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The NuSTAR X-ray Spectrum of Hercules X-1: A Radiation-Dominated Radiative Shock

Wolff, Michael T. and Becker, Peter A. and Gottlieb, Amy M. and Fürst, Felix and Hemphill, Paul B. and Marcu-Cheatham, Diana M. and Pottschmidt, Katja and Schwarm, Fritz-Walter and Wilms, Jörn and Wood, Kent S. (2016) The NuSTAR X-ray Spectrum of Hercules X-1: A Radiation-Dominated Radiative Shock. Astrophysical Journal, 831 (2). Art. No. 194. ISSN 0004-637X. doi:10.3847/0004-637X/831/2/194.

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We report on new spectral modeling of the accreting X-ray pulsar Hercules X-1. Our radiation-dominated radiative shock model is an implementation of the analytic work of Becker & Wolff on Comptonized accretion flows onto magnetic neutron stars. We obtain a good fit to the spin-phase-averaged 4–78 keV X-ray spectrum observed by the Nuclear Spectroscopic Telescope Array during a main-on phase of the Her X-1 35 day accretion disk precession period. This model allows us to estimate the accretion rate, the Comptonizing temperature of the radiating plasma, the radius of the magnetic polar cap, and the average scattering opacity parameters in the accretion column. This is in contrast to previous phenomenological models that characterized the shape of the X-ray spectrum, but could not determine the physical parameters of the accretion flow. We describe the spectral fitting details and discuss the interpretation of the accretion flow physical parameters.

Item Type:Article
Related URLs:
URLURL TypeDescription Paper
Wolff, Michael T.0000-0002-4013-5650
Fürst, Felix0000-0003-0388-0560
Hemphill, Paul B.0000-0002-1676-6954
Marcu-Cheatham, Diana M.0000-0001-8061-611X
Pottschmidt, Katja0000-0002-4656-6881
Wilms, Jörn0000-0003-2065-5410
Wood, Kent S.0000-0002-7376-3151
Additional Information:© 2016 American Astronomical Society. Received 2015 September 24; revised 2016 August 22; accepted 2016 August 23; published 2016 November 8. The authors thank Dr. Carlo Ferrigno and Dr. Kenneth Wolfram for valuable help in formulating the numerical implementation of many of the analytical expressions. We thank Dr. Richard Rothschild for a number of stimulating discussions. We also thank an anonymous referee for a number of insightful comments that helped improve the manuscript. This research was supported by the National Aeronautics and Space Administration Astrophysical Data Analysis Program under Grant 12-ADAP12-0118. MTW and KSW are also supported by the Chief of Naval Research. JW and F-WS are grateful for support by the Deutsche Forschungsgemeinschaft. This work made use of data from the NuSTAR mission, a project led by the California Institute of Technology, managed by the Jet Propulsion Laboratory, and funded by the National Aeronautics and Space Administration. This research has also made use of the NuSTAR Data Analysis Software (NuSTARDAS) jointly developed by the ASI Science Data Center (ASDC, Italy) and the California Institute of Technology (USA).
Funding AgencyGrant Number
Chief of Naval ResearchUNSPECIFIED
Deutsche Forschungsgemeinschaft (DFG)UNSPECIFIED
Subject Keywords:methods: data analysis; X-rays: binaries; stars: individual (Her X-1) ; stars: neutron; radiative transfer
Issue or Number:2
Record Number:CaltechAUTHORS:20161109-092115164
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Official Citation:Michael T. Wolff et al 2016 ApJ 831 194
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:71871
Deposited By: Ruth Sustaita
Deposited On:09 Nov 2016 18:06
Last Modified:11 Nov 2021 04:52

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