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Astron. Astrophys. 338, L17-L20 (1998)

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Letter to the Editor

Beppo SAX observations of GRB970402

L. Nicastro 1, L. Amati 2, 8, L.A. Antonelli 3, R.C. Butler 9, E. Costa 2, G. Cusumano 1, M. Feroci 2, F. Frontera 4, 5, J. Heise 6, K. Hurley 10, J.M. Muller 3, 6, A. Owens 7 and L. Piro 2

1 Istituto di Fisica Cosmica con Applicazioni all'Informatica, CNR, Via U. La Malfa 153, I-90146 Palermo, Italy
2 Istituto Astrofisica Spaziale, CNR, Via Fosso del Cavaliere, I-00131 Roma, Italy
3 BeppoSAX Scientific Data Center, Via Corcolle 19, I-00131 Roma, Italy
4 Istituto Tecnologie e Studio Radiazione Extraterrestre, CNR, Via Gobetti 101, I-40129 Bologna, Italy
5 Dipartimento di Fisica, Università di Ferrara, Via Paradiso 11, I-44100 Ferrara, Italy
6 Space Research Organization in the Netherlands, Sorbonnelaan 2, 3584 CA Utrecht, The Netherlands
7 Astrophysics Division, Space Science Department of ESA, ESTEC, P.O. Box 299, 2200 AG Noordwijk, The Netherlands
8 Istituto Astronomico, Università degli Studi "La Sapienza", via Lancisi 29, Rome, Italy
9 Agenzia Spaziale Italiana, V.le R. Margherita 120, Roma, Italy
10 Space Sciences Laboratory, University of California, Berkeley, CA 94720-7450, USA

Received 15 June 1998 / Accepted 12 August 1998


GRB970402 is the fourth gamma-ray burst detected by Beppo SAX simultaneously in the Gamma Ray Burst Monitor (GRBM) and one of the two Wide Field Cameras (WFCs). A rapid pointing of the Beppo SAX Narrow Field Instruments (NFIs) 8 hours after the GRB led to the identification of an unknown weak X-ray source: 1SAX J1450.1-6920. Its position was approximately at the center of the 3 arcmin error circle derived from the WFC image. Both the Medium Energy (MECS, 2-10 keV) and Low Energy (LECS, 0.1-10 keV) concentrators detected the source. A follow-up observation performed 1.5 days later and lasting 54 ks showed that the source had faded almost to, but not below the detectability threshold. The flux decrease between the two observations was a factor [FORMULA]. 1SAX J1450.1-6920 was the second X-ray afterglow associated with a GRB. Searches promptly started at other wavelengths (optical, IR, radio) did not reveal any transient event within the 3 arcmin error circle.

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

Send offprint requests to: nicastro@ifcai.pa.cnr.it

© European Southern Observatory (ESO) 1998

Online publication: September 8, 1998