Photoionization Models for High-density Gas
Relativistically broadened and redshifted 6.4–6.9 keV iron K lines are observed from many accretion powered objects, including X-ray binaries and active galactic nuclei. The existence of gas close to the central engine implies large radiation intensities and correspondingly large gas densities if the gas is to remain partially ionized. Simple estimates indicate that high gas densities are needed to allow for the survival of iron against ionization. These are high enough that rates for many atomic processes are affected by mechanisms related to interactions with nearby ions and electrons. Radiation intensities are high enough that stimulated processes can be important. Most models currently in use for interpreting relativistic lines use atomic rate coefficients designed for use at low densities and neglect stimulated processes. In our work so far we have presented atomic structure calculations with the goal of providing physically appropriate models at densities consistent with line-emitting gas near compact objects. In this paper we apply these rates to photoionization calculations, and produce ionization balance curves and X-ray emissivities and opacities that are appropriate for high densities and high radiation intensities. The final step in our program will be presented in a subsequent paper in which model atmosphere calculations will incorporate these rates into synthetic spectra.
Additional Information© 2021 The American Astronomical Society. Received 2020 August 5; revised 2020 November 9; accepted 2020 November 20; published 2021 February 16. Partial support for this work was provided by grant 80NSSC17K0345 through the NASA APRA program. J.A.G. acknowledges support from NASA ADAP grant 80NSSC19K0586, and from the Alexander von Humboldt Foundation. J.D. is a Research Fellow of the Belgian Fund for Research Training in Industry and Agriculture (FRIA), while P.P. and P.Q. are, respectively, Research Associate and Research Director of the Belgian Fund for Scientific Research (F.R.S.-FNRS). A.O. is supported by NASA under award number 80GSFC17M0002. We are very grateful to the referee for several constructive suggestions.
Published - Kallman_2021_ApJ_908_94.pdf
Submitted - 2011.10603.pdf