Astron. Astrophys. Suppl. Ser. 138, 447-448

The X-ray, optical and infrared counterpart to GRB 980703

P.M. Vreeswijk¹ - T.J. Galama¹ - A.N. Owens² - T. Oosterbroek² - T. Geballe³ - J. van Paradijs^1,4 - C. Kouveliotou^5,6 - N. Tanvir⁷ - E. Pian⁸ - E. Palazzi⁸ - F. Frontera⁸ - N. Masetti⁸

1 - Astronomical Institute "Anton Pannekoek'', University of Amsterdam, & Center for High Energy Astrophysics, Kruislaan 403, 1098 SJ Amsterdam, The Netherlands
2 - Astrophysics Division, Space Science Department of ESA, European Space Research and Technology Centre, 2200 AG Noordwijk, The Netherlands
3 - Joint Astronomy Centre, 660 N. A'ohoku Place, Hilo, Hawaii 9672 0, U.S.A.
4 - Physics Department, University of Alabama in Huntsville, Huntsville AL 35899, U.S.A.
5 - Universities Space Research Association
6 - NASA/MSFC, Code ES-84, Huntsville AL 35812, U.S.A.
7 - Institute of Astronomy, Madingley Road, Cambridge CB3 0HA, UK
8 - Istituto Tecnologie e Studio Radiazioni Extraterrestri (TESRE), CNR, Via P. Gobetti 101, 40 129 Bologna, Italy

Received December 29, 1998; accepted March 10, 1999

Abstract:

We report on X-ray, optical and infrared follow-up observations of GRB980703. We detect a previously unknown X-ray source in the GRB error box; assuming a power law decline we find for its decay index $\alpha <-0.91 (3\sigma )$. 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: $\nu_{\rm c}\gt 1.3\ 10^{17}$ Hz. For this epoch we obtain an extinction of $A_V=1.50 \pm 0.11$.From the X-ray data we estimate the optical extinction to be A_V = 20.2^+12.3_-7.3, inconsistent with the former value. Following Wijers & Galama (1998), we determine intrinsic fireball properties for this burst.

Key words: gamma-rays: bursts -- radiation mechanisms: non-thermal