L. Ballo

X-ray spectral variability in PG 1535+547: the changing look of a "soft X-ray weak" AGN

Context. PG 1535+547 is a bright Narrow Line Seyfert 1 galaxy, whose high-energy emission shows strong variability both in shape and flux. On the basis of ROSAT observations, it is classified as “soft X-ray weak quasi-stellar object (QSO)”, a class of objects whose X-ray-to-optical flux ratio is smaller than in typical QSOs. Their X-ray spectra are often characterized by highly-ionized, complex absorbers and/or reflection from the inner accretion disk, and the relative importance of the two is currently debated. Whatever the correct interpretation may be, the presence of such features implies that we are looking at matter located in the innermost regions of these AGN. Aims. We want to clarify the nature of the X-ray emission of PG 1535+547, and constrain the physical properties of its innermost regions, where this emission originates. Methods. We present new XMM-Newton observations of PG 1535+547 (90 ks exposure time, January 2006), from which we obtained two spectra European Photon Imaging Camera (EPIC) separated by about one week. We compare these spectra with those from a previous (November 2002) XMM-Newton observation. Results. These latest observations support the complex and variable nature of the X-ray emission of PG 1535+547. The broadband observed flux increases by a factor ∼2.3 in three years, and then decreases by a factor ∼1.3 in about one week. In the new spectra, strong absorption features at E < 3 keV and a complex spectral shape in the iron-line energy range are evident, coupled with a drop in the emission at higher energies. We describe all the different states in a consistent way, assuming either a warm absorber plus a relativistically-blurred ionized reflection, or a two-phase warm absorber partially covering the source with the addition of a scattered component. Conclusions. The observed variability can be ascribed mostly to warm absorbing gas in the innermost regions of PG 1535+547, which appears to vary in its physical properties on timescales of both years and days. In the blurred reflection scenario, all the analyzed states require a high fraction of reflection from the disk, calling for some mechanisms able to increase the reflection component with respect to the intrinsic continuum. Finally, the strong variability observed in the X-ray band opposed to a more constant emission at optical frequencies, changes the value of the X-ray-to-optical spectral index, implying that PG 1535+547 can not actually be classified as a soft X-ray weak active galactic nucleus (AGN).

X-RAY ABSORPTION, NUCLEAR INFRARED EMISSION, AND DUST COVERING FACTORS OF AGNs: TESTING UNIFICATION SCHEMES

We present the distributions of the geometrical covering factors of the dusty tori (f2) of active galactic nuclei (AGNs) using an X-ray selected complete sample of 227 AGNs drawn from the Bright Ultra-hard XMM-Newton Survey. The AGNs have z from 0.05 to 1.7, 2–10 keV luminosities between 10 42 and 10 46 erg s −1 , and Comptonthin X-ray absorption. Employing data from UKIDSS, 2MASS, and the Wide-field Infrared Survey Explorer in a previous work, we determined the rest-frame 1–20 μm continuum emission from the torus, which we model here with the clumpy torus models of Nenkova et al. Optically classified type 1 and type 2 AGNs are intrinsically different, with type 2 AGNs having, on average, tori with higher f2 than type 1 AGNs. Nevertheless, ∼20% of type 1 AGNs have tori with large covering factors, while ∼23%–28% of type 2 AGNs have tori with small covering factors. Low f2 are preferred at high AGN luminosities, as postulated by simple receding torus models, although for type 2 AGNs the effect is certainly small. f2 increases with the X-ray column density, which implies that dust extinction and X-ray absorption take place in material that share an overall geometry and most likely belong to the same structure, the putative torus. Based on our results, the viewing angle, AGN luminosity, and also f2 determine the optical appearance of an AGN and control the shape of the rest-frame ∼1–20 μm nuclear continuum emission. Thus, the torus geometrical covering factor is a key ingredient of unification schemes.

XMM-Newton observation of the deep minimum state of PG 2112+059 A spectrum dominated by reflection from the accretion disk?

Context. Highly ionised absorbers and the frequent occurrence of relativistically broad iron fluorescence lines characterize the 0.2-10 keV spectra of (soft) X-ray weak quasars. Aims. We constrain the physical conditions of the absorber and the broad iron line of the X-ray weak quasar PG 2112+059 in greater detail than in previous studies. Methods. We analyse a 75 ks XMM-Newton observation of PG 2112+059 performed in November 2005 and compare it with a 15 ks XMM-Newton observation taken in May 2003. Results. PG 2112+059 was found in a deep minimum state as its 0.2-12 keV flux decreased by a factor of 10 in comparison to the May 2003 observation. During the deep minimum state the spectra show strong emission in excess of the continuum in the 3-6 keV region. The excess emission corresponds to an

X-ray observation of ULAS J1120+0641, the most distant quasar at z = 7.08

{EW} = 26.1~\rm{keV}

An Enshrouded Active Galactic Nucleus in the Merging Starburst System Arp 299 Revealed by [CLC][ITAL]BeppoSAX[/ITAL][/CLC]

whereas its shape resembles that of heavily absorbed objects. 
The spectra of both observations of PG 2112+059 can be explained statistically by a combination of two absorbers where one shows a high column density,

A Focused, Hard X-Ray Look at Arp 299 with NuSTAR

N_{\rm H} \rm \sim 4.5 \times 10^{23}~cm^{-2}

Absorption at the dust sublimation radius and the dichotomy between X-ray and optical classification in the Seyfert galaxy H0557-385

, and the other high ionisation parameters. As the ionisation parameter of the high flux state,

The XMM–Newton Bright Survey sample of absorbed quasars: X-ray and accretion properties

\rm \xi \sim 34~erg\,cm\,s^{-1}

Exploring the active galactic nuclei population with extreme X-ray-to-optical flux ratios (fx/fo > 50)

, is lower than the value found for the deep minimum state,

Proving strong magnetic fields near to the central black hole in the quasar PG0043+039 via cyclotron lines

\rm \xi \sim 110~erg\,cm\,s^{-1}