GB2 - The energy compositions and acceleration processes of GRB jets |
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Speaker |
Wang, Xiangyu |
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Coauthors |
Qing-Wen Tang, Fang-Kun Peng, Xiang-Yu Wang, Pak-Hin Thomas Tam |
| Talk Title |
Measuring the bulk Lorentz factors of gamma-ray bursts with Fermi-LAT |
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Abstract |
Gamma-ray bursts (GRBs) are powered by ultra-relativistic jets. The value of the Lorentz factor of the relativistic bulk motion can be obtained if a spectral cutoff due to pair-production absorption is detected. With the good spectral coverage of the Large Area Telescope (LAT) on Fermi, measurements of such cutoff become possible, and two cases (GRB 090926A and GRB 100724B) have been reported to have high-energy cutoffs or breaks. We systematically search for such high energy spectral cutoffs/breaks from the LAT and the Gamma-ray burst monitor (GBM) observations of the prompt emission of GRBs detected since August 2011. Six more GRBs are found to have cutoff-like spectral feature at energies of ¡« 10−500 MeV. Assuming that these cutoffs are caused by pair-production absorption within the source, the bulk Lorentz factors of these GRBs are obtained. We further find that the Lorentz factors are correlated with the isotropic gamma-ray luminosity of the bursts, indicating that more powerful GRB jets move faster. |
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