Testing Astrophysical Models of Black Hole Accretion Disk Plasmas Using The Z machine at Sandia National Laboratories
Patricia Cho, University of Texas at Austin
The Z machine at Sandia National Laboratories generates powerful X-ray radiation fluxes. This enables experiments to produce and study macroscopic quantities of matter at extreme conditions. Z experiments expand our understanding of the essential physics for stockpile stewardship, nuclear fusion, and astrophysics. Astronomers use extraordinary spectra collected with satellite telescopes to construct models for the behavior of accretion powered plasmas around black holes in both active galactic nuclei and X-ray binaries. However, complex models for these non-Local-Thermodynamic-Equilibrium (NLTE) plasmas are mostly untested with laboratory data. A novel platform developed on the Z machine for expanding foil photoionized plasma experiments opens a new regime for benchmark measurements of NLTE plasmas. It creates plasmas at the same conditions as those inferred in black hole accretion disks. The data have revealed difficulties in modeling both emission intensities and the level of ionization in the plasma. Current experiments aim to inform the "Super-Solar" iron abundance problem. Iron abundances in accretion disks inferred from X-ray spectra emitted by photoionized plasma surrounding about a dozen black holes appear to contain five to 20 times more iron than the Sun. This contradicts the widely held expectation that most objects in the universe have the Sun's composition. Additionally, Super-Solar iron abundances are inferred for systems with vastly different parameters — stellar mass black holes in X-ray binaries and super massive black holes in AGN — likely indicating a systematic modeling error. The prevailing hypothesis suggests accretion plasma densities are in reality, orders of magnitude higher than previously believed. Reinterpreting the X-ray spectra with updated high density models resolved much of the discrepancy. However, a key question still remains: do photoionized plasma spectral models accurately account for X-ray emission? We use the photoionized plasma platform developed over the last decade at Z to interrogate that question in the context of the Super-Solar Fe abundance problem.
Authors: Patricia B. Cho1, Guillaume P. Loisel2, Daniel Mayes1, Isaac Huegel1, Jim Bailey2, Taisuke Nagayama2, Tim Kallman3, Javier Garcia4
1Department of Astronomy, University of Texas at Austin, USA
2Sandia National Laboratories, New Mexico, USA
3NASA Goddard Space Flight Center, USA
4California Institute of Technology, USA
Abstract Author(s): (see above entries)