BEPPOSAX OBSERVATIONS OF GRB970508 - FIRST EVIDENCE OF BURSTING ACTIVITY CONTINUING ON VERY LONG-TIME SCALE

The gamma-ray burst GRB970508 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 1.9' radius. A series of follow-up observations with the Narrow Field Intruments (N FI) was then performed in a period from similar to 6 hours to 6 days a fter the main event. A previously unknown source, which we associate w ith 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 de cays as similar to t(-1.1) up to similar to 6 x 10(4) s. This is follo wed by a burst of activity with a duration similar to 10(5) s. The ene rgy produced in this event is a substantial fraction of the total ener gy 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 t he same.