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Polarization of accreting X-ray pulsars – II. Hercules X-1

Caiazzo, Ilaria and Heyl, Jeremy (2021) Polarization of accreting X-ray pulsars – II. Hercules X-1. Monthly Notices of the Royal Astronomical Society, 501 (1). pp. 129-136. ISSN 0035-8711. doi:10.1093/mnras/staa3429.

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We employ our new model for the polarized emission of accreting X-ray pulsars to describe the emission from the luminous X-ray pulsar Hercules X-1. In contrast with previous works, our model predicts the polarization parameters independently of spectral formation, and considers the structure and dynamics of the accretion column, as well as the additional effects on propagation due to general relativity and quantum electrodynamics. We find that our model can describe the observed pulse fraction and the pulse shape of the main peak, as well as the modulation of the cyclotron line with phase. We pick two geometries, assuming a single accretion column or two columns at the magnetic poles, that can describe current observations of pulse shape and cyclotron modulation with phase. Both models predict a high polarization fraction, between 60 and 80 per cent in the 1–10 keV range, that is phase and energy dependent, and that peaks at the same phase as the intensity. The phase and energy dependence of the polarization fraction and of the polarization angle can help discern between the different geometries.

Item Type:Article
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URLURL TypeDescription ItemData
Caiazzo, Ilaria0000-0002-4770-5388
Heyl, Jeremy0000-0001-9739-367X
Additional Information:© 2020 The Author(s). Published by Oxford University Press on behalf of Royal Astronomical Society. This article is published and distributed under the terms of the Oxford University Press, Standard Journals Publication Model ( Accepted 2020 October 29. Received 2020 October 29; in original form 2020 May 27. Published: 05 November 2020. We would like to thank Michael Wolff, Peter Becker, and the XMAG collaboration for valuable input, and Sterl Phinney for useful comments. The research was supported by NSERC Canada, Compute Canada, a Burke Fellowship at Caltech, and a Four-Year Fellowship at UBC. Data Availability: The values for the predicted polarization fraction and angle as function of phase and energy displayed in Figs 6 and 7 can be reproduced following the equations introduced in Paper I, and are also available in the public Github repository
Group:TAPIR, Walter Burke Institute for Theoretical Physics
Funding AgencyGrant Number
Natural Sciences and Engineering Research Council of Canada (NSERC)UNSPECIFIED
Walter Burke Institute for Theoretical Physics, CaltechUNSPECIFIED
University of British ColumbiaUNSPECIFIED
Subject Keywords:accretion, accretion discs – polarization – relativistic processes – scattering – pulsars: individual: Hercules X-1 – Xrays: binaries
Issue or Number:1
Record Number:CaltechAUTHORS:20210211-103847742
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Official Citation:Ilaria Caiazzo, Jeremy Heyl, Polarization of accreting X-ray pulsars – II. Hercules X-1, Monthly Notices of the Royal Astronomical Society, Volume 501, Issue 1, February 2021, Pages 129–136,
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:108004
Deposited By: Tony Diaz
Deposited On:11 Feb 2021 19:12
Last Modified:16 Nov 2021 19:08

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