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Fausto Vagnetti, Astrofisica,
Dipartimento di Fisica, Universita` di Roma Tor Vergata
via della Ricerca Scientifica, I-00133 ROMA, Italy
room E014
http://www.fisica.uniroma2.it/~vagnetti/          .
phone +39 06 7259 4426                         ~\_/]
fax +39 06 2023507                       d_| d_| /|\
fausto.vagnetti (at) roma2.infn.it      \------------/
CURRENT RESEARCH TOPICS

Ensemble X-ray variability of AGNs
We study the ensemble variability properties of a rich AGN sample, the Multi-Epoch XMM Serendipitous AGN Sample (MEXSAS2), extracted from the 6th release of the XMM-Newton Serendipitous Source Catalogue, and comprising over 3000 quasars with information from the SDSS quasar catalogues DR7Q and DR12Q.
  •     Excess Variance and Structure Function. MEXSAS2 updates our previous catalogue MEXSAS (Vagnetti et al 2016), which we used to discuss on the use of the normalised excess variance, showing that it may lead to underestimate variability if used improperly, and proposed a correction taking account of the light-curve duration in the rest-frame (Middei et al 2016). We update our previous analysis of the structure function (Vagnetti et al 2011), finding an ensemble increase of the X-ray variability with the rest-frame time lag tau, as tau^0.12. We confirm an inverse dependence on the X-ray luminosity, approximately as L_X^-0.19. An analysis at longer time scales is then performed combining ROSAT and XMM-Newton observations, indicating an increase of the structure function up to 20 years (Middei et al 2017).
  •     Spectral variability. We analyse the spectral variations finding a softer when brighter trend which we quantify in terms of the spectral variability parameter beta, defined as the ratio between the change in the photon index Gamma and the corresponding logarithmic flux variation (Serafinelli et al 2016 2017).We estimate an ensemble value beta ~ -0.69 for the MEXSAS sample, and individual values for a few well correlated sources ranging between -0.8 and -3.5. A detailed analysis of the spectral variations for a small list of sources is in progress, including the treatment of complex emission and absorption features.
  •     Variability of the X-ray/optical ratio. We combine the MEXSAS2 sample with the latest release of the XMM-Newton serendipitous OM catalogue (SUSS3), to study the X-ray/Optical ratio, updating our previous analyses (Vagnetti et al 2010, 2013), where we found that variability accounts for ~30% of the scatter around the average alpha_ox-L_UV relation, while the remaining is due to intrinsic differences in the average alpha_ox values from source to source, or "inter-source dispersion. In the new analysis (Chiaraluce et al 2018), we find a higher variability contribution, ~56% of the total variance, due to the increased amount of alpha_ox variability at longer time lags, while the residual dispersion is attributed to dependence on physical and observational parameters, such as black hole mass, Edddington ratio, orientation.
X-ray spectral analysis of outflows in active galactic nuclei
We analyse (Serafinelli et al submitted) 12 XMM-Newton serendipitous observations of the quasar PG1114+445, extracted from the MEXSAS catalogue, finding evidence of outflowing absorbers of various kinds, a warm absorber (WA), an ultra-fast highly ionized outflow (UFO), and a less ionized fast outflow which we interpret as an entrained UFO (E-UFO). We present the novel emission model WINE, for the analysis of the ultra fast outflow in the quasar PDS 456 (Luminari et al 2018). We extract and analyse the two brightest AGNs serendipitously observed from NuSTAR, the quite typical Seyfert Galaxy HE 0436-4717 (Middei et al 2018) and the Narrow Line Seyfert 1 galaxy 1E 0754.6+3928, which shows evidence of an outflowing absorber (Middei et al in preparation).