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Astron. Astrophys. 331, L41-L44 (1998)


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Letter to the Editor

Evidence for a late-time outburst of the X-ray afterglow of GB970508 from BeppoSAX

L. Piro 1, L. Amati 1, 10, L.A. Antonelli 2, R.C. Butler 3, E. Costa 1, G. Cusumano 4, M. Feroci 1, F. Frontera 5, 8, J. Heise 6, J.J.M. in , 't Zand 6, S. Molendi 7, J. Muller 2, 6, L. Nicastro 8, M. Orlandini 8, A. Owens 9, A.N. Parmar 9, P. Soffitta 1 and M. Tavani 7, 11

1 Istituto Astrofisica Spaziale, C.N.R., Via Fosso del Cavaliere, I-00131 Roma, Italy
2 BeppoSAX Science Data Center, Via Corcolle 19, I-00131 Roma, Italy
3 Agenzia Spaziale Italiana, V.le R. Margherita 120, Roma, Italy
4 Istituto Fisica Cosmica e Applicazioni Calcolo Informatico, Palermo
5 Dip. Fisica, Università Ferrara, Via Paradiso 12, Ferrara, Italy
6 Space Research Organization Netherlands, Sorbonnelaan 2, 3584 CA Utrecht, The Netherlands
7 Istituto Fisica Cosmica e Tecnologie Relative, C.N.R., Milano
8 Istituto TeSRE, C.N.R., Via Gobetti 101, I-40129 Bologna, Italy
9 Space Science Department of ESA, ESTEC PO 299, 2200AG Noordwijk, The Netherlands
10 Istituto Astronomico, Università degli Studi "La Sapienza", via Lancisi 29, Rome, Italy
11 Columbia Astrophysics Laboratory, Columbia University, New York, 10027, USA

Received 4 November 1997 / Accepted 20 November 1997

Abstract

The [FORMULA] ray burst GB970508 was observed simultaneously by the Gamma Ray Burst Monitor (GRBM) and one of the X-ray Wide Field Cameras (WFC) aboard BeppoSAX. The latter provided a position within [FORMULA] radius. A series of follow-up observations with the Narrow Field Intruments (NFI) was then performed in a period from [FORMULA] hours to 6 days after the main event. A previously unknown source, which we associate with the afterglow of the GRB, was discovered in the error box. We find that, after the initial burst, X-ray emission is still present and decays as [FORMULA] up to [FORMULA] s. This is followed by a burst of activity with a duration [FORMULA] s. The energy produced in this event is a substantial fraction of the total energy of the GRB, which means that the afterglow is not a remnant of the initial burst (the GRB) that fades away smoothly. Our results support the idea that the processes generating the GRB and its afterglow are the same.

Key words: Gamma rays: bursts - X-rays: bursts

Send offprint requests to: L. Piro (e-mail: piro@alpha1.ias.rm.cnr.it)

© European Southern Observatory (ESO) 1998

Online publication: March 3, 1998
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