Details

Autor(en) / Beteiligte

• Pintore, F.
• Marelli, M.
• Salvaterra, R.
• Israel, G. L.
• Castillo, G. A. Rodríguez
• Esposito, P.
• Belfiore, A.
• Luca, A. De
• Wolter, A.
• Mereghetti, S.
• Stella, L.
• Rigoselli, M.
• Earnshaw, H. P.
• Pinto, C.
• Roberts, T. P.
• Walton, D. J.
• Bernardini, F.
• Haberl, F.
• Salvaggio, C.
• Tiengo, A.
• Zampieri, L.
• Bachetti, M.
• Brightman, M.
• Casella, P.
• D'Agostino, D.
• Dall'Osso, S.
• Fürst, F.
• Harrison, F. A.
• Mapelli, M.
• Papitto, A.
• Middleton, M.

Titel

The Ultraluminous X-Ray Sources Population of the Galaxy NGC 7456

Ist Teil von

• The Astrophysical journal, 2020-02, Vol.890 (2), p.166

Ort / Verlag

Philadelphia: The American Astronomical Society

Erscheinungsjahr

2020

Quelle

EZB Electronic Journals Library

Beschreibungen/Notizen

• 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.