XMM–Newton observations of ultraluminous X–ray sources in nearby galaxies

Authors :: Foschini, L.
Di Cocco, G.
Ho, L. C.
Bassani, L.
Cappi, M.
Dadina, M.
Gianotti, F.
Malaguti, G.
Panessa, F.
Piconcelli, E.
Stephen, J. B.
Trifoglio, M.
Foschini, L.
Di Cocco, G.
Ho, L. C.
Bassani, L.
Cappi, M.
Dadina, M.
Gianotti, F.
Malaguti, G.
Panessa, F.
Piconcelli, E.
Stephen, J. B.
Trifoglio, M.
Source :: Astronomy and Astrophysics; September 2002, Vol. 392 Issue: 3 p817-825, 9p
Publication Year :: 2002
Abstract: An XMM–Newtonstudy of ultraluminous X–ray sources (ULX) has been performed in a sample of 10 nearby Seyfert galaxies. Eighteen ULX have been found with positional uncertainty of about $4''$. The large collecting area of XMM–Newtonmakes the statistics sufficient to perform spectral fitting with simple models in 8 cases. The main results of the present minisurvey strengthen the theory that the ULX could be accreting black holes in hard or soft state. In some cases, the contribution of the ULX to the overall X–ray flux appears to be dominant with respect to that of the active nucleus. In addition, 6 ULX present probable counterparts at other wavelengths (optical/infrared, radio). A multiwavelength observing strategy is required to better assess the nature of these sources.