Evolution of the Low-Energy Photon Spectral in Gamma-Ray Bursts
Abstract
We report evidence that the asymptotic low-energy power-law slope α (below the spectral break) of BATSE gamma-ray burst (GRB) photon spectra evolves with time rather than remaining constant. We find that a high degree of positive correlation exists between the time-resolved spectral break energy Epk and α. In samples of 18 ``hard-to-soft'' and 12 ``tracking'' pulses, evolution of α was found to correlate with that of the spectral break energy Epk at the 99.7% and 98% confidence levels, respectively. We also find that in the flux rise phase of hard-to-soft pulses, the mean value of α is often positive, and in some bursts the maximum value of α is consistent with a value > +1. BATSE burst 3B 910927, for example, has an αmax equal to 1.6 +/- 0.3. These findings challenge GRB spectral models in which α must be negative or remain constant.
- Publication:
-
The Astrophysical Journal
- Pub Date:
- April 1997
- DOI:
- 10.1086/310574
- arXiv:
- arXiv:astro-ph/9612118
- Bibcode:
- 1997ApJ...479L..39C
- Keywords:
-
- GAMMA RAYS: BURSTS;
- GAMMA RAYS: OBSERVATIONS;
- METHODS: STATISTICAL;
- Gamma Rays: Bursts;
- Gamma Rays: Observations;
- Methods: Statistical;
- Astrophysics
- E-Print:
- 12 pages (including 6 figures), accepted to ApJ