GRB 990704: the most X-ray rich BeppoSAX gamma-ray burst

M. Feroci; L. A. Antonelli; P. Soffitta; J. J. M. in 't Zand; L. Amati; E. Costa; L. Piro; F. Frontera; E. Pian; J. Heise; L. Nicastro

doi:10.1051/0004-6361:20011192

paper

GRB 990704: the most X-ray rich BeppoSAX gamma-ray burst

arXiv:astro-ph/0108414 · doi:10.1051/0004-6361:20011192

Abstract

We present the X- and $γ$ -ray detection of GRB 990704 and the discovery and study of its X-ray afterglow, 1SAX J1219.5-0350. Two pointed BeppoSAX observations with the narrow field instruments were performed on this source, separated in time by one week. The decay of the X-ray flux within the first observation appears unusually slow, being best-fit by a power law with negative index 0.83 $\pm$ 0.16. Such a slow decay is consistent with the non-detection in our second observation, but its back-extrapolation to the time of the GRB largely underestimates the detected GRB X-ray prompt emission. In addition, the GRB prompt event shows, among the BeppoSAX-WFC detected sample, unprecedentedly high ratios of X- and gamma-ray peak fluxes (F $_{2 - 10 k e V}$ /F $_{40 - 700 k e V}$ $\sim$ 0.6, and F $_{2 - 26 k e V}$ /F $_{40 - 700 k e V}$ $\sim$ 1.6) and fluences (S $_{2 - 10 k e V}$ /S $_{40 - 700 k e V}$ $\sim$ 1.5 and S $_{2 - 26 k e V}$ /S $_{40 - 700 k e V}$ $\sim$ 2.8), making it, among the BeppoSAX arcminute-localized GRBs, the closest to the recently discovered class of Fast X-ray Transients.

Accepted for publication on Astronomy & Astrophysics, Main Journal. 14 pages, Figure 6 in color

GRB 990704: the most X-ray rich BeppoSAX gamma-ray burst

Abstract

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