1 RXS J180408 .9-342058：具有瞬态射流的超紧凑X射线二元候选物
1RXS J180408.9-342058: an ultra compact X-ray binary candidate with a transient jet
摘要：
我们提出了一个详细的近红外/光学/紫外研究瞬态低质量X射线二进制1 RXS J180408.9-342058在其2015年爆发期间进行，旨在确定其伴星的性质。我们在2.1米圣佩德罗马蒂尔天文台望远镜（墨西哥）获得了三个光谱。我们用位于拉西拉的REM望远镜和新技术望远镜（NTT）进行了光学和近红外光度观测。我们从Swift档案中获得了光学和紫外线观测结果。最后，我们使用安装在NTT上的EFOSC 2仪器对光源进行了光学偏振测量。源的光谱几乎没有特征，因为通常在LMXB中观察到的氢和He I发射线没有被检测到。同样，也没有观察到碳线和氧线。我们勉强检测到的He II 4686 AA发射线，这表明在吸积盘氦的存在。未观察到显著的光学偏振水平。光谱中缺乏氢和He I发射线意味着伴星可能不是主序星。由He II 4686 AA发射线的试探性探测驱动，我们认为该系统可能存在一颗氦白矮星。如果是这样的话，1 RXS J180408.9-342058将是一个超紧凑的X射线双星。通过结合质量吸积率的估计与演化轨迹的He白矮星，我们得到了一个暂定的轨道周期~ 40分钟。另一方面，我们还建立了近红外-光学-紫外光谱能量分布（SED）的源在两个不同的时代。当源处于软X射线状态时，收集到一个SED，并且它与单个热分量的存在一致。第二个SED是在源处于硬X射线状态时获得的，在NIR中显示了热分量和尾部，可能表明存在（瞬态）射流。
英文摘要：
We present a detailed NIR/optical/UV study of the transient low mass X-ray binary 1RXS J180408.9-342058 performed during its 2015 outburst, aimed at determining the nature of its companion star. We obtained three optical spectra at the 2.1 m San Pedro Martir Observatory telescope (Mexico). We performed optical and NIR photometric observations with both the REM telescope and the New Technology Telescope (NTT) in La Silla. We obtained optical and UV observations from the Swift archive. Finally, we performed optical polarimetry of the source by using the EFOSC2 instrument mounted on the NTT. The optical spectrum of the source is almost featureless since the hydrogen and He I emissions lines, typically observed in LMXBs, are not detected. Similarly, carbon and oxygen lines are neither observed. We marginally detect the He II 4686 AA emission line, suggesting the presence of helium in the accretion disc. No significant optical polarisation level was observed. The lack of hydrogen and He I emission lines in the spectrum implies that the companion is likely not a main sequence star. Driven by the tentative detection of the He II 4686 AA emission line, we suggest that the system could harbour a helium white dwarf. If this is the case, 1RXS J180408.9-342058 would be an ultra-compact X-ray binary. By combining an estimate of the mass accretion rate together with evolutionary tracks for a He white dwarf, we obtain a tentative orbital period of ~ 40 min. On the other hand, we also built the NIR-optical-UV spectral energy distribution (SED) of the source at two different epochs. One SED was gathered when the source was in the soft X-ray state, and it is consistent with the presence of a single thermal component. The second SED, obtained when the source was in the hard X-ray state, shows a thermal component together with a tail in the NIR, likely indicating the presence of a (transient) jet.
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