ИСТИНА

We consider the possibility of detecting the accompanying X-ray emission from two types of transient sources: fast radio bursts and neurton star - white dwarf mergers with the SRG/eROSITA telescope. We show that up to 300 radio bursts can fall within the eROSITA field of view in four years of survey observations. About 1% of them will be detected by ground-based radio telescopes. At a total X-ray energy release of ∼10^46 erg, a flare with a thermal spectrum with kT=200 keV and strong absorption can be detected only from 1 Mpc. But in the case of a power-law spectrum with Γ = 2 and realistic absorption the limiting distance grows up to 1 Gpc. Thus, eROSITA can provide important constraints on parameters of the sources of fast radio bursts and, probably, also can help to identify the sources in the X-ray band, which will make it possible to choose the models describing the formation of these bursts. 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. 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 (however, collimation of X-ray emission can be important). Smaller, but comparable number of transients is expected in the case of ART-XC telescope. Due to relatively short duration — <= 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.