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

The (Re)appearance of NGC 925 ULX-3, a New Transient ULX
The (Re)appearance of NGC 925 ULX-3, a New Transient ULX
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 gsim26. 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 ${\rm{\Gamma }}={1.8}_{-0.1}^{+0.2}$, 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.
0004-637X
Earnshaw, Hannah P.
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Heida, Marianne
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Brightman, Murray
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Fürst, Felix
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Harrison, Fiona A.
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Jaodand, Amruta
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Middleton, Matthew
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Roberts, Timothy P.
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Sathyaprakash, Rajath
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Stern, Daniel
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Earnshaw, Hannah P.
11572d2c-fb3f-4e4f-a87e-023edaf2b2f9
Heida, Marianne
5def730d-b1c2-43e2-9d44-57689bb3a604
Brightman, Murray
f518c4bb-5948-4789-a9e8-644df0f31d72
Fürst, Felix
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Harrison, Fiona A.
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Jaodand, Amruta
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Middleton, Matthew
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Roberts, Timothy P.
c9042178-0c23-4150-a55a-a427edcef58e
Sathyaprakash, Rajath
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Stern, Daniel
706c0b8a-18b8-4c04-aa8c-75da94ffb3da

Earnshaw, Hannah P., Heida, Marianne, Brightman, Murray, Fürst, Felix, Harrison, Fiona A., Jaodand, Amruta, Middleton, Matthew, Roberts, Timothy P., Sathyaprakash, Rajath and Stern, Daniel (2020) The (Re)appearance of NGC 925 ULX-3, a New Transient ULX. Astrophysical Journal. (doi:10.3847/1538-4357/ab77b8/meta).

Record type: Article

Abstract

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 gsim26. 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 ${\rm{\Gamma }}={1.8}_{-0.1}^{+0.2}$, 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.

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The (Re)appearance of NGC 925 ULX-3, a New Transient ULX - Accepted Manuscript
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Accepted/In Press date: 17 February 2020
e-pub ahead of print date: 16 March 2020

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Local EPrints ID: 439704
URI: http://eprints.soton.ac.uk/id/eprint/439704
ISSN: 0004-637X
PURE UUID: 4b2681ec-65f8-4046-8b94-3af3ed66787e

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Date deposited: 30 Apr 2020 16:30
Last modified: 06 Oct 2020 20:19

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Contributors

Author: Hannah P. Earnshaw
Author: Marianne Heida
Author: Murray Brightman
Author: Felix Fürst
Author: Fiona A. Harrison
Author: Amruta Jaodand
Author: Timothy P. Roberts
Author: Rajath Sathyaprakash
Author: Daniel Stern

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