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Published June 2016 | Published
Journal Article Open

A Hard X-Ray Study of the Normal Star-forming Galaxy M83 with NuSTAR

Abstract

We present the results from sensitive, multi-epoch NuSTAR observations of the late-type star-forming galaxy M83 (d = 4.6 Mpc). This is the first investigation to spatially resolve the hard (E > 10 keV) X-ray emission of this galaxy. The nuclear region and ~20 off-nuclear point sources, including a previously discovered ultraluminous X-ray source, are detected in our NuSTAR observations. The X-ray hardnesses and luminosities of the majority of the point sources are consistent with hard X-ray sources resolved in the starburst galaxy NGC 253. We infer that the hard X-ray emission is most likely dominated by intermediate accretion state black hole binaries and neutron star low-mass X-ray binaries (Z-sources). We construct the X-ray binary luminosity function (XLF) in the NuSTAR band for an extragalactic environment for the first time. The M83 XLF has a steeper XLF than the X-ray binary XLF in NGC 253, which is consistent with previous measurements by Chandra at softer X-ray energies. The NuSTAR integrated galaxy spectrum of M83 drops quickly above 10 keV, which is also seen in the starburst galaxies NGC 253, NGC 3310, and NGC 3256. The NuSTAR observations constrain any active galactic nucleus (AGN) to be either highly obscured or to have an extremely low luminosity of ≾ 10^(38) erg s^(−1) (10–30 keV), implying that it is emitting at a very low Eddington ratio. An X-ray point source that is consistent with the location of the nuclear star cluster with an X-ray luminosity of a few times 10^(38) erg s^(−1) may be a low-luminosity AGN but is more consistent with being an X-ray binary.

Additional Information

© 2016. The American Astronomical Society. Received 2015 September 9; accepted 2016 March 25; published 2016 June 20. We thank the referee for useful comments and suggests that improved this paper. 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 sincerely thank Karl Forster and Brian Grefenstette for their work on the complicated stray light pattern and for assistance in designing the NuSTAR observational setup for minimizing this contamination. We also thank NuSTAR and Chandra mission planners for making the Chandra and NuSTAR observations simultaneous. We also thank P. Tzanavaris and D. Swartz for helpful discussion. Support for this work was provided by the National Aeronautics and Space Administration through Chandra Award Number GO4-15086Z issued by the Chandra X-ray Observatory Center, which is operated by the Smithsonian Astrophysical Observatory for and on behalf of the National Aeronautics Space Administration under contract NAS8-03060. R.K. acknowledges support from Russian Science Foundation (grant 14-12-01315). Facilities: Chandra - , NuSTAR - The NuSTAR (Nuclear Spectroscopic Telescope Array) mission, XMM-Newton - .

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August 20, 2023
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