Coalescences of neutron stars and white dwarfs are relatively frequent phenomena, outnumbering other types of compact object mergers (neutron stars and black holes without involving white dwarfs) altogether. Such event potentially can produce not only optical, but also an X-ray burst. Transient source CDF-S XT2 (Xue et al., 2019) can be an example of this type of events as suggested by Fernández et al. (2019). In this note we estimate the rate of these transients in the field of view of X-ray instruments on-board Spectrum-RG satellite. We demonstrate that during four years of the survey program several thousand of events related to neutron star — white dwarf mergers might appear in the field of view of eROSITA. Collimation of X-ray emission can reduce this number. Smaller, but comparable number of transients is expected in the case of ART-XC telescope. However, due to relatively short duration — $\lesssim {10}^4$ s, — mostly such transients might be visible just in one scan of telescopes (∼40 s), and so only a few photons are expected to be detected which makes definite identification without additional information very problematic.

中子星和白矮星的聚结是相对频繁的现象，总数超过其他类型的紧凑物体合并（中子星和黑洞而不涉及白矮星）。这样的事件不仅可能产生光学现象，而且还会产生X射线猝发。费尔南德斯（Fernández）等人建议，瞬态源CDF-S XT2（Xue等人，2019）可能是此类事件的一个例子。（2019）。在本文中，我们估计了Spectrum-RG卫星上X射线仪器视场中这些瞬变的速率。我们证明，在调查计划的四年中，与etrona领域相关的中子星-白矮星合并可能发生了数千起事件。X射线发射的准直可以减少该数目。较小的 但在使用ART-XC望远镜的情况下，预计会有相当数量的瞬变。但是，由于持续时间相对较短-$\lesssim {10}^4$ s – —仅在一次望远镜扫描（约40 s）中，此类瞬态现象可能才可见，因此只能检测到几个光子，这使得在没有附加信息的情况下进行确定的识别非常困难。