In the first part, prospects of the SRG/eROSITA mission for detecting two types of extragalactic X-ray transients, X-ray afterglows of gamma-ray bursts and X-ray flares associated with tidal disruption events (TDEs), are considered along with results of the systematic search for TDEs in the archived data of ROSAT and XMM-Newton. The developed detection techniques are based on the main trademarks of these transients in conjunction with the characteristics of the eROSITA All-Sky Survey, that allows systematic measuring of variability of detected sources on time-scales in the exceptionally wide range. Expected detection rates and properties of the resultant sample are presented for several assumptions regarding properties of the parent populations. Additionally, systematic search for TDEs amongst sources in the ROSAT Bright Source Catalogue by means of cross-correlation with the data of subsequent observations by XMM-Newton is described, which provided up to four new candidates with various confidence of association with TDE and allowed to obtain an estimate for the averaged frequency of such events in a typical galaxy.

In the second part, we present results of the detailed calculations of X-ray emission from a baryonic relativistic jet in an XRB with the main focus on characteristics of the brightest X-ray lines, that are subject to resonant scattering inside the jets and such effects as collisional and photo- de-excitation. Observational consequences are discussed in application to the unique Galactic X-ray binary SS 433 for the currently available (Chandra HETG) and the coming-soon (ASTRO-H) quality of X-ray spectroscopic data.

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