2023MNRAS.519L..79K

Relativistic reflection observed in the hard states of accreting black holes (BH) often shows a weak amplitude relative to the main Comptonization component, which may result from either a disc truncation or a non-isotropy of the X-ray source, e.g. due to a motion away from the reflector. We investigate here the latter case, assuming that the X-ray source is located on the symmetry axis of the Kerr BH. We discuss effects relevant to a proper computation of the reflected radiation, and we implement them in the model for data analysis, REFLKERRV. We apply it to the simultaneous Suzaku and NuSTAR observation of Cyg X-1 in the hard state, and we find a good fit for an untruncated disc irradiated by the source moving away from it at 0.36 c. However, we find a slightly better solution in a geometry closely approximating the truncated disc irradiated by an inner hot flow. In this solution, we either still need a subrelativistic outflow or the source opposite to the observer must contribute to the directly observed radiation. We also discuss differences between the implementation of the outflow effect in REFLKERRV and in RELXILLLPCP.