Can we probe the Lorentz factor of gamma-ray bursts from GeV-TeV spectra integrated over internal shocks?

Junichi Aoi, Kohta Murase, Keitaro Takahashi, Kunihito Ioka, Shigehiro Nagataki

Research output: Contribution to journalArticlepeer-review

15 Scopus citations

Abstract

We revisit the high-energy spectral cutoff originating from the electron-positron pair creation in the prompt phase of gamma-ray bursts (GRBs) with numerical and analytical calculations. We show that the conventional exponential and/or broken power-law cutoff should be drastically modified to a shallower broken power law in practical observations that integrate emissions from different internal shocks. Since the steepening is tiny for observations, this "smearing" effect can generally reduce the previous estimates of the Lorentz factor of the GRB outflows. We apply our formulation to GRB 080916C, recently detected by the Large Area Telescope detector on the Fermi satellite, and find that the minimum Lorentz factor can be ∼600 (or even smaller values), which is below but consistent with the previous result of ∼900. Observing the steepening energy (the so-called "pair-break energy") is crucial to diagnosing the Lorentz factor and/or the emission site in future observations, especially current and future Cherenkov telescopes such as MAGIC, VERITAS, and CTA.

Original languageEnglish (US)
Pages (from-to)440-451
Number of pages12
JournalAstrophysical Journal
Volume722
Issue number1
DOIs
StatePublished - Oct 10 2010

All Science Journal Classification (ASJC) codes

  • Astronomy and Astrophysics
  • Space and Planetary Science

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