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arXiv 1706.03556astro-ph.HEastro-ph.CO
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用Fermi / GBM伽马射线暴数据检验各向同性宇宙

Testing Isotropic Universe Using the Gamma-Ray Burst Data of Fermi / GBM

Jakub Ripa, Arman Shafieloo

摘要:

伽马射线暴(GRB)的天空分布已经被各种研究小组研究了二十多年。这些研究大多是基于天数密度分布来检验伽玛暴的各向同性。在这项工作中,我们提出了一种方法来测试宇宙的各向同性通过检查的性质,如伽玛暴的持续时间,注量和峰值流量在不同的能量带和不同的时间尺度的各向同性。我们将此方法应用于包含1591个伽玛暴的{ \em Fermi} /伽马射线暴监测器(GBM)数据样本。我们发现的最明显的特征是在银河系坐标$l\approx 30^\circ$、$b\approx 15^\circ$和半径$r\approx 20^\circ-40^\circ$附近。推导出的概率发生这样的各向异性信号(在一个随机的各向同性样品)是小于百分之一的一些测试,而其他测试给出的结果与各向同性一致。这些是基于来自真实数据的结果与随机混洗数据样本的比较。考虑到我们在这项工作中使用的大量统计数据(其中一些是相互关联的),我们可以预期检测到的特征可能是统计波动的结果。此外,我们注意到在这个特殊的补丁,这可能是由于一些仪器或观测效果,从而可以通过一些系统影响我们的统计数字相当低的伽玛暴数量。进一步的研究是非常必要的,以澄清这一结果,例如,利用更大的未来{ \em费米} / GBM数据样本以及其他伽玛射线暴任务的数据样本,并寻找可能的系统。

英文摘要:

The sky distribution of Gamma-Ray Bursts (GRBs) has been intensively studied by various groups for more than two decades. Most of these studies test the isotropy of GRBs based on their sky number density distribution. In this work we propose an approach to test the isotropy of the Universe through inspecting the isotropy of the properties of GRBs such as their duration, fluences and peak fluxes at various energy bands and different time scales. We apply this method on the {\em Fermi} / Gamma-ray Burst Monitor (GBM) data sample containing 1591 GRBs. The most noticeable feature we found is near the Galactic coordinates $l\approx 30^\circ$, $b\approx 15^\circ$ and radius $r\approx 20^\circ-40^\circ$. The inferred probability for the occurrence of such an anisotropic signal (in a random isotropic sample) is derived to be less than a percent in some of the tests while the other tests give results consistent with isotropy. These are based on the comparison of the results from the real data with the randomly shuffled data samples. Considering large number of statistics we used in this work (which some of them are correlated to each other) we can anticipate that the detected feature could be result of statistical fluctuations. Moreover, we noticed a considerably low number of GRBs in this particular patch which might be due to some instrumentation or observational effects that can consequently affect our statistics through some systematics. Further investigation is highly desirable in order clarify about this result, e.g. utilizing a larger future {\em Fermi} / GBM data sample as well as data samples of other GRB missions and also looking for possible systematics.

机构、总结、中文摘要均由AI分析而来,可能存在错误,请以论文正文为准。

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