Two‐dimensional Monte Carlo/Fokker‐Planck Simulations of Flares in Accretion Disk Corona Models

Abstract

We present and discuss first results of space- and time-dependent Monte Carlo/Fokker-Planck radiation transport/electron dynamics simulations of flares in accretion disk corona systems in two-dimensional, cylindrical geometry. Following a brief, general description of the code, two fundamentally different flaring mechanisms will be considered: (1) flares originating in the optically thick, geometrically thin accretion disk, whose radiation is subsequently processed through a hot, optically thin corona sandwiching the accretion disk; and (2) flares originating in the corona (e.g., magnetic flares), leading to enhanced energy release in a small portion of the corona over a short period of time. We present energy- and angle-dependent light curves, angle- and time-dependent photon spectra, and time and phase lag spectra for both classes of flaring scenarios. We also illustrate the detailed, time-dependent effect of both types of flares on the electron temperature distribution in the corona, which is calculated self-consistently, including both thermal and nonthermal heating and cooling mechanisms. Whereas for the disk-flaring scenario, the flaring is mostly restricted to X-rays below ~10 keV, accompanied by spectral softening during the flare, the coronal flaring scenario produces predominantly hard X-ray flares (restricted to E 10 keV) with spectral hardening during the flare. Both hard and soft lags may result in the disk-flaring scenario, which predicts a slight hardening of the high-frequency power spectra with increasing photon energy. In the coronal-flaring scenario, the variability around ~10 keV leads variations at other photon energies, and no dependence of the power spectra on photon energy is found.