Follow-up of eROSITA discovered X-ray binaries with NuSTAR and XMM

We report on the first follow-up observations of galactic X-ray binary candidates identified in the ongoing SRG/eRosita all-sky survey, with NuSTAR (~60ks) and XMM-Newton (26ks and 27ks). This analysis is part of a project in the eROSTEP (eROsita view of STellar EndPoints) network, with a focus on search and identification of galactic X-ray binaries. Preliminary analysis of the broadband X-ray spectrum of eRASSU J084850 observed with NuSTAR shows that the continuum can be well described either with a comptonization spectrum, or emission from an accretion disk (diskbb) along with a reflection component. There is no significant evidence of a cyclotron resonant scattering feature and no pulsations are present in the lightcurve. The most likely optical counterpart of the source is identified as a Be star, UCAC2 13726137, ~3'' away, suggesting that the compact object is most likely a neutron star. Analysis of XMM data of eRASSU J061331 and eRASSU J161201 allowed better localization of both X-ray sources and their optical counterparts. In both cases, low counting statistics precluded detection of significant pulsations in the lightcurves from XMM. The XMM spectra are consistent with thermal emission from collisionally ionised plasma and there is no strong evidence for the presence of a power-law type continuum component. Moreover, their X-ray and optical behaviour appear more similar to chromospheric active stars than X-ray binaries. Further confirmation of this is pending