高红移爆发源作为早期宇宙和第一代天体的探针

High redshift gamma-ray bursts as a probe of the early universe and first stars

伽玛暴是宇宙中最为明亮的爆发现象,由于它们的高光度,人们可探测到发生在极早期宇宙处的伽玛暴.高红移伽玛暴可作为宇宙深处的灯塔,它们是探索早期宇宙性质的理想工具.利用高红移伽玛暴可以限制暗能量和宇宙学参数,测量高红移的恒星形成率,揭示第一代天体的性质,研究宇宙再电离和金属增丰历史.因此,高红移伽玛暴的观测具有重要的科学意义.相比目前的探测卫星,爱因斯坦探针(EP)拥有更高的灵敏度和更宽的观测视场,且主要观测能段为软X射线波段(0.5–4 keV),非常适合高红移伽玛暴的观测.考虑EP的能力和观测模式,并且借助能够很好解释目前Swift卫星的伽玛暴观测样本的理论模型,详细计算了未来EP对高红移伽玛暴的可能探测率.我们预测EP对z>6伽玛暴的探测率约为20 events yr^(-1) sr^(-1),对z>8伽玛暴的探测率约为6 events yr^(-1) sr^(-1),对z>12伽玛暴的探测率约为1 events yr^(-1) sr^(-1).估计在3年的运行时间内,EP将能探测到约65个z>6的伽玛暴,其中包括~20个z>8的伽玛暴和~3个z>12的伽玛暴.总之,EP有望显著提高高红移伽玛暴的观测能力,这些丰富的观测信息将很有可能揭开早期宇宙的部分科学谜团.

Gamma-ray bursts （GRBs） are the most violent explosions in the universe. Thanks to their extreme brightness, GRBs can be detected up to the edge of the visible universe. As bright beacons in the deep universe, high-redshift GRBs have been considered as an ideal tool to explore the properties of the early universe： including the dark energy and cosmological parameters, star formation rate, first stars, the reionization and metal enrichment history of the universe. So the detection of high-z GRBs has important scientific significance. Compared to current missions, Einstein Probe has a higher sensitivity and a wider field-of-view, operating the soft X-ray band （0.5-4 keV）, which would be suitable for the detection of high-z GRBs. With its observational mode and ability, we compute the expected detection rate of high-z GRBs by Einstein Probe by means of a observational tested population synthesis model of Swift GRBs. Our results show that the detection rates are expected to be about 20 events yr-1 sr-1 for z 〉 6 bursts, 6 events yr-a sr-1 for z 〉 8 bursts, and 1 events yr-1 sr-1 for z 〉 12 bursts, respectively. Over the 3 yr lifetime of the mission, Einstein Probe will able to detect about 65 GRBs at z 〉 6, including - 20 GRBs at z 〉 8 and - 3 GRBs at z 〉 12. In sum, Einstein Probe would significantly improve the detection of high-z GRBs, and these abundant observational information would probably reveal some scientific mysteries of the early universe.