A new candidate pulsating ULX in NGC 7793. Issue 4 (22nd March 2021)

• Record Type: Journal Article
• Authors: Quintin, E; Webb, N A; Gúrpide, A; Bachetti, M; Fürst, F
• Is Part Of: Monthly notices of the Royal Astronomical Society. Volume 503:Issue 4(2021)
• Page Start: 5485
• Page End: 5494
• Publication Date: 2021-03-22
• Subjects: accretion, accretion discs -- stars: neutron -- X-rays: binaries; Astronomy -- Periodicals; Periodicals; 520.5
• DOI: 10.1093/mnras/stab814
• Languages: English
• ISSNs: 0035-8711

Abstract

ABSTRACT: We report here the discovery of NGC 7793 ULX-4, a new transient ultraluminous X-ray source (ULX) in NGC 7793, a spiral galaxy already well known for harbouring several ULXs. This new source underwent an outburst in 2012, when it was detected by XMM–Newton and the Swift X-ray telescope. The outburst reached a peak luminosity of 3.4 × 10 39 erg s −1 and lasted for about eight months, after which the source went below a luminosity of 10 37 erg s −1 ; previous Chandra observations constrain the low-state luminosity below ∼2 × 10 36 erg s −1, implying a variability of at least a factor 1000. We propose four possible optical counterparts, found in archival HST observations of the galaxy. A pulsation in the XMM–Newton signal was found at 2.52 Hz, with a significance of $\sim 3.4\, \sigma$, and an associated spin-up of $\dot{f} = 3.5\times 10^{-8}$ Hz s −1 . NGC 7793 is therefore the first galaxy to host more than one pulsating ULX.