Cyclotron resonant scattering feature simulations

I. Thermally averaged cyclotron scattering cross sections, mean free photon-path tables, and electron momentum sampling^⋆

¹ Dr. Karl Remeis-Sternwarte and Erlangen Centre for Astroparticle Physics, Sternwartstrasse 7, 96049 Bamberg, Germany
e-mail: fritz.schwarm@sternwarte.uni-erlangen.de
² Leibniz-Institut für Astrophysik Potsdam (AIP), An der Sternwarte 16, 14482 Potsdam, Germany
³ CRESST, Department of Physics, and Center for Space Science and Technology, UMBC, Baltimore, MD 21250, USA
⁴ NASA Goddard Space Flight Center, Code 661, Greenbelt, MD 20771, USA
⁵ Space Science Division, Naval Research Laboratory, Washington, DC 20375-5352, USA
⁶ Department of Physics & Astronomy, George Mason University, Fairfax, VA 22030-4444, USA
⁷ Faculty of Physics, M. V. Lomonosov Moscow State University, Leninskie Gory, 119991 Moscow, Russia
⁸ Sternberg Astronomical Institute, Moscow M. V. Lomonosov State University, Universitetskij pr., 13, 119992 Moscow, Russia
⁹ Institut für Astronomie und Astrophysik, Universität Tübingen (IAAT), Sand 1, 72076 Tübingen, Germany
¹⁰ ISDC Data Center for Astrophysics, Université de Genève, chemin d’Écogia 16, 1290 Versoix, Switzerland
¹¹ Cahill Center for Astronomy and Astrophysics, California Institute of Technology, Pasadena, CA 91125, USA
¹² Center for Astrophysics and Space Sciences, University of California, San Diego, 9500 Gilman Dr., La Jolla, CA 92093-0424, USA

Received: 20 July 2016
Accepted: 30 August 2016

Abstract

Context. Electron cyclotron resonant scattering features (CRSFs) are observed as absorption-like lines in the spectra of X-ray pulsars. A significant fraction of the computing time for Monte Carlo simulations of these quantum mechanical features is spent on the calculation of the mean free path for each individual photon before scattering, since it involves a complex numerical integration over the scattering cross section and the (thermal) velocity distribution of the scattering electrons.

Aims. We aim to numerically calculate interpolation tables which can be used in CRSF simulations to sample the mean free path of the scattering photon and the momentum of the scattering electron. The tables also contain all the information required for sampling the scattering electron’s final spin.

Methods. The tables were calculated using an adaptive Simpson integration scheme. The energy and angle grids were refined until a prescribed accuracy is reached. The tables are used by our simulation code to produce artificial CRSF spectra. The electron momenta sampled during these simulations were analyzed and justified using theoretically determined boundaries.

Results. We present a complete set of tables suited for mean free path calculations of Monte Carlo simulations of the cyclotron scattering process for conditions expected in typical X-ray pulsar accretion columns (0.01 ≤ B/B_crit ≤ 0.12, where B_crit = 4.413 × 10¹³ G, and 3 keV ≤ k_BT ≤ 15 keV). The sampling of the tables is chosen such that the results have an estimated relative error of at most 1/15 for all points in the grid. The tables are available online (see link in footnote, page 1).