THE XMM-NEWTON LONG LOOK OF NGC 1365: LACK OF A HIGH/SOFT STATE IN ITS ULTRALUMINOUS X-RAY SOURCES

Based on our long (similar to 300 ks) 2007 XMM-Newton observation of the Seyfert galaxy NGC 1365, we report here on the spectral and timing behavior of two ultraluminous X-ray sources (ULXs), which had previously reached isotropic X-ray luminosities L-X approximate to 4 x 10(40) erg s(-1) (0.3- 10 keV band). In 2007, they were in a lower state ( L-X approximate to 5 x 10(39) and 1.5 x 10(39) erg s(-1) for X1 and X2, respectively). Their X-ray spectra were dominated by power laws with photon indices Gamma approximate to 1.8 and 1.2, respectively. Thus, their spectra were similar to those at their outburst peaks. Both sources have been seen to vary by a factor of 20 in luminosity over the years, but their spectra are always dominated by a hard power law; unlike most stellar-mass black holes, they have never been found in a canonical high/soft state dominated by a standard disk. The lack of a canonical high/soft state seems to be a common feature of ULXs. We speculate that the different kind of donor star and/or a persistently super-Eddington accretion rate during their outbursts may prevent accretion flows in ULXs from settling into steady standard disks.