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(3σ). We invoke host galaxy extinction to match the observed spectral slope with the slope expected from "fire-ball" 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 = 20.2-7.3+12.3, inconsistent with the former value. Following Wijers & Galama (1998), we determine intrinsic fireball properties for this burst.