In recent years, various authors modelled general-relativistic
effects on X-ray spectra from accreting BH sources. In particular,
GR distortions of line profiles have been computed under various
physical and geometrical assumptions, also considering spinning BHs,
i.e. in Kerr metric (see, among others:
Martocchia et al. 2000, Laor 1991, Kojima 1991,
Bromley et al. 1997, Fanton et al. 1997,
Dabrowsky et al. 1997).
In particular, three of us (Martocchia et al. 2000) developed
a fully relativistic code in Kerr metric, aimed to
calculate the effects expected on both the reflection continuum
and the line profile in the "standard" accretion scenario
(Shakura & Sunyaev 1973, Thorne 1974), and further developed the routine
in order to implement it into the XSPEC data analysis package and thus to
perform fits to satellites X-ray data (Martocchia 2000). The routine, named
kerrspec,
allows to vary assumptions on the geometry and physics of the system,
for instance considering disc emissivity laws appropriate for
illumination by a central X-ray primary source
including GR effects (Martocchia & Matt 1996),
or giving an arbitrary local spectrum as input, which may account for
Compton-reflection as well as for other features.
In galactic BHCs, a consistent GR treatment for the thermal disk emission
should be employed, too (e.g., Makishima K. et al. 2000). Historically,
the first to perform GR (Kerr) computations of distortions of
blackbody spectra was Cunningham in 1975; recently, the issue was addressed
by Gierlinski et al. (1999, 2001), who developed an XSPEC
routine for data fitting (diskpn).