arXiv subjects

M. Guainazzi

Publications and source records attributed to M. Guainazzi.

At least 91 records · Page 5Linked to original sources

arXiv2009

3C 33: another case of photoionized soft X-ray emission in radio galaxies

All the observations available in the Chandra and XMM-Newton archives have been used to investigate the X-ray spectral properties of 3C 33. In this paper is presented a complete X-ray analysis of the nuclear emission of this narrow line radio galaxy. The broad band spectrum of 3C 33 is complex. The hard part resembles that of Seyfert 2 galaxies, with a heavily obscured nuclear continuum (N_H~10^23 cm^-2) and a prominent Fe Kalpha line. This represents the nuclear radiation directly observed in transmission through a cold circumnuclear gas. On the other hand an unabsorbed continuum plus emission lines seem to fit well the soft part of the spectrum (0.5-2 keV) suggesting that the jet does not significantly contribute to the X-ray emission. We discuss the possible collisional or photoionized origin of the gas that emits the soft X-ray lines. Our results, strengthened by optical spectroscopy favor the photoionization scenario.

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arXiv2008

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

We present an analysis of the extreme obscuration variability observed during an XMM-Newton 5-days continuous monitoring of the AGN in NGC 1365. The source was in a reflection-dominated state in the first ~1.5 days, then a strong increase of the 7-10 keV emission was observed in ~10 hours, followed by a symmetric decrease. The spectral analysis of the different states clearly shows that this variation is due to an uncovering of the X-ray source. From this observation we estimate a size of the X-ray source D_S<10^13 cm, a distance of the obscuring clouds R~10^16 cm and a density n~10^11 cm^{-3}. These values suggest that the X-ray absorption/reflection originate from the broad line region clouds. This is also supported by the resolved width of the iron narrow Kalpha emission line, consistent with the width of the broad Hbeta line.

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arXiv2008

XMM-Newton observation of MACHO 104.20906.960: a dwarf nova candidate with a 2 h period

The binaries known as cataclysmic variables are particular binary systems in which the primary star (a white dwarf) accretes material from a secondary via Roche-lobe mechanism. Usually, these objects have orbital period of a few hours so that a detailed temporal analysis can be performed. Here, we present Chandra ${\it XMM}$-Newton observations of a dwarf nova candidate identified in the past by optical observations towards the galactic Bulge and labeled as MACHO 104.20906.960. After a spectral analysis, we used the Lomb-Scargle technique for the period search and evaluated the confidence level using Monte-Carlo simulations. In this case, we found that the $X$-ray source shows a period of $2.03_{-0.07}^{+0.09} $ hours (3$σ$ error) so that it is most likely a system of interacting objects. The modulation of the signal was found with a confidence level of $>$99%. The spectrum can be described by a two thermal plasma components with X-ray flux in the 0.3--10 keV energy band of $1.77_{-0.19}^{+0.16}\times10^{-13}$ erg s$^{-1}$ cm$^{-2}$. We find that the distance of the source is approximately 1 kpc thus corresponding to a luminosity $L_{X}\simeq 2\times 10^{31}$ erg s$^{-1}$.

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arXiv2008

Obscuring clouds playing hide-and-seek in the Active Nucleus H0557-385

This paper reports on two XMM-Newton observations of the Seyfert 1 Galaxy H0557-385 obtained in 2006, which show the source at an historical low flux state, more than a factor of 10 lower than a previous XMM-Newton look in 2002. The low flux spectrum presents a strong Fe Kalpha line associated to a Compton reflection continuum. An additional spectral line around 6.6 keV is required to fit Kalpha emission from Fe XXV. The spectral curvature below 6 keV implies obscuration by neutral gas with a column density of 8*10^{23}cm^{-2} partially covering the primary emission, which still contributes for a few percent of the soft X-ray emission. Absorption by ionised material on the line of sight is required to fit the deep trough below 1 keV. The comparison of the two spectral states shows that the flux transition is to be ascribed entirely to intervening line-of-sight clouds with high column density.

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arXiv2008

The Seyfert 1 Galaxy Mrk 335 at a very low flux state: mapping the soft X-ray photoionised gas

This paper reports on an XMM-Newton observation of the Seyfert 1 Galaxy Mrk 335 performed as a Target of Opportunity when the source was in an unusually low flux state. The low level of continuum emission unveiled an underlying line-rich soft X-ray spectrum, which can be studied with the Reflection Grating Spectrometer. The emission features have been analysed at high resolution with unprecedented detail for this source. Line ratios diagnostic from H-like and He-like ions indicates that the line emission arises in X-ray photoionised plasma. Extensive simulations have been performed with the CLOUDY photoionisation code. From the comparison of the expected and observed line intensities the physical properties of the line emitting material were derived. Because of the degeneracy in the ionisation parameter, a number of different solutions in terms of electron density and column density of the gas are consistent with the spectral diagnostics. This prevents us from determining uniquely the properties of the plasma; however, the location(s) of the X-ray photoionised gas can be constrained to be within 0.06 pc (outer boundary). This limit places the X-ray line emitting gas at the inner edge of the material where the broad optical lines are produced (Broad Line Region).

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arXiv2007

Heavy absorption and soft X-ray emission lines in the XMM-Newton spectrum of the Type 2 radio-loud quasar 3C 234

We report results on a 40 ks XMM-Newton observation of the Type 2 quasar 3C 234. Optical spectropolarimetric data have demonstrated the presence of a hidden broad-line region in this powerful (M_V <~ -24.2 after reddening and starlight correction) narrow-line FRII radio galaxy. Our analysis is aimed at investigating the X-ray spectral properties of this peculiar source which have remained poorly known so far. We analyze the 0.5--10 keV spectroscopic data collected by the EPIC cameras in 2006. The X-ray spectrum of this radio-loud quasar is typical of a local Compton-thin Seyfert 2 galaxy. It exhibits strong absorption (Nh~3.5 x 10^{23} cm^{-2}) and a narrow, neutral Fe Kalpha emission line with an equivalent width of ~140+/-40 eV. Our observation also reveals that the soft portion of the spectrum is characterized by strong emission lines with a very low level of scattered primary continuum. A possible explanation of these features in terms of thermal emission from a two-temperature collisionally ionized plasma emission seems to be unlikely due to the high luminosity estimated for this component (L(0.5-2) ~ 6 x 10^{42} erg/s). It is likely that most of the soft X-ray emission originates from a photoionized plasma as commonly observed in obscured, radio-quiet Seyfert-like AGNs. This X-ray observation has definitively confirmed the presence of a hidden quasar in 3C 234. The line-rich spectrum and the steepness of the hard X-ray continuum (Gamma ~ 1.7) found in this source weaken the hypothesis that the bulk ofthe X-ray emission in radio-loud AGNs with high excitation optical lines arises from jet non-thermal emission.

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arXiv2007

The globular cluster NGC 6388: $XMM$-Newton and $Chandra$ observations

By studying the optical brightness surface density of the globular cluster NGC 6388, it has been recently proposed that it harbors a central intermediate-mass black hole with mass $\simeq 5.7\times 10^3$ M$_{\odot}$. We expect that the compact object in the center of NGC 6388 emits radiation in the $X$-ray band as a consequence of the accretion from the surrounding matter. We searched for $XMM$-Newton and $Chandra$ observations towards NGC 6388 to test this hypothesis. The $Chandra$ satellite disentangles several point-like $X$-ray sources, probably low mass $X$-ray binaries, well within the core radius of the globular cluster. However, three of them, coinciding with the cluster center of gravity, remain unresolved. Their total luminosity is $L_X^{Obs}\simeq 2.7\times 10^{33}$ erg s$^{-1}$. If one of these sources is the $X$-ray counterpart of the intermediate-mass black hole in NGC 6388, the corresponding upper limit on the accretion efficiency, with respect to the Eddington luminosity, is $3\times 10^{-9}$. This measurement could be tightened if moderately deep radio observations of the field were performed.

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arXiv2007

XMM observation of 1RXS J180431.1-273932: a new M-type X-ray binary with a 494 s-pulse period neutron star?

Low-mass X-ray binaries are binary systems composed of a compact object and a low-mass star. Recently, a new class of these systems, known as symbiotic $X$-ray binaries (with a neutron star with a M-type giant companion), has been discovered. Here, we present long-duration ${\it XMM}$ observations of the source 1RXS J180431.1-273932. Temporal and spectral analysis of the source was performed along with a search for an optical counterpart. We used a Lomb-Scargle periodogram analysis for the period search and evaluated the confidence level using Monte-Carlo simulations. The source is characterized by regular pulses so that it is most likely a neutron star. A modulation of $494.1\pm0.2$ s (3$σ$ error) was found with a confidence level of $>$99%. Evidence of variability is also present, since the data show a rate of change in the signal of $\sim -7.7\times 10^{-4}$ counts s$^{-1}$ hr$^{-1}$. A longer observation will be necessary in order to determine if the source shows any periodic behavior. The spectrum can be described by a power law with photon index $Γ\sim 1$ and a Gaussian line at 6.6 keV. The X-ray flux in the 0.2--10 keV energy band is $5.4\times 10^{-12}$ erg s$^{-1}$ cm$^{-2}$. The identification of an optical counterpart (possibly an M6III red-giant star with an apparent visual magnitude of $\simeq 17.6$) allows a conservative distance of $\sim 10$ kpc to be estimated. Other possibilities are also discussed. Once the distance was estimated, we got an $X$-ray luminosity of $L_X\ut<6\times 10^{34}$ erg s$^{-1}$, which is consistent with the typical $X$-ray luminosity of a symbiotic LMXB system.

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arXiv2007

FERO (Finding Extreme Relativistic Objects): statistics of relativistic broad Fe K alpha lines in AGN

The properties of the relativistically broadened Fe K alpha line emitted in Active Galactic Nuclei (AGN) are still debated among the AGN community. Recent works seem to exclude that the broad Fe line is a common feature of AGN. The analysis of a large sample composed by 157 XMM-Newton archival observations of radio quiet AGN is presented here. This ongoing project is a development of the work reported in Guainazzi et al. 2006.

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arXiv2007

X-ray properties of a sample of polar-scattered Seyfert galaxies

We present the results on an XMM-Newton systematic analysis of a sample of nine Seyfert 1 galaxies. When observed in polarised light, the spectra of the selected sources are similar to those of Seyfert 2 galaxies. This peculiarity strongly suggests that these AGN are viewed with an inclination comparable with the torus opening angle. Our results are consistent with this scenario and, taking advantage of this favourable geometrical condition, we were able to investigate in detail the physical properties and the distribution of the circumnuclear gas in these sources.

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arXiv2007

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

We analyse a 75ks XMM-Newton observation of PG 2112+059 performed in November 2005 and compare it with a 15ks XMM-Newton observation taken in May 2003. 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 EW = 26.1 keV 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, $N_{H} \sim 4.5 \times 10^{23} cm^{-2}$, and the other high ionisation parameters. As the ionisation parameter of the high flux state, $ξ\sim 34 erg cm s^{-1}$, is lower than the value found for the deep minimum state, $ξ\sim 110 erg cm s^{-1}$, either the absorbers are physically different or the absorbing material is moving with respect to the X-ray source. The spectra can also be explained by a continuum plus X-ray ionised reflection on the accretion disk, seen behind a warm absorber. The ionisation parameter of the high state ($ξ\sim 5.6 erg cm s^{-1}$) is higher than the ionisation parameter of the deep minimum state ($ξ\sim 0.2 erg cm s^{-1}$), as expected for a stationary absorber. The values found for the ionisation parameters are in the range typical for AGNs. The spectra observed during the deep minimum state are reflection dominated and show no continuum emission. These can be understood in the context of light bending near the supermassive black hole as predicted by Minutti and Fabian.

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arXiv2007

XMM-Newton unveils the type 2 nature of the BLRG 3C 445

We present an observation of XMM-Newton that unambiguously reveals the ``Seyfert 2'' nature of the Broad Line Radio Galaxy 3C 445. For the first time the soft excess of this source has been resolved. It consists of unobscured scattered continuum flux and emission lines, likely produced in a warm photoionized gas near the pole of an obscuring torus. The presence of circumnuclear (likely stratified) matter is supported by the complex obscuration of the nuclear region. Seventy percent of the nuclear radiation (first component) is indeed obscured by a column density ~4*10^{23} cm^{-2}, and 30 % (second component) is filtered by ~7* 10^{22} cm^{-2}. The first component is nuclear radiation directly observed by transmission through the thicker regions. The second one is of more uncertain nature. If the observer has a deep view into the nucleus but near the edge of the torus, it could be light scattered by the inner wall of the torus and/or by photoionized gas within the Broad Line Region observed through the thinner rim of the circumnuclear matter.

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arXiv2007

XMM-Newton view of galaxy pairs: activation of quiescent black holes?

We report on XMM-Newton observations of three nearby galaxy pairs, AM0707-273, AM1211-465, and AM2040-674. All six galaxies were previously classified as HII galaxies based on optical and IR spectroscopic analysis. All galaxies were detected with XMM-Newton and each member was isolated and analyzed independently. The X-ray spectra reveal strong evidence of AGN activity in the NE member of AM1211-465 pair. We measured a luminosity of 1.94(+0.11/-0.15)x10^42 erg/s in the 2-10 keV band and the presence of a neutral FeK_alpha line with a confidence level of 98.8%. The high nH value, 2.2+/-0.2x10^22 cm^-2, would explain the misclassification of the source. Marginal evidence of AGN nature was found in the X-ray spectra of AM1211-465SW and AM0707-273E. The X-ray emission of the three remaining galaxies can be explained by starburst activity.

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arXiv2007

XMM-Newton broad-band observations of NGC 7582: Nh variations and fading out of the active nucleus

We present results from two XMM-Newton observations of the bright classical Seyfert 2 galaxy NGC 7582 taken four years apart (2001 May and 2005 April). We present the analysis of the high-resolution (0.3-1 keV) RGS and low-resolution (0.3-10 keV) EPIC spectroscopic data. A comparison with a 1998 BeppoSAX observation suggests that XMM-Newton caught the source in a `reflection-dominated' phase, measuring the lowest continuum flux level ever (F(2-10 keV) = 2.3 x 10^(-12) erg cm^-2 s^-1) in 2005. NGC 7582 therefore experienced a dramatic spectral transition most likely due to the partial switching-off of the nuclear activity. The XMM-Newton spectrum of the continuum emission is very complex. It can be well described by a model consisting of a combination of a heavily absorbed (Nh ~ 10^(24) cm^-2) power law and a pure reflection component both obscured by a column density of ~ 4 x 10^(22) cm^-2. Notably, we detect a significant increase by a factor of ~2 in the column density of the inner, thicker absorber covering the primary X-ray source between 2001 and 2005. The 2005 XMM-Newton spectra show the strongest Fe Kalpha emission line ever measured in this source. This is consistent with the line delayed time response to the decrease of the nuclear activity. Our analysis also reveals that the soft X-ray spectrum is dominated by emission lines from highly ionized metals. The detection of a narrow OVIII radiative recombination continuum suggests an origin in a photoionized plasma.

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arXiv2007

An X-ray look at the Seyfert 1 Galaxy Mrk 590: XMM-Newton and Chandra reveal complexity in circumnuclear gas

This paper reports on a partially simultaneous observation of the bright Seyfert 1 Galaxy Mrk590, performed by XMM-Newton and Chandra. The long exposure (~100 ks) allows to investigate with great detail the Fe K complex at 6-7 keV and the presence of soft X-ray spectral features. We have analysed XMM-Newton data from the European Photon Imaging Camera (EPIC) in the 0.5-12 keV band and from the Reflection Grating Spectrometer (RGS) in the 0.35-2.5 keV band, and data from the High Energy Transmission Gratings (HETGs) onboard Chandra. UV and optical data from the Optical Monitor (OM) onboard XMM-Newton are also included in the analysis. The broad band spectrum is well described by an unabsorbed power law and three unresolved Fe~K lines in the 6-7 keV range. The presence of a Compton reflection component and a narrow Fe K line at 6.4 keV is consistent with an origin via torus reflection. The ionised Fe lines at ~6.7 and 7 keV are instead most likely originated by scattering on a warm and ionised gas. The soft X-ray spectrum appears to be almost featureless due to the very bright continuum emission, except for one emission line identified as OVIII Ly alpha detected at ~19 Angstrom by both RGS and Chandra-MEG. The emerging picture consists of an active nucleus seen directly on a "clean" line of sight without intervening material, surrounded by photoionised circumnuclear gas at a high ionisation level. We also study three serendipitous sources in the field of view of Chandra and XMM-Newton. One of these sources may be identified with an ULX of L_{0.3-10 keV}~10^{40} ergs/s.

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arXiv2006

Search for narrow energy-shifted lines in XMM-Newton AGN spectra

The detection of X-ray narrow spectral features in the 5-7 keV band is becoming increasingly more common in AGN observations, thanks to the capabilities of current X-ray satellites. Such lines, both in emission and in absorption, are mostly interpreted as arising from Iron atoms. When observed with some displacement from their rest frame position, these lines carry the potential to study the motion of circumnuclear gas in AGN, providing a diagnostic of the effects of the gravitational field of the central black hole. These narrow features have been often found with marginal statistical significance. We are carrying on a systematic search for narrow features using spectra of bright type 1 AGNs available in the XMM-Newton archive. The aim of this work is to characterise the occurrence of the narrow features phenomenon on a large sample of objects and to estimate the significance of the features through Monte Carlo simulations. The project and preliminary results are presented.

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arXiv2006

The XMM-Newton/INTEGRAL monitoring campaign of IGR J16318-4848

IGR J16318-4848 is the prototype and one of the more extreme examples of the new class of highly obscured Galactic X-ray sources discovered by INTEGRAL. A monitoring campaign on this source has been carried out by XMM-Newton and INTEGRAL, consisting in three simultaneous observations performed in February, March and August 2004. The long-term variability of the Compton-thick absorption and emission line complexes will be used to probe the properties of the circumstellar matter. A detailed timing and spectral analysis of the three observations is performed, along with the reanalysis of the XMM-Newton observation performed in February 2003. The results are compared with predictions from numerical radiative transfer simulations to derive the parameters of the circumstellar matter. Despite the large flux dynamic range observed (almost a factor 3 between observations performed a few months apart), the source remained bright (suggesting it is a persistent source) and Compton-thick (NH >1.2x10^24 cm-2). Large Equivalent Width (EW) emission lines from Fe Kalpha, Fe Kbeta and Ni Kalpha were present in all spectra. The addition of a Fe Kalpha Compton Shoulder improves the fits, especially in the 2004 observations. Sporadic occurrences of rapid X-ray flux risings were observed in three of the four observations. The Fe Kalpha light curve followed the continuum almost instantaneously, suggesting that the emission lines are produced by illumination of small-scale optically-thick matter around the high-energy continuum source. Using the iron line EW and Compton Shoulder as diagnostic of the geometry of the matter, we suggest that the obscuring matter is in a flattened configuration seen almost edge-on.

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arXiv2006

XMM-Newton view of the double-peaked Fe K-alpha complex in E1821+643

We present the results of the analysis of the hard band XMM-Newton spectra of the luminous, L(2-10keV)~3.4E+45 erg/s, radio-quiet quasar, E1821+643. Two emission features were observed in the 6-7 keV rest frame band, confirming previous Chandra detection of these structures. We interpret these features as two single emission lines, one consistent with the neutral Fe K-alpha line at 6.4 keV and the other most likely due to FeXXVI. If related to the quasar, the high-energy emission line should originate in highly ionised matter, i.e. the accretion disc or the clouds of the emission line regions. Alternatively, it may be related to the intergalactic medium of the rich galaxy cluster in which E1821+643 is embedded. A composite broad emission line in combination with an absorption line model, however, also fits the data well. We discuss the possible physical interpretations of the origin of these features.

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