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|Title:||The Ultraluminous X-Ray Sources Population of the Galaxy NGC 7456||Authors:||Pintore, Fabio
ISRAEL, Gian Luca
Castillo, G. A. Rodríguez
Luca, A. De
WOLTER, Anna Luisa Maria
Earnshaw, H. P.
Roberts, T. P.
Walton, D. J.
Harrison, F. A.
|Issue Date:||2020||Journal:||THE ASTROPHYSICAL JOURNAL||Number:||890||Issue:||2||First Page:||166||Abstract:||Ultraluminous X-ray sources (ULXs) are a class of accreting compact objects with X-ray luminosities above 1039 erg s-1. The ULX population counts several hundred objects but only a fraction are well studied. Here we present a detailed analysis of all ULXs hosted in the galaxy NGC 7456. It was observed in X-rays only once in the past (in 2005) by XMM-Newton. but the observation was short and strongly affected by high background. In 2018, we obtained a new, deeper (∼90 ks) XMM-Newton observation that allowed us to perform a detailed characterization of the ULXs hosted in the galaxy. ULX-1 and ULX-2, the two brightest objects (LX ∼ 6-10 × 1039 erg s-1), have spectra that can be described by a model with two thermal components, as often found in ULXs. ULX-1 also shows one order of magnitude in flux variability on short-term timescales (hundreds to thousands of kiloseconds). The other sources (ULX-3 and ULX-4) show flux changes of at least an order of magnitude, and these objects may be candidate transient ULXs, although longer X-ray monitoring or further studies are required to ascribe them to the ULX population. In addition, we found a previously undetected source that might be a new candidate ULX (labeled as ULX-5), with a luminosity of ∼1039 erg s-1 and hard power-law spectral shape, whose nature is still unclear and for which a background active galactic nucleus cannot be excluded. We discuss the properties of all the ULXs in NGC 7456 within the framework of super-Eddington accretion onto stellar-mass compact objects. Although no pulsations were detected, we cannot exclude that the sources host neutron stars.||URI:||http://hdl.handle.net/20.500.12386/29951||URL:||https://iopscience.iop.org/article/10.3847/1538-4357/ab6ffd||ISSN:||0004-637X||DOI:||10.3847/1538-4357/ab6ffd||Bibcode ADS:||2020ApJ...890..166P||Fulltext:||open|
|Appears in Collections:||1.01 Articoli in rivista|
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