The iron line profile from warped black hole accretion disks

The profile of the fluorescent iron line from black hole accretion disks is a powerful diagnostic of black hole properties, such as spin and inclination. The state of the art, however, considers an accretion disk whose angular momentum is aligned with that of the black hole; this is a very constraining assumption that is unlikely to apply to many astrophysical systems. Here, we present the first simulation of the reflection spectrum from warped accretion disks using a realistic model of the reflected emission based on the XILLVER code. We present the effects that the radial location of the warp and the tilt angle have on the line profile, showing that the affect becomes significant at relatively low angles, between 5° and 15°. We highlight that the results are highly dependent on the azimuth position of the observer relative to the tilt angle. We fit these profiles in XSPEC with the standard relxill lamppost model to quantify the effect that neglecting the disk warps has on the inferred black hole spins and inclinations, finding that the spin parameter can be off by as much as 0.2. We show that fits with two-component relxill can be used to derive more accurate parameter estimates and can recover the radial location of the warp.