Matteo Guainazzi

Changing look: from Compton-thick to Compton-thin, or the rebirth of fossil active galactic nuclei

We discuss the properties of a small sample of type 2 Seyfert galaxies whose X-ray spectra changed appearance on time-scales of years, becoming reflection-dominated from Compton-thin, or vice versa. A reflection-dominated spectrum is usually taken as evidence of Compton-thick absorption, but we instead argue that such a spectrum is due to a temporary switching-off of the nuclear radiation. The observations discussed here may help to explain mismatches between optical and X-ray classifications, and provide new strong and direct evidence for the presence of more than one cold circumnuclear region in type 2 Seyfert galaxies.

Chandra unveils a binary Active Galactic Nucleus in Mrk 463

We analyse Chandra, XMM‐Newton and Hubble Space Telescope (HST) data of the doublenucleus Ultraluminous Infrared Galaxy (ULIRG), Mrk 463. The Chandra detection of two luminous (L2‐10 keV = 1.5 × 10 43 and 3.8 × 10 42 erg cm −2 s −1 ), unresolved nuclei in Mrk 463 indicates that this galaxy hosts a binary active galactic nucleus (AGN), with a projected separation of � 3.8 kpc (3.83 ± 0.01 arcsec). While the East nucleus was already known to be a type 2 Seyfert (and this is further confirmed by our Chandra detection of a neutral iron line), this is the first unambiguous evidence in favour of the AGN nature of the West nucleus. Mrk 463 is therefore the clearest case so far for a binary AGN, after NGC 6240.

Cross-calibrating X-ray detectors with clusters of galaxies: an IACHEC study

Aims. We used a sample of 11 nearby relaxed clusters of galaxies observed with the X-ray instruments XMM-Newton (EPIC) pn and MOS, Chandra ACIS-S and ACIS-I and BeppoSAX MECS to examine the cross-calibration of the energy dependence and normalisation of the effective area of these instruments as of December 2009. We also examined the Fe XXV/XXVI line ratio temperature measurement method for the pn and MOS. Methods. We performed X-ray spectral analysis on the XMM-Newton and Chandra data for a sample of 11 clusters. We obtained the information for BeppoSAX from DeGrandi & Molendi (2002). We compared the spectroscopic results obtained with different instruments for the same clusters in order to examine possible systematic calibration effects between the instruments. Results. We did not detect any significant systematic differences between the temperatures derived in the 2−7 keV band using the different instruments. Also, the EPIC temperatures derived from the bremsstrahlung continuum agreed with those obtained from the Fe XXV/XXVI emission line ratio, implying that the energy dependence of the hard band effective area of the above instruments is accurately calibrated. This also indicates that deviations from ionisation equilibrium and a Maxwellian electron velocity distribution are negligible in the regions studied in the cluster sample. We thus consider the IACHEC sample of clusters of galaxies as standard candles for the calibration of the energy dependence of the hard band (2− 7k eV) effective area of X-ray telescopes. On the other hand, the hard band EPIC/ACIS fluxes disagreed by 5−10% (i.e. at 6−25σ level) which indicates a similar level of uncertainty in the normalisations of the effective areas of these instruments in the 2−7 keV band. In the soft energy band (0.5−2.0 keV) there are greater cross-calibration differences between EPIC and ACIS. We found an energy-dependent increase of ACIS versus pn bias in the cross-calibration of the eff ective area by∼10% in the 0.5−2.0 keV band. This amounts to a systematic difference of (∼20%) in the temperatures measured by the ACIS and the EPIC-pn cameras in this band. Due to the high statistical weight of the soft band data, the 0.5−7.0 keV band temperature measurements of clusters of galaxies with EPIC/XMM-Newton or ACIS/Chandra are uncertain by ∼10−15% on average. These uncertainties will also affect the analysis of the wide band continuum spectra of other types of objects using ACIS or EPIC.

THE BROADBAND SPECTRAL VARIABILITY OF MCG–6-30-15 OBSERVED BY NUSTAR AND XMM-NEWTON

MCG–6-30-15, at a distance of 37 Mpc (z = 0.008), is the archetypical Seyfert 1 galaxy showing very broad Fe Kα emission. We present results from a joint NuSTAR and XMM-Newton observational campaign that, for the first time, allows a sensitive, time-resolved spectral analysis from 0.35 keV up to 80 keV. The strong variability of the source is best explained in terms of intrinsic X-ray flux variations and in the context of the light-bending model: the primary, variable emission is reprocessed by the accretion disk, which produces secondary, less variable, reflected emission. The broad Fe Kα profile is, as usual for this source, well explained by relativistic effects occurring in the innermost regions of the accretion disk around a rapidly rotating black hole. We also discuss the alternative model in which the broadening of the Fe Kα is due to the complex nature of the circumnuclear absorbing structure. Even if this model cannot be ruled out, it is disfavored on statistical grounds. We also detected an occultation event likely caused by broad-line region clouds crossing the line of sight.

A broad-line region origin for the iron Kα line in NGC 7213

The X-ray spectrum of NGC7213 is known to present no evidence for Compton reflection, a unique result among bright Seyfert 1s. The observed neutral iron K

The XMM–Newton long look of NGC 1365: uncovering of the obscured X-ray source

\alpha

The soft-X-ray emission of Ark 120. XMM–Newton, NuSTAR, and the importance of taking the broad view

line, therefore, cannot be associated with a Compton-thick material, like the disc or the torus, but is due to Compton-thin gas, with the Broad Line Region (BLR) as the most likely candidate. To check this hypothesis, a long Chandra HETG observation, together with a quasi-simultaneous optical spectroscopic observation at the ESO NTT EMMI were performed. We found that the iron line is resolved with a FWHM=

Ultrafast outflows in radio-loud active galactic nuclei

2 400^{+1 100}_{-600}

The properties of the absorbing and line-emitting material in IGR J16318 — 4848

km/s, in perfect agreement with the value measured for the broad component of the H

CAIXA: a catalogue of AGN in the XMM-Newton archive II. Multiwavelength correlations

\alpha