arXiv subjects

A. L. Longinotti

Publications and source records attributed to A. L. Longinotti.

125 records · Page 7Linked 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.

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arXiv2011

On the driver of relativistic effects strength in Seyfert galaxies

Spectroscopy of X-ray emission lines emitted in accretion discs around supermassive black holes is one of the most powerful probes of the accretion flow physics and geometry, while also providing in principle observational constraints on the black hole spin.[...] We aim at determining the ultimate physical driver of the strength of this relativistic reprocessing feature. We first extend the hard X-ray flux-limited sample of Seyfert galaxies studied so far (FERO, de la Calle Perez et al. 2010) to obscured objects up to a column density N_H=6x10^23 atoms/cm/cm. We verify that none of the line properties depends on the AGN optical classification, as expected from the Seyfert unification scenarios. There is also no correlation between the accretion disc inclination, as derived from formal fits of the line profiles, and the optical type or host galaxy aspect angle, suggesting that the innermost regions of the accretion disc and the host galaxy plane are not aligned. [...]. Data are not sensitive enough to the detailed ionisation state of the line-emitting disc. However, the lack of dependency of the line EW on either the luminosity or the rest-frame centroid energy rules out that disc ionisation plays an important role on the EW dynamical range in Seyferts. The dynamical range of the relativistically broadened K-alpha iron line EW in nearby Seyferts appears to be mainly determined by the properties of the innermost accretion flow. We discuss several mechanisms (disc ionisation, disc truncation, aberration due to a mildly relativistic outflowing corona) which can explain this. [...] Observational data are still not in contradiction with scenarios invoking different mechanisms for the spectral complexity around the iron line, most notably the "partial covering" absorption scenario. (abridged).

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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.

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arXiv2010

A characterization of the NGC 4051 soft X-ray spectrum as observed by XMM-Newton

Soft X-rays high resolution spectroscopy of obscured AGNs shows the existence of a complex soft $X$-ray spectrum dominated by emission lines of He and H-like transitions of elements from Carbon to Neon, as well as L-shell transitions due to iron ions. In this paper we characterize the XMM-Newton RGS spectrum of the Seyfert 1 galaxy NGC 4051 observed during a low flux state and infer the physical properties of the emitting and absorbing gas in the soft X-ray regime. X-ray high-resolution spectroscopy offers a powerful diagnostic tool since the observed spectral features strongly depend on the physical properties of matter (ionization parameter U, electron density n_e, hydrogen column density N_H), which in turn are tightly related to the location and size of the X-ray emitting clouds. We carried out a phenomenological study to identify the atomic transitions detected in the spectra. This study suggests that the spectrum is dominated by emission from a photoionised plasma. Then, we used the photoionization code Cloudy to produce synthetic models for the emission line component and the warm absorber observed during phases of high intrinsic luminosity. The low state spectrum cannot be described by a single photoionization component. A multi-ionization phase gas with ionization parameter in the range log U = 0.63-1.90 and column density log N_H = 22.10-22.72 cm^-2 is required, while the electron density n_e remains unconstrained. A warm absorber medium is required by the fit with parameters log U = 0.85, log N_H = 23.40 and log n_e \ut< 5. The model is consistent with an X-ray emitting regions at a distance > 5 x 10^-2 pc from the central engine.

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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.

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arXiv2009

First high-resolution detection of a warm absorber in the Broad Line Radio Galaxy 3C 382

Recent high-resolution measurements suggest that the soft X-ray spectrum of obscured Radio Galaxies (RG) exhibits signatures of photoionised gas (e.g. 3C 445 and 3C 33) similar to those observed in radio-quiet obscured Active Galactic Nuclei (AGN). While signatures of warm absorbing gas covering a wide range of temperature and ionisation states have been detected in about one half of the population of nearby Seyfert 1 galaxies, no traces of warm absorber gas have been reported to date in the high-resolution spectra of Broad Line Radio Galaxies (BLRG). We present here the first detection of a soft X-ray warm absorber in the powerful FRII BLRG 3C 382 using the Reflection Grating Spectrometer (RGS) on-board XMM-Newton. The absorption gas appears to be highly ionised, with column density of the order of 10^{22} cm^{-2}, ionisation parameter logξ>2 erg cm s^{-1} and outflow velocities of the order of 10^{3} km s^{-1}. The absorption lines may come from regions located outside the torus, however at distances less than 60 pc. This result may indicate that a plasma ejected at velocities near the speed of light and a photoionised gas with slower, outflow velocities can coexist in the same source beyond the Broad Line Regions.

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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

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

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.

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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

Relativistic inflow in the Seyfert 1 Mrk 335 revealed through X-ray absorption

The analysis of hard X-ray features in XMM-Newton data of the bright Sy 1 galaxy Mrk 335 is reported here. The presence of a broad, ionised iron K alpha emission line in the spectrum, first found by Gondoin et al.(2002), is confirmed. The broad line can be modeled successfully by relativistic accretion disc reflection models. Regardless of the underlying continuum we report, for the first time in this source, the detection of a narrow absorption feature at the rest frame energy of ~5.9 keV. If the feature is identified with a resonance absorption line of iron in a highly ionised medium, the redshift of the line corresponds to an inflow velocity of ~0.11-0.15 c. Preliminary results from a longer (100ks) exposure are also presented.

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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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arXiv2005

Energy-shifted lines in XMM-Newton spectra of Seyfert Galaxies

In the recent literature on AGNs it has been often reported that spectra of Seyfert 1 Galaxies show resonant absorption lines of Fe K which are redshifted from the rest frame position. Such lines are often found with marginal significance but, if real, could potentially open up new avenues to study the circumnuclear gas in the black hole environment. It is also extremely important to take them into account in X-ray spectral analysis because of the influence they have in the correct estimation of spectral parameters, Fe K alpha line in primis. An XMM-Newton observation of Mrk 335 is reported here as a case study: a narrow feature has been detected at 5.9 keV, i.e. with a redshift corresponding to a velocity of v ~ 0.15c. Preliminary results on the statistical significance of narrow absorption and emission lines in a sample of PG QSOs observed by XMM-Newton are also included.

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arXiv2004

On the variability of the iron line in Mrk 841

Petrucci et al. (2002; hereafter P02) have reported extraordinary behaviour of the iron K alpha line in the type 1 AGN Mrk 841. At the XMM-Newton/EPIC resolution, a narrow line was observed in a short observation, which then apparently disappeared around 0.5 days later when another observation was performed. The limits are such that the line cannot both be narrow, and variable at this level, as the light-travel time places the material at a radius where broadening by the black hole's gravitational field is inevitable. Adding an additional observation taken before the P02 data, we present a different interpretation of the apparent variability. The data support the hypothesis that the line in fact varies in width, not only in flux. Rather than showing no line, and despite the strong Compton reflection component, the final observation exhibits broad emission at ~ 6.2-6.4 keV, with a width of ~0.8 keV, typical of a relativistic accretion disc. We suggest that the apparently narrow line in the early observations arises from local illumination by a flare inducing an hotspot in the inner disc, which then becomes progressively broadened as the disc rotates.

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arXiv2003

The complex FeK line of the Narrow-Line Seyfert 1 galaxy IRAS13349+2438

The observation of the Narrow-Line Seyfert 1 galaxy IRAS13349+2438 performed by XMM-Newton European Photon Imaging Camera between 0.3-10 keV, is presented here. The broadband spectrum of the source is dominated at low energies (E < 2 keV) by a strong excess of emission and by complex emission/absorption features between 5.5-8.0 keV. The soft X-ray spectrum is consistent with ionized absorption found by the Reflection Grating Spectrometer (Sako et al. (2001)). We focus on the 2-10 keV spectrum which shows clear evidence for a broad, complex FeK alpha line, previously unseen by ASCA, and for an Fe K-shell edge detected at ~7.3-7.4 keV (rest-frame). The presence of this edge could be explained by either partial covering or ionized/relativistic reflection models, with the latter being preferred and with a resulting power law slope of Gamma \~2.2. The line profile is complex, with a broad bump between ~ 5.5-6.5 keV and a narrow emission line at ~ 7 keV, separated by a sharp drop at ~ 6.8 keV. This profile is compatible with two possible scenarios: i) a broad, ionized and gravitationally redshifted Laor diskline plus a narrow and ionized emission line; ii) a broad, ionized and single Schwarzschild (double-peaked) diskline with a superimposed narrow absorption line.

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arXiv2002

XMM-NEWTON Observation of the Seyfert 2 Galaxy NGC 4138

The XMM-Newton data presented here are the first X-ray observation of the Seyfert 2 galaxy NGC4138. Although the galaxy has been pointed by ROSAT-HRI, it was not detected, with a flux upper limit of about 1.1x10^-13 erg cm^-2 s^-1 in the 0.2-2.4 keV energy band. XMM-Newton performed the observation on 26 November 2001. The source is detected for the first time in X-rays with F[0.2-2.4]=1.0x10^-13 erg cm^-2 s^-1, in agreement with the upper limit of ROSAT. The source spectrum is typical of Seyfert 2 galaxies. We find heavy obscuration (N_H about 8x10^22 cm^-2) and a flat photon index (1.6). The source intrinsic luminosity is about 5x10^41 erg/s in the 0.5-10 keV energy band.

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