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A new transient ultraluminous X-ray source in NGC 7090

Walton, DJ; Heida, M; Bachetti, M; Fürst, F; Brightman, M; Earnshaw, H; Evans, PA; Fabian, AC; Grefenstette, BW; Harrison, FA; Israel, GL; Lansbury, GB; Middleton, MJ; Pike, S; Rana, V; Roberts, TP; Rodriguez Castillo, GA; Salvaterra, R; Song, X; Stern, D

A new transient ultraluminous X-ray source in NGC 7090 Thumbnail


DJ Walton

M Heida

M Bachetti

F Fürst

M Brightman

H Earnshaw

PA Evans

AC Fabian

BW Grefenstette

FA Harrison

GL Israel

GB Lansbury

MJ Middleton

S Pike

V Rana

GA Rodriguez Castillo

R Salvaterra

X Song

D Stern


We report on the discovery of a new, transient ultraluminous X-ray source (ULX) in the galaxy NGC 7090. This new ULX, which we refer to as NGC 7090 ULX3, was discovered via monitoring with Swift during 2019–2020, and to date has exhibited a peak luminosity of LX ∼ 6 × 1039 erg s−1. Archival searches show that, prior to its recent transition into the ULX regime, ULX3 appeared to exhibit a fairly stable luminosity of LX ∼ 1038 erg s−1. Such strong long-time-scale variability may be reminiscent of the small population of known ULX pulsars, although deep follow-up observations with XMM–Newton and NuSTAR do not reveal any robust X-ray pulsation signals. Pulsations similar to those seen from known ULX pulsars cannot be completely excluded, however, as the limit on the pulsed fraction of any signal that remains undetected in these data is ≲20 per cent. The broad-band spectrum from these observations is well modelled with a simple thin disc model, consistent with sub-Eddington accretion, which may instead imply a moderately large black hole accretor (MBH ∼ 40 M⊙). Similarly, though, more complex models consistent with the super-Eddington spectra seen in other ULXs (and the known ULX pulsars) cannot be excluded given the limited signal-to-noise ratio of the available broad-band data. The nature of the accretor powering this new ULX therefore remains uncertain.


Walton, D., Heida, M., Bachetti, M., Fürst, F., Brightman, M., Earnshaw, H., …Stern, D. (2021). A new transient ultraluminous X-ray source in NGC 7090. Monthly Notices of the Royal Astronomical Society, 501(1), 1002-1012.

Journal Article Type Article
Acceptance Date Nov 18, 2020
Online Publication Date Nov 25, 2020
Publication Date 2021-02
Deposit Date Jul 1, 2021
Publicly Available Date Jul 1, 2021
Journal Monthly Notices of the Royal Astronomical Society
Print ISSN 0035-8711
Electronic ISSN 1365-2966
Publisher Royal Astronomical Society
Peer Reviewed Peer Reviewed
Volume 501
Issue 1
Pages 1002-1012


Published Journal Article (1.4 Mb)

Copyright Statement
This article has been accepted for publication in Monthly Notices of the Royal Astronomical Society ©: 2020, The Authors. Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved.

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