A Caltech Library Service

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

Yukita, M. and Ptak, A. and Hornschemeier, A. E. and Wik, D. and Maccarone, T. J. and Pottschmidt, K. and Zezas, A. and Antoniou, V. and Ballhausen, R. and Lehmer, B. D. and Lien, A. and Williams, B. and Baganoff, F. and Boyd, P. T. and Enoto, T. and Kennea, J. and Page, K. L. and Choi, Y. (2017) Identification of the Hard X-ray Source Dominating the E > 25 keV Emission of the Nearby Galaxy M31. Astrophysical Journal, 838 (1). Art. No. 47. ISSN 1538-4357. doi:10.3847/1538-4357/aa62a3.

[img] PDF - Accepted Version
See Usage Policy.


Use this Persistent URL to link to this item:


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 SwiftBAT 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 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⊙) 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⊙) companion or a symbiotic X-ray binary. We discuss other possibilities in more detail.

Item Type:Article
Related URLs:
URLURL TypeDescription Paper
Yukita, M.0000-0001-6366-3459
Ptak, A.0000-0001-5655-1440
Hornschemeier, A. E.0000-0001-8667-2681
Wik, D.0000-0001-8952-676X
Maccarone, T. J.0000-0003-0976-4755
Pottschmidt, K.0000-0002-4656-6881
Zezas, A.0000-0001-8952-676X
Antoniou, V.0000-0001-7539-1593
Lehmer, B. D.0000-0003-2192-3296
Williams, B.0000-0002-7502-0597
Boyd, P. T.0000-0003-0442-4284
Enoto, T.0000-0003-1244-3100
Kennea, J.0000-0002-6745-4790
Page, K. L.0000-0001-5624-2613
Additional Information:© 2017 The American Astronomical Society. Received 2016 September 16; revised 2017 February 17; accepted 2017 February 21; published 2017 March 22. We would like to thank the referee for his/her comments, which improved our manuscript. We sincerely thank Neil Gehrels for approving the Swift DDT observations used in this work. We also thank NuSTAR and Swift mission planners for making the Swift and NuSTAR observations simultaneous. 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 (Caltech, USA). This work was supported by NuSTAR GO NNX15AV30G. We are grateful to Antara Basu-Zych, Hans Krimm, Craig Markwardt, Ryan Hickox, Dheeraj Pasham, Koji Mukai, Lennart van Haaften, and Panayiotis Tzanavaris for helpful discussions. K.L.P. acknowledges funding from the UK Space Agency. R.B. acknowledges funding from the Deutsches Zentrum für Luft- und Raumfahrt grant 50 OR 1410. Facilities: NuSTAR - The NuSTAR (Nuclear Spectroscopic Telescope Array) mission, Swift.
Subject Keywords:galaxies: bulges – galaxies: individual (M31) – pulsars: general – stars: neutron – X-rays: binaries
Issue or Number:1
Record Number:CaltechAUTHORS:20170327-085423420
Persistent URL:
Official Citation:M. Yukita et al 2017 ApJ 838 47
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:75402
Deposited By: Joy Painter
Deposited On:27 Mar 2017 16:09
Last Modified:15 Nov 2021 16:33

Repository Staff Only: item control page