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Matteo Guainazzi

Publications and source records attributed to Matteo Guainazzi.

At least 127 records · Page 7Linked to original sources
arXiv2008

A BLR origin for the iron K$α$ line in NGC7213

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$α$ 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=$2 400^{+1 100}_{-600}$ km/s, in perfect agreement with the value measured for the broad component of the H$α$, $2640^{+110}_{-90}$ km/s. Therefore, NGC7213 is the only Seyfert 1 galaxy whose iron K$α$ line is unambiguously produced in the BLR. We also confirmed the presence of two ionised iron lines and studied them in greater detail than before. The resonant line is the dominant component in the Fe XXV triplet, therefore suggesting an origin in collisionally ionised gas. If this is the case, the blueshift of around 1000 km/s of the two ionised iron lines could be the first measure of the velocity of a starburst wind from its X-ray emission.

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arXiv2008

Chandra unveils a binary Active Galactic Nucleus in Mrk463

We analyse Chandra, XMM-Newton and HST data of the double-nucleus Ultraluminous Infrared Galaxy (ULIRG), Mrk463. The Chandra detection of two luminous ($\mathrm{L}_\mathrm{2-10 keV}=1.5\times10^{43}$ and $3.8\times10^{42}$ erg cm$^{-2}$ s$^{-1}$), unresolved nuclei in Mrk~463 indicates that this galaxy hosts a binary AGN, with a projected separation of $\simeq3.8$ kpc ($3.83\pm0.01$ arcsec). While the East nucleus was already known to be a Seyfert 2 (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. Mrk463 is therefore the clearest case so far for a binary AGN, after NGC6240.

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arXiv2007

The X-ray view of the ionization cone in NGC5252

We present the results of a Chandra soft X-ray observation of the spectacular ionization cone in the nearby Seyfert 2 galaxy NGC 5252. As almost invariably observed in obscured AGN, the soft X-ray emission exhibits a remarkable morphological concidence with the cone ionized gas as traced by HST O[III] images. Energy-resolved images and high-resolution spectroscopy suggest that the X-ray emitting gas is photoionized by the AGN, at least on scales as large as the innermost gas and stellar ring (<3 kpc). Assuming that the whole cone is photoionized by the AGN, we reconstruct the history of the active nucles in the last 100000 years.

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arXiv2007

On the Iwasawa-Taniguchi effect of radio-quiet AGN

The existence of an anti-correlation between the Equivalent Width (EW) of the neutral narrow core of the iron Kalpha emission line and the 2-10 keV luminosity (the so-called `X-ray Baldwin' or `Iwasawa-Taniguchi' effect) has been debated in the last years. We aim at testing this claim on the largest catalogue of radio quiet AGN high-quality X-ray spectra ever published. The final sample comprises 157 objects. We search for a relation of the iron line EW not only with the X-ray luminosity, but also with the Black Hole mass, the Eddington ratio and the cosmological distance. The data presented here were analyzed homogeneously, all spectra are from the same instrument and with high Signal-to-Noise Ratio. A linear censored fit on the EW versus 2-10 keV luminosity is highly significant and yields $\log(EW_{Fe}) = (1.73\pm0.03) + (-0.17\pm0.03) \log(L_{X,44})$, where $EW_{Fe}$ is the EW of the neutral iron Kalpha line in eV and $L_{x,44}$ is the 2-10 keV X-ray luminosity in units of $10^{44}$ erg s$^{-1}$. The anti-correlation with the Eddington ratio is also very significant, while no dependence of the iron EW on the BH mass is apparent.

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arXiv2006

The properties of unobscured AGN observed by XMM-Newton

Multiwavelength analysis on large samples of AGN provides an excellent tool to understand the physics of these objects. We present the largest catalog of XMM-Newton targeted AGN, all with high SNR X-ray spectra. It includes all the radio-quiet objects observed by XMM-Newton, in targeted observations of the AGN panel. The principal X-ray properties of the catalog are complemented by multiwavelength data found in the literature (optical magnitudes, radio fluxes, Hbeta FWHM, BH masses). We present here some results on the correlation of these quantities. In particular, we find convincing evidence for an `Iwasawa effect' on the narrow component of the Fe Kalpha line and a correlation between the soft-to-hard X-ray luminosity ratio and the Hbeta FWHM.

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arXiv2006

The nature of the soft X-ray emission in obscured AGN

The origin of the soft X-ray emission in obscured AGN is still largely unknown. However, important progresses have been made thanks to the high energy and spatial resolution of XMM-Newton and Chandra. We review here the latest results on this issue, focusing on the physical properties of the material responsible for the soft X-ray emission and its relation to the circumnuclear environment, putting them in the general context of our understanding of the AGN structure and its feedback to the host galaxy.

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arXiv2006

X-ray obscuration in local Universe AGN

I review the constraints that X-ray observations impose on the physical properties and the geometrical distribution of cold absorbing gas in nearby obscured Active Galactic Nuclei (AGN), as well as their implications for AGN structure models.

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arXiv2006

On the origin of soft X-rays in obscured AGN: answers from high-resolution spectroscopy with XMM-Newton

We present results of a high-resolution soft X-ray (0.2-2 keV) spectroscopic study of a sample of 69 nearby obscured Active Galactic Nuclei (AGN) observed with the Reflection Grating Spectrometer (RGS) on board XMM-Newton. This is the largest sample ever studied with this technique so far. The main conclusions of our study can be summarized as follows: a) narrow Radiative Recombination Continua are detected in about 36% of the objects in our sample (in 26% their intrinsic width is <10 eV); b) higher order transitions are generally enhanced with respect to pure photoionization, indicating that resonant scattering plays an important role in the ionization/excitation balance. These results support the scenario, whereby the active nucleus is responsible for the X-ray ``soft excess'' almost ubiquitously observed in nearby obscured AGN via photoionization of circumnuclear gas. They confirm on a statistical basis the conclusions drawn from the detailed study of the brightest spectra in the sample. Furthermore, we propose a criterion to statistically discriminate between AGN-photoionized sources and starburst galaxies, based on intensity of the forbidden component of the OVII He-alpha triplet (once normalized to the OVIII Ly-alpha) coupled with the integrated luminosity in He-like and H-like oxygen lines.

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arXiv2006

A multiwavelength map of the nuclear region of NGC7582

We performed a detailed analysis of the Chandra and HST images of the Seyfert 2 galaxy, NGC7582. The dust lane, as mapped by the HST NIR and optical images, strongly influences the morphology of the soft X-ray emission, being spatially coincident with excess of X-ray absorption. Two 'hot spots', i.e. regions where emission from higher ionization stages of O and Ne is stronger, are observed in the soft X-ray image. They can be tracers of variations of the ionization parameter, even if, at least for one of them, absorption may be the dominant effect. The positions of the `hot spots' suggest that they are not affected by the star-formation regions observed with HST, being located far away from them. Therefore, the starburst does not seem to play an important role in the photoionization of the soft X-ray emitting gas. The resulting picture is consistent with modified unification scenarios, where the Compton-thick torus coexists with a large-scale Compton-thin material associated with the dust lane and circumnuclear gas is photoionized by the AGN along torus-free lines of sight.

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arXiv2005

The soft X-ray/NLR connection: a single photoionized medium?

We present a sample of 8 nearby Seyfert 2 galaxies observed by HST and Chandra. All of the sources present soft X-ray emission which is coincident in extension and overall morphology with the [OIII] emission. The spectral analysis reveals that the soft X-ray emission of all the objects is likely to be dominated by a photoionized gas. This is strongly supported by the 190 ks combined XMM-Newton/RGS spectrum of Mrk3, which different diagnostic tools confirm as being produced in a gas in photoionization equilibrium with an important contribution from resonant scattering. We tested with the code CLOUDY a simple scenario where the same gas photoionized by the nuclear continuum produces both the soft X-ray and the [OIII] emission. Solutions satisfying the observed ratio between the two components exist, and require the density to decrease with radius roughly like $r^{-2}$, similarly to what often found for the Narrow Line Region.

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arXiv2005

Obscured AGN: clues from high-resolution imaging and spectroscopy

We present a sample of 8 Seyfert 2 galaxies observed by HST, Chandra and XMM-Newton. All of the sources present soft X-ray emission which is coincident in extension and overall morphology with the [OIII] emission. The spectral analysis reveals that the soft X-ray emission of all the objects is likely to be dominated by a photoionized gas. We tested with the code CLOUDY a simple scenario where the same gas photoionized by the nuclear continuum produces both the soft X-ray and the [OIII] emission. Solutions satisfying the observed ratio between the two components exist, and require the density to decrease with radius roughly like $r^{-2}$, similarly to what often found for the Narrow Line Region.

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arXiv2004

The X-ray properties of the PG QSO sample observed with XMM-Newton

We present preliminary results of a systematic analysis of the XMM-Newton spectra of nearby optically-bright QSOs. The objects have been optically selected from the Bright Quasar Survey sample. The goal of this project is to characterise the X-ray spectral properties of optically selected QSOs in the 0.3-12 keV energy band. A power law component accounts the hard band spectra with a average photon index of 2.0+/-0.2. No single model is able to account for the ubiquitous soft excess. We discuss several possibilities such single and multi-temperature black-body, power law and bremsstrahlung. We observed a X-ray Baldwin effect in our sample.

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arXiv2003

The high energy emission line spectrum of NGC 1068

We present and discuss the high energy (E>4 keV) XMM-Newton spectrum of the Seyfert 2 galaxy, NGC 1068. Possible evidence for flux variability in both the neutral and ionized reflectors with respect to a BeppoSAX observation taken 3.5 years before is found. Several Fe and Ni emission lines, from both neutral and highly ionized material, are detected. The intensity of the iron K$α$ Compton shoulder implies that the neutral reflector is Compton--thick, likely the visible inner wall of the $N_H > 10^{25}$ cm$^{-2}$ absorber. From the equivalent width of the ionized iron lines a column density of a few $\times 10^{21}$ cm$^{-2}$ is deduced for the hot ionized reflector. Finally, an iron (nickel) overabundance, when compared to solar values, of about 2 (4) with respect to lower Z elements, is found.

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arXiv2003

Nuclear activity and massive star formation in the low luminosity AGN NGC4303: Chandra X-ray observations

We present evidence of the co-existence of either an AGN or an ultraluminous X-ray source (ULX), together with a young super stellar cluster in the 3 central parsecs of NGC4303. The galaxy contains a low luminosity AGN and hosts a number of starburst regions in a circumnuclear spiral, as well as in the nucleus itself. A high spatial resolution Chandra image of this source reveals that the soft X-ray emission traces the ultraviolet nuclear spiral down to a core, which is unresolved both in soft and hard X-rays. The astrometry of the X-ray core coincides with the UV core within the Chandra positioning accuracy. The total X-ray luminosity of the core, 1.5*10^{39} erg/s, is similar to that from some LINERs or from the weakest Seyferts detected so far. The soft X-rays in both the core and the extended structure surrounding it can be well reproduced by evolutionary synthesis models (which include the emission expected from single stars, the hot diffuse gas, supernova remnants and binary systems), consistent with the properties of the young stellar clusters identified in the UV. The hard X-ray tail detected in the core spectrum, however, most likely requires the presence of an additional source. This additional source could either be a weak active nucleus black hole or an ultraluminous X-ray object. The implications of these results are discussed.

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arXiv2003

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

We have performed a detailed analysis of the XMM-Newton observation of IGR J16318-4848, to study the properties of the matter responsible for the obscuration and for the emission of Fe and Ni lines. Even if the line of sight material has a column density of about 2x10^24 cm^-2, from the Fe Kalpha line EW and Compton Shoulder we argue that the matter should have an average column density of a few x10^23 cm^-2, along with a covering factor of about 0.1-0.2. The iron Kalpha line varies on time scales as short as 1000 s, implying a size of the emitting region smaller than about 3x10^13 cm. The flux of the line roughly follows the variations of the continuum, but not exactly, suggesting a variation of the geometrical properties of the emitting region on similar time scales.

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arXiv2002

Detection of X-ray Emission from the Eastern Radio Lobe of PICTOR A

The XMM-Newton satellite has revealed extended X-ray emission from the eastern radio lobe of the Fanaroff-Riley II Radio Galaxy Pictor A. The X-ray spectrum, accumulated on a region covering about half the entire radio lobe, is well described by both a thermal model and a power law. The X-ray emission could be thermal and produced by circum-galactic gas shocked by the expanding radio lobe or, alternatively, by Inverse Compton (IC) of cosmic microwave background photons by relativistic electrons in the lobe. The latter possibility seems to be supported by the good agreement between the lobe-average synchrotron radio index and the X-ray energy slope. However, if this is the case, the magnetic field, as deduced from the comparison of the IC X-ray and radio fluxes, is more than a factor 2 below the equipartition value estimated in the same X-ray region.

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arXiv2002

XMM-Newton observations of the neutron star X-ray transient KS 1731-260 in quiescence

We report on XMM-Newton observations performed on 2001 September 13-14 of the neutron star X-ray transient KS 1731-260 in quiescence. The source was detected at an unabsorbed 0.5-10 keV flux of only 4 - 8 x 10^{-14} erg/s, depending on the model used to fit the data, which for a distance of 7 kpc implies a 0.5-10 keV X-ray luminosity of approximately 2 - 5 x 10^{32} erg/s. The September 2001 quiescent flux of KS 1731-260 is lower than that observed during the Chandra observation in March 2001. In the cooling neutron star model for the quiescent X-ray emission of neutron star X-ray transients, this decrease in the quiescent flux implies that the crust of the neutron star in KS 1731-260 cooled down rapidly between the two epochs, indicating that the crust has a high conductivity. Furthermore, enhanced cooling in the neutron star core is also favored by our results.

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