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تسجيل مستخدم جديدA new candidate pulsating ULX in NGC 7793
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Erwan Quintin
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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 textit{XMM-Newton} and the textit{Swift} X-ray telescope. The outburst reached a peak luminosity of 3.4$times 10^{39}$ erg s$^{-1}$ and lasted for about 8 months, after which the source went below a luminosity of $10^{37}$ erg s$^{-1}$; previous textit{Chandra} observations constrain the low-state luminosity below $sim$ 2$times 10^{36}$ 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 textit{XMM-Newton} signal was found at 2.52 Hz, with a significance of $sim3.4,sigma$, and an associated spin-up of $dot{f} = 3.5times10^{-8}$ Hz.s$^{-1}$. NGC 7793 is therefore the first galaxy to host more than one pulsating ULX.
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