GRB 990510i ON THE POSSIBILITY OF A BEAMED X-RAY AFTERGLOW

摘要

We discuss the prompt emission of the y-ray burst GRB 990510 and its subsequent X-ray afterglow from 8.0 to 44.3 hr after the prompt emission, using observations with the Gamma-Ray Burst Monitor and Narrow Field Instruments on BeppoSAX. In the 40-700 keV band, GRB 990510 had a fluence of ~ 1.9 x 10~-5 ergs cm~-2, whereas it reached a peak flux of ~2.4 x 10~-6 ergs cm~-2 s~-1. The X-ray after- glow decay light curve can be satisfactorily described by a single power law with an index of -l.42 ± 0.07. Both the X-ray and optical behavior of the afterglow can be explained by y-ray burst debris expanding as a jet, we find that the cooling frequency is (fixed) between the optical and X-ray wavelength bands.