arXiv subjects

G. Matt

Publications and source records attributed to G. Matt.

At least 145 records · Page 8Linked to original sources

arXiv2009

Unabsorbed Seyfert 2 galaxies: the case of "naked" AGN

Hawkins (2004) reported on a class of "naked" AGN characterized by strong amplitude optical brightness variability and the complete absence of broad emission lines in the optical spectrum. The variability suggests that the nucleus is seen directly, however the absence of broad lines contradicts the simple formulation of Unified Models for AGN. We present the results of quasi-simultaneous spectroscopic observations with XMM-Newton and NTT (La Silla) of two "naked" AGN. We confirm the "naked" nature of Q2131-427 for which no broad emission line components have been detected in the optical spectrum and its X-ray spectrum shows no signs of intrinsic absorption. The optical and X-ray mismatch in this source cannot be ascribed to a high nuclear dust-to-gas ratio and a Compton Thick nature is ruled out on the basis of the high F(X)/F([OIII]) ratio. The Broad Line Region (BLR) may be completely absent in this source, possibly as a consequence of its low Eddington ratio. On the other hand, the optical spectrum of Q2130-431 shows H(alpha) and H(beta) broad emission line components, revealing the presence of a BLR. A mild X-ray absorption is expected in intermediate type 1.8 Seyfert galaxies like Q2130-431, however we put a very low upper limit on the column density (< 2 x 10^(20) cm^(-2)), also the low Balmer decrement suggests that the BLR itself does not suffer from reddening. We propose that in this object the BLR is intrinsically weak, making a case of "true" intermediate Seyfert galaxy. We also report on the X-ray detection of the Abell 3783 galaxy cluster in the XMM-Newton field-of-view of the Q2131-427 observation.

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arXiv2009

The bolometric luminosity of type 2 AGN from extinction-corrected [OIII]: no evidence for Eddington-limited sources

There have been recent claims that a significant fraction of type 2 AGN accrete close or even above the Eddington limit. In type 2 AGN the bolometric luminosity (L_b) is generally inferred from the [OIII] emission line luminosity (L_OIII). The key issue, in order to estimate the bolometric luminosity in these AGN, is therefore to know the bolometric correction to be applied to L_OIII. A complication arises from the fact that the observed L_OIII is affected by extinction, likely due to dust within the narrow line region. The extinction-corrected [OIII] luminosity (L^c_OIII) is a better estimator of the nuclear luminosity than L_OIII. However, so far only the bolometric correction to be applied to the uncorrected L_OIII has been evaluated. This paper is devoted to estimate the bolometric correction C_OIII=L_b/L^c_OIII in order to derive the Eddington ratios for the type 2 AGN in a sample of SDSS objects. We have collected from the literature 61 sources with reliable estimate of both L^c_OIII and X-ray luminosities (L_X). To estimate C_OIII, we combined the observed correlation between L^c_OIII and L_X with the X-ray bolometric correction. We found, contrary to previous studies, a linear correlation between L^c_OIII and L_X. We estimated C_OIII using the luminosity-dependent X-ray bolometric correction of Marconi et al. (2004), and we found a mean value of C_OIII in the luminosity ranges log L_OIII=38-40, 40-42, and 42-44 of 87, 142 and 454 respectively. We used it to calculate the Eddington ratio distribution of type 2 SDSS AGN at 0.3<z<0.4 and we found that these sources are not accreting near their Eddington limit, contrary to previous claims.

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arXiv2009

The Behavior of Matter under Extreme Conditions

The cores of neutron stars harbor the highest matter densities known to occur in nature, up to several times the densities in atomic nuclei. Similarly, magnetic field strengths can exceed the strongest fields generated in terrestrial laboratories by ten orders of magnitude. Hyperon-dominated matter, deconfined quark matter, superfluidity, even superconductivity are predicted in neutron stars. Similarly, quantum electrodynamics predicts that in strong magnetic fields the vacuum becomes birefringent. The properties of matter under such conditions is governed by Quantum Chromodynamics (QCD) and Quantum Electrodynamics (QED), and the close study of the properties of neutron stars offers the unique opportunity to test and explore the richness of QCD and QED in a regime that is utterly beyond the reach of terrestrial experiments. Experimentally, this is almost virgin territory.

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arXiv2009

Stellar-Mass Black Holes and Their Progenitors

If a black hole has a low spin value, it must double its mass to reach a high spin parameter. Although this is easily accomplished through mergers or accretion in the case of supermassive black holes in galactic centers, it is impossible for stellar-mass black holes in X-ray binaries. Thus, the spin distribution of stellar-mass black holes is almost pristine, largely reflective of the angular momentum imparted at the time of their creation. This fact can help provide insights on two fundamental questions: What is the nature of the central engine in supernovae and gamma-ray bursts? and What was the spin distribution of the first black holes in the universe?

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arXiv2009

Fundamental Accretion and Ejection Astrophysics

Disk accretion may be the fundamental astrophysical process. Stars and planets form through the accretion of gas in a disk. Black holes and galaxies co-evolve through efficient disk accretion onto the central supermassive black hole. Indeed, approximately 20 percent of the ionizing radiation in the universe is supplied by disk accretion onto black holes. And large-scale structures - galaxy clusters - are dramatically affected by the relativistic jets that result from accretion onto black holes. Yet, we are still searching for observational answers to some very basic questions that underlie all aspects of the feedback between black holes and their host galaxies: How do disks transfer angular momentum to deliver gas onto compact objects? How do accretion disks launch winds and jets?

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arXiv2009

Spin and Relativistic Phenomena Around Black Holes

Since the seminal work of Penrose (1969) and Blandford & Znajek (1977), it has been realized that black hole spin may be an important energy source in astrophysics. The radio-loud/radio-quiet dichotomy in the AGN population is usually attributed to differences in black hole spin, with correlations between black hole spin and host galaxy morphology being hypothesized in order to explain why radio-loud AGN occur in early-type galaxies. X-ray observations are uniquely able to answer: Does black hole spin play a crucial role in powering relativistic jets such as those seen from radio-loud active galactic nuclei (AGN), Galactic microquasars, and Gamma-Ray Bursts? Indeed, the importance of black hole spin goes beyond its role as a possible power source: the spin of a supermassive black hole is a fossil record of its formation and subsequent growth history.

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arXiv2009

Suzaku observation of the Phoenix Galaxy

In recent years, several Seyfert 2 galaxies have been discovered that change state when observed in X-rays a few years apart, switching from Compton-thin to reflection-dominated or viceversa. We observed a member of this class of "Changing-look" sources, the Phoenix Galaxy, with Suzaku, with the aim of better understanding the nature of the variations. The Suzaku spectrum was analyzed, and the results compared with previous ASCA and XMM-Newton observations. The source was caught in a Compton-thin state, as in XMM-Newton, but differently from ASCA. Comparing the Suzaku and XMM-Newton observations, a variation in the column density of the absorber on a time scale of years is discovered. A similar change, but on much shorter time scales (i.e. ks) may also explain the count-rate variations during the Suzaku observations. A soft excess is also present, likely due to continuum and line emission from photoionized circumnuclear matter.

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arXiv2009

Variable partial covering and a relativistic iron line in NGC 1365

We present a complete analysis of the hard X-ray (2-10 keV) properties of the Seyfert galaxy NGC 1365, based on a 60 ks XMM-Newton observation performed in January 2004. The two main results are: 1) We detect an obscuring cloud with N_H~3.5x10^23 cm^(-2) crossing the line of sight in ~25 ks. This implies a dimension of the X-ray source not larger than a few 10^13 cm and a distance of the obscuring cloud of the order of 10^16 cm. Adopting the black hole mass M(BH) estimated from the M(BH)-velocity dispersion relation, the source size is D_S<20 R_G and the distance and density of the obscuring clouds are R~3000-10000 R_G and n~10^(10) cm^(-3), i.e. typical values for broad line region clouds. 2) An iron emission line with a relativistic profile is detected with high statistical significance. A time integrated fit of the line+continuum reflection components suggests a high iron abundance (~3 times solar) and an origin of these components in the inner part (~10 R_G) of the accretion disk, in agreement with the small source size inferred from the analysis of the absorption variability.

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arXiv2009

XMM-Newton and Suzaku analysis of the Fe K complex in the Seyfert 1 galaxy Mrk 509

We report on partially overlapping XMM-Newton (~260 ks) and Suzaku (~100 ks) observations of the iron K band in the nearby, bright Seyfert 1 galaxy Mrk 509. The source shows a resolved neutral Fe K line, most probably produced in the outer part of the accretion disc. Moreover, the source shows further emission blue-ward of the 6.4 keV line due to ionized material. This emission is well reproduced by a broad line produced in the accretion disc, while it cannot be easily described by scattering or emission from photo-ionized gas at rest. The summed spectrum of all XMM-Newton observations shows the presence of a narrow absorption line at 7.3 keV produced by highly ionized outflowing material. A spectral variability study of the XMM-Newton data shows an indication for an excess of variability at 6.6-6.7 keV. These variations may be produced in the red wing of the broad ionized line or by variation of a further absorption structure. The Suzaku data indicate that the neutral Fe Kalpha line intensity is consistent with being constant on long timescales (of a few years) and they also confirm as most likely the interpretation of the excess blueshifted emission in terms of a broad ionized Fe line. The average Suzaku spectrum differs from the XMM-Newton one for the disappearance of the 7.3 keV absorption line and around 6.7 keV, where the XMM-Newton data alone suggested variability.

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arXiv2008

Disk reflection signatures in the spectrum of the bright Z-source GX 340+0

We present the preliminary results of a 50 ks long XMM-Newton observation of the bright Z-source GX 340+0. In this Letter we focus on the study of a broad asymmetric emission line in the Fe K alpha energy band, whose shape is clearly resolved and compatible with a relativistically smeared profile arising from reflection on a hot accretion disk extending close to the central accreting neutron star. By combining temporal and spectral analysis, we are able to follow the evolution of the source along its Horizontal Branch. However, despite a significant change in the continuum emission and luminosity, the line profile does not show any strong correlated variation. This broad line is produced by recombination of highly ionized iron (Fe XXV) at an inferred inner radius close to 13 gravitational radii while the fit requires a high value for the outer disk radius. The inclination of the source is extremely well constrained at 35 deg, while the emissivity index is -2.50.

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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

Detection of blueshifted emission and absorption and a relativistic Iron line in the X-ray spectrum of ESO 323-G077

We report on the X-ray observation of the Seyfert 1 ESO323-G077 performed with XMM-Newton. The spectra show a complex spectrum with conspicuous absorption and emission features. The continuum emission can be modelled with a power law with an index of 1.99+/-0.02 in the whole XMM-Newton energy band, marginally consistent with typical values of Type-I objects. An absorption component with an uncommonly high equivalent Hydrogen column, n_H=5.82(+0.12/-0.11)x10^22 cm-2, is affecting the soft part of the spectrum. Additionally, two warm absorption components are also present. The lower ionised one has an ionisation parameter of Log(U)=2.14(+0.06/-0.07) and an outflowing velocity of v=3200(+600/-200) km/s. Two absorption lines located at ~6.7 and ~7.0 keV can be modelled with the highly ionised absorber. The ionisation parameter and outflowing velocity of the gas measured are Log(U)=3.26(+0.19/-0.15) and v=1700(+600/-400) km/s, respectively. Four emission lines were also detected in the soft energy band. The most likely explanation for these emission lines is that they are associated with an outflowing gas with a velocity of ~2000 km/s. The data suggest that the same gas which is causing the absorption could also being responsible of these emission features. Finally, the spectrum shows the presence of a relativistic iron emission line likely originated in the accretion disc of a Kerr BH with an inclination of ~25 deg. We propose a model to explain the observed X-ray properties which invokes the presence of a two-phase outflow with cone-like structure and a velocity of the order of 2,000-4,000 km/s. The inner layer of the cone would be less ionised, or even neutral, than the outer layer. The inclination angle would be lower than the opening angle of the outflowing cone.

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arXiv2008

Suzaku Observations of the Circinus galaxy

We report Suzaku observations of the active, Compton-thick Circinus galaxy. Observations were obtained with both the X-ray Imaging spectrometer (XIS) and the Hard X-ray Detector (HXD). Below 10 keV, the nuclear spectrum is dominated by radiation reflected from cold dense gas of high column density, while above 13 keV the radiation is directly transmitted nuclear emission seen through a column density of $~ 4 x 10^{24} cm^-2. In the 0.2--10 keV band, the XIS spectrum is contaminated at 5% level by the brightest off-nuclear source in Circinus (CG X-1), but drops to 1% in the 5-10 keV and is negligible at higher energies. We find no significant evidence for variability in the hard (>12 keV) emission. The Circinus is marginally detected with the HXD/GSO in the 50--100 keV band at 2.5σlevel. We model the 3-70 keV band XIS+PIN spectra with a four components: the Compton transmitted nuclear emission, the reflected nuclear emission, a soft power law (representing a combination of scattered nuclear emission, extended emission and contamination by sources in the galaxy below a few keV). The hard nuclear power-law is found to have a photon index Gamma_h ~= 1.6, very similar to the soft power-law. The high energy cut-off is E_C ~= 49 keV. These results agree with those from BeppoSax. An extrapolation of this model up to the GSO band shows good agreement with the GSO spectrum and supports our detection of the Circinus up to ~= 100keV.

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arXiv2008

Thermal disc emission from a rotating black hole: X-ray polarization signatures

Thermal emission from the accretion disc around a black hole can be polarized, due to Thomson scattering in a disc atmosphere. In Newtonian space, the polarization angle must be either parallel or perpendicular to the projection of the disc axis on the sky. As first pointed out by Stark and Connors in 1977, General Relativity effects strongly modify the polarization properties of the thermal radiation as observed at infinity. Among these effects, the rotation of the polarization angle with energy is particularly useful as a diagnostic tool. In this paper, we extend the Stark and Connors calculations by including the spectral hardening factor, several values of the optical depth of the scattering atmosphere and rendering the results to the expected performances of planned X-ray polarimeters. In particular, to assess the perspectives for the next generation of X-ray polarimeters, we consider the expected sensitivity of the detectors onboard the planned POLARIX and IXO missions. We assume the two cases of a Schwarzschild and an extreme Kerr black hole with a standard thin disc and a scattering atmosphere. We compute the expected polarization degree and the angle as functions of the energy as they could be measured for different inclinations of the observer, optical thickness of the atmosphere and different values of the black hole spin. We assume the thermal emission dominates the X-ray band. Using the flux level of the microquasar GRS 1915+105 in the thermal state, we calculate the observed polarization.

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arXiv2008

Two new Intermediate Polars with a soft X-ray component

We analyze the first X-ray observations with XMM-Newton of RXS J070407.9+262501 and 1RXS 180340.0+401214, in order to characterize their broad-band temporal and spectral properties, also in the UV/optical domain, and to confirm them as Intermediate Polars. For both objects, we performed a timing analysis of the X-ray and UV/optical light curves to detect the white dwarf spin pulsations and study their energy dependence. For 1RXS 180340.0+401214 we also analyzed optical spectroscopic data to determine the orbital period. X-ray spectra were analyzed in the 0.2-10.0 keV range to characterize the emission properties of both sources. We find that the X-ray light curves of both systems are energy dependent and are dominated, below 3-5 keV, by strong pulsations at the white dwarf rotational periods (480 s for 1RXS J070407.9+262501 and 1520.5 s for 1RXS 180340.0+401214). In 1RXS 180340.0+401214 we also detect an X-ray beat variability at 1697 s which, together with our new optical spectroscopy, favours an orbital period of 4.4 hr that is longer than previously estimated. Both systems show complex spectra with a hard (up to 40 keV) optically thin and a soft (85-100 eV) optically thick components heavily absorbed by material partially covering the X-ray sources. Our observations confirm the two systems as Intermediate Polars and also add them as new members of the growing group of 'soft' systems which show the presence of a soft X-ray blackbody component. Differences in the temperatures of the blackbodies are qualitatively explained in terms of reprocessing over different sizes of the white dwarf spot. We suggest that systems showing cooler soft X-ray blackbody components also possess white dwarfs irradiated by cyclotron radiation.

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arXiv2008

X-ray absorption in Compton-thin AGN: the predictions of a model revisited

The evidence of a decrease with increasing luminosity of the fraction f_{abs} of absorbed and Compton-thin among X-ray (2-10 keV) selected AGN is observationally rather well supported, while that of an increase of f_{abs} with redshift is rather controversial. In Lamastra, Perola & Matt (2006) the gravitational effect of the SMBH on the molecular interstellar gas, in the central region of the host galaxy, was shown to predict an anti-correlation between f_{abs} and M_{BH}. The most recent findings on the distribution of the Eddington ratio λ=L_b/L_E as a function of M_{BH} and z are used to convert that relationship into one between f_{abs} and both bolometric (L_b) and X-ray (L_X) luminosities at various values of z. The findings on λ(M_{BH},z) are properly treated in order to ensure completeness in the prediction of f_{abs} above a certain luminosity, at values of z=0.1, 0.35, 0.7 and >1. To verify the consequence of these findings alone, we adopted in a first istance a distribution of gas surface density Σ, observed in a sample of local spiral galaxies, irrespective of the galaxy morphological type and z. Assuming in the λ(M_{BH},z) distribution the Eddington limit, λ=1, as a ``natural'' cut-off, the predictions are consistent with the existence of an anti-correlation between f_{abs} and L_X, but fail to reproduce an increase of f_{abs} with z. Because the early type galaxies on average are much poorer in molecular gas than late type ones, a quantitative agreement with the local value of f_{abs} requires the existence of a correlation between Σand the central activity. An increase of typical values of Σwith z, correlated with the activity, might explain an increase of f_{abs} with z. However, at the highest luminosities f_{abs} could hardly exceed about 0.3.

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arXiv2008

XMM-Newton observations of 4 luminous radio-quiet AGN, and the soft X-ray excess problem

The nature and origin of the soft X-ray excess in radio quiet AGN is still an open issue. The interpretation in terms of thermal disc emission has been challanged by the discovery of the constancy of the effective temperature despite the wide range of Black Hole masses of the observed sources. Alternative models are reflection from ionized matter and absorption in a relativistically smeared wind. We analyzed XMM-Newton observations of four luminous radio quiet AGN with the aim of characterising their main properties and in particular the soft excess. Different spectral models for the soft excess were tried: thermal disc emission, Comptonization, ionized reflection, relativistically smeared winds. Comptonization of thermal emission and the smeared winds provide the best fits, but the other models also provide acceptable fits. All models, however, return parameters very similar from source to source, despite the large differences in luminosities, Black Hole masses and Eddington ratios. Moreover, the smeared wind model require very large smearing velocities. The UV to X-ray fluxes ratios are very different, but do not correlate with any other parameter. No fully satisfactory explanation for the soft X-ray excess is found. Better data, like e.g. observations in a broader energy band, are needed to make further progresses.

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arXiv2008

1RXSJ173021.5-055933: a cataclysmic variable with a fast-spinning magnetic white dwarf

We present the first X-ray observations with the XMM-Newton and INTEGRAL satellites of the recently discovered cataclysmic variable 1RXSJ173021.5-055933, together with simultaneous UV and coordinated optical photometry aiming at characterising its broad-band temporal and spectral properties and classifying this system as a magnetic one. We find that the X-ray light curve is dominated by the 128s spin period of the accreting white dwarf in contrast to the far-UV range, which turns out to be unmodulated at a 3sigma level. Near-UV and optical pulses are instead detected at twice the spin frequency. We identify the contributions from two accreting poles that imply a moderately inclined dipole field allowing, one pole to dominate at energies at least up to 10keV, and a secondary that instead is negligible above 5keV. X-ray spectral analysis reveals the presence of multiple emission components consisting of optically thin plasma with temperatures ranging from 0.17keV to 60keV and a hot blackbody at ~90eV. The spectrum is also strongly affected by peculiar absorption components consisting of two high-density (~3x10^(21)cm^(-2) and ~2x10^(23)cm^(-2)) intervening columns, plus a warm absorber. The last is detected from an OVII absorption edge at 0.74keV, which suggests that photoionization of pre-shock material is also occurring in this system. The observed properties indicate that the accretor in 1RXSJ173021.5-055933 is a white dwarf with a likely weak magnetic field, thus confirming this cataclysmic variable as an intermediate polar (IP) with one of the most extreme spin-to-orbit period ratios. This system also joins the small group of IPs showing a soft X-ray reprocessed component, suggesting that this characteristics is not uncommon in these systems.

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