The X-Ray, Optical, and Infrared Counterpart to GRB 980703
Abstract
We report on X-ray, optical, and infrared follow-up observations of GRB 980703. We detect a previously unknown X-ray source in the GRB error box; assuming a power-law decline, we find for its decay index α<-0.91 (3 σ). We invoke host-galaxy extinction to match the observed spectral slope with the slope expected from ``fireball'' models. We find no evidence for a spectral break in the infrared to X-ray spectral range on 1998 July 4.4, and determine a lower limit of the cooling break frequency, νc>1.3×1017 Hz. For this epoch we obtain an extinction of AV=1.50+/-0.11. From the X-ray data we estimate the optical extinction to be AV=20.2+12.3-7.3, inconsistent with the former value. Our optical spectra confirm the redshift of z=0.966. We compare the afterglow of GRB 980703 with that of GRB 970508 and find that the fraction of the energy in the magnetic field, ɛB<6×10-5, is much lower in the case of GRB 980703, as a consequence of the high frequency of the cooling break.
- Publication:
-
The Astrophysical Journal
- Pub Date:
- September 1999
- DOI:
- 10.1086/307740
- arXiv:
- arXiv:astro-ph/9904286
- Bibcode:
- 1999ApJ...523..171V
- Keywords:
-
- GAMMA RAYS: BURSTS;
- INFRARED: GALAXIES;
- RADIATION MECHANISMS: NONTHERMAL;
- X-RAYS: GALAXIES;
- Gamma Rays: Bursts;
- Infrared: Galaxies;
- Radiation Mechanisms: Nonthermal;
- X-Rays: Galaxies;
- Astrophysics
- E-Print:
- Accepted for publication in Part 1 of The Astrophysical Journal