The X-ray, optical, and infrared counterpart to GRB 980703
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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, 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.
author list (cited authors)
Vreeswijk, P. M., Galama, T. J., Owens, A., Oosterbroek, T., Geballe, T. R., Van Paradijs, J., ... Suntzeff, N
complete list of authors
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