Journal article
(Original article)

Publication Details

Author(s): 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
Journal: Astrophysical Journal
Publisher: American Astronomical Society
Publication year: 2016
Volume: 822
Journal issue: 2
ISSN: 0004-637X


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.

FAU Authors / FAU Editors

Funk, Stefan Prof. Dr.
Lehrstuhl für Physik

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

How to cite

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

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


Last updated on 2018-07-08 at 00:08