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Evidence for Intermediate Polars as the Origin of the Galactic Center Hard X-ray Emission

Hailey, Charles J. and Mori, Kaya and Perez, Kerstin and Canipe, Alicia M. and Hong, Jaesub and Tomsick, John A. and Boggs, Steven E. and Christensen, Finn E. and Craig, William W. and Fornasini, Francesca and Grindlay, Jonathan E. and Harrison, Fiona A. and Nynka, Melania and Rahoui, Farid and Stern, Daniel and Zhang, Shuo and Zhang, William W. (2016) Evidence for Intermediate Polars as the Origin of the Galactic Center Hard X-ray Emission. Astrophysical Journal, 826 (2). Art. No. 160. ISSN 0004-637X. doi:10.3847/0004-637X/826/2/160.

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Recently, unresolved hard (20–40 keV) X-ray emission has been discovered within the central 10 pc of the Galaxy, possibly indicating a large population of intermediate polars (IPs). Chandra and XMM-Newton measurements in the surrounding ~50 pc imply a much lighter population of IPs with〈M_(WD)〉 ≈ 0.5M⊙. Here we use broadband NuSTAR observations of two IPs: TV Columbae, which has a fairly typical but widely varying reported mass of M_(WD) ≈ 0.5-1.0M⊙, and IGR J17303–0601, with a heavy reported mass of M_(WD) ≈ 1.0-1.2M⊙. We investigate how varying spectral models and observed energy ranges influences estimated white dwarf mass. Observations of the inner 10 pc can be accounted for by IPs with M_(WD) ≈ 0.9M⊙, consistent with that of the CV population in general and the X-ray observed field IPs in particular. The lower mass derived by Chandra and XMM-Newton appears to be an artifact of narrow energy-band fitting. To explain the (unresolved) central hard X-ray emission (CHXE) by IPs requires an X-ray (2–8 keV) luminosity function (XLF) extending down to at least 5 × 10^(31) erg s^(−1). The CHXE XLF, if extended to the surrounding ~50 pc observed by Chandra and XMM-Newton, requires that at least ~20%–40% of the ~9000 point sources are IPs. If the XLF extends just a factor of a few lower in luminosity, then the vast majority of these sources are IPs. This is in contrast to recent observations of the Galactic ridge, where the bulk of the 2–8 keV emission is ascribed to non-magnetic CVs.

Item Type:Article
Related URLs:
URLURL TypeDescription Paper
Mori, Kaya0000-0002-9709-5389
Perez, Kerstin0000-0002-6404-4737
Tomsick, John A.0000-0001-5506-9855
Boggs, Steven E.0000-0001-9567-4224
Christensen, Finn E.0000-0001-5679-1946
Grindlay, Jonathan E.0000-0002-1323-5314
Harrison, Fiona A.0000-0003-2992-8024
Nynka, Melania0000-0002-3310-1946
Rahoui, Farid0000-0001-7655-4120
Stern, Daniel0000-0003-2686-9241
Zhang, Shuo0000-0002-2967-790X
Zhang, William W.0000-0002-1426-9698
Additional Information:© 2016 The American Astronomical Society. Received 2015 December 4; revised 2016 May 16; accepted 2016 May 19; published 2016 July 28. This work was supported under NASA Contract No. NNG08FD60C, and 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. We thank the NuSTAR Operations, Software and Calibration teams for support with the execution and analysis of these observations. This research has 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). The authors thank K Mukai and QD Wang for valuable discussions.
Funding AgencyGrant Number
Subject Keywords:Galaxy: center – novae, cataclysmic variables – X-rays: diffuse background
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Other Numbering System NameOther Numbering System ID
Space Radiation Laboratory2016-52
Issue or Number:2
Record Number:CaltechAUTHORS:20160729-154753481
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Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:69336
Deposited By: Tony Diaz
Deposited On:29 Jul 2016 23:04
Last Modified:11 Nov 2021 04:12

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