Testing High Density Accretion Disk Models with Photoionized Iron and Calcium Plasma Experiments

Patricia Cho, University of Texas at Austin

Photo of Patricia Cho

Astrophysical models of black hole accretion disks suggest high iron abundances in multiple systems that are often many times the iron abundance in the sun. This phenomenon is known as the supersolar iron abundance problem. Historically, these models imposed an upper bound on the plasma density in the accretion disk which is lower than what recent observations suggest. This low density limit was suspected to be a large part of the reason for many of the supersolar iron abundance determinations. Recently, high density effects have been incorporated into one astrophysical photoionized plasma model known as XSTAR. The effects have significantly revised iron abundances to lower values for many systems. However, the physical assumptions underlying photoionized plasma codes have not previously been tested against laboratory data. The key question of whether photoionized plasma spectral models can accurately account for the x-ray emission remains an open one. Photoionized iron and calcium plasma experiments have been performed at astrophyiscally relevant parameters using the Z-machine at Sandia National Laboratories. Iron L-shell and calcium K-shell emission data were recorded using an expanded foil sample driven by the high x-ray flux of the z-pinch. Both of these data sets are the first of their kind ever to be collected in a laboratory setting. We will describe our motivations, experiment, and the data collected. We will also discuss the data’s potential to assess the validity of the physical assumptions relevant to the new high density effects in XSTAR.

Abstract Author(s): P.B. Cho, G.P. Loisel, T. Nagayama, T.Kallman, J. Garcia, J.E. Bailey