[论文解读] X-Ray Binary Systems in the Small Magellanic Cloud

P. Kahabka, W. Pietsch|arXiv (Cornell University)|Jun 9, 1997

Astrophysical Phenomena and Observations参考文献 6被引用 4

一句话总结

本研究利用1991–1993年ROSAT PSPC数据，对大麦哲伦云中的X射线双星系统进行了系统性搜索，识别出7个硬X射线双星候选体和4个软X射线双星候选体，其光度均超过3×10³⁵ erg/s。主要发现包括：在SMC X-1中检测到变温和食变行为；重新探测到Be暂现源SMC X-2；发现了新的变源，如RX J0101.0-7206和RX J0032.9-7348，其中部分源可能在爱丁顿极限附近辐射。

ABSTRACT

We present the result of a systematic search for spectrally hard and soft X-ray binary systems in the Small Magellanic Cloud (SMC). This search has been applied to ROSAT PSPC data (0.1-2.4 keV) collected during 9 pointed observations towards this galaxy covering a time span of 2 years from October 91 till October 93. Selection criteria have been defined in order to confine the sample of candidates. Finally 7 spectrally hard and 4 spectrally soft sources were selected from the list as candidates for binaries in the SMC. The sample is luminosity limited (>3.10**35 erg/s). SMC X-1 has been observed during a full binary orbit starting with a low-state covering an X-ray eclipse and emerging into a bright long-duration flare with two short-duration flares separated by 10 hours. The Be type transient SMC X-2 has been redetected with ROSAT. Variability has been found in the sources RX J0051.8-7231 and RX J0052.1-731 already discovered with Einstein. RX J0101.0-7206 has been discovered at the north-eastern boundary of the giant SMC HII region N66 during an X-ray outburst and half a year later during a quiescent phase. A variable source, RX J0049.1-7250, located north-east of the SMC supernova remnant N19 and which may either be an X-ray binary or an AGN turns out to be strongly absorbed. It may be located behind the SMC. If it is an X-ray binary then it radiates at the Eddington limit in the X-ray bright state. Another variable and hard X-ray source RX J0032.9-7348 has been discovered at the south-eastern border of the body of the SMC. A high mass X-ray binary nature is favored for this source. We searched for CAL87 like systems in the SMC catalog and found none. A new candidate supersoft source RX J0103.8-7254 has been detected. We cannot exclude that it is a foreground object.

研究动机与目标

• 利用X射线数据识别并表征大麦哲伦云（SMC）中的X射线双星系统。
• 基于光谱特性，区分硬X射线双星候选体与软X射线双星候选体。
• 研究已知及新探测到的X射线源的变光性和轨道行为。
• 评估大麦哲伦云中是否存在CAL87型系统和超软X射线源。
• 确定高度吸收源（如RX J0049.1-7250）的距离和本质，其可能位于大麦哲伦云之后。

提出的方法

• 分析1991年10月至1993年10月间为期两年、共9次指向观测所获得的ROSAT PSPC数据。
• 应用光谱选择标准，筛选出光度大于3×10³⁵ erg/s的硬X射线和软X射线源。
• 将变光性和光谱硬度作为关键指标，用于分类候选X射线双星。
• 将源位置与已知的SMC结构（如电离氢区和超新星遗迹）进行比对，以推断距离和关联性。
• 通过X射线通量和光谱建模评估吸收水平，以评估源的距离和本质。
• 与早期的Einstein观测结果进行交叉识别，以确认变光性并追踪长期行为。

实验结果

研究问题

• RQ1 大麦哲伦云中的哪些X射线源表现出大质量X射线双星的特征？
• RQ2 SMC X-1和SMC X-2的X射线光 light curves 和光谱特性在轨道周期内如何随时间变化？
• RQ3 像RX J0049.1-7250这样的高度吸收变源是否可确认为X射线双星，还是更可能是前景活动星系核？
• RQ4 大麦哲伦云中是否存在类似CAL87的系统——即持续的超软X射线源？
• RQ5 如果RX J0049.1-7250是X射线双星，其在明亮状态下的爱丁顿极限X射线光度是多少？

主要发现

• SMC X-1在整个双星轨道周期内被观测到，表现出低态、X射线食变以及持续时间较长的耀发，包含两次10小时的耀发。
• Be型暂现源SMC X-2成功被ROSAT重新探测到，证实了其双星本质。
• 先前由Einstein探测到的变源RX J0051.8-7231和RX J0052.1-731在ROSAT数据中表现出显著变光。
• RX J0101.0-7206在HII区N66的东北边缘于一次X射线爆发期间被发现，后在宁静态被再次观测到。
• 位于SMC超新星遗迹N19东北方的源RX J0049.1-7250高度吸收，可能位于大麦哲伦云之后；若为X射线双星，其在明亮状态下的辐射接近爱丁顿极限。
• 在大麦哲伦云东南边界新发现一个硬X射线源RX J0032.9-7348，其大质量X射线双星性质更受青睐。