Volume 378, Number 2, November I 2001
|Page(s)||441 - 448|
|Section||Cosmology (including clusters of galaxies)|
|Published online||15 November 2001|
GRB 990704: The most X-ray rich BeppoSAX gamma-ray burst
Istituto Astrofisica Spaziale, C.N.R., Area di Tor Vergata, Via Fosso del Cavaliere 100, 00133 Roma, Italy
2 Osservatorio Astronomico di Roma, Via Frascati 33, 00040 Monteporzio Catone, Italy
3 Space Research Organization in the Netherlands, Sorbonnelaan 2, 3584, CA Utrecht, The Netherlands
4 Istituto Tecnologie e Studio Radiazioni Extraterrestri, CNR, Via Gobetti 101, 40129 Bologna, Italy
5 Dipartimento di Fisica, Università di Ferrara, Via Paradiso 12, 44100 Ferrara, Italy
6 Osservatorio Astronomico di Trieste, Via G.B. Tiepolo 11, 34131, Trieste, Italy
7 Istituto di Fisica Cosmica ed Applicazioni dell'Informatica, CNR, Via Ugo La Malfa 153, 90138 Palermo, Italy
Corresponding author: M. Feroci, firstname.lastname@example.org
Accepted: 22 August 2001
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 . 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 (F2-10 keV/, and F2-26 keV/) and fluences (S2-10 keV/ and S2-26 keV/), making it, among the BeppoSAX arcminute-localized GRBs, the closest to the recently discovered class of Fast X-ray Transients.
Key words: gamma-rays: bursts / stars: individual: 1SAX J1219.5-0350
© ESO, 2001
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