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

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 < -0.91 (3 ). 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, vc > 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. 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, B < 6 10-5, is much lower in the case of GRB 980703, as a consequence of the high frequency of the cooling break.

Vreeswijk, P. M., Galama, T. J., Owens, A., Oosterbroek, T., Geballe, T. R., Van Paradijs, J., ... Suntzeff, N.

Vreeswijk, PM||Galama, TJ||Owens, A||Oosterbroek, T||Geballe, TR||Van Paradijs, J||Groot, PJ||Kouveliotou, C||Koshut, T||Tanvir, N||Wijers, RAMJ||Pian, E||Palazzi, E||Frontera, F||Masetti, N||Robinson, C||Briggs, M||In 'T Zand, JJM||Heise, J||Piro, L||Costa, E||Feroci, M||Antonelli, LA||Hurley, K||Greiner, J||Smith, DA||Levine, AM||Lipkin, Y||Leibowitz, E||Lidman, C||Pizzella, A||Böhnhardt, H||Doublier, V||Chaty, S||Smail, I||Blain, A||Hough, JH||Young, S||Suntzeff, N

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