FERMI LAT STACKING ANALYSIS OF SWIFT LOCALIZED GRBs

Ackermann M, Ajello M, Anderson B, Atwood WB, Axelsson M, Baldini L, Barbiellini G, Bastieri D, Bellazzini R, Bhat PN, Bissaldi E, Bonino R, Bottacini E, Brandt TJ, Bregeon J, Bruel P, Buehler R, Buson S, Caliandro GA, Cameron RA, Caragiulo M, Caraveo PA, Cecchi C, Charles E, Chekhtman A, Chiang J, Chiaro G, Ciprini S, Claus R, Cohen-Tanugi J, Conrad J, Cutini S, D'Ammando F, De Angelis A, De Palma F, Desiante R, Di Venere L, Drell PS, Favuzzi C, Focke WB, Franckowiak A, Funk S, Fusco P, Gargano F, Gasparrini D, Gehrels N, Giglietto N, Giordano F, Giroletti M, Godfrey G, Grenier IA, Grove JE, Guiriec S, Hewitt JW, Hill AB, Horan D, Johannesson G, Kocevski D, Kouveliotou C, Kuss M, Larsson S, Li J, Li L, Longo F, Loparco F, Lovellette MN, Lubrano P, Mayer M, Mazziotta MN, Mcenery JE, Michelson PF, Mizuno T, Monzani ME, Morselli A, Murgia S, Nemmen R, Nuss E, Ohno M, Ohsugi T, Omodei N, Orienti M, Orlando E, Paneque D, Perkins JS, Pesce-Rollins M, Piron F, Pivato G, Porter TA, Racusin JL, Raino S, Rando R, Razzano M, Reimer A, Reimer O, Schaal M, Schulz A, Sgro C, Siskind EJ, Spada F, Spandre G, Spinelli P, Takahashi H, Thayer JB, Tibaldo L, Tinivella M, Torres DF, Tosti G, Troja E, Vianello G, Von Kienlin A, Werner M, Wood KS (2016)

Publication Status: Published

Publication Type: Journal article, Original article

Publication year: 2016

Journal

Publisher: American Astronomical Society

Book Volume: 822

Journal Issue: 2

DOI: 10.3847/0004-637X/822/2/68

Abstract

We perform a comprehensive stacking analysis of data collected by the Fermi. Large Area Telescope (LAT) of gamma-ray bursts (GRBs) localized by the Swift. spacecraft, which were not detected by the LAT but which fell within the instrument's field of view at the time of trigger. We examine a total of 79 GRBs by comparing the observed counts over a range of time intervals to that expected from designated background orbits, as well as by using a joint likelihood technique to model the expected distribution of stacked counts. We find strong evidence for subthreshold emission at MeV to GeV energies using both techniques. This observed excess is detected during intervals that include and exceed the durations typically characterizing the prompt emission observed at keV energies and lasts at least 2700 s after the co-aligned burst trigger. By utilizing a novel cumulative likelihood analysis, we find that although a burst's prompt gamma-ray and afterglow X-ray flux both correlate with the strength of the subthreshold emission, the X-ray afterglow flux measured by Swift's X-ray Telescope at 11 hr post trigger correlates far more significantly. Overall, the extended nature of the subthreshold emission and its connection to the burst's afterglow brightness lend. further support to the external forward shock origin of the late-time emission detected by the LAT. These results suggest that the extended high-energy emission observed by the LAT may be a relatively common feature but remains undetected in a majority of bursts owing. to instrumental threshold effects.

Authors with CRIS profile

Involved external institutions

National Institute for Astrophysics / Istituto Nazionale Astrofisica (INAF) Italy (IT) U.S. Naval Research Laboratory United States (USA) (US) Royal Institute of Technology / Kungliga Tekniska Högskolan (KTH) Sweden (SE) University of California Irvine United States (USA) (US) National Institute for Nuclear Physics / Istituto Nazionale di Fisica Nucleare (INFN) Italy (IT) University of São Paulo / Universidade de São Paulo (USP) Brazil (BR) George Washington University (GWU) United States (USA) (US) Leopold-Franzens-Universität Innsbruck / University of Innsbruck Austria (AT) Spanish National Research Council / Consejo Superior de Investigaciones Científicas (CSIC) Spain (ES) University of Maryland, Baltimore County United States (USA) (US) Max-Planck-Institut für extraterrestrische Physik (MPE) / Max Planck Institute for Extraterrestrial Physics Germany (DE) University of Pisa / Università di Pisa (UniPi) Italy (IT) Stanford University United States (USA) (US) Hiroshima University Japan (JP) Stockholm University / Stockholms universitet Sweden (SE) National Aeronautics and Space Administration (NASA) United States (USA) (US) University of Iceland (UI) / Háskóli Íslands Iceland (IS) University of California Santa Cruz United States (USA) (US) University of Bari Aldo Moro / Università degli Studi di Bari Aldo Moro Italy (IT) École Polytechnique - Université Paris-Saclay France (FR) Deutsches Elektronen-Synchrotron DESY Germany (DE) University of Montpellier / Université Montpellier France (FR) Clemson University United States (USA) (US) George Mason University United States (USA) (US) University of Padua / Universita degli Studi di Padova Italy (IT) University of Udine / Università degli Studi di Udine Italy (IT) NYCB Real-Time Computing, Inc. United States (USA) (US) University of Alabama in Huntsville (UAH) United States (USA) (US) University of Paris 7 - Denis Diderot / Université Paris VII Denis Diderot France (FR)

How to cite

APA:

Ackermann, M., Ajello, M., Anderson, B., Atwood, W.B., Axelsson, M., Baldini, L.,... Wood, K.S. (2016). FERMI LAT STACKING ANALYSIS OF SWIFT LOCALIZED GRBs. Astrophysical Journal, 822(2). https://dx.doi.org/10.3847/0004-637X/822/2/68

MLA:

Ackermann, M., et al. "FERMI LAT STACKING ANALYSIS OF SWIFT LOCALIZED GRBs." Astrophysical Journal 822.2 (2016).

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