Identification of the Hard X-Ray Source Dominating the E > 25 keV Emission of the Nearby Galaxy M31
Hornschemeier, A. E.
Maccarone, T. J.
Lehmer, B. D.
Boyd, P. T.
Page, K. L.
AffiliationUniv Arizona, Steward Observ
MetadataShow full item record
PublisherIOP PUBLISHING LTD
CitationIdentification of the Hard X-Ray Source Dominating the E > 25 keV Emission of the Nearby Galaxy M31 2017, 838 (1):47 The Astrophysical Journal
JournalThe Astrophysical Journal
Rights© 2017. The American Astronomical Society. All rights reserved.
Collection InformationThis item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at firstname.lastname@example.org.
AbstractWe 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 similar to 0.2 keV) plus a hard spectrum with a power law of Gamma similar to 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-circle dot) 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-circle dot) companion or a symbiotic X-ray binary. We discuss other possibilities in more detail.
VersionFinal published version
SponsorsNuSTAR GO [NNX15AV30G]; UK Space Agency; Deutsches Zentrum fur Luft- und Raumfahrt [50 OR 1410]