A transient ultraluminous X-ray source in NGC 55
| Autor: | A Robba, C Pinto, F Pintore, G Rodriguez, E Ambrosi, F Barra, G Cusumano, A D’Aì, M Del Santo, P Kosec, A Marino, M Middleton, T Roberts, C Salvaggio, R Soria, A Wolter, D Walton |
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| Přispěvatelé: | A Robba, C Pinto, F Pintore, G Rodriguez, E Ambrosi, F Barra, G Cusumano, A D???A??, M Del Santo, P Kosec, A Marino, M Middleton, T Robert, C Salvaggio, R Soria, A Wolter, D Walton |
| Jazyk: | angličtina |
| Rok vydání: | 2022 |
| Předmět: |
High Energy Astrophysical Phenomena (astro-ph.HE)
Settore FIS/05 - Astronomia E Astrofisica accretion Space and Planetary Science accretion disc FOS: Physical sciences Astronomy and Astrophysics Astrophysics - High Energy Astrophysical Phenomena X-rays: binarie X-rays: individual: XMMU J001446.81-391123.48 |
| Zdroj: | Monthly Notices of the Royal Astronomical Society, 2022, Vol.515(4), pp.4669-4674 [Peer Reviewed Journal] |
| Popis: | Ultraluminous X-ray sources (ULXs) are a class of accreting compact objects with X-ray luminosities above 10$^{39}$ erg s$^{-1}$. The average number of ULXs per galaxy is still not well constrained, especially given the uncertainty on the fraction of ULX transients. Here, we report the identification of a new transient ULX in the galaxy NGC 55 (which we label as ULX-2), thanks to recent XMM-Newton and the Neil Gehrels Swift Observatory observations. This object was previously classified as a transient X-ray source with a luminosity around a few 10$^{38}$ erg s$^{-1}$ in a 2010 XMM-Newton observation. Thanks to new and deeper observations ($\sim$ 130 ks each), we show that the source reaches a luminosity peak $>1.6 \times 10^{39}$ erg s$^{-1}$. The X-ray spectrum of ULX-2 is much softer than in previous observations and fits in the class of soft ULXs. It can be well described using a model with two thermal components, as often found in ULXs. The time scales of the X-ray variability are of the order of a month and are likely driven by small changes in the accretion rate or due to super-orbital modulations, attributed to precession of the accretion disc, which is similar to other ULXs. 6 pages, including 4 figures and 2 tables, accepted for pubblication in MNRAS |
| Databáze: | OpenAIRE |
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