihilation channels.