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Measuring interacting binary mass functions with X-ray fluorescence

Measuring interacting binary mass functions with X-ray fluorescence
Measuring interacting binary mass functions with X-ray fluorescence

The masses of compact objects in X-ray binaries are best constrained through dynamical measurements, relying on radial velocity curves of the companion star. In anticipation of upcoming high X-ray spectral resolution telescopes, we explore their potential to constrain the mass function of the compact object. Fe K line fluorescence is a common feature in the spectra of luminous X-ray binaries, with a Doppler-broadened component from the inner accretion disc extensively studied. If a corresponding narrow line from the X-ray irradiated companion can be isolated, this provides an opportunity to further constrain the binary system properties. Here, we model binary geometry to determine the companion star’s solid angle, and deduce the iron line’s equivalent width. We find that for systems with a mass ratio q > 0.1, the expected Kα equivalent width is 2–40 eV. Simulations using XSPEC indicate that new microcalorimeters will have sufficient resolution to be able to produce Kα emission-line radial velocity measurements with precision of 5–40 km s −1, for source continuum fluxes exceeding 10 −12 erg cm −2 s −1. Several caveats need to be considered; this method is dependent on successful isolation of the narrow line from the broad component, and the observation of clear changes in velocity independent of scatter arising from complex wind and disc behaviour. These issues remain to be proven with microcalorimeters, but this method has the potential to constrain binary parameters where optical measurements are not viable.

X-rays: binaries, black hole physics, techniques: spectroscopic
1365-2966
2426-2435
Brown, Cordelia Dashwood
a2c1eee6-ddbb-48df-96d2-676317382475
Gandhi, Poshak
5bc3b5af-42b0-4dd8-8f1f-f74048d4d4a9
Charles, Phil
acb7a76a-7b9a-4f0b-8b34-1c4772594d7a
Brown, Cordelia Dashwood
a2c1eee6-ddbb-48df-96d2-676317382475
Gandhi, Poshak
5bc3b5af-42b0-4dd8-8f1f-f74048d4d4a9
Charles, Phil
acb7a76a-7b9a-4f0b-8b34-1c4772594d7a

Brown, Cordelia Dashwood, Gandhi, Poshak and Charles, Phil (2022) Measuring interacting binary mass functions with X-ray fluorescence. Monthly Notices of the Royal Astronomical Society, 517 (2), 2426-2435. (doi:10.1093/mnras/stac2725).

Record type: Article

Abstract

The masses of compact objects in X-ray binaries are best constrained through dynamical measurements, relying on radial velocity curves of the companion star. In anticipation of upcoming high X-ray spectral resolution telescopes, we explore their potential to constrain the mass function of the compact object. Fe K line fluorescence is a common feature in the spectra of luminous X-ray binaries, with a Doppler-broadened component from the inner accretion disc extensively studied. If a corresponding narrow line from the X-ray irradiated companion can be isolated, this provides an opportunity to further constrain the binary system properties. Here, we model binary geometry to determine the companion star’s solid angle, and deduce the iron line’s equivalent width. We find that for systems with a mass ratio q > 0.1, the expected Kα equivalent width is 2–40 eV. Simulations using XSPEC indicate that new microcalorimeters will have sufficient resolution to be able to produce Kα emission-line radial velocity measurements with precision of 5–40 km s −1, for source continuum fluxes exceeding 10 −12 erg cm −2 s −1. Several caveats need to be considered; this method is dependent on successful isolation of the narrow line from the broad component, and the observation of clear changes in velocity independent of scatter arising from complex wind and disc behaviour. These issues remain to be proven with microcalorimeters, but this method has the potential to constrain binary parameters where optical measurements are not viable.

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2209.09920v1 - Accepted Manuscript
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Accepted/In Press date: 20 September 2022
Published date: 24 September 2022
Additional Information: MNRAS in press. 10 pages, 6 figures Funding Information: This work is funded by STFC grant reference ST/V001000/1. We would like to thank A. Veledina, J. Casares, A. Zdziarski, and M. Diaz Trigo for helpful comments and corrections. We are grateful to V. Grinberg and members of the NuSTAR Binaries science team for very useful discussions. In particular, J. M. Miller helped with additional useful references and food-for-thought. We also thank our referee for their feedback and insight. Publisher Copyright: © 2022 The Author(s) arXiv:2209.09920V1
Keywords: X-rays: binaries, black hole physics, techniques: spectroscopic

Identifiers

Local EPrints ID: 473432
URI: http://eprints.soton.ac.uk/id/eprint/473432
ISSN: 1365-2966
PURE UUID: 85ef2570-733a-48a8-8ae0-d3226ad5c8e4
ORCID for Poshak Gandhi: ORCID iD orcid.org/0000-0003-3105-2615

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Date deposited: 18 Jan 2023 17:32
Last modified: 18 Mar 2024 03:31

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Contributors

Author: Cordelia Dashwood Brown
Author: Poshak Gandhi ORCID iD
Author: Phil Charles

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