The Iron Line Profile from Warped Black Hole Accretion Disks

Abstract: 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 which is unlikely to apply to many or even most 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, and 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. We show that fits with two-component relxill can be used to derive more accurate spin and inclination estimates.