Swift/XRT对黑洞双星GS2023+338（V404 Cyg）在2015年的爆发观测∗

摘要

After a quiescence of 26 years, the black hole binary system V404 Cyg underwent another outburst in June 2015. During the later phase of this outburst, Swift/XRT (X-ray Telescope) detected for the first time a unique structure of a series of concentric rings in an imaging mode. In this paper, by analyzing the public Swift/XRT data, we derived the spectral and temporal properties upon these ring structures. Our results show that, the spectrum of the rings is highly softened with respect to that of the central source, and the strength of the spectrum is also variable as the rings are moving outward. These results can be understood in the model of a cloud which is located between the source and the observer at a distance of roughly 6842 light years (about 2.1 kpc). We found that under this assumption the burst observed by XRT around MJD 57199–57200 is the most probable producer of the inner ring.%在经历了26 yr的沉寂后,黑洞双星GS2023+338(V404 Cyg,简称V404)在2015年6月再次爆发,并且在爆发末期, Swift上搭载的X射线望远镜(X-ray Telescope,简称Swift/XRT)在光子计数(Photon Counting,简称PC)模式下首次观测到了奇特的同心圆环结构。主要通过分析Swift/XRT观测数据,对该圆环结构进行了能谱和时变分析,给出了圆环的能谱和流量等信息。在此基础上采用云团模型来解释观测到的圆环,并对圆环特性及其与爆发源之间的关联等性质给出了限制。