Astron. Astrophys. Suppl. Ser. 138, 437-438

The X-ray afterglow of GRB 980519

L. Nicastro¹ - L. Amati² - L.A. Antonelli^3,4 - E. Costa⁵ - G. Cusumano¹ - M. Feroci⁵ - F. Frontera^2,6 - E. Palazzi² - E. Pian² - L. Piro⁵

Send offprint request: nicastro@ifcai.pa.cnr.it

1 - Istituto di Fisica Cosmica con Applicazioni all'Informatica, CNR, Via U. La Malfa 153, I-90146 Palermo, Italy
2 - Istituto Tecnologie e Studio Radiazione Extraterrestre, CNR, Via Gobetti 101, I-40129 Bologna, Italy
3 - Osservatorio Astronomico di Roma, Via Frascati 33, I-00040 Monteporzio Catone (RM), Italy
4 - BeppoSAX Scientific Data Center, Via Corcolle 19, I-00131 Roma, Italy
5 - Istituto Astrofisica Spaziale, CNR, Via Fosso del Cavaliere, I-00131 Roma, Italy
6 - Dipartimento di Fisica, Università di Ferrara, Via Paradiso 11, I-44100 Ferrara, Italy

Received December 29, 1998; accepted March 10, 1999

Abstract:

Over a total of 20 gamma-ray bursts localized with arcmin accuracies, GRB 980519 represents the 13$^{\rm th}$ detected by the BeppoSAX Wide Field Cameras (WFCs). An X-ray TOO observation performed by the BeppoSAX Narrow Field Instruments (NFIs), starting about 9.5 hours after the high energy event, revealed X-ray afterglow emission in the 0.1-10 keV energy range. The flux decay was particularly fast with a power-law index of $\simeq 1.8$.This is the fastest decay so far measured. Signs of bursting activity are evident. The power-law spectral index of 2.8^+0.6_-0.5 is quite soft but not unique among GRB afterglows.

$VR_{\rm c}I_{\rm c}$ optical emission was detected as soon as 8 hours after the GRB and the power-law flux decay in all these bands were all consistent with $\delta \simeq 2.0$. As for the X-ray, this is the fastest of all the 9 optically identified afterglows but GRB 980326. A candidate host galaxy with magnitude $R_{\rm c} = 26$ has been reported and variable radio emission detected.

Key words: gamma-rays: bursts -- gamma-rays: observation -- X-rays: bursts