New Atomic Data For Iron-Peak Elements For Use In Astrophysical Modeling

Abstract

Supernovae (SN) and supernova remnant (SNR) plasmas represent some of the most extreme and unusual objects in the universe. X-ray spectra of supernova remnant plasmas are key to understanding the mechanism and dynamics of supernova explosions. In recent years, there have been observations of Cr and Mn X-ray emission lines from a wide range of supernova remnant plasmas. Diagnostics that use these emission features are currently hampered by a lack of atomic data for these Fe-peak elements. The purpose of this research is to generate the high quality atomic data needed by the astrophysics community. We focus on the atomic data for He-like Fe-peak elements Cr22+, Mn23+, Fe24+, Co25+, and Ni26+. As an example of the use of this new data, our spectral analysis is carried out for the Galactic supernova remnant W49B. The new electron-impact excitation data are calculated using a Dirac R-matrix suite of codes and include the infinite energy limit points on the collision strengths. The data are compared with available literature values, including recent Dirac R-matrix calculations, quantifying the influence of radiation damping and relativistic effects on the new collision data. This dataset includes calculated dipole and non-dipole radiative rates. For each ion, level-resolved electron-impact excitation cross sections and Maxwellian rate coefficients are generated for the 1s nl configurations for 1s < nl < 5g. He-like K photon emissivities are calculated for each ion, and the importance of including the two photon transition is shown. The photon emissivity coefficients (PECs) are used, along with previously calculated data for the H-like ion stages, to investigate the evidence of overionization in the SNR plasma W49B. The He-like data are then used to determine relative abundances of Cr and Mn to Fe in W49B. The role of recombination as a populating mechanism for the He-like line emission is investigated. We discuss the implications of this work, both for the general diagnostics using these He-like lines, and in answering some of the current uncertainties over the nature and makeup of W49B.