Leveraging high‐resolution spectra to understand black hole spectra

Abstract

For the past 17 years, both XMM‐Newton and Chandra have brought the powerful combination of high spatial and spectral resolution to the study of black hole systems. Each of these attributes requires special consideration—in comparison to lower spatial resolution charge‐coupled device (CCD)‐quality spectra—when modeling observations obtained by these spacecraft. A good understanding of the high‐resolution spectra is in fact required to model properly lower resolution CCD spectra, with the reflection grating spectrometer (RGS) instrument on XMM‐Newton maintaining the highest “figure of merit” at soft X‐ray energies for all missions flying or currently planned for the next decade. Thanks to its even higher spectral resolution, the use of Chandra high‐energy transmission gratings (HETGs), albeit with longer integration times, allows for one to bring further clarity to RGS studies. A further promising route for continued studies is the combination of high spectral resolution at soft X‐rays, via RGS and/or HETG, with contemporaneous broadband coverage extending to hard X‐rays (e.g., NuSTAR or INTEGRAL spectra). Such studies offer special promise for answering fundamental questions about accretion in black hole systems; however, they have received only moderate consideration to date. This may be due in part to the difficulty of analyzing high‐resolution spectra. In response, we must continue to develop software tools that make the analysis of high‐resolution X‐ray spectra more accessible to the wider astrophysics community.