BeppoSAX detection and follow-up of GRB 980425

¹ Istituto Te.S.R.E., CNR, via Gobetti 101, I-40129 Bologna, Italy
² Osservatorio Astronomico di Roma, sede di Monteporzio Catone, Via Frascati 33, 00040 Monteporzio Catone, Italy
³ Agenzia Spaziale Italiana, Viale Regina Margherita 120, Roma, Italy
⁴ I.A.S., C.N.R., Via Fosso del Cavaliere, Area della Ricerca di Tor Vergata, I-00131 Rome, Italy
⁵ I.F.C.A.I., CNR, via Ugo La Malfa 153, I-90146 Palermo, Italy
⁶ Osservatorio Astronomico di Trieste, Via G.B. Tiepolo 11, I-34131 Trieste, Italy
⁷ BeppoSAX Scientific Data Center, Via Corcolle 19, I-00131 Rome, Italy
⁸ Dip. di Fisica, Univ. di Ferrara, Via Paradiso 11, I-44100 Ferrara, Italy
⁹ Astrophysics Division, SSD of ESA, ESTEC, P.O. Box 299, 2200 AG Noordwijk, The Netherlands
¹⁰ IAA-CSIC, Granada, Spain and LAEFF-INTA, Madrid, Spain
¹¹ Space Research Organization Netherlands, Sorbonnelaan 2, 3584 CA Utrecht, The Netherlands

Received: 16 March 1999
Accepted: 5 July 1999

Abstract

We present BeppoSAX GRBM and WFC light curves of GRB 980425 and NFI follow-up data taken in 1998 April, May, and November. The first NFI observation has detected within the radius error box of the GRB an X-ray source positionally consistent with the supernova SN 1998bw, exploded within a day of GRB 980425, and a fainter X-ray source, not consistent with the position of the supernova. The former source is detected in the following NFI pointings and exhibits a decline of a factor of two in six months. If it is associated with SN 1998bw, this is the first detection of hard X-ray emission from a Type I supernova. The latter source exhibits only marginally significant variability. Based on these data, it is not possible to select either source as a firm candidate for the GRB counterpart.