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Discovery of a red supergiant counterpart to RX J004722.4–252051, a ULX in NGC 253

Heida, M. and Torres, M. A. P. and Jonker, P. G. and Servillat, M. and Repetto, S. and Roberts, T. P. and Walton, D. J. and Moon, D.-S. and Harrison, F. A. (2015) Discovery of a red supergiant counterpart to RX J004722.4–252051, a ULX in NGC 253. Monthly Notices of the Royal Astronomical Society, 453 (4). pp. 3510-3518. ISSN 0035-8711. doi:10.1093/mnras/stv1853.

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We present two epochs of near-infrared spectroscopy of the candidate red supergiant counterpart to RX J004722.4–252051, a ULX in NGC 253. We measure radial velocities of the object and its approximate spectral type by cross-correlating our spectra with those of known red supergiants. Our VLT/X-shooter spectrum is best matched by that of early M-type supergiants, confirming the red supergiant nature of the candidate counterpart. The radial velocity of the spectrum, taken on 2014 August 23, is 417 ± 4 km s^(−1). This is consistent with the radial velocity measured in our spectrum taken with Magellan/MMIRS on 2013 June 28, of 410 ± 70 km s^(−1), although the large error on the latter implies that a radial velocity shift expected for a black hole of tens of M⊙ can easily be hidden. Using nebular emission lines we find that the radial velocity due to the rotation of NGC 253 is 351 ± 4 km s^(−1) at the position of the ULX. Thus the radial velocity of the counterpart confirms that the source is located in NGC 253, but also shows an offset with respect to the local bulk motion of the galaxy of 66 ± 6 km s^(−1). We argue that the most likely origin for this displacement lies either in a SN kick, requiring a system containing a ≳ 50 M_⊙ black hole, and/or in orbital radial velocity variations in the ULX binary system, requiring a ≳ 100 M_⊙ black hole. We therefore conclude that RX J004722.4–252051 is a strong candidate for a ULX containing a massive stellar black hole.

Item Type:Article
Related URLs:
URLURL TypeDescription Paper
Heida, M.0000-0002-1082-7496
Jonker, P. G.0000-0001-5679-0695
Servillat, M.0000-0001-5443-4128
Repetto, S.0000-0001-5029-0059
Roberts, T. P.0000-0001-8252-6337
Walton, D. J.0000-0001-5819-3552
Moon, D.-S.0000-0003-4200-5064
Harrison, F. A.0000-0003-2992-8024
Additional Information:© 2015 The Authors. Published by Oxford University Press on behalf of the Royal Astronomical Society. Accepted 2015 August 8. Received 2015 July 10; in original form 2015 April 20. Observations based on ESO programme 093.D-0256. We thank the anonymous referee for their comments that helped improve the paper. We want to thank Ben Davies for sharing his X-shooter RSG spectra and Tom Marsh for developing MOLLY. This paper uses data products produced by the OIR Telescope Data Center, supported by the Smithsonian Astrophysical Observatory. Based on observations made with ESO Telescopes at the La Silla Paranal Observatory under programme ID 093.D-0256. TPR's contributions were funded as part of the STFC consolidated grant award ST/L00075X/1.
Group:Space Radiation Laboratory
Funding AgencyGrant Number
European Southern Observatory (ESO)093.D-0256
Smithsonian Astrophysical ObservatoryUNSPECIFIED
Science and Technology Facilities Council (STFC)ST/L00075X/1
Subject Keywords:supergiants – infrared: stars – X-rays: binaries – X-rays: individual: RX J004722.4-252051
Other Numbering System:
Other Numbering System NameOther Numbering System ID
Space Radiation Laboratory2015-24
Issue or Number:4
Record Number:CaltechAUTHORS:20151119-140541346
Persistent URL:
Official Citation:M. Heida, M. A. P. Torres, P. G. Jonker, M. Servillat, S. Repetto, T. P. Roberts, D. J. Walton, D.-S. Moon, and F. A. Harrison Discovery of a red supergiant counterpart to RX J004722.4–252051, a ULX in NGC 253 MNRAS (November 11, 2015) Vol. 453 3510-3518 doi:10.1093/mnras/stv1853 First published online September 9, 2015
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:62259
Deposited By: George Porter
Deposited On:19 Nov 2015 23:17
Last Modified:10 Nov 2021 23:00

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