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The (Re)appearance of NGC 925 ULX-3, a New Transient ULX

Earnshaw, Hannah P. and Heida, Marianne and Brightman, Murray and Fürst, Felix and Harrison, Fiona A. and Jaodand, Amruta and Middleton, Matthew J. and Roberts, Timothy P. and Sathyaprakash, Rajath and Stern, Daniel and Walton, Dominic J. (2020) The (Re)appearance of NGC 925 ULX-3, a New Transient ULX. Astrophysical Journal, 891 (2). Art. No. 153. ISSN 1538-4357. doi:10.3847/1538-4357/ab77b8.

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We report the discovery of a third ULX in NGC 925 (ULX-3), detected in 2017 November by Chandra at a luminosity of L_X = (7.8 ± 0.8) × 10³⁹ erg s⁻¹. Examination of archival data for NGC 925 reveals that ULX-3 was detected by Swift at a similarly high luminosity in 2011, as well as by XMM-Newton in 2017 January at a much lower luminosity of L_X = (3.8 ± 0.5) × 10³⁸ erg s⁻¹. With an additional Chandra nondetection in 2005, this object demonstrates a high dynamic range of flux of factor ≳26. In its high-luminosity detections, ULX-3 exhibits a hard power-law spectrum with Γ = 1.6 ± 0.1, whereas the XMM-Newton detection is slightly softer, with Γ = 1.8_(-0.1)^(+0.2), and is also well-fitted with a broadened disk model. The long-term light curve is sparsely covered and could be consistent either with the propeller effect or with a large-amplitude superorbital period, both of which are seen in ULXs, in particular those with neutron star accretors. Further systematic monitoring of ULX-3 will allow us to determine the mechanism by which ULX-3 undergoes its extreme variability and to better understand the accretion processes of ULXs.

Item Type:Article
Related URLs:
URLURL TypeDescription Paper
Earnshaw, Hannah P.0000-0001-5857-5622
Heida, Marianne0000-0002-1082-7496
Brightman, Murray0000-0002-8147-2602
Fürst, Felix0000-0003-0388-0560
Harrison, Fiona A.0000-0003-2992-8024
Jaodand, Amruta0000-0002-3850-6651
Middleton, Matthew J.0000-0002-8183-2970
Roberts, Timothy P.0000-0001-8252-6337
Sathyaprakash, Rajath0000-0002-5254-3969
Stern, Daniel0000-0003-2686-9241
Walton, Dominic J.0000-0001-5819-3552
Additional Information:© 2020. The American Astronomical Society. Received 2019 November 20; revised 2020 January 31; accepted 2020 February 17; published 2020 March 16. We thank our anonymous referee for useful comments on this paper. This work was supported under NASA contract NNG08FD60C. D.J.W. and M.J.M. acknowledge support from STFC in the form of Ernest Rutherford Fellowships. T.P.R. was funded as part of the STFC consolidated grant ST/K000861/1, and R.S. was funded by STFC studentship grant ST/N50404X/1. The scientific results reported in this article are based on observations made by the Chandra X-ray Observatory, as well as archival observations by XMM-Newton, an ESA science mission with instruments and contributions directly funded by ESA Member States and NASA, archival observations by the NuSTAR mission, a project led by the California Institute of Technology, managed by JPL, and funded by NASA, and observations from the Swift data archive. Facilities: XMM - Newton X-Ray Multimirror Mission satellite, CXO - , Swift(XRT) - , NuSTAR. - Software: astropy (Astropy Collaboration et al. 2013), CIAO (Fruscione et al. 2006), FTOOLS (Nasa High Energy Astrophysics Science Archive Research Center (Heasarc), 2014), XMM-Newton SAS.
Group:Space Radiation Laboratory, NuSTAR, Astronomy Department
Funding AgencyGrant Number
Science and Technology Facilities Council (STFC)ST/K000861/1
Science and Technology Facilities Council (STFC)ST/N50404X/1
Subject Keywords:Accretion ; Neutron stars ; X-ray binary stars ; Light curves ; Black holes ; X-ray transient sources
Issue or Number:2
Classification Code:Unified Astronomy Thesaurus concepts: Accretion (14); Neutron stars (1108); X-ray binary stars (1811); Light curves (918); Black holes (162); X-ray transient sources (1852)
Record Number:CaltechAUTHORS:20200316-150528314
Persistent URL:
Official Citation:Hannah P. Earnshaw et al 2020 ApJ 891 153
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:101925
Deposited By: George Porter
Deposited On:17 Mar 2020 15:07
Last Modified:16 Nov 2021 18:07

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