An Off-Axis Jet Model For GRB 980425 and Low-Energy Gamma-Ray Bursts
Abstract
Using a simple off-axis jet model of gamma-ray bursts (GRBs), we can reproduce the observed unusual properties of the prompt emission of GRB 980425, such as the extremely low isotropic equivalent γ-ray energy, the low peak energy, the high fluence ratio, and the long spectral lag when the jet with the standard energy of ~1051 ergs and the opening half-angle of 10deg<~Δθ<~30deg is seen from the off-axis viewing angle θv~Δθ+10γ-1, where γ is a Lorentz factor of the jet. For our adopted fiducial parameters, if the jet that caused GRB 980425 is viewed from the on-axis direction, the intrinsic peak energy Ep(1+z) is ~2.0-4.0 MeV, which corresponds to those of GRB 990123 and GRB 021004. We also discuss the connection of GRB 980425 in our model with the X-ray flash, and the origin of a class of GRBs with small Eγ.
- Publication:
-
The Astrophysical Journal
- Pub Date:
- September 2003
- DOI:
- 10.1086/378736
- arXiv:
- arXiv:astro-ph/0306615
- Bibcode:
- 2003ApJ...594L..79Y
- Keywords:
-
- Gamma Rays: Bursts;
- Gamma Rays: Theory;
- Astrophysics
- E-Print:
- 12 pages, 3 eps figures