标题： 哈勃空间望远镜对GRB970508宿主星系的观测 显示英文标题

标题： HST Observations of the Host Galaxy of GRB970508

摘要： 我们报告了对GRB~970508区域在1998年8月初进行的观测，即爆发后454天，使用哈勃空间望远镜上的STIS电荷耦合器件相机进行的观测。 这些图像以开放滤光片（50CCD）模式拍摄，清楚地显示出一个星系的存在，该星系在早期（1997年6月）的HST图像中因光学暂现源（OT）的辐射而被遮挡。 该星系形状规则：在修正了HST/STIS点扩散函数后，它很好地由一个尺度长度为0.046 +/- 0.006和椭率0.70 +/- 0.07的指数盘拟合。 所有观测结果与从爆发后两天开始的t^{-1.3}连续下降的OT辐射大致一致；然而，我们在图像中没有直接证据显示来自OT的辐射，如果假设OT辐射可以忽略不计，则星系的表面亮度轮廓最为规则，这表明OT可能在晚期比幂律衰减预测的更快地消退。 由于STIS清晰模式的带宽较宽，所估计的星系亮度取决于所假设的星系光谱。 利用后期地面观测获得的颜色来限制光谱，我们发现V = 25.4 +/- 0.15，比之前通过观测星系和OT的总光并假设OT按单一幂律衰减后减去估计的OT亮度得到的地面观测值亮了几十分之一星等。 这再次表明，OT可能在晚期比幂律预测的更快地消退。 OT的位置与星系等照度中心一致，精度为0."01。 这一显著的一致性提出了GRB可能与活动星系核或核星暴有关的可能性。 显示英文摘要

摘要： We report on observations of the field of GRB~970508 made in early August 1998, 454 days after outburst, with the STIS CCD camera onboard the Hubble Space Telescope. The images, taken in open filter (50CCD) mode, clearly reveal the presence of a galaxy which was obscured in earlier (June 1997) HST images by emission from the optical transient (OT). The galaxy is regular in shape: after correcting for the HST/STIS PSF, it is well-fitted by an exponential disk with a scale length of 0."046 +/- 0."006 and an ellipticity of 0.70 +/- 0.07. All observations are marginally consistent with a continuous decline in OT emission as t^{-1.3} beginning two days after outburst; however, we find no direct evidence in the image for emission from the OT, and the surface brightness profile of the galaxy is most regular if we assume that the OT emission is negligible, suggesting that the OT may have faded more rapidly at late times than is predicted by the power-law decay. Due to the wide bandwidth of the STIS clear mode, the estimated magnitude of the galaxy is dependent on the galaxy spectrum that is assumed. Using colors obtained from late-time ground-based observations to constrain the spectrum, we find V = 25.4 +/- 0.15, a few tenths of a magnitude brighter than earlier ground-based estimates that were obtained by observing the total light of the galaxy and the OT and then subtracting the estimated OT brightness assuming it fades as a single power-law. This again suggests that the OT may have faded faster at late time than the power-law predicts. The position of the OT agrees with that of the isophotal center of the galaxy to 0."01. This remarkable agreement raises the possibility that the GRB may have been associated with either an active galactic nucleus or a nuclear starburst.