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arXiv 2007.03715astro-ph.HE
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在$z =1.754$发现短GRB181123B的光学余辉和宿主星系:延迟时间分布的意义

Discovery of the optical afterglow and host galaxy of short GRB181123B at $z =1.754$: Implications for Delay Time Distributions

K. Paterson, W. Fong, A. Nugent, A. Rouco Escorial, J. Leja, T. Laskar, R. Chornock, A. A. Miller, J. Scharwächter, S. B. Cenko, D. Perley, N. R. Tanvir, A. Lev… 展开作者

K. Paterson, W. Fong, A. Nugent, A. Rouco Escorial, J. Leja, T. Laskar, R. Chornock, A. A. Miller, J. Scharwächter, S. B. Cenko, D. Perley, N. R. Tanvir, A. Levan, A. Cucchiara, B. E. Cobb, K. De, E. Berger, G. Terreran, K. D. Alexander, M. Nicholl, P. K. Blanchard, D. Cornish

摘要:

本文报道了GRB 181123 B短伽玛射线暴的光学余辉和宿主星系的发现。双子座北星系在爆发后的$\approx 9.1$ ~hr开始观测,显示出一个微弱的光学余辉,其亮度为$i\approx25.1$ ~mag,与其宿主星系的角度偏移为0.59 $\pm$ 0.16 $''$。利用$grizYJHK$观测,我们测量了主星系$z = 1.77^{+0.30}_{-0.17}$的光度红移。从4500-18000~ 1800 GRB\,181123 B的主星系性质与其他SGRB主星系的性质相似,推测恒星质量为$\approx 1.7 \times 10^{10}\,M_{\odot}$,质量加权年龄为$\approx 0.9$ ~Gyr,光学光度为$\approx 0.9L^{*}$ .在$z=1.754$,GRB 181123 B是最远的安全SGRB,具有光学余辉探测,是$z>1.5$仅有的三个之一。受越来越多的高$z$ SGRB的激励,我们探索了当前{ \it Swift}样本中缺失的$z>1.5$ SGRB群体对延迟时间分布模型的影响。我们发现,平均延迟时间为$\approx 4-6$ ~Gyr的对数正态模型与观察到的分布一致,但可以排除$95\%$置信度与额外的$\approx1-5$ ~{ \it Swift} SGRB在$z>1.5$恢复。相比之下,具有$\propto$ $t^{-1}$的幂律模型与红移分布一致,并且可以在这些红移处容纳多达$\approx30$ SGRB。在该模型下,我们预测当前{ \it Swift} SGRB群体的$\approx 1/3$处于$z>1$。未来发现或恢复现有的高$z$ SGRB将提供对它们的延迟时间分布的显著区分能力,并因此提供对它们的形成通道的显著区分能力。

英文摘要:

We present the discovery of the optical afterglow and host galaxy of the {\it Swift} short-duration gamma-ray burst, GRB\,181123B. Observations with Gemini-North starting at $\approx 9.1$~hr after the burst reveal a faint optical afterglow with $i\approx25.1$~mag, at an angular offset of 0.59 $\pm$ 0.16$''$ from its host galaxy. Using $grizYJHK$ observations, we measure a photometric redshift of the host galaxy of $z = 1.77^{+0.30}_{-0.17}$. From a combination of Gemini and Keck spectroscopy of the host galaxy spanning 4500-18000~Å, we detect a single emission line at 13390~Å, inferred as H$β$ at $z = 1.754 \pm 0.001$ and corroborating the photometric redshift. The host galaxy properties of GRB\,181123B are typical to those of other SGRB hosts, with an inferred stellar mass of $\approx 1.7 \times 10^{10}\,M_{\odot}$, mass-weighted age of $\approx 0.9$~Gyr and optical luminosity of $\approx 0.9L^{*}$. At $z=1.754$, GRB\,181123B is the most distant secure SGRB with an optical afterglow detection, and one of only three at $z>1.5$. Motivated by a growing number of high-$z$ SGRBs, we explore the effects of a missing $z>1.5$ SGRB population among the current {\it Swift} sample on delay time distribution models. We find that log-normal models with mean delay times of $\approx 4-6$~Gyr are consistent with the observed distribution, but can be ruled out to $95\%$ confidence with an additional $\approx1-5$~{\it Swift} SGRBs recovered at $z>1.5$. In contrast, power-law models with $\propto$ $t^{-1}$ are consistent with the redshift distribution and can accommodate up to $\approx30$ SGRBs at these redshifts. Under this model, we predict that $\approx 1/3$ of the current {\it Swift} population of SGRBs is at $z>1$. The future discovery or recovery of existing high-$z$ SGRBs will provide significant discriminating power on their delay time distributions, and thus their formation channels.

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