We discuss the prompt emission of the gamma-ray burst (GRB) 990510 and its subsequent X-ray afterglow from 8.0 to 44.3 hrs after the prompt emission, using observations with the Gamma-ray Burst Monitor and Narrow Field Instruments on BeppoSAX. In the 40-700 keV band, GRB990510 had a fluence of \~1.9x10^{-5}erg cm^{-2}, whereas it reached a peak flux of ~2.4x10^{-6}erg cm^{-2} s^{-1}. The X-ray afterglow decay light curve can be satisfactorily described by a single power law with index of -1.42+/-0.07. Both the X-ray and optical behaviour of the afterglow can be explained by gamma-ray burst debris expanding as a jet; we find that the cooling frequency is (fixed) between the optical and X-ray wavelength bands.
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机译：我们使用BeppoSAX上的伽马射线爆裂监测仪和窄场仪器进行观测，讨论了瞬态发射后8.0到44.3小时的伽马射线暴（GRB）990510的迅速发射及其随后的X射线余辉。在40-700 keV频带中，GRB990510的通量为\〜1.9x10 ^ {-5} erg cm ^ {-2}，而峰值通量为〜2.4x10 ^ {-6} erg cm ^ {- 2} s ^ {-1}。 X射线余辉衰减光曲线可以用指数为-1.42 +/- 0.07的单一幂定律令人满意地描述。余辉的X射线和光学行为都可以通过射流扩展的伽马射线爆裂碎片来解释。我们发现冷却频率固定在光学和X射线波段之间。
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