disnht: Modeling X-ray absorption from distributed column densities

¹ Max-Planck-Institut für Extraterrestrische Physik (MPE), Giessenbachstrasse 1, 85748 Garching bei München, Germany
e-mail: nlocat@mpe.mpg.de
² INAF – Osservatorio Astronomico di Brera, via E. Bianchi 46, 23807 Merate (LC), Italy
³ Dipartimento di Matematica e Fisica, Universitá degli Studi Roma Tre, via della Vasca Navale 84, 00146 Roma, Italy

Received: 12 November 2021
Accepted: 27 December 2021

Abstract

Collecting and analyzing X-ray photons over either spatial or temporal scales encompassing varying optical depth values requires knowledge about the optical depth distribution. For a sufficiently broad optical depth distribution, assuming a single column density value leads to a misleading interpretation of the source emission properties, nominally its spectral model. We present a model description for the interstellar medium absorption in X-ray spectra at moderate energy resolution, extracted over spatial or temporal regions encompassing a set of independent column densities. The absorption model (called disnht) approximates the distribution with a lognormal distribution and is presented in table format. The solution table and source code are made available and can be further generalized or tailored for arbitrary optical depth distributions encompassed by the extraction region. The disnht absorption model and its generalized solution are expected to be relevant for current and upcoming large angular scale analyses of diffuse X-ray emission, such as those from the extended ROentgen Survey with an Imaging Telescope Array (eROSITA) and the future Athena missions.