A bright, soft X-ray source was detected on 2010 July 14 during an XMM--Newton slew at a position consistent with the galaxy GSN 069 (z=0.018). Previous ROSAT observations failed to detect the source and imply that GSN 069 is now >240 times brighter
than it was in 1994 in the soft X-ray band. We report here results from a ~1 yr monitoring with Swift and XMM-Newton, as well as from optical spectroscopy. GSN 069 is an unabsorbed, ultra-soft source in X-rays, with no flux detected above ~1 keV. The soft X-rays exhibit significant variability down to timescales of hundreds of seconds. The UV-to-X-ray spectrum of GSN 069 is consistent with a pure accretion disc model which implies an Eddington ratio of ~0.5 and a black hole mass of ~ 1.2 million solar masses. A new optical spectrum, obtained ~3.5 months after the XMM-Newton slew detection, is consistent with earlier spectra and lacks any broad line component, classifying the source as a Seyfert 2 galaxy. The lack of cold X-ray absorption and the short timescale variability in the soft X-rays rule out a standard Seyfert 2 interpretation of the X-ray data. We discuss our results within the framework of two possible scenarios for the broad-line-region (BLR) in AGN, namely the two-phase model (cold BLR clouds in pressure equilibrium with a hotter medium), and models in which the BLR is part of an outflow, or disc-wind. Finally, we point out that GSN 069 may be a member of a population of super-soft AGN whose SED is completely dominated by accretion disc emission, as it is the case in some black hole X-ray binary transients during their outburst evolution. The disc emission for a typical AGN with larger black hole mass than GSN 069 does not enters the soft X-ray band, so that GSN 069-like objects would likely be missed by current X-ray surveys, or mis-classified as Compton-thick candidates. (ABRIDGED)
PHL 1092 is a z~0.4 high-luminosity counterpart of the class of Narrow-Line Seyfert 1 galaxies. In 2008, PHL 1092 was found to be in a remarkably low X-ray flux state during an XMM-Newton observation. Its 2 keV flux density had dropped by a factor of
~260 with respect to a previous observation performed 4.5 yr earlier. The UV flux remained almost constant, resulting in a significant steepening of the optical-to-X-ray slope alpha_ox from -1.57 to -2.51, making PHL 1092 one of the most extreme X-ray weak quasars with no observed broad absorption lines (BALs) in the UV. We have monitored the source since 2008 with three further XMM-Newton observations, producing a simultaneous UV and X-ray database spanning almost 10 yr in total in the activity of the source. Our monitoring program demonstrates that the alpha_ox variability in PHL 1092 is entirely driven by long-term X-ray flux changes. We apply a series of physically-motivated models with the goal of explaining the UV-to-X-ray spectral energy distribution (SED) and the extreme X-ray and alpha_ox variability. We consider three possible models: i) A breathing corona scenario in which the size of the X-ray emitting corona is correlated with the X-ray flux. In this case, the lowest X-ray flux states of PHL 1092 are associated with an almost complete collapse of the X-ray corona down to the marginal stable orbit; ii) An absorption scenario in which the X-ray flux variability is entirely due to intervening absorption. If so, PHL 1092 is a quasar with standard X-ray output for its optical luminosity, appearing as X-ray weak at times due to absorption; iii) A disc-reflection-dominated scenario in which the X-ray emitting corona is confined within a few gravitational radii from the black hole at all times. In this case, the intrinsic variability of PHL 1092 only needs to be a factor of ~10 rather than the observed factor of ~260.
We have observed with XMM-Newton four radiatively efficient active type 1 galaxies with black hole masses < 10^6 Msun, selected optically from the SDSS. We show here that their soft X-ray spectrum exhibits a soft excess with the same characteristics
as that observed ubiquitously in radio-quiet Seyfert 1 galaxies and type 1 quasars, both in terms of temperatures and strength. However, even when the soft X-ray excess is modelled with a pure thermal disc, its luminosity turns out to be much lower than that expected from accretion theory for the given temperature, casting further doubts on a thermal interpretation for soft excesses. While alternative scenarios for the nature of the soft excess (namely smeared ionized absorption and disc reflection) cannot be distinguished on a pure statistical basis, we point out that the absorption model produces a strong correlation between absorbing column density and ionization state, which may be difficult to interpret and is most likely spurious. As for reflection, it does only invoke standard ingredients of any accretion model for radiatively efficient sources such as a hard X-rays source and a relatively cold (though partially ionized) accretion disc, and therefore seems the natural choice to explain the soft excess in most (if not all) cases. The reflection model is also consistent with the additional presence of a thermal disc component with the theoretically expected temperature (although, again, with smaller-than-expected total luminosity). The observed active galaxies are among the most variable in X-rays and their excess variance is among the largest. This is in line with their relatively small black hole mass and with expectations from simple power spectra models. (abridged)
