October 7
Spectral radiative transfer post-processing of GRMHD simulations of black hole accretion
Speaker: Chris Nagele, JHU
Abstract: Spectral observations of accreting black holes are one of our most powerful tools for understanding these enigmatic objects. Black hole spectra contain complex phenomenology, including quasi-thermal components, power law components, broadened emission lines and spectral state transitions in stellar mass black holes (but not supermassive ones). Relating these spectra to simulations, however, has proven challenging given the many radiative processes at play. We present radiative transfer post-processing of three dimensional general relativistic magnetohydrodymanic (GRMHD) simulations. We partition simulations into an optically thin corona, in which we solve the radiative transfer problem using a relativistic Monte-Carlo code, and an optically thick diskbody, in which we solve for the radiation field and for ionization balance using a Feautrier solver. We discuss the dependence of our predicted spectra on black hole mass and accretion rate. We find that the relativistic Fe K$\alpha$ emission line is broadened in our spectra, despite most Fe K$\alpha$ photons originating at tens of gravitational radii. We comment on the implications of this finding for spin measurements and reverberation mapping campaigns. We then compare the predictions for polarized spectra to recent IXPE observations of Cyg X-1 and X-3. We conclude by briefly discussing planned extensions of this method to the optical and the MeV.
Host: Prof. Chris Reynolds