论文标题
低亮度GRB 171205a的最低频率排放的1000天
1000 days of lowest frequency emission from the low-luminosity GRB 171205A
论文作者
论文摘要
我们报告了升级的巨型Metrewave射电望远镜（UGMRT）的伽马射线爆发（GRB）171205a的最低频率测量值，该频率范围从250--1450 MHz和$ 4-937的频率范围为$ 4-937 $。这是在250--500 MHz频率范围内检测到的第一个GRB余辉，也是UGMRT检测到的第二亮GRB。即使观察到了将近1000天的GRB，也没有过渡到非权威主义制度的证据。我们还分析了档案$ {\ it chandra} $ x射线数据$ \ sim 70 $和$ \ sim 200 $。我们也没有发现从组合数据分析中断裂的证据。我们符合由相对论，各向同性，自相似减速以及广角茧的冲击突出引起的同步余辉发射。我们的数据还使我们能够辨别Circumburst介质的性质和密度。我们发现密度曲线与标准的恒定密度介质偏离，并表明GRB像介质一样在分层的风中爆炸。我们的分析表明，涵盖光曲线吸收部分的最低频率测量对于揭开GRB环境至关重要。我们的数据与其他已发表的测量结果结合在一起表明，无线电余波具有两个组成部分的贡献：弱的，可能是稍微偏外的射流和周围更宽的茧，与Izzo等人的结果一致。 （2019）。茧的发射可能在早期时期占主导地位，而射流在后期的时期开始占主导地位，导致无线电曲面。
We report the lowest frequency measurements of gamma-ray burst (GRB) 171205A with the upgraded Giant Metrewave Radio Telescope (uGMRT) covering a frequency range from 250--1450 MHz and a period of $4-937$ days. It is the first GRB afterglow detected at 250--500 MHz frequency range and the second brightest GRB detected with the uGMRT. Even though the GRB is observed for nearly 1000 days, there is no evidence of transition to non-relativistic regime. We also analyse the archival ${\it Chandra}$ X-ray data on day $\sim 70$ and day $\sim 200$. We also find no evidence of a jet break from the analysis of combined data. We fit synchrotron afterglow emission arising from a relativistic, isotropic, self-similar deceleration as well as from a shock-breakout of wide-angle cocoon. Our data also allow us to discern the nature and the density of the circumburst medium. We find that the density profile deviates from a standard constant density medium and suggests that the GRB exploded in a stratified wind like medium. Our analysis shows that the lowest frequency measurements covering the absorbed part of the light curves are critical to unravel the GRB environment. Our data combined with other published measurements indicate that the radio afterglow has contribution from two components: a weak, possibly slightly off-axis jet and a surrounding wider cocoon, consistent with the results of Izzo et al. (2019). The cocoon emission likely dominates at early epochs, whereas the jet starts to dominate at later epochs, resulting in flatter radio lightcurves.
