NEW FERMI -LAT EVENT RECONSTRUCTION REVEALS MORE HIGH-ENERGY GAMMA RAYS FROM GAMMA-RAY BURSTS

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 reconstructi...

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Bibliographic Details
Published in:The Astrophysical journal 2013-09, Vol.774 (1), p.1-6
Main Authors: Atwood, W B, Baldini, L, BREGEON, J, Bruel, P, CHEKHTMAN, A, Cohen-Tanugi, J, Drlica-Wagner, A, Granot, J, Longo, F, Omodei, N
Format: Article
Language:English
Subjects:
ASTRONOMY AND ASTROPHYSICS
astroparticle physics
Background radiation
Constraining
cosmology: observations
Energy use
Gamma ray bursts
Gamma rays
gamma rays: general
Lorentz factor
methods: data analysis
Reconstruction
X-rays
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Summary: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.
ISSN:0004-637X
1538-4357
1538-4357
DOI:10.1088/0004-637X/774/1/76