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Giorgio Matt

Publications and source records attributed to Giorgio Matt.

At least 163 records · Page 9Linked to original sources
arXiv2005

A puzzling event during the X-ray emission of the binary system GX 1+4

We report on a long X-ray observation of the slow-rotating binary pulsar GX 1+4. BeppoSAX observed, in the 0.1-200 keV energy range, an event in which the source flux dropped for almost a day, and then recovered. During this event only the high-energy emission was found to be pulsed and the pulsations were shifted in phase of ~0.2 . The spectrum during the event was well fitted by a Compton-reflection model. A broad iron line at ~6.55 keV was present outside of the event, where instead two narrow emission lines at ~6.47 keV and ~7.05 keV were detected. The pulse profile was highly variable as a function of both energy and time. We interpret this low-flux event as an occultation of the direct X-ray emission, due to the increase of a torus-like accretion disk; we then discuss similarities between this source and the recently discovered highly absorbed INTEGRAL sources.

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arXiv2004

Fe XXV and Fe XXVI lines from low velocity, photoionised gas in the X-ray spectra of AGN

We have calculated the equivalent widths of the absorption lines produced by Fe XXV and Fe XXVI in a Compton-thin, low-velocity photoionised material illuminated by the nuclear continuum in AGN. The results, plotted against the ionisation parameter and the column density of the gas, are a complement to those presented by Bianchi & Matt 2002 for the emission lines from the same ionic species. As an extension to the work by Bianchi & Matt 2002, we also present a qualitative discussion on the different contributions to the He-like iron emission line complex in the regimes where recombination or resonant scattering dominates, providing a useful diagnostic tool to measure the column density of the gas. Future high resolution missions (e.g., Astro-E2) will allow us to fully take advantage of these plasma diagnostics. In the meantime, we compare our results with an up-to-date list of Compton-thick and unobscured (at least at the iron line energy) Seyfert galaxies with emission and/or absorption lines from H- and He-like iron observed with Chandra and XMM-Newton.

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arXiv2004

The complex X-ray spectrum of NGC 4507

XMM-Newton and Chandra/HETG spectra of the Compton-thin (NH 4x10^{23} cm^{-2}) Seyfert 2 galaxy, NGC 4507, are analyzed and discussed. The main results are: a) the soft X-ray emission is rich in emission lines; an (at least) two--zone photoionization region is required to explain the large range of ionization states. b) The 6.4 keV iron line is likely emitted from Compton-thick matter, implying the presence of two circumnuclear cold regions, one Compton-thick (the emitter), one Compton-thin (the cold absorber). c) Evidence of an Fe xxv absorption line is found in the Chandra/HETG spectrum. The column density of the ionized absorber is estimated to be a few x10^{22} cm^{-2}.

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arXiv2004

X-ray polarization properties of the accretion column in magnetic CVs

The accretion column in magnetic Cataclysmic Variables may have a not negligible Thomson optical depth. A fraction of the thermal radiation from the post-shock region may therefore be scattered - and then polarized - before escaping the column. Moreover, part of the thermal radiation is reflected - and again polarized - by the White Dwarf surface. We show that X-ray polarimetry can provide valuable, and probably unique informations on the geometry and physical parameters of the accretion column by calculating, by means of Monte Carlo simulations, the expected polarization properties of magnetic CVs as a function of the geometrical parameters (assuming a cylindrical geometry) and the Thomson optical depth of the column. We find that degrees of polarization as high as about 4% can be present, and apply our calculations to the archetypal magnetic CV, AM Herculis.

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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

Iron and Nickel properties in the X-ray reflecting region of the Circinus Galaxy

We discuss the iron and nickel properties in the nuclear X-ray reflecting region of the Circinus Galaxy, studied with XMM-Newton. The main results are: a) from the depth of the Fe Kalpha edge, a value of A_Fe=1.7 in number with respect to the cosmic value (as for Anders & Grevesse 1989) is measured, if the (not directly visible) illuminating spectrum is assumed to be that measured by BeppoSAX. If the slope of the primary power law is left free to vary, a steeper spectrum and a lower iron abundance (about 1.2) are found. b) From the Ni to Fe Kalpha lines flux ratio, a nickel-to-iron abundance ratio of 0.055-0.075 is found. c) The Fe Kbeta/Kalpha flux ratio is slightly lower than expected, possibly due to a mild ionization of iron (which however cannot be much more ionized than X). d) The presence of the Fe Kalpha Compton Shoulder, already discovered by Chandra, is confirmed, its relative flux implying Compton-thick matter. This further supports the identification of the reflecting region with the absorber.

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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

Ionized iron Kαlines in AGN X-ray spectra

The Equivalent Widths (EW) of the He- and H-like iron lines produced in photoionized, circumnuclear matter of AGN are calculated with respect to both the reflected and the total continua. We found that the EWs with respect tothe total continuum may be as large as a few tens of eV, making them observable in bright Seyfert 1s by instruments on board Chandra and XMM-Newton. We apply our calculations to the XMM-Newton spectrum of NGC 5506 and found a good agreement with the data at the expense of a modest iron overabundance.

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arXiv2002

On the origin of the broad, relativistic iron line of MCG-6-30-15 observed by XMM-Newton

The relativistic iron line profile recently observed by XMM-Newton in the spectrum of the Seyfert 1 galaxy MCG--6-30-15 (Wilms et al., 2001) is discussed in the framework of the lamp-post model. It is shown that the steep disc emissivity, the large line equivalent width and the amount of Compton reflection can be self- consistently reproduced in this scenario.

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arXiv2001

The X-ray view of highly obscured AGN

The properties of Compton-thick AGN are reviewed, with particular emphasis on BeppoSAX hard X-ray observations. I also discuss evidence for the presence of Compton-thick, circumnuclear matter in unobscured AGN, and I briefly introduce the HELLAS2XMM 5-10 keV survey, discussed in more details in other contributions to this volume.

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arXiv2001

Weak Reprocessed Features in the Broad Line Radio Galaxy 3C382

We present a detailed X-ray study of the Broad Line Radio Galaxy 3C382, observed with the BeppoSAX satellite in a very bright state. The continuum emission is well modeled with a power law that steepens at high energies, with an e-folding energy of about 120 keV. At soft energies a clear excess of emission is detected, which can not be explained solely by the extended thermal halo seen in a ROSAT HRI image. A second, more intense soft X-ray component, possibly related to an accretion disk, is required by the data. Both a reflection component (R=0.3) and an iron line (EW \sim 50) are detected, at levels much weaker than in Seyfert galaxies, suggesting a common origin. Combining our measurements with results from the literature we find that the iron line has remained approximately constant over 9 years while the continuum varied by a factor of 5. Thus the fluorescent gas does not respond promptly to the variations of the X-ray primary source, suggesting that the reprocessing site is located away, likely at parsec distances. While the continuum shape indicates that X-rays derive from a thermal Comptonization process, the weakness of other spectral features implies that either the upper layers of the optically thick accretion disk are completely ionized or the corona above the disk is outflowing with mildly relativistic velocity.

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arXiv2000

The circumnuclear X-ray reflectors in NGC 1068 and the Circinus Galaxy

The ASCA and BeppoSAX spectra of the Circinus Galaxy and NGC 1068 are analysed and compared with photoionization models based on cloudy. In the case of Circinus, a single, mildly ionized reflector can account for the line spectrum, while in NGC 1068 at least three different reflectors (with different ionization states) are needed. We suggest that the reflector in Circinus, and the low ionized one in NGC1068 are the inner and visible part of the material responsible for the X-ray absorption. With this assumption, we estimate for the inner radius of the absorber a value of 0.2 pc for Circinus and of a few parsecs for NGC 1068.

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arXiv2000

The BeppoSAX observation of Mrk 766

The Narrow Line Seyfert 1 galaxy Mrk 766 has been observed by BeppoSAX on May 1997. The source was fairly variable, both in flux and spectrum, during the observation. The variability is the largest around 2 keV, possibly due to variations in the warm absorber properties. An oxygen line is clearly detected, at least in the first part of the observation. An edge around 7.5 keV, coupled with the lack of any detectable iron line, suggests either reprocessing of the primary X-rays by a mildly ionized disc or absorption by a further, thicker and more ionized material.

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arXiv2000

Resolving the 10-40 keV Cosmic X-ray Background with Constellation-X

The energy density of the Cosmic X-ray background (XRB) peaks around 30 keV (see Figure 1), an energy not yet probed by focussing imaging instruments. The first hard X-ray telescope due to fly on a space mission will be that on board Constellation-X. The imaging capability, besides providing an improvement of several orders of magnitude in sensitivity over current passively collimated detectors, will permit for the first time to resolve a fraction of the XRB at this most crucial energy. Synthesis models of the XRB based on obscured AGN predict that at least 40% of the 10-40 keV XRB will be resolved by Constellation-X.

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arXiv2000

Dust lanes, thick absorbers, and the unification model for Seyfert galaxies

A modification of the popular unification model for Seyfert galaxies is proposed, which takes into account recent observational findings on the statistical properties of both type 1 and type 2 Seyferts. In the proposed scenario, Compton-thick Seyfert 2 galaxies are those sources observed through compact, thick matter (the `torus'), while Compton-thin/intermediate Seyfert galaxies are obscured by dust lanes at larger distances.

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arXiv1999

The hard X-ray spectrum of Compton-thick Seyfert 2 galaxies and the synthesis of the XRB

A synthesis model for the cosmic X-ray Background (XRB) is presented, which includes a proper treatment of Compton scattering in the absorbing matter for type 2 AGN. Evidence for a decrease of the relative importance of type 2 AGN at high redshift is found, which may be due either to a decrease of the relative number of obscured sources, or (more plausibly) to an increase of the fraction of Compton-thick absorbed sources. The XRB spectrum, soft X-rays and hard X-rays source counts can be simultaneously fitted only if the XRB normalization as derived from BeppoSAX/MECS measurements is adopted.

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