arXiv subjects

M. Guainazzi

Publications and source records attributed to M. Guainazzi.

At least 109 records · Page 6Linked to original sources

arXiv2006

Statistics of relativistically broadened Fe K-alpha lines in AGN

We present preliminary results on the properties of relativistically broadened Fe K-alpha lines in a collection of more then 100 Active Galactic Nuclei (AGN) observed by the XMM-Newton EPIC-pn camera. Our main conclusions can be summarized as follows: a) we detect broad lines in about 25% of the sample objects. This fraction increases to 42+/-13% if we consider only objects with more than 10000 counts in the hard (2-10 keV) band, and to 50+/-32% for the small sub-sample (6 objects) of type~1 Piccinotti AGN with optimal XMM-Newton exposure (at least 200000 counts in the hard band); b) we find no significant difference in the detection rate of broad lines between obscured and unobscured AGN; c) the strongest relativistic profiles are measured in low-luminosity (< 10^43 erg/s) AGN; d) Equivalent Widths (EWs) associated with relativistic profiles in stacked spectra are ~150 eV for all luminosity classes; e) models of relativistically broadened iron line profiles ("kyrline", Dovciak et al. 2005), which include full relativistic treatment of the accretion disk emission around a Kerr black hole in the strong gravity regime, yield an average disk inclination angle ~30 degrees, and a radial dependence of the disk emissivity profile ~-3. The distribution of EW is very broad, with =2.4. We estimate that an investment of about 1 Ms of XMM-Newton time would be required to put these results on a sound statistical basis.

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arXiv2006

4U 1344-60: a bright intermediate Seyfert galaxy at z=0.012 with a relativistic Fe Kalpha emission line

We present analysis of the optical and X-ray spectra of the low Galactic latitude bright (F(2-10) = 3.6 10^{-11} erg/cm2/s) source 4U 1344-60. On the basis of the optical data we propose to classify 4U 1344-60 as an intermediate type Seyfert galaxy and we measure a value of z=0.012+/-0.001 for its redshift. From the XMM-Newton observation we find that the overall X-ray spectral shape of 4U 1344-60 is complex and can be described by a power-law continuum (Gamma ~ 1.55) obscured by two neutral absorption components (Nh(f) ~ 10^{22} cm^{-2} and Nh(p) ~ 4 10^{22} cm^{-2}), the latter covering only the ~50% of the primary X-ray source. The X-ray data therefore lend support to our classification of 4U 1344-60. It exhibits a broad and skewed Fe Kalpha line at 6.4 keV, which suggests the existence of an accretion disk that is able to reprocess the primary continuum down to a few gravitational radii. Such a line represents one of the clearest examples of a relativistic line observed by XMM-Newton so far. Our analysis has also revealed the marginal presence of two narrow line-like emission features at ~4.9 and ~5.2 keV.

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arXiv2005

A new XMM-Newton observation of Pictor A radio lobes confirms the non-thermal origin of the X-ray emission

X-ray emission from the eastern radio lobe of the FRII Radio Galaxy Pictor A was serendipitously discovered by a short observation of XMM-Newton in 2001. The X-ray spectrum, accumulated on a region covering about half of the entire radio lobe, was well described by both a thermal model and a power law, making non-univocal the physical interpretation. A new XMM-Newton observation performed in 2005 has allowed the detection of the X-ray emission from both radio lobes and unambiguously revealed its non-thermal origin. The X-ray emission is due to Inverse Compton (IC) of the cosmic microwave background photons by relativistic electrons in the lobe. We confirm the discrepancy between the magnetic field, as deduced from the comparison of the IC X-ray and radio fluxes, and the equipartition value.

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arXiv2005

The hard X-ray view of Giga-Hertz Peaked Spectrum Radio Galaxies

We present the first broadband X-ray observations of four Giga-Hertz Peaked Spectrum (GPS) radio galaxies at redshift <~1 performed by Chandra and XMM-Newton. These observations more than double the number of members of this class with measured spectra in hard (E > 2 keV) X-rays. All sources were detected. Their radio-to-X-ray spectral energy distributions are similar, except for PKS0941-080, which is X-ray under-luminous by about two orders of magnitude. The comparison between the full sample of GPS galaxies with measurements in hard X-rays and a control sample of radio galaxies rules out intrinsic X-ray weakness as causing a lower detection rate of GPS sources in X-ray surveys. Four out of seven GPS galaxies exhibit high X-ray column densities, whereas for the remaining three this measurement is hampered by the poor spectral statistics. Bearing in mind the low number statistics in both the GPS and the control sample, the average column density measured in GPS galaxies is larger than in FRI or Broad Line Region FR II radio galaxies, but consistent with that measured in High-Excitation FRII galaxies. This leads to a location the absorbing gas in an obscuring ``torus'', which prevents us from observing the nuclear region along lines-of-sight perpendicular to the radio axis. This interpretation is supported by the discovery of rapid (timescale ~1000 s) X-ray variability in the GPS galaxy COINSJ0029+3456, and by an almost order-of-magnitude difference between the HI column density measured in radio and X-rays in PKS0500+019.

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arXiv2005

XMM-Newton discovery of soft X-ray absorption in the high-z superluminous Blazar RBS 315

We present the analysis and the results of a 20 ks XMM-Newton observation of the extremely X-ray loud (L_X ~ 5 x 10^{47} erg/s) flat-spectrum radio quasar RBS 315 at a redshift of 2.69. This EPIC observation has allowed us to strongly constrain the slope of the continuum (Gamma = 1.23+/-0.01) as well as to discover the presence of a sharp drop below ~ 2 keV in its spectrum. Such a flat photon index and the huge luminosity suggest that the X-ray emission is due to the low energy tail of the Comptonized spectrum, produced from plasma in a relativistic jet oriented close to our line of sight. Even though the hypothesis of a break in the continuum cannot be completely discarded as an explanation of the soft X-ray cutoff, the presence of intrinsic absorption appears more plausible. Spectral fits with cold (Nh(z) = 1.62+/-0.09 x 10^{22} cm^{-2}) and lukewarm (Nh(z) = 2.2^{+0.9}_{-0.3} x 10^{22} cm^{-2}; xi = 15^{+38}_{-12} erg/cm^{2}/s) absorbers are statistically indistinguishable. Remarkably, our results are very similar to those reported so far for other absorbed high-z Blazars observed by XMM-Newton. The existence of this ``homogeneous'' class of jet-dominated superluminous obscured QSOs at high z therefore could be important in the context of the formation and cosmological evolution of radio-loud objects

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arXiv2005

X-ray obscuration and obscured AGN in the local universe

In this paper we discuss the X-ray properties of 49 local (z<0.035) Seyfert 2 galaxies with HST/WFC2 high-resolution optical coverage. It includes the results of 26 still unpublished Chandra and XMM-Newton observations, which yield 25 (22) new X-ray detections in the 0.5-2 keV (2-10 keV) energy band. Our sample covers a range in the 2-10 keV observed flux from 3x10^{-11} to 6x10^{-15} erg cm$^{-2}$ s$^{-1}$. The percentage of the objects which are likely obscured by Compton-thick matter (column density, N_H>1.6x10^{24} atoms/cm/cm) is ~50%, and reaches ~80% for log(F_{2-10})<12.3. Hence, K-alpha fluorescent iron lines with large Equivalent Width (EW > 0.6 keV) are common in our sample (6 new detections at a confidence level >2 sigma). They are explained as due to reflection off the illuminated side of optically thick material. We confirm a correlation between the presence of a ~100-pc scale nuclear dust in the WFC2 images and Compton-thin obscuration. We interpret this correlation as due to the large covering fraction of gas associated with the dust lanes following an idea originally proposed by Malkan et al. 1998, and Matt 2000). The X-ray spectra of highly obscured AGN invariably present a prominent soft excess emission above the extrapolation of the hard X-ray component. This soft component can account for a very large fraction of the overall X-ray energy budget. As this component is generally unobscured - and therefore likely produced in extended gas structures - it may lead to a severe underestimation of the nuclear obscuration in z~1 absorbed AGN, if standard X-ray colors are used to classify them. As a by-product of our study, we report the discovery of a soft X-ray, luminous (~7x10^{40} erg/s) halo embedding the interacting galaxy pair Mkn266.

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arXiv2005

A search for changing-look AGN in the Grossan catalog

We observed with XMM-Newton 4 objects selected from the Grossan catalog, with the aim to search for new 'changing-look' AGN. The sample includes all the sources which showed in subsequent observations a flux much lower than the one measured with HEAO A-1: NGC 7674, NGC 4968, IRAS 13218+0552 and NGC 1667. None of the sources was caught in a high flux state during the XMM-Newton observations, whose analysis reveal they are all likely Compton-thick objects. We suggest that, for all the sources, potential problems with the HEAO A-1 source identification and flux measurement prevent us from being certain that the HEAO A-1 data represent a putative 'high' state for these objects. Nonetheless, based on the high flux state and Compton-thin spectrum of its GINGA observation, NGC 7674 represents probably the sixth known case of a 'changing-look' Seyfert 2 galaxy. From the X-ray variability pattern, we can estimate a likely lower limit of a few parsec to the distance of the inner walls of the torus in this object. Remarkably, IRAS 13218+0552 was not detected by XMM-Newton, despite being currently classified as a Seyfert 1 with a large [OIII] flux. However, the original classification was likely to be affected by an extreme velocity outflow component in the emission lines. The object likely harbors an highly obscured AGN and should be re-classified as a Type 2 source.

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arXiv2005

X-ray Emission from NGC 1808: More than a Complex Starburst

Earlier observations of NGC 1808 in various wavebands (X-ray, optical, near-infrared, radio) provided evidence for the existence of either a starburst or a Seyfert 2 nucleus. We here present the results of multiwavelength XMM-Newton and Chandra observations, which directly prove the co-existence of thermal diffuse plasma and non-nuclear unresolved point-like sources associated with the starburst activity, along with a Low Luminosity Active Galactic Nucleus (LLAGN) or an Ultra Luminous X-ray source (ULX). The broad bandwidth of XMM-Newton allows us to show that the unresolved nuclear source in NGC 1808 dominates the hard X-ray spectrum, while the emission in the soft regime, below 1 keV, is dominated by a thermal component associated to an extended starburst. Both EPIC and RGS data provide reliable detections of a number of emission lines from heavy elements, with abundances ranging from roughly 0.7 to 2.2 Z_sol for different elements. However, no 6.4 keV Fe K-alpha fluorescence line emission was detected. The analysis of the nuclear region of NGC 1808 allows us to detect and disentangle the contribution of an unresolved nuclear X-ray source and the starburst region, but the exact nature of the nucleus remains unknown. The observed luminosity of NGC 1808 is L(2-10 keV)=(1.61+/-0.06)E+40 erg/s. A comparison of our OM 212 nm image with a CTIO 4-m telescope H-alpha frame shows a good general correspondence between the emission from massive stars and warm ionized gas, with minor deviations near the ends of the bar in NGC 1808. An aditional, very soft thermal spectral component with kT~0.1 keV has been discovered in the XMM-Newton spectral analysis, which most likely originates from the halo of NGC 1808.

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arXiv2005

The XMM-Newton view of PG quasars: II. Properties of the Fe K-alpha line

The properties of the fluorescence Fe K-alpha emission lines of a sample of 38 quasars (QSOs) observed with XMM-Newton are studied. These objects are included in the optically selected sample from the Palomar-Green (PG) Bright Quasar Survey with an X-ray luminosity 1.3E43<L(2-10 keV)<5.1E45 ergs/s and z<1.72. For each object in the sample, we investigated the presence of both narrow and broad iron lines in detail. A total of 20 out of the 38 QSOs show evidence of an Fe K-alpha emission line with a narrow profile. The majority of the lines are consistent with an origin in low ionization material, which is likely to be located in the outer parts of the accretion disk, the molecular torus, and/or the Broad Line Region. The average properties of the narrow Fe K-alpha emission line observed in the sample are similar to those of Seyfert type galaxies as inferred from recent XMM-Newton and Chandra studies. A broad line has been significantly detected in only three objects. Furthermore, we studied the relationship between the equivalent width (EW) of the iron line and the hard band X-ray luminosity for radio quiet quasars. The analysis indicates that no clear correlation between the strength of the line and the hard X-ray luminosity is present, and our results do not show compelling evidence for an anticorrelation between these two quantities, i.e. the so-called X-ray Baldwin effect.

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arXiv2004

The XMM-Newton spectrum of the high-z optically-obscured QSO RX J1343.4+0001: a classic radio quiet QSO

We present a 30 ks XMM-Newton observation of the z = 2.35 Type II radio quiet quasar RX J1343.4+0001. These data provide the first good quality X-ray spectrum for this object. We measured a continuum slope Gamma = 1.85+/-0.10 with only an upper limit on the column density of the absorbing material of Nh(z) <~ 10^22 cm^-2 as well as an Fe Kalpha emission line at the 3 sigma confidence level. We do not find therefore a highly absorbed object nor a truly flat spectrum as suggested on the basis of previous less sensitive ROSAT and ASCA measurements. The Nh(z) upper limit is fully consistent with the optical extinction 3 <A_V <10 inferred from IR observations. The Fe Kalpha line is consistent with fluorescence from neutral iron and, noteworthy, is one of the most distant observed so far. The X-ray spectral properties of RX J1343.4+0001 agree well with the steep continuum slope (Gamma ~ 1.9) being independent of increasing redshift and luminosity as inferred by X-ray studies of large samples of RQ QSOs.

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arXiv2004

Investigating the EGRET-radio galaxies link with INTEGRAL: the case of 3EG J1621+8203 and NGC 6251

The analysis of an INTEGRAL AO2 observation of the error contours of the EGRET source 3EG J1621+8203 is presented. The only source found inside the error contours for energies between 20 and 30 keV at 5 sigma detection significance is the FR I radio galaxy NGC 6251. This supports the identification of NGC 6251 with 3EG J1621+8203. The observed flux is higher and softer than observed in the past, but consistent with a variable blazar-like spectral energy distribution.

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arXiv2004

The early stage of a cosmic collision? XMM-Newton unveils two obscured AGN in the galaxy pair ESO509-IG066

We report the XMM-Newton discovery of a X-ray bright AGN pair in the interacting galaxy system ESO509-IG066. Both galaxies host an X-ray luminous (L_X ~10^{43} erg/s) obscured nucleus with column densities N_H~7x10^{22} and N_H~5x10^{21} atoms/cm/cm. The optical morphology is only mildly disturbed, suggesting a merging system in the early stage of its evolution. Still, the pair is probably gravitationally bound, and might eventually evolve into a compact, fully gas embedded systems such as NGC6240.

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arXiv2004

The XMM-Newton view of PG quasars I. X-ray continuum and absorption

We present results of a systematic analysis of the XMM-Newton spectra of 40 quasars (QSOs) (z<1.72) from the Palomar-Green (PG) Bright Quasar Survey sample (M_B<-23). The sample includes 35 radio-quiet quasars (RQQs) and 5 radio-loud quasars (RLQs). The analysis of the spectra above 2 keV reveals that the hard X-ray continuum emission can be modeled with a power law component with = 1.89+/-0.11 and = 1.63^(+0.02)_(-0.01) for the RQQs and RLQs, respectively. Below 2 keV, a strong, broad excess is present in most QSO spectra. This feature has been fitted with four different models assuming several physical scenarios. All tested models (blackbody, multicolor blackbody, bremsstrahlung and power law) satisfactorily fitted the majority of the spectra. However, none of them is able to provide an adequate parameterization for the soft excess emission in all QSOs, indicating the absence of an universal shape for this spectral feature. An additional cold absorption component was required only in three sources. On the other hand, as recently pointed out by Porquet et al. (2004) for a smaller sample of PG QSOs, warm absorber features are present in ~50% of the QSO spectra in contrast with their rare occurrence (~5-10%) found in previous studies. The XMM-Newton view of optically-selected bright QSOs therefore suggests that there are no significant difference in the X-ray spectral properties once compared with the low-luminosity Seyfert 1 galaxies. Properties of the Fe Kalpha emission lines are presented in a companion paper.

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arXiv2004

On the transmission- to reprocessing-dominated spectral state transitions in Seyfert 2 galaxies

We present Chandra and XMM-Newton observations of a small sample (11 objects) of optically-selected Seyfert~2 galaxies, for which ASCA and BeppoSAX had suggested Compton-thick obscuration of the Active Nucleus (AGN). The main goal of this study is to estimate the rate of transitions between "transmission-" and "reprocessing-dominated" states. We discover one new transition in NGC4939, with a possible additional candidate in NGC5643. This indicates a typical occurrence rate of at least ~0.02/year. These transitions could be due to large changes of the obscuring gas column density, or to a transient dimming of the AGN activity, the latter scenario being supported by detailed analysis of the best studied events. Independently of the ultimate mechanism, comparison of the observed spectral dynamics with Monte-Carlo simulations demonstrates that the obscuring gas is largely inhomogeneous, with multiple absorbing components possibly spread through the whole range of distances from the nucleus between a fraction of parsecs up to several hundreds parsecs. As a by-product of this study, we report the first measurement ever of the column density covering the AGN in NGC3393 (N_H ~ 4.4x10^{24} atoms/cm/cm), and the discovery of soft X-ray extended emission, apparently aligned along the host galaxy main axis in NGC5005. The latter object hosts most likely an historically misclassified low-luminosity Compton-thin AGN.

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arXiv2004

The X-ray variability properties of PG quasars: XMM-Newton results

This paper presents preliminary results of a systematic study on the X-ray spectral variability of PG quasars with XMM-Newton. We concentrate on those objects, whose X-ray spectra are well fit in the framework of the ``double Comptonization'' model. On short (<1000 seconds) timescales, variability between the soft (E<2 keV) and the hard (E>2 keV) bands is uncorrelated. In the two objects, for which observations at different epochs are available, spectral variability in the soft X-ray regime is unveiled. Its timescale is constrained in the range between ~1 week and ~1 year.

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arXiv2004

Unveiling the nature of the highly obscured AGN in NGC5643 with XMM-Newton

We present results from an XMM-Newton observation of the nearby Seyfert 2 galaxy NGC5643. The nucleus exhibits a very flat X-ray continuum above 2 keV, together with a prominent K-alpha fluorescent iron line. This indicates heavy obscuration. We measure an absorbing column density N_H in the range 6-10 x 10^{23} atoms/cm/cm, either directly covering the nuclear emission, or covering its Compton-reflection. In the latter case, we might be observing a rather unusual geometry for the absorber, whereby reflection from the inner far side of a torus is in turn obscured by its near side outer atmosphere. The nuclear emission might be then either covered by a Compton-thick absorber, or undergoing a transient state of low activity. A second source (christened "X-1" in this paper) at the outskirts of NGC5643 optical surface outshines the nucleus in X-rays. If belonging to NGC5643, it is the third brightest (L_X ~ 4 x 10^{40} erg/s) known Ultra Luminous X-ray source. Comparison with past large aperture spectra of NGC 5643 unveils dramatic X-ray spectral changes above 1 keV. We interpret them as due to variability of the active nucleus and of source X-1 intrinsic X-ray powers by a factor >10 and 5, respectively.

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arXiv2004

X-ray reprocessing in Seyfert Galaxies: simultaneous XMM-Newton/BeppoSAX observations

We selected a sample of eight bright unobscured (at least at the iron line energy) Seyfert Galaxies observed simultaneously by XMM-Newton and BeppoSAX, taking advantage of the complementary characteristics of the two missions. The main results of our analysis can be summarized as follows: narrow neutral iron lines are confirmed to be an ubiquitous component in Seyfert spectra; none of the analyzed sources shows unambiguously a broad relativistic iron line; all the sources of our sample (with a single exception) show the presence of a Compton reflection component; emission lines from ionized iron are observed in some sources; peculiar weak features around 5-6 keV (possibly arising from rotating spots on the accretion disk) are detected in two sources. The scenario emerging from these results strongly requires some corrections for the classical model of reprocessing from the accretion disk. As for materials farther away from the Black Hole, our results represent a positive test for the Unification Model, suggesting the presence of the torus in (almost) all sources, even if unobscured.

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arXiv2004

Evidence for a multizone warm absorber in the XMM-Newton spectrum of Markarian 304

We present a XMM-Newton observation of Markarian 304, a Seyfert 1 galaxy at z = 0.066. The EPIC data show that MKN 304 is affected by heavy (Nh ~10^{23} cm{-2}) obscuration due to ionized gas. A two-phase warm absorber provides an adequate parameterization of this gas. The ionization parameter of the two components is ξ~6 erg/cm2/s and ξ~90 erg/cm2/s, respectively. The observed continuum photon index (Gamma ~1.9) is typical for Seyfert 1 galaxies. Two significant emission lines are detected at 0.57 keV and 6.4 keV, respectively. The former is mostly likely due to He-like oxygen triplet emission arising from an ionized plasma (maybe the warm absorber itself). The latter is due to fluorescent emission of K-shell iron in a low-ionization state (FeI--XV). The upper limit for the line width of sigma_{Kα} <0.18 keV most likely rules out an origin in the inner parts of the accretion disk. Interestingly, the strength of such line is consistent with the possibility that the emission is produced in the warm absorber itself. However, a substantial contribution from the torus is plausible too. We have also found a weak (4% of the primary continuum) soft excess emission component. The presence of this excess could be explained by either emission/scattering from a warm gas or partial covering, or a combination of them.

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