Peculiarly Narrow SED of GRB 090926B with MAXI and Fermi/GBM
Abstract
The monitor of the all-sky X-ray image (MAXI) Gas Slit Camera (GSC) on the International Space Station (ISS) detected a gamma-ray burst (GRB) on 2009, September 26, GRB 090926B. This GRB had extremely hard spectra in the X-ray energy range. Joint spectral fitting with the Gamma-ray Burst Monitor on the Fermi Gamma-ray Space Telescope shows that this burst had a peculiarly narrow spectral energy distribution, which can be represented by a Comptonized blackbody model. This spectrum can be interpreted as photospheric emission from a low baryon-load GRB fireball. Calculating the parameter of the fireball, we found the size of the base of the flow to be r0 = (4.3±0.9) × 109Y '-3/2 cm, the Lorentz factor of the plasma is Γ = (110±10) Y '1/4, where Y ' is a ratio between the total fireball energy and the energy in the blackbody component of the gamma-ray emission. This r0 is a factor of a few times larger, and the Lorentz factor of 110 is smaller by also factor of a few than other bursts that have blackbody components in the spectra.
- Publication:
-
Publications of the Astronomical Society of Japan
- Pub Date:
- November 2011
- DOI:
- 10.1093/pasj/63.sp3.S1035
- arXiv:
- arXiv:1107.4844
- Bibcode:
- 2011PASJ...63S1035S
- Keywords:
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- gamma rays: bursts;
- methods: data analysis;
- Astrophysics - High Energy Astrophysical Phenomena
- E-Print:
- 7 pages, 6 figures