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Published August 1, 2016 | Version Published + Submitted
Journal Article Open

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

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Abstract

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.

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.

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Published - apj_826_2_160.pdf

Submitted - 1605.06066v1.pdf

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Additional details

Identifiers

Eprint ID
69336
Resolver ID
CaltechAUTHORS:20160729-154753481

Related works

Describes
https://arxiv.org/abs/1605.06066 (URL)

Funding

NASA
NNG08FD60C
NASA/JPL/Caltech

Dates

Created
2016-07-29
Created from EPrint's datestamp field
Updated
2021-11-11
Created from EPrint's last_modified field

Caltech Custom Metadata

Caltech groups
NuSTAR
Other Numbering System Name
Space Radiation Laboratory
Other Numbering System Identifier
2016-52