High-density plasma effects in photoionization models

Black hole spin can be inferred by modeling the distortion of the iron K emission complex. The emitting regions of such lines are thought to be characterized by quite high densities (up to 1e22 cm-3). Such plasma conditions affect the atomic structure and processes and may thus provoke changes in the X-ray spectra. However, atomic data used in the standard photoionization and reflection models (such as XSTAR and XILLVER) are computed assuming an isolated ion approximation. This shortcoming thus needs to be addressed, especially in light of the new era of very high-resolution X-ray spectrometers. In this context, new atomic data taking high-density effects into account have recently been computed using a sophisticated atomic computation method modified for such purpose. In particular, effects such as the continuum lowering, the suppression of dielectronic recombination, and stimulated processes have been considered in these calculations. These new atomic data for the high density regime have been implemented in XSTAR. In this work, present a first sample of photoionization simulations obtained using this new set of atomic databases to investigate the changes stemming from such high-density effects.