用ATCA探测伽玛暴的银河系HI前景图象
Exploring the pattern of the Galactic HI foreground of GRBs with the ATCA
摘要：
伽马射线暴（GRB）的余辉可以让我们对它的宿主星系的性质有价值的了解。为了正确地解释余辉光谱，我们需要对我们银河系中的前景星际介质（ISM）有很好的了解。校正前景的通常做法是使用莱顿/阿根廷/波恩（LAB）调查的中性氢（HI）数据。然而，单皿数据的差的空间分辨率可能对导出的柱密度具有显著影响。为了研究这一点，我们提出了新的高分辨率HI观测与澳大利亚望远镜紧凑阵列（ATCA）对4伽玛暴。我们结合干涉ATCA数据与单碟数据从银河系全天巡天（GASS），并得出新的银河系HI柱密度对伽玛暴。我们使用这些新的前景柱密度，以适应雨燕XRT X射线光谱和计算新的固有的氢柱密度值的伽玛射线暴宿主星系。我们发现，新的ATCA数据显示更高的银河HI柱密度相比，以前的单碟数据，这导致在较低的固有列密度的主机。我们研究了伽玛暴附近的视线光学深度，发现它对其中一个伽玛暴可能是不可忽略的，这表明其宿主星系的内禀氢柱密度可能更低。此外，我们比较我们的结果来自远红外数据的列密度，并找到一个合理的协议与HI数据。
英文摘要：
The afterglow of a gamma ray burst (GRB) can give us valuable insight into the properties of its host galaxy. To correctly interpret the spectra of the afterglow we need to have a good understanding of the foreground interstellar medium (ISM) in our own Galaxy. The common practice to correct for the foreground is to use neutral hydrogen (HI) data from the Leiden/Argentina/Bonn (LAB) survey. However, the poor spatial resolution of the single dish data may have a significant effect on the derived column densities. To investigate this, we present new high-resolution HI observations with the Australia Telescope Compact Array (ATCA) towards 4 GRBs. We combine the interferometric ATCA data with single dish data from the Galactic All Sky Survey (GASS) and derive new Galactic HI column densities towards the GRBs. We use these new foreground column densities to fit the Swift XRT X-ray spectra and calculate new intrinsic hydrogen column density values for the GRB host galaxies. We find that the new ATCA data shows higher Galactic HI column densities compared to the previous single dish data, which results in lower intrinsic column densities for the hosts. We investigate the line of sight optical depth near the GRBs and find that it may not be negligible towards one of the GRBs, which indicates that the intrinsic hydrogen column density of its host galaxy may be even lower. In addition, we compare our results to column densities derived from far-infrared data and find a reasonable agreement with the HI data.
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