arXiv subjects

P. O. Petrucci

Publications and source records attributed to P. O. Petrucci.

At least 55 records · Page 3Linked to original sources

arXiv2011

Suzaku broad-band observations of the Seyfert 1 galaxies Mrk 509 and Mrk 841

We report an analysis and modelling of new Suzaku observations of the Seyfert 1 galaxies Mrk509 and Mrk841, taken between April and November 2006,for Mrk509,and between January and July 2007,for Mrk841,for a total exposure time of ~100 ks each.Data from XIS and HXD/PIN instruments,going from 0.5 to 60 keV,represent the highest spectral resolution simultaneous broad-band X-ray spectrum for these objects.We fitted the broad-band spectrum of both sources with a double Comptonisation model,adding neutral reflection from distant material and a two-phase warm absorber.We then studied the two competing models developed to explain the soft excess in terms of atomic processes:a blurred ionised disc reflection and an ionised absorption by a high velocity material.When fitting the data in the 3-10 keV range with a power law spectrum,and extrapolating this result to low energies,a soft excess is clearly observed below 2 keV:its strength is however weak compared to previous observations of both sources.A moderate hard excess is seen at energies greater than 10 keV,together with a neutral Fe K_a narrow emission line at E~6.4 keV and a broad Fe emission line.For Mrk509,the broad Fe emission line is required in all the three physical models in order to have a good fit to the data:this finding suggests that the blurred reflection model correctly describes the soft excess,but that it underestimates the broad Fe emission line.For the smeared absorption model,this suggests instead that the continuum spectrum absorbed by the outflowing gas should contain indeed a reflected component.For Mrk841,all three models that we tested provide a good fit to the data,and we cannot invalidate any of them.A broad emission line is required in the double Comptonisation and smeared absorption models,while the blurred reflection model consistently fits the broad-band spectrum,without adding any extra emission-line component.

astro-ph.CO↗

arXiv2011

The influence of the jet opening angle on the appearance of relativistic jets

We reinvestigate the problem of the appearance of relativistic jets when geometrical opening is taken into account. We propose a new criterion to define apparent velocities and Doppler factors, which we think being determined by the brightest zone of the jet. We numerically compute the apparent velocity and the Doppler factor of a non homokinetic jet using different velocity profiles. We argue that if the motion is relativistic, the high superluminal velocities beta_{app} ~ gamma, expected in the case of an homokinetic jet, are only possible for geometrical collimation smaller than the relativistic beaming angle 1/gamma. This is relatively independent of the jet velocity profile. For jet collimation angles larger than 1/gamma, the apparent image of the jet will always be dominated by parts of the jet traveling directly towards the observer at lorentz factors < gamma resulting in maximal apparent velocities smaller than gamma}. Furthermore, getting rid of the homokinetic hypothesis yields a complex relation between the observing angle and the Doppler factor, resulting in important consequences for the numerical computation of AGN population and unification scheme model.

astro-ph.HE↗

arXiv2010

The influence of collimation on the appearance of relativistic jets

The question of the collimation of relativistic jets is the subject of a lively debate in the community. We numerically compute the apparent velocity and the Doppler factor of a non homokinetic jet using different velocity profile, to study the effect of collimation on the appearance of relativistic jets (apparent velocity and Doppler factor). We argue that if the motion is relativistic, the high superluminal velocities are possible only if the geometrical collimation is smaller than the relativistic beaming angle $γ^{-1}$. In the opposite case, the apparent image will be dominated by the part of the jet traveling directly towards the observer resulting in a smaller apparent velocity. Furthermore, getting rid of the homokinetic hypothesis yields a complex relation between the observing angle and the Doppler factor, resulting in important consequences for the numerical computation of AGN population and unification scheme model.

astro-ph.HE↗

arXiv2010

FERO: Finding Extreme Relativistic Objects. I. Statistics of Relativistic Fe Kalpha lines in Radio-Quiet Type 1 AGN

Accretion models predict that fluorescence lines broadened by relativistic effects should arise from reflection of X-ray emission onto the inner region of the accretion disc surrounding the central black hole of active galactic nuclei (AGN). The theory behind the origin of relativistic lines is well established, and observational evidence from a moderate number of sources seems to support the existence of these lines. The aim of this work is to establish the fraction of AGN with relativistic Fe Kalpha lines, and study possible correlations with source physical properties. An XMM-Newton collection of 149 radio-quiet Type 1 AGN has been systematically and uniformly analyzed in order to search for significant evidence of a relativistically broadened Fe Kalpha line. To enable statistical studies, an almost complete, flux-limited subsample of 31 sources has been defined. The 2-10 keV spectra of the FERO sources have been compared with a complex model including most of the physical components observed in the X-ray spectra of Seyfert galaxies: a power law primary continuum modified by non-relativistic Compton reflection and warm absorption, plus a series of narrow Fe line reflection features. The observed fraction of sources in the flux-limited sample that show significant evidence of a relativistic Fe Kalpha line is 36%. The average line Equivalent Width (EW) is of the order of 100 eV, while the average disc inclination angle is 28+/-5 deg and the average power-law index of the radial disc emissivity law is 2.4+/-0.4. The spin value is well constrained only in 2 cases (MCG-6-30-15 and MRK509), and in the rest of the cases, whenever a constraint can be placed, it always implies the rejection of the static black hole solution. The Fe Kalpha line EW does not correlate with disc parameters or with system physical properties, such as black hole mass, accretion rate and hard X-ray luminosity.

astro-ph.HE↗

arXiv2010

The pertinence of Jet Emitting Discs physics to Microquasars: Application to Cygnus X-1

The interpretation of the X-ray spectra of X-ray binaries during their hard states requires a hot, optically thin medium. There are several accretion disc models in the literature that account for this aspect. However, none is designed to simultaneously explain the presence of powerful jets detected during these states. A new quasi-keplerian hot accretion disc solution, a Jet Emitting disc (JED hereafter), which is part of a global disc-jet MHD structure producing stationary super-alfvénic ejection, is investigated here. Its radiative and energetic properties are then compared to the observational constraints found in Cygnus X-1. We solve the disc energy equation by balancing the local heating term with advection and cooling by synchrotron, bremsstrahlung and Comptonization processes. The heating term, disc density, accretion velocity and magnetic field amplitude were taken from published self-similar models of accretion-ejection structures. Both optically thin and thick regimes are considered in a one temperature gas supported disc. Three branches of solutions are found possible at a given radius but we investigate only the hot, optically thin and geometrically slim solutions. These solutions give simultaneously, and in a consistent way, the radiative and energetics properties of the disc-jet system. They are able to very well reproduce the accretion-ejection properties of Cygnus X-1, namely its X-ray spectral emission, jet power and jet velocity. About half of the released accretion power is used to produce two mildly relativistic (v/c~0.5) jets and for a luminosity of the order of 1\% of the Eddington luminosity, the JED temperature and optical depth are close to that observed in the hard state Cygnus X-1. The JEDs properties are in agreement with the observations of the prototypical black hole binary Cygnus X-1. and are likely to be relevant to the whole class of microquasars.

astro-ph.HE↗

arXiv2010

High resolution X-ray spectroscopy of the Seyfert 1 Mrk841: insights into the warm absorber and warm emitter

The Seyfert 1 galaxy Mrk841 was observed five times between 2001 and 2005 by the XMM-Newton X-ray observatory. The source is well known for showing spectral complexity in the variable iron line and in the soft X-ray excess. This paper reports on the first study of Mrk841 soft X-ray spectrum at high spectral resolution. The availability of multiple exposures obtained by the Reflection Grating Spectrometer (RGS) cameras allows a thorough study of the complex absorption and emission spectral features in the soft X-ray band.The three combined exposures obtained in January 2001 and the two obtained in January and July 2005 were analysed using the SPEX software. We detect a two-phase warm absorber: a medium ionisation component (logxi~1.5-2.2 ergs s cm^{-1}) is responsible for a deep absorption feature in the Unresolved Transition Array of the Fe M-shell and for several absorption lines in the OVI-VIII band; a higher ionisation phase with logxi~3 ergs s cm^{-1} is required to fit absorption in the NeIX-X band. The ionisation state and the column density of the gas present moderate variation from 2001 to 2005 for both phases. The high ionisation component of the warm absorber has no effect in the Fe K band. No significant velocity shift of the absorption lines is measured in the RGS data. Remarkably, the 2005 spectra show emission features consistent with photoionisation in a high density (n_e>10^{11} cm^{-3}) gas: a prominent OVII line triplet is clearly observed in January 2005 and narrow Radiative Recombination Continua (RRC) of OVII and CVI are observed in both 2005 data sets. A broad Gaussian line around 21.7 Angstrom is also required to fit all the data sets. The derived radial distance for the emission lines seems to suggest that the photoionisation takes place within the optical Broad Line Region of the source.

astro-ph.HE↗

arXiv2009

X-ray evidence for a mildly relativistic and variable outflow in the luminous Seyfert 1 galaxy Mrk509

There is growing evidence for the presence of blueshifted Fe K absorption lines in a number of radio-quiet AGNs and QSOs. These may be fundamental to probe flow dynamics near supermassive black holes. Here we aim at verifying and better characterising the existence of such Fe K absorption at ~8-10 keV in the luminous Seyfert 1 galaxy Mrk509, one of the most promising target for these studies. We present a comprehensive spectral analysis of the six XMM-Newton observations of the source (for a total of ~200 ks), focusing on the detailed and systematic search for absorption features in the high-energy data. We detect several absorption features at rest-frame energies ~8-8.5 keV and ~9.7 keV. The lines are consistent with being produced by H-like iron Ka and Kb shell absorptions associated with an outflow with mildly relativistic velocity of ~0.14-0.2 c. The lines are found to be variable in energy and, marginally in intensity, implying that variations in either the column density, geometry and/or ionization structure of the outflow are common in this source.

astro-ph.HE↗

arXiv2009

Compton reflection in AGN with Simbol-X

AGN exhibit complex hard X-ray spectra. Our current understanding is that the emission is dominated by inverse Compton processes which take place in the corona above the accretion disk, and that absorption and reflection in a distant absorber play a major role. These processes can be directly observed through the shape of the continuum, the Compton reflection hump around 30 keV, and the iron fluorescence line at 6.4 keV. We demonstrate the capabilities of Simbol-X to constrain complex models for cases like MCG-05-23-016, NGC 4151, NGC 2110, and NGC 4051 in short (10 ksec) observations. We compare the simulations with recent observations on these sources by INTEGRAL, Swift and Suzaku. Constraining reflection models for AGN with Simbol-X will help us to get a clear view of the processes and geometry near to the central engine in AGN, and will give insight to which sources are responsible for the Cosmic X-ray background at energies above 20 keV.

astro-ph.HE↗

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.

astro-ph.HE↗

arXiv2007

The role of the disk magnetization on the hysteresis behavior of X-ray binaries

We present a framework for understanding the dynamical and spectral properties of X-ray Binaries, where the presence of an organized large scale magnetic field plays a major role. Such a field is threading the whole accretion disk with an amplitude measured by the disk magnetization $μ(r,t) =B_z^2/(μ_o P_{tot})$, where $P_{tot}$ is the total, gas and radiation, pressure. Below a transition radius $r_J$, a jet emitting disk (the JED) is settled and drives self-collimated non relativistic jets. Beyond $r_J$, no jet is produced despite the presence of the magnetic field and a standard accretion disc (the SAD) is established. The radial distribution of the disk magnetization $μ$ adjusts itself to any change of the disk accretion rate $\dot m$, thereby modifying the transition radius $r_J$. We propose that a SAD-to-JED transition occurs locally, at a given radius, in a SAD when $μ=μ_{max} \simeq 1$ while the reverse transition occurs in a JED only when $μ=μ_{min}\simeq 0.1$. This bimodal behavior of the accretion disk provides a promising way to explain the hysteresis cycles followed by X-ray binaries during outbursts.

astro-ph↗

arXiv2007

Status of QGSJET

Basic physics concepts of the QGSJET model are discussed, starting from the general picture of high energy hadronic interactions and addressing in some detail the treatment of multiple scattering processes, contributions of ``soft'' and ``semihard'' parton dynamics, implementation of non-linear interaction effects. The predictions of the new model version (QGSJET II.03) are compared to selected accelerator data. Future developments are outlined and the expected input from the LHC collider for constraining model predictions is discussed.

hep-ph↗

arXiv2007

Unveiling the broad band X-ray continuum and iron line complex in Mkr 841

Mkr 841 is a bright Seyfert 1 galaxy known to harbor a strong soft excess and a variable K$α$ iron line. It has been observed during 3 different periods by XMM for a total cumulated exposure time of $\sim$108 ks. We present in this paper a broad band spectral analysis of the complete EPIC-pn data sets. We were able to test two different models for the soft excess, a relativistically blurred photoionized reflection (\r model) and a relativistically smeared ionized absorption (\a model). The continuum is modeled by a simple cut-off power law and we also add a neutral reflection. These observations reveal the extreme and puzzling spectral and temporal behaviors of the soft excess and iron line. The 0.5-3 keV soft X-ray flux decreases by a factor 3 between 2001 and 2005 and the line shape appears to be a mixture of broad and narrow components. We succeed in describing this complex broad-band 0.5-10 keV spectral variability using either \r or \a to fit the soft excess. Both models give statistically equivalent results even including simultaneous BeppoSAX data up to 200 keV. Both models are consistent with the presence of remote reflection characterized by a constant narrow component in the data. However they differ in the presence of a broad line component present in \r but not needed in \a. This study also reveals the sporadic presence of relativistically redshifted narrow iron lines.

astro-ph↗

arXiv2006

The origin of the strong soft excess and puzzling iron line complex in Mkn 841

Mkn 841 has been observed during 3 different periods (January 2001, January 2005 and July 2005) by XMM-Newton for a total cumulated exposure time of ~108 ks. We present in this paper a broad band spectral analysis of the complete EPIC-pn data sets. These observations confirm the presence of the strong soft excess and complex iron line profile known to be present in this source since a long time. They also reveal their extreme and puzzling spectral and temporal behaviors. Indeed, the 0.5-2 keV soft X-ray flux decreases by a factor 3 between 2001 and 2005 and the line shape appears to be a mixed of broad and narrow components, both variable but on differen timescales. The broad-band 0.5-10 keV spectra are well described by a model including a primary power law continuum, a blurred photoionized reflection and a narrow iron line, the blurred reflection fitting self-consistently the soft excess and the broad line component. The origin and nature of the narrow component is unclear.

astro-ph↗

arXiv2006

A unified paradigm for the spectral and temporal evolution of Black Hole X-ray Binaries

We present a unified picture to explain the spectral states of BH binaries based on the two-flow model. In our view, the central regions have a multi-flow configuration consisting in (1) an outer standard accretion disc (SAD) down to a transition radius $r_{tr}$, (2) an inner magnetized jet emitting disc (JED) below $r_{tr}$ driving (3) a self-collimated non relativistic MHD jet surrounding, when conditions for pair creation are met, (4) a ultra relativistic pair beam. Large values of $r_{tr}$ correspond to Hard states while small values correspond to Soft states. In between these extremes, in the high intermediate state, $r_{tr}$ can reach values that switch on a pair cascade process giving birth to ultra-relativistic pair blobs that explain the superluminal events. In this model the accretion rate but also the disc magnetization $μ$ play important roles, the latter being necessarily in the range 0.1-1 for the MHD jet to exist. Then, with simple assumptions on $μ$, we propose an explanation for the hysteresis behavior observed in microquasars during their outburst. We also discuss the nature, in our framework, of the X-ray corona and the origin of the X-ray variability in the hard state. Preliminary results are discussed.

astro-ph↗

arXiv2006

The broad band spectrum and variability of NGC 4151 observed by BeppoSAX

We present an analysis of all SAX observations of NGC 4151. This source was observed 5 times from 1996 to 2001 with durations ranging from a day to four days. The intrinsic continuum, is absorbed at low energies by a complex system: a cold patchy absorber plus a warm uniform screen photoionized by the central continuum. We find that this dual absorber is the main driver of the observed variability, up to a factor of eight, at 3 keV. In particular the covering fraction of the cold absorber changes on time scales of the order of a day, supporting its association with the Broad Line Region. The column density of the warm gas varies on a longer time scale (months to year). Some of the small amplitude spectral variability above 10 keV can be explained with an intrinsic variation (ΔΓ~0.2).The flux below 1 keV remains constant confirming an extended origin. Its spectrum is reproduced by a combination of a thermal component and a power law with the same slope as the intrinsic continuum but with an intensity a few per cent. A Compton reflection component is significantly detected in 1996 (averaged value of Ω/2π~0.4), with intensity decreasing on time scale of year, and it desappears in 2000 and 2001. The long time scale of variations argues for an association with an optically thick torus at a distance of few light years. An iron line was detected in all spectra. Its energy is consistent with fluorescence by cold iron. We find that the line is variable. Its behaviour is reproduced by a variable component proportional to the level of the reflection flux plus a constant component. The flux of the latter is consistent with the extended line emission observed by Chandra. We conclude that the first component is likely arising from the torus and the second is produced in the extended Narrow Line Region.

astro-ph↗

arXiv2005

Bimodal spectral variability of Cygnus X-1 in an intermediate state

We report the results of an observation of Cygnus X-1 with INTEGRAL, that we combine with simultaneous radio observations with the Ryle telescope. Both spectral and variability properties of the source indicate that Cygnus X-1 was in an Intermediate State. The INTEGRAL spectrum shows a high-energy cut-off or break around 100 keV. The shape of this cut-off differs from pure thermal Comptonisation, suggesting the presence of a non-thermal component at higher energies.The average broad band spectrum is well represented by hybrid thermal/non-thermal Comptonisation models. During the 4 day long observation the source showed an important spectral and flux variability. A principal component analysis demonstrates that most of this variability occurs through 2 independent modes. The first mode consists in changes in the overall luminosity on time scale of hours with almost constant spectra that are strikingly uncorrelated with the variable radio flux. We interpret this variability mode as variations of the dissipation rate in the corona. The second variability mode consists in a pivoting of the spectrum around 10 keV. It acts on a longer time-scale: initially soft, the spectrum hardens in the first part of the observation and then softens again. This pivoting pattern is strongly correlated with the radio (15 GHz) emission: radio fluxes are stronger when the INTEGRAL spectrum is harder. We propose that the pivoting mode represents a 'mini' state transition from a nearly High Soft State to a nearly Low Hard State, and back. This mini-transition would be caused by changes in the soft cooling photons flux in the hot Comptonising plasma associated with an increase of the temperature of the accretion disc. The jet power then appears to be anti-correlated with the disc luminosity and unrelated to the coronal power.

astro-ph↗

arXiv2005

A unified accretion-ejection paradigm for Black Hole X-ray Binaries

We present a new picture for the central regions of Black Hole X-ray Binaries. In our view, these central regions have a multi-flow configuration which consists in (1) an outer standard accretion disc down to a transition radius r_J, (2) an inner magnetized accretion disc below r_J driving (3) a non relativistic self-collimated electron-proton jet surrounding, when adequate conditions for pair creation are met, (4) a ultra relativistic electron-positron beam. This accretion-ejection paradigm provides a simple explanation to the canonical spectral states by varying the transition radius r_J and disc accretion rate independently. Large values of r_J correspond to the Quiescent state for low $\dot m$ and the Hard state for larger $\dot m$. These states are characterized by the presence of a steady electron-proton MHD jet emitted by the disc below r_J. The hard X-ray component is expected to form at the jet basis. When r_j becomes smaller than the marginally stable orbit r_i, the whole disc resembles a standard accretion disc, characteristic of the Soft state. Intermediate states correspond to situations where r_J ~ r_i. At large $\dot m$, an unsteady pair cascade process is triggered within the jet axis, giving birth to ejection of relativistic pair blobs. This would correspond to the luminous intermediate state, with its associated superluminal motions. The variation of r_J independently of $\dot m$ is a necessary ingredient in this picture, arising from the presence of a large scale vertical magnetic field threading the disc.

astro-ph↗

arXiv2004

Integral observation of Cyg X-1 in an intermediate state

We present preliminary results of an observation of Cygnus X-1 with INTEGRAL performed on June 7-11 2003. Both spectral and variability properties of the source indicate that Cygnus X-1 was in an intermediate state. As expected during state transitions, we find an anticorrelation between the 3-10 keV and the 15 GHz radio fluxes and a strong correlation between the 3-200 keV hardness and radio flux.

astro-ph↗