Atomic data and spectral modeling constraints from high-resolution X-ray observations of the Perseus cluster with Hitomi

TL;DR

The Hitomi SXS spectrum of the Perseus cluster provides a high-resolution benchmark for atomic modeling in hot plasmas, highlighting current successes and challenges in atomic codes and emphasizing the need for updates and laboratory measurements.

Contribution

This study compares leading atomic codes using Hitomi data, revealing discrepancies and emphasizing the importance of atomic data accuracy for astrophysical plasma analysis.

Findings

Reasonable fits achieved by AtomDB, SPEX, and CHIANTI.

16% difference in Fe abundance measurements between APEC and SPEX.

Atomic code differences significantly impact derived plasma parameters.

Abstract

The Hitomi SXS spectrum of the Perseus cluster, with $\sim$5 eV resolution in the 2-9 keV band, offers an unprecedented benchmark of the atomic modeling and database for hot collisional plasmas. It reveals both successes and challenges of the current atomic codes. The latest versions of AtomDB/APEC (3.0.8), SPEX (3.03.00), and CHIANTI (8.0) all provide reasonable fits to the broad-band spectrum, and are in close agreement on best-fit temperature, emission measure, and abundances of a few elements such as Ni. For the Fe abundance, the APEC and SPEX measurements differ by 16%, which is 17 times higher than the statistical uncertainty. This is mostly attributed to the differences in adopted collisional excitation and dielectronic recombination rates of the strongest emission lines. We further investigate and compare the sensitivity of the derived physical parameters to the astrophysical source modeling and instrumental effects. The Hitomi results show that an accurate atomic code is as important as the astrophysical modeling and instrumental calibration aspects. Substantial updates of atomic databases and targeted laboratory measurements are needed to get the current codes ready for the data from the next Hitomi-level mission.