Can a Relativistic Iron K Line Be Resolved in Cyg X-1 withSIXA?

Abstract

Broad, asymmetric iron K lines have been detected in the x-ray spectra of abouta dozen Active Galactic Nuclei (AGN). The distorted line profiles are most probablydue to strong relativistic effects in the innermost parts of an optically thickaccretion disk around a central black hole. However, none of the Galactic BlackHole Candidates (GBHC) has exhibited any clear evidence of a relativistic ironline profile. Observations of the persistently bright black hole candidate Cyg X-1have only revealed a narrow Gaussian line. Weak relativistic features may nothave been detected due to insufficient signal-to-noise and energy resolution.We present simulated observations of a relativistic iron K line in the spectrumof Cyg X-1 obtained with SIXA onboard SPECTRUM-RÖNTGEN-GAMMA.We studied the feasibility of detecting the relativistic effects in the line profileboth in the hard and soft state of the source. Our results show that a relativisticline profile can be resolved in Cyg X-1 within a 50–100 ksec observation if theaccretion disk extends within ~ 100 rg from the compact object and the equivalent width of the relativistic component exceeds ~ 30–40 eV.