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Title: New Fermi-LAT event reconstruction reveals more high-energy gamma rays from gamma-ray bursts

Here, based on the experience gained during the four and a half years of the mission, the Fermi-LAT Collaboration has undertaken a comprehensive revision of the event-level analysis going under the name of Pass 8. Although it is not yet finalized, we can test the improvements in the new event reconstruction with the special case of the prompt phase of bright gamma-ray bursts (GRBs), where the signal-to-noise ratio is large enough that loose selection cuts are sufficient to identify gamma rays associated with the source. Using the new event reconstruction, we have re-analyzed 10 GRBs previously detected by the Large Area Telescope (LAT) for which an X-ray/optical follow-up was possible and found four new gamma rays with energies greater than 10 GeV in addition to the seven previously known. Among these four is a 27.4 GeV gamma ray from GRB 080916C, which has a redshift of 4.35, thus making it the gamma ray with the highest intrinsic energy (~147 GeV) detected from a GRB. We present here the salient aspects of the new event reconstruction and discuss the scientific implications of these new high-energy gamma rays, such as constraining extragalactic background light models, Lorentz invariance violation tests, the prompt emissionmore » mechanism, and the bulk Lorentz factor of the emitting region.« less
Authors:
 [1] ;  [2] ;  [3] ;  [4] ;  [5] ;  [6] ;  [7] ;  [8] ;  [9] ;  [7] ;  [3] ;  [10] ;  [7] ;  [3] ;  [3] ;  [7] ;  [11]
  1. Univ. of California, Santa Cruz, CA (United States)
  2. Univ. di Pisa and Istituto Nazionale di Fisica Nucleare, Pisa (Italy)
  3. Istituto Nazionale di Fisica Nucleare, Pisa (Italy)
  4. Ecole polytechnique, Palaiseau (France)
  5. George Mason Univ., Fairfax, VA (United States); Naval Research Lab., Washington, D.C. (United States)
  6. Univ. Montpellier, Montpellier (France)
  7. Stanford Univ., Stanford, CA (United States). SLAC National Accelerator Lab.
  8. The Open Univ. of Israel, Ra'anana (Israel)
  9. Istituto Nazionale di Fisica Nucleare, Trieste (Italy); Univ. di Trieste, Trieste (Italy)
  10. Univ. of Johannesburg, Auckland Park (South Africa)
  11. Stockholm Univ., Stockholm (Sweden); The Oskar Klein Centre for Cosmoparticle Physics, Stockholm (Sweden)
Publication Date:
Grant/Contract Number:
AC02-76SF00515
Type:
Accepted Manuscript
Journal Name:
Astrophysical Journal
Additional Journal Information:
Journal Volume: 774; Journal Issue: 1; Journal ID: ISSN 0004-637X
Publisher:
Institute of Physics (IOP)
Research Org:
SLAC National Accelerator Lab., Menlo Park, CA (United States)
Sponsoring Org:
USDOE
Country of Publication:
United States
Language:
English
Subject:
79 ASTRONOMY AND ASTROPHYSICS; astroparticle physics; cosmology: observations; gamma rays: general; methods: data analysis
OSTI Identifier:
1356566

Atwood, W. B., Baldini, L., Bregeon, J., Bruel, P., Chekhtman, A., Cohen-Tanugi, J., Drlica-Wagner, A., Granot, J., Longo, F., Omodei, Nicola, Pesce-Rollins, Melissa, Razzaque, S., Rochester, L. S., Sgrò, C., Tinivella, M., Usher, T. L., and Zimmer, S.. New Fermi-LAT event reconstruction reveals more high-energy gamma rays from gamma-ray bursts. United States: N. p., Web. doi:10.1088/0004-637X/774/1/76.
Atwood, W. B., Baldini, L., Bregeon, J., Bruel, P., Chekhtman, A., Cohen-Tanugi, J., Drlica-Wagner, A., Granot, J., Longo, F., Omodei, Nicola, Pesce-Rollins, Melissa, Razzaque, S., Rochester, L. S., Sgrò, C., Tinivella, M., Usher, T. L., & Zimmer, S.. New Fermi-LAT event reconstruction reveals more high-energy gamma rays from gamma-ray bursts. United States. doi:10.1088/0004-637X/774/1/76.
Atwood, W. B., Baldini, L., Bregeon, J., Bruel, P., Chekhtman, A., Cohen-Tanugi, J., Drlica-Wagner, A., Granot, J., Longo, F., Omodei, Nicola, Pesce-Rollins, Melissa, Razzaque, S., Rochester, L. S., Sgrò, C., Tinivella, M., Usher, T. L., and Zimmer, S.. 2013. "New Fermi-LAT event reconstruction reveals more high-energy gamma rays from gamma-ray bursts". United States. doi:10.1088/0004-637X/774/1/76. https://www.osti.gov/servlets/purl/1356566.
@article{osti_1356566,
title = {New Fermi-LAT event reconstruction reveals more high-energy gamma rays from gamma-ray bursts},
author = {Atwood, W. B. and Baldini, L. and Bregeon, J. and Bruel, P. and Chekhtman, A. and Cohen-Tanugi, J. and Drlica-Wagner, A. and Granot, J. and Longo, F. and Omodei, Nicola and Pesce-Rollins, Melissa and Razzaque, S. and Rochester, L. S. and Sgrò, C. and Tinivella, M. and Usher, T. L. and Zimmer, S.},
abstractNote = {Here, based on the experience gained during the four and a half years of the mission, the Fermi-LAT Collaboration has undertaken a comprehensive revision of the event-level analysis going under the name of Pass 8. Although it is not yet finalized, we can test the improvements in the new event reconstruction with the special case of the prompt phase of bright gamma-ray bursts (GRBs), where the signal-to-noise ratio is large enough that loose selection cuts are sufficient to identify gamma rays associated with the source. Using the new event reconstruction, we have re-analyzed 10 GRBs previously detected by the Large Area Telescope (LAT) for which an X-ray/optical follow-up was possible and found four new gamma rays with energies greater than 10 GeV in addition to the seven previously known. Among these four is a 27.4 GeV gamma ray from GRB 080916C, which has a redshift of 4.35, thus making it the gamma ray with the highest intrinsic energy (~147 GeV) detected from a GRB. We present here the salient aspects of the new event reconstruction and discuss the scientific implications of these new high-energy gamma rays, such as constraining extragalactic background light models, Lorentz invariance violation tests, the prompt emission mechanism, and the bulk Lorentz factor of the emitting region.},
doi = {10.1088/0004-637X/774/1/76},
journal = {Astrophysical Journal},
number = 1,
volume = 774,
place = {United States},
year = {2013},
month = {8}
}