Identification of the Hard X-Ray Source Dominating the E > 25 keV Emission of the Nearby Galaxy M31

Journal Article · Mon Mar 20 00:00:00 EDT 2017 · Astrophysical Journal

DOI:https://doi.org/10.3847/1538-4357/AA62A3· OSTI ID:22869188

Yukita, M.; Ptak, A.; Hornschemeier, A. E.; Wik, D. ^[1]; Maccarone, T. J. ^[2]; Pottschmidt, K.; Lien, A. ^[3]; Zezas, A.; Antoniou, V. ^[4]; Ballhausen, R. ^[5]; Lehmer, B. D. ^[6]; Williams, B. ^[7]; Baganoff, F. ^[8]; Boyd, P. T. ^[9]; Enoto, T. ^[10]; Kennea, J. ^[11]; Page, K. L. ^[12]; Choi, Y. ^[13]

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1. Johns Hopkins University, Homewood Campus, Baltimore, MD 21218 (United States)
2. Department of Physics and Astronomy, Texas Tech University, Lubbock, TX 79409 (United States)
3. CRESST, Department of Physics, and Center for Space Science and Technology, UMBC, Baltimore, MD 21250 (United States)
4. Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States)
5. Dr. Karl-Remeis-Sternwarte and Erlangen Centre for Astroparticle Physics, Sternwartstrasse 7, D-96049 Bamberg (Germany)
6. Department of Physics, University of Arkansas, 226 Physics Building, 835 West Dickson Street, Fayetteville, AR 72701 (United States)
7. Department of Astronomy, University of Washington, Seattle, WA 98195 (United States)
8. MIT Kavli Institute for Astrophysics and Space Research, 77 Massachusetts Avenue, Cambridge, MA 02139 (United States)
9. NASA Goddard Space Flight Center, Code 662, Greenbelt, MD 20771 (United States)
10. The Hakubi Center for Advanced Research, Kyoto University, Kyoto 606-8302 (Japan)
11. Department of Astronomy and Astrophysics, The Pennsylvania State University, 525 Davey Lab, University Park, PA 16802 (United States)
12. Department of Physics and Astronomy, University of Leicester, Leicester LE1 7RH (United Kingdom)
13. Steward Observatory, University of Arizona, 933 North Cherry Avenue, Tucson, AZ 85721 (United States)

We report the identification of a bright hard X-ray source dominating the M31 bulge above 25 keV from a simultaneous NuSTAR–Swift observation. We find that this source is the counterpart to Swift J0042.6+4112, which was previously detected in the Swift BAT All-sky Hard X-ray Survey. This Swift BAT source had been suggested to be the combined emission from a number of point sources; our new observations have identified a single X-ray source from 0.5 to 50 keV as the counterpart for the first time. In the 0.5–10 keV band, the source had been classified as an X-ray Binary candidate in various Chandra and XMM-Newton studies; however, since it was not clearly associated with Swift J0042.6+4112, the previous E < 10 keV observations did not generate much attention. This source has a spectrum with a soft X-ray excess (kT ∼ 0.2 keV) plus a hard spectrum with a power law of Γ∼1 and a cutoff around 15–20 keV, typical of the spectral characteristics of accreting pulsars. Unfortunately, any potential pulsation was undetected in the NuSTAR data, possibly due to insufficient photon statistics. The existing deep HST images exclude high-mass (>3 M{sub ⊙}) donors at the location of this source. The best interpretation for the nature of this source is an X-ray pulsar with an intermediate-mass (<3 M{sub ⊙}) companion or a symbiotic X-ray binary. We discuss other possibilities in more detail.

• OSTI ID: 22869188
• Journal Information: Astrophysical Journal, Vol. 838, Issue 1; Other Information: Country of input: International Atomic Energy Agency (IAEA); ISSN 0004-637X
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTROPHYSICS
COSMOLOGY AND ASTRONOMY
EMISSION
GALAXIES
HARD X RADIATION
KEV RANGE
MASS
NEUTRON STARS
POINT SOURCES
PULSARS
PULSATIONS
SOFT X RADIATION
SPECTRA
STATISTICS
X-RAY SOURCES