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On the magnetic field in M51 ULX-8

Middleton, M. J. and Brightman, M. and Pintore, F. and Bachetti, M. and Fabian, A. C. and Fürst, F. and Walton, D. J. (2019) On the magnetic field in M51 ULX-8. Monthly Notices of the Royal Astronomical Society, 486 (1). pp. 2-9. ISSN 0035-8711. doi:10.1093/mnras/stz436.

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The reported discovery of a cyclotron resonance scattering feature (CRSF) in the spectrum of M51 ULX-8 may provide an important clue as to the nature of the magnetic field in those ultraluminous X-ray sources hosting neutron stars. In this paper, we present the covariance (linearly correlated variability) spectrum of M51 ULX-8 on long (>2000 s) time-scales. This allows us to unambiguously decompose the spectrum which requires multiple components in order to explain the broadband emission. Having a clearer picture of the spectral decomposition leads to various tests for the dipole field strength of the neutron star which can be extended to other ULXs when certain criteria are met. In the case of M51 ULX-8, we rule out a very strong (10^(15) G) dipole solution with either a sub- or supercritical disc. Instead, our tests indicate an upper limit on the dipole field of 10^(12) G and a classical supercritical inflow, similar to that inferred in other ULXs found to harbour neutron stars, although we do not rule out the presence of an additional, strong (10^(15) G) multipole field falling off steeply with distance from the neutron star.

Item Type:Article
Related URLs:
URLURL TypeDescription Paper
Middleton, M. J.0000-0002-8183-2970
Brightman, M.0000-0002-8147-2602
Bachetti, M.0000-0002-4576-9337
Fabian, A. C.0000-0002-9378-4072
Fürst, F.0000-0003-0388-0560
Walton, D. J.0000-0001-5819-3552
Additional Information:© 2019 The Author(s) Published by Oxford University Press on behalf of the Royal Astronomical Society. This article is published and distributed under the terms of the Oxford University Press, Standard Journals Publication Model ( Accepted 2019 February 7. Received 2019 February 7; in original form 2018 June 13. Published: 19 February 2019. The authors thank the anonymous referee. MJM and DJW appreciate support from Ernest Rutherford STFC fellowships.
Group:Space Radiation Laboratory
Funding AgencyGrant Number
Science and Technology Facilities Council (STFC)UNSPECIFIED
Subject Keywords:accretion, accretion discs –X-rays: binaries
Issue or Number:1
Record Number:CaltechAUTHORS:20190222-103643130
Persistent URL:
Official Citation:M J Middleton, M Brightman, F Pintore, M Bachetti, A C Fabian, F Fürst, D J Walton, On the magnetic field in M51 ULX-8, Monthly Notices of the Royal Astronomical Society, Volume 486, Issue 1, June 2019, Pages 2–9,
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:93184
Deposited By: Tony Diaz
Deposited On:25 Feb 2019 16:54
Last Modified:16 Nov 2021 16:56

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