后期VLA再观测排除了大部分雨燕前长持续时间伽马射线暴的类ULIRG主星系
Late-Time VLA Reobservations Rule Out ULIRG-Like Host Galaxies For Most Pre-Swift Long-Duration Gamma-Ray Bursts
摘要：
我们提出了新的Jansky甚大阵列的五个前斯威夫特伽马射线暴的观测，其中一个超亮（SFR > 100 M_sun/yr）的尘埃宿主星系以前推断从无线电或亚毫米观测后的几年内爆发。在五种情况中的四种情况下，我们不再在宿主位置检测到任何源，从而比最初的观测结果要暗得多，排除了存在任何这些GRB的超亮星系。我们继续在GRB 980703的位置探测到一个源，但它比十年前暗得多，推断的射电星形成率（~80 M_sun）相对适中。在这个伽玛暴的光变曲线中观察到的200-1000天的射电平坦可能是由一个与观察者成180度角的减速反喷流引起的，尽管一个无喷流的风模型也可以解释这些数据。我们的研究结果消除了所有公认的雨燕前ULIRG主机，和所有的情况下，一个清晰的伽玛射线暴被发现在一个星系为主的严重模糊的恒星形成。当伽玛暴确实发生在ULIRGs的余辉几乎总是被观察到严重模糊，符合这些系统的大尘埃不透明度和高尘埃覆盖率的特点。
英文摘要：
We present new Jansky Very Large Array observations of five pre-Swift gamma-ray bursts for which an ultraluminous (SFR > 100 M_sun/yr) dusty host galaxy had previously been inferred from radio or submillimetre observations taken within a few years after the burst. In four of the five cases we no longer detect any source at the host location to limits much fainter than the original observations, ruling out the existence of an ultraluminous galaxy hosting any of these GRBs. We continue to detect a source at the position of GRB 980703, but it is much fainter than it was a decade ago and the inferred radio star-formation rate (~80 M_sun) is relatively modest. The radio flattening at 200-1000 days observed in the light curve of this GRB may have been caused by a decelerating counterjet oriented 180 degrees away from the viewer, although an unjetted wind model can also explain the data. Our results eliminate all well-established pre-Swift ULIRG hosts, and all cases for which an unobscured GRB was found in a galaxy dominated by heavily-obscured star-formation. When GRBs do occur in ULIRGs the afterglow is almost always observed to be heavily obscured, consistent with the large dust opacities and high dust covering fractions characteristic of these systems.
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