Radiative-hydrodynamical simulations of X-ray burst-induced accretion disk coronae

X-ray burst sources, which contain a neutron star that explosively burns freshly accreted fuel every few hours, emit a variable X-ray flux that increases by an order of magnitude or more during the transient event. These are ideal systems in which to explore the structure of the surrounding accretion disk and its response to the changing conditions at the central source. In particular, a burst-induced accretion disk corona can significantly alter the observable characteristics of the burst profile. Here we use a fully self-consistent radiative-hydrodynamical algorithm developed earlier to study the "steady" state coronae in order to simulate the response of the evaporated outflow to a time-dependent irradiation of the disk's surface. We find that the burst definition is altered at both low and high inclination angles i. At i ≳ 45°, the detectable flux is enhanced (as much as 50%) by X-rays scattered into the line of sight from the radiation propagating through the corona, and (≳ 30%) by X-rays reflected off the corona when i ≲ 45°. For observation angles i → 90°, the severe attenuation of the direct X-ray flux leads to burst characteristics not unlike those of the transient event detected in the coronal source 4U 2129+47. These include (1) an increase in the apparent rise time, (2) a peak flux considerably smaller than the presumed intrinsic one, and (3) a slow decay.