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Galactic sources detected in the NuSTAR serendipitous survey.

Tomsick, John A. and Lansbury, George B. and Rahoui, Farid and Clavel, Maïca and Fornasini, Francesca M. and Hong, JaeSub and Aird, James and Alexander, David M. and Bodaghee, Arash and Chiu, Jeng-Lun and Grindlay, Jonathan E. and Hailey, Charles J. and Harrison, Fiona A. and Krivonos, Roman A. and Mori, Kaya and Stern, Daniel (2017) 'Galactic sources detected in the NuSTAR serendipitous survey.', Astrophysical journal supplement series., 230 (2). p. 25.


The Nuclear Spectroscopic Telescope Array (NuSTAR) provides an improvement in sensitivity at energies above 10 keV by two orders of magnitude over non-focusing satellites, making it possible to probe deeper into the Galaxy and universe. Lansbury and collaborators recently completed a catalog of 497 sources serendipitously detected in the 3–24 keV band using 13 deg2 of NuSTAR coverage. Here, we report on an optical and X-ray study of 16 Galactic sources in the catalog. We identify 8 of them as stars (but some or all could have binary companions), and use information from Gaia to report distances and X-ray luminosities for 3 of them. There are 4 CVs or CV candidates, and we argue that NuSTAR J233426–2343.9 is a relatively strong CV candidate based partly on an X-ray spectrum from XMM-Newton. NuSTAR J092418–3142.2, which is the brightest serendipitous source in the Lansbury catalog, and NuSTAR J073959–3147.8 are low-mass X-ray binary candidates, but it is also possible that these 2 sources are CVs. One of the sources is a known high-mass X-ray binary (HMXB), and NuSTAR J105008–5958.8 is a new HMXB candidate that has strong Balmer emission lines in its optical spectrum and a hard X-ray spectrum. We discuss the implications of finding these HMXBs for the surface density (log N–log S) and luminosity function of Galactic HMXBs. We conclude that with the large fraction of unclassified sources in the Galactic plane detected by NuSTAR in the 8–24 keV band, there could be a significant population of low-luminosity HMXBs.

Item Type:Article
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Publisher statement:© 2017. The American Astronomical Society. All rights reserved.
Date accepted:23 May 2017
Date deposited:13 July 2017
Date of first online publication:23 June 2017
Date first made open access:13 July 2017

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