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Title: Fermi LAT Stacking Analysis of Swift Localized GRBs

In this paper, we perform a comprehensive stacking analysis of data collected by the Fermi Large Area Telescope (LAT) of γ-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 γ-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 afterglowmore » brightness lend further support to the external forward shock origin of the late-time emission detected by the LAT. Finally, 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.« less
Authors:
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Publication Date:
Grant/Contract Number:
AC02-76SF00515
Type:
Accepted Manuscript
Journal Name:
The Astrophysical Journal (Online)
Additional Journal Information:
Journal Name: The Astrophysical Journal (Online); Journal Volume: 822; Journal Issue: 2; Journal ID: ISSN 1538-4357
Publisher:
Institute of Physics (IOP)
Research Org:
SLAC National Accelerator Lab., Menlo Park, CA (United States)
Sponsoring Org:
USDOE; National Aeronautics and Space Administration (NASA); Japan Aerospace Exploration Agency (JAXA); K.A. Wallenberg Foundation; Swedish Research Council (SRC)
Contributing Orgs:
Fermi LAT Collaboration
Country of Publication:
United States
Language:
English
Subject:
79 ASTRONOMY AND ASTROPHYSICS; gamma-ray burst; gamma rays; data analysis methods; X-ray bursts
OSTI Identifier:
1355697

Ackermann, M., Ajello, M., Anderson, B., Atwood, W. B., Axelsson, M., Baldini, L., Barbiellini, G., Bastieri, D., Bellazzini, R., Bhat, P. N., Bissaldi, E., Bonino, R., Bottacini, E., Brandt, T. J., Bregeon, J., Bruel, P., Buehler, R., Buson, S., Caliandro, G. A., Cameron, R. A., Caragiulo, M., Caraveo, P. A., 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, P. S., Favuzzi, C., Focke, W. B., Franckowiak, A., Funk, S., Fusco, P., Gargano, F., Gasparrini, D., Gehrels, N., Giglietto, N., Giordano, F., Giroletti, M., Godfrey, G., Grenier, I. A., Grove, J. E., Guiriec, S., Hewitt, J. W., Hill, A. B., Horan, D., Jóhannesson, G., Kocevski, D., Kouveliotou, C., Kuss, M., Larsson, S., Li, J., Li, L., Longo, F., Loparco, F., Lovellette, M. N., Lubrano, P., Mayer, M., Mazziotta, M. N., McEnery, J. E., Michelson, P. F., Mizuno, T., Monzani, M. E., Morselli, A., Murgia, S., Nemmen, R., Nuss, E., Ohno, M., Ohsugi, T., Omodei, N., Orienti, M., Orlando, E., Paneque, D., Perkins, J. S., Pesce-Rollins, M., Piron, F., Pivato, G., Porter, T. A., Racusin, J. L., Rainò, S., Rando, R., Razzano, M., Reimer, A., Reimer, O., Schaal, M., Schulz, A., Sgrò, C., Siskind, E. J., Spada, F., Spandre, G., Spinelli, P., Takahashi, H., Thayer, J. B., Tibaldo, L., Tinivella, M., Torres, D. F., Tosti, G., Troja, E., Vianello, G., Kienlin, A. von, Werner, M., and Wood, K. S.. Fermi LAT Stacking Analysis of Swift Localized GRBs. United States: N. p., Web. doi:10.3847/0004-637X/822/2/68.
Ackermann, M., Ajello, M., Anderson, B., Atwood, W. B., Axelsson, M., Baldini, L., Barbiellini, G., Bastieri, D., Bellazzini, R., Bhat, P. N., Bissaldi, E., Bonino, R., Bottacini, E., Brandt, T. J., Bregeon, J., Bruel, P., Buehler, R., Buson, S., Caliandro, G. A., Cameron, R. A., Caragiulo, M., Caraveo, P. A., 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, P. S., Favuzzi, C., Focke, W. B., Franckowiak, A., Funk, S., Fusco, P., Gargano, F., Gasparrini, D., Gehrels, N., Giglietto, N., Giordano, F., Giroletti, M., Godfrey, G., Grenier, I. A., Grove, J. E., Guiriec, S., Hewitt, J. W., Hill, A. B., Horan, D., Jóhannesson, G., Kocevski, D., Kouveliotou, C., Kuss, M., Larsson, S., Li, J., Li, L., Longo, F., Loparco, F., Lovellette, M. N., Lubrano, P., Mayer, M., Mazziotta, M. N., McEnery, J. E., Michelson, P. F., Mizuno, T., Monzani, M. E., Morselli, A., Murgia, S., Nemmen, R., Nuss, E., Ohno, M., Ohsugi, T., Omodei, N., Orienti, M., Orlando, E., Paneque, D., Perkins, J. S., Pesce-Rollins, M., Piron, F., Pivato, G., Porter, T. A., Racusin, J. L., Rainò, S., Rando, R., Razzano, M., Reimer, A., Reimer, O., Schaal, M., Schulz, A., Sgrò, C., Siskind, E. J., Spada, F., Spandre, G., Spinelli, P., Takahashi, H., Thayer, J. B., Tibaldo, L., Tinivella, M., Torres, D. F., Tosti, G., Troja, E., Vianello, G., Kienlin, A. von, Werner, M., & Wood, K. S.. Fermi LAT Stacking Analysis of Swift Localized GRBs. United States. doi:10.3847/0004-637X/822/2/68.
Ackermann, M., Ajello, M., Anderson, B., Atwood, W. B., Axelsson, M., Baldini, L., Barbiellini, G., Bastieri, D., Bellazzini, R., Bhat, P. N., Bissaldi, E., Bonino, R., Bottacini, E., Brandt, T. J., Bregeon, J., Bruel, P., Buehler, R., Buson, S., Caliandro, G. A., Cameron, R. A., Caragiulo, M., Caraveo, P. A., 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, P. S., Favuzzi, C., Focke, W. B., Franckowiak, A., Funk, S., Fusco, P., Gargano, F., Gasparrini, D., Gehrels, N., Giglietto, N., Giordano, F., Giroletti, M., Godfrey, G., Grenier, I. A., Grove, J. E., Guiriec, S., Hewitt, J. W., Hill, A. B., Horan, D., Jóhannesson, G., Kocevski, D., Kouveliotou, C., Kuss, M., Larsson, S., Li, J., Li, L., Longo, F., Loparco, F., Lovellette, M. N., Lubrano, P., Mayer, M., Mazziotta, M. N., McEnery, J. E., Michelson, P. F., Mizuno, T., Monzani, M. E., Morselli, A., Murgia, S., Nemmen, R., Nuss, E., Ohno, M., Ohsugi, T., Omodei, N., Orienti, M., Orlando, E., Paneque, D., Perkins, J. S., Pesce-Rollins, M., Piron, F., Pivato, G., Porter, T. A., Racusin, J. L., Rainò, S., Rando, R., Razzano, M., Reimer, A., Reimer, O., Schaal, M., Schulz, A., Sgrò, C., Siskind, E. J., Spada, F., Spandre, G., Spinelli, P., Takahashi, H., Thayer, J. B., Tibaldo, L., Tinivella, M., Torres, D. F., Tosti, G., Troja, E., Vianello, G., Kienlin, A. von, Werner, M., and Wood, K. S.. 2016. "Fermi LAT Stacking Analysis of Swift Localized GRBs". United States. doi:10.3847/0004-637X/822/2/68. https://www.osti.gov/servlets/purl/1355697.
@article{osti_1355697,
title = {Fermi LAT Stacking Analysis of Swift Localized GRBs},
author = {Ackermann, M. and Ajello, M. and Anderson, B. and Atwood, W. B. and Axelsson, M. and Baldini, L. and Barbiellini, G. and Bastieri, D. and Bellazzini, R. and Bhat, P. N. and Bissaldi, E. and Bonino, R. and Bottacini, E. and Brandt, T. J. and Bregeon, J. and Bruel, P. and Buehler, R. and Buson, S. and Caliandro, G. A. and Cameron, R. A. and Caragiulo, M. and Caraveo, P. A. and Cecchi, C. and Charles, E. and Chekhtman, A. and Chiang, J. and Chiaro, G. and Ciprini, S. and Claus, R. and Cohen-Tanugi, J. and Conrad, J. and Cutini, S. and D’Ammando, F. and de Angelis, A. and de Palma, F. and Desiante, R. and Di Venere, L. and Drell, P. S. and Favuzzi, C. and Focke, W. B. and Franckowiak, A. and Funk, S. and Fusco, P. and Gargano, F. and Gasparrini, D. and Gehrels, N. and Giglietto, N. and Giordano, F. and Giroletti, M. and Godfrey, G. and Grenier, I. A. and Grove, J. E. and Guiriec, S. and Hewitt, J. W. and Hill, A. B. and Horan, D. and Jóhannesson, G. and Kocevski, D. and Kouveliotou, C. and Kuss, M. and Larsson, S. and Li, J. and Li, L. and Longo, F. and Loparco, F. and Lovellette, M. N. and Lubrano, P. and Mayer, M. and Mazziotta, M. N. and McEnery, J. E. and Michelson, P. F. and Mizuno, T. and Monzani, M. E. and Morselli, A. and Murgia, S. and Nemmen, R. and Nuss, E. and Ohno, M. and Ohsugi, T. and Omodei, N. and Orienti, M. and Orlando, E. and Paneque, D. and Perkins, J. S. and Pesce-Rollins, M. and Piron, F. and Pivato, G. and Porter, T. A. and Racusin, J. L. and Rainò, S. and Rando, R. and Razzano, M. and Reimer, A. and Reimer, O. and Schaal, M. and Schulz, A. and Sgrò, C. and Siskind, E. J. and Spada, F. and Spandre, G. and Spinelli, P. and Takahashi, H. and Thayer, J. B. and Tibaldo, L. and Tinivella, M. and Torres, D. F. and Tosti, G. and Troja, E. and Vianello, G. and Kienlin, A. von and Werner, M. and Wood, K. S.},
abstractNote = {In this paper, we perform a comprehensive stacking analysis of data collected by the Fermi Large Area Telescope (LAT) of γ-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 γ-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. Finally, 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.},
doi = {10.3847/0004-637X/822/2/68},
journal = {The Astrophysical Journal (Online)},
number = 2,
volume = 822,
place = {United States},
year = {2016},
month = {5}
}