arXiv subjects

F. Panessa

Publications and source records attributed to F. Panessa.

At least 91 records · Page 5Linked to original sources

arXiv2010

The Soft X-ray Imager on board EXIST

The Soft X-ray Imager (SXI) is one of the three instruments on board EXIST, a multi-wavelength observatory in charge of performing a global survey of the sky in hard X-rays searching for Super-massive Black Holes (Grindlay & Natalucci, these Proceedings). One of the primary objectives of EXIST is also to study with unprecedented sensitivity the most unknown high energy sources in the Universe, like high redshift GRBs, which will be pointed promptly by the Spacecraft by autonomous trigger based on hard X-ray localization on board. The presence of a soft X-ray telescope with an effective area of about 950cm2 in the energy band 0.2-3 keV and extended response up to 10 keV will allow to make broadband studies from 0.1 to 600 keV. In particular, investigations of the spectra components and states of AGNs and monitoring of variability of sources, study of the prompt and afterglow emission of GRBs since the early phases, which will help to constrain the emission models and finally, help the identification of sources in the EXIST hard X-ray survey and the characterization of the transient events detected. SXI will also perform surveys: a scanning survey with sky coverage 2pi and a limiting flux of 5x10^(-14) cgs plus other serendipitous.

astro-ph.IM↗

arXiv2009

The SXI telescope on board EXIST: scientific performances

The SXI telescope is one of the three instruments on board EXIST, a multiwavelength observatory in charge of performing a global survey of the sky in hard X-rays searching for Supermassive Black Holes. One of the primary objectives of EXIST is also to study with unprecedented sensitivity the most unknown high energy sources in the Universe, like high redshift GRBs, which will be pointed promptly by the Spacecraft by autonomous trigger based on hard X-ray localization on board. The recent addition of a soft X-ray telescope to the EXIST payload complement, with an effective area of ~950 cm2 in the energy band 0.2-3 keV and extended response up to 10 keV will allow to make broadband studies from 0.1 to 600 keV. In particular, investigations of the spectra components and states of AGNs and monitoring of variability of sources, study of the prompt and afterglow emission of GRBs since the early phases, which will help to constrain the emission models and finally, help the identification of sources in the EXIST hard X-ray survey and the characterization of the transient events detected. SXI will also perform surveys: a scanning survey with sky coverage of about 2pi and limiting flux of 5x10^{-14}cgs plus other serendipitous. We give an overview of the SXI scientific performance and also describe the status of its design emphasizing how it has been derived by the scientific requirements.

astro-ph.IM↗

arXiv2009

The fraction of Compton-thick sources in an INTEGRAL complete AGN sample

We study the NH distribution in a complete sample of 88 AGN selected in the 20-40 keV band from INTEGRAL/IBIS observations. We find that the fraction of absorbed (NH > 10^{22} cm^2) sources is 43% while the Compton thick AGN comprise 7% of the sample. While these estimates are fully compatible with previous soft gamma-ray surveys, they would appear to be in contrast with results reported by Risaliti et al. (1999) using an optically selected sample. This apparent difference can be explained as being due to a selection bias caused by the reduction in high energy flux in Compton thick objects rendering them invisible at our sensitivity limit. Taking this into account we estimate that the fraction of highly absorbed sources is actually in close agreement with the optically selected sample. Furthermore we show that the measured fraction of absorbed sources in our sample decreases from 80% to about 20-30% as a function of redshift with all Compton thick AGN having z < 0.015. If we limit our analysis to this distance and compare only the type 2 objects in our sample with the Risaliti et al. objects below this redshift value, we find a perfect match to their NH distribution. We conclude that in the low redshift bin we are seeing almost the entire AGN population, from unabsorbed to at least mildly Compton thick objects, while in the total sample we lose the heavily absorbed 'counterparts' of distant and therefore dim sources with little or no absorption. Taking therefore this low z bin as the only one able to provide the 'true' distribution of absorption in type 1 and 2 AGN, we estimate the fraction of Compton thick objects to be >24%.

astro-ph.HE↗

arXiv2009

The INTEGRAL Complete Sample of Type 1 AGN

In this paper we discuss the broad-band X-ray characteristics of a complete sample of 36 type 1 AGN, detected by INTEGRAL in the 20-40 keV band above the 5.5sigma level. We present, for all the objects in the sample, the broad-band (1-110 keV) spectral analysis obtained by using INTEGRAL/Swift-BAT observations together with XMM-Newton, Chandra, ASCA and Swift/XRT data. We also present the general average properties of the sample, i.e. the distribution of photon indices, high energy cut-offs, reflection fractions and absorption properties, together with an in-depth analysis of their parameter space. We find that the average Seyfert 1 power law has an index of 1.7 with a dispersion of 0.2. The mean cut-off energy is at around 100 keV, with most objects displaying Ec in the range 50-150 keV; the average amount of Compton reflection is 1.5 with a typical dispersion of 0.7. We do not find any convincing correlation between the various parameters, an indication that our analysis is not strongly dependent by the interplay between them. Finally, we investigate how the results presented in this work fit into current frameworks for AGN spectral modeling and Cosmic Diffuse X-ray Background synthesis models.

astro-ph.CO↗

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.

astro-ph.CO↗

arXiv2009

An intermediate black hole spin in the NLS1 galaxy SWIFT J2127.4+5654: chaotic accretion or spin energy extraction?

We have observed the hard X-ray selected Narrow-Line Seyfert 1 galaxy SWIFT J2127.4+5654 with Suzaku. We report the detection of a broad relativistic iron emission line from the inner accretion disc. By assuming that the inner edge of the accretion disc corresponds to the innermost stable circular orbit of the black hole spacetime, the line profile enables us to measure a black hole spin a= 0.6\pm0.2. However, a non-rotating Schwarzschild spacetime is excluded at just above the 3 sigma level, while a maximally spinning Kerr black hole is excluded at the ~5 sigma level. The intermediate spin we measure may indicate that accretion-driven black hole growth in this source proceeds through short-lived episodes with chaotic angular momentum alignment between the disc and the hole rather than via prolonged accretion. The measured steep emissivity index (q~5) constrains the irradiating X-ray source to be very centrally concentrated. Light bending may help focus the primary emission towards the innermost accretion disc, thus steepening the irradiation profile. On the other hand, steep profiles can also be reached if magnetic extraction of the hole rotational energy is at work. If this is the case, the interplay between accretion (spinning up the black hole) and rotational energy extraction (spinning it down) forces the hole to reach an equilibrium spin value which, under standard assumptions, is remarkably consistent with our measurement. Rotational energy extraction would then be able to simultaneously account for the intermediate spin and steep emissivity profile we infer from our spectral analysis without the need to invoke chaotic accretion episodes. (abridged)

astro-ph.HE↗

arXiv2009

IGR J16351-5806: another close by Compton-thick AGN

IGR J16351-5806 has been associated with the Seyfert 2 galaxy ESO 137-G34, having been first reported as a high energy emitter in the third INTEGRAL/IBIS survey. Using a new diagnostic tool based on X-ray column density measurements vs softness ratios, Malizia et al. (2007) identified this source as a candidate Compton thick AGN. In the present work we have analysed combined XMM-Newton and INTEGRAL data of IGR J16351-5806 in order to study its broad band spectrum and investigate its Compton thick nature. The prominent K_alpha fluorescence line around 6.4 keV (EW > 1 keV) together with a flat 2-10 keV spectrum immediately point to a highly obscured source. The overall spectrum can be interpreted in terms of a transmission scenario where some of the high energy radiation is able to penetrate through the thick absorption but a good fit is also obtained using a pure reflection spectrum. An alternative possibility is that of a complex absorption, where two layers of absorbing matter each partially covering the central nucleus are present in IGR J16351-5806. All three scenarios are compatible from a statistical viewpoint and provide reasonable AGN spectral parameters; more importantly all point to a source with an absorbing column greater than 1.5 x 10^24 cm^-2, i.e. to a Compton thick AGN. Because of this heavy obscuration, some extra components which would otherwise be hidden are able to emerge at low energies and can be studied. By providing strong evidence for the Compton thick nature of IGR J16351-5806, we indirectly confirm the validity of the Malizia et al. diagnostic diagram.

astro-ph.GA↗

arXiv2008

A broad-band spectral analysis of eight radio loud type 1 AGN selected in the hard X-ray band

Starting from a complete sample of type I AGN observed by INTEGRAL in the 20-40 keV band, we have selected a set of 8 AGN which can be classified as radio loud objects according to their 1.4 GHz power density, radio to hard X-ray flux flux density ratio and radio morphology. The sample contains 6 Broad Line Radio Galaxies and 2 candidate ones. Most of the objects in our sample display a double lobe morphology, both on small and large scales. For all the objects, we present broad-band (1-110 keV) spectral analysis using INTEGRAL observations together with archival XMM-Newton, Chandra, Swift/XRT and Swift/BAT data. We constrain the primary continuum (photon index and cut-off energy), intrinsic absorption and reprocessing features (iron line and reflection) in most of the objects. The sources analysed here show remarkable similarities to radio quiet type 1 AGN with respect to most of the parameters analysed; we only find marginal evidence for weaker reprocessing features in our objects compared to their radio quiet counterparts. Similarly we do not find any correlation between the spectral parameters studied and the source core dominance or radio to 20-100 keV flux density ratios, suggesting that what makes our objects radio loud has no effect on their high energy characteristics.

astro-ph↗

arXiv2008

First high energy observations of Narrow Line Seyfert 1s with INTEGRAL/IBIS

Narrow Line Seyfert 1 galaxies (NLS1) are very interesting objects which display peculiar properties when compared to their broad line analogues (BLS1). Although well studied in many wavebands, their behaviour at >10 keV is poorly studied and yet important to discriminate between models invoked to explain the complexity observed in the X-ray band. Here we present for the first time high energy observations (17-100 keV) of five NLS1 galaxies (3 bona fide and 2 candidates) detected by INTEGRAL/IBIS and provide for all of them a broad band spectral analysis using data obtained by Swift/XRT below 10 keV. The combined INTEGRAL spectrum is found to be steeper (Gamma=2.6 +/- 0.3) than those of classical Seyfert 1 objects. This is due to a high energy cutoff, which is required in some individual fits as in the average broad band spectrum. The location of this high energy cutoff is at lower energies (E < 60 keV) than typically seen in classical type 1 AGNs; a reflection component may also be present but its value (R < 0.8) is compatible with those seen in standard Seyfert 1s. We do not detect a soft excess in individual objects but only in their cumulative spectrum. Our results suggest a lower plasma temperature for the accreting plasma which combined to the high accretion rates (close to the Eddington rate) point to different nuclear conditions in broad and narrow line Seyfert 1 galaxies, likely related to different evolutionary stages.

astro-ph↗

arXiv2008

The broad-band XMM-Newton and INTEGRAL spectra of bright type 1 Seyfert galaxies

The 0.5-150 keV broad-band spectra of a sample of nine bright type 1 Seyfert galaxies are analyzed here. These sources have been discovered/detected by INTEGRAL and subsequently observed with XMM--Newton for the first time with high sensitivity below 10 keV. The sample, although small, is representative of the population of type 1 AGN which are now being observed above 20 keV. The intrinsic continuum has been modeled using three different parameterizations: a power-law model, an exponential cut-off power-law and an exponential cut-off power-law with a Compton reflection component. In each model the presence of intrinsic absorption, a soft component and emission line reprocessing features has also been tested. A simple power-law model is a statistically good description of most of the spectra presented here; an FeK line, fully and/or partial covering absorption and a soft spectral component are detected in the majority of the sample sources. The average photon index (< Gamma > = 1.7 $\pm$ 0.2) is consistent, within errors, with the canonical spectral slope often observed in AGN although the photon index distribution peaks in our case at flat Gamma (~ 1.5) values. For four sources, we find a significantly improved fit when the power-law is exponentially cut-off at an energy which is constrained to be below ~ 150 keV. The Compton reflection parameter could be estimated in only two objects of the sample and in both cases is found to be R > 1.

astro-ph↗

arXiv2008

Unveiling the nature of INTEGRAL objects through optical spectroscopy. VI. A multi-observatory identification campaign

Using 8 telescopes in the northern and southern hemispheres, plus archival data from two on-line sky surveys, we performed a systematic optical spectroscopic study of 39 putative counterparts of unidentified or poorly studied INTEGRAL sources in order to determine or at least better assess their nature. This was implemented within the framework of our campaign to reveal the nature of newly-discovered and/or unidentified sources detected by INTEGRAL. Our results show that 29 of these objects are active galactic nuclei (13 of which are of Seyfert 1 type, 15 are Seyfert 2 galaxies and one is possibly a BL Lac object) with redshifts between 0.011 and 0.316, 7 are X-ray binaries (5 with high-mass companions and 2 with low-mass secondaries), one is a magnetic cataclysmic variable, one is a symbiotic star and one is possibly an active star. Thus, the large majority (74%) of the identifications in this sample belongs to the AGN class. When possible, the main physical parameters for these hard X-ray sources were also computed using the multiwavelength information available in the literature. These identifications further underscore the importance of INTEGRAL in studying the hard X-ray spectra of all classes of X-ray emitting objects, and the effectiveness of a strategy of multi-catalogue cross-correlation plus optical spectroscopy to securely pinpoint the actual nature of still unidentified hard X-ray sources.

astro-ph↗

arXiv2008

An X-ray view of absorbed INTEGRAL AGN

Aims. We present a 0.2--200 keV broad-band study of absorbed AGN observed with INTEGRAL, XMM-Newton, Chandra and ASCA to investigate the continuum shape and the absorbing/reflecting medium properties. Methods. The sources are selected in the INTEGRAL AGN sample to have a 20--100 keV flux below 8$\times10^{-11}$ $\flux$ (5 mCrab), and are characterized by a 2--10 keV flux in the range (0.8--10)$\times10^{-11}$ $\flux$. The good statistics allow us a detailed study of the intrinsic and reflected continuum components. In particular, the analysis performed on the combined broad-band spectra allow us to investigate the presence of Compton reflection features and high energy cut-off in these objects. Results. The column density of the absorbing gas establishes the Compton thin nature for three sources in which a measure of the absorption was still missing. The Compton thin nature of all the sources in this small sample is also confirmed by the diagnostic ratios F$x/F[OIII]. The Compton reflection components we measure, reflection continuum and iron line, are not immediately compatible with a scenario in which the absorbing and reflecting media are one and the same, i.e. the obscuring torus. A possible solution is that the absorption is more effective than reflection, e.g. under the hypothesis that the absorbing/reflecting medium is not uniform, like a clumpy torus, or that the source is observed through a torus with a very shallow opening angle. The high energy cut-off (a lower limit in two cases) is found in all sources of our sample and the range of values is in good agreement with that found in type 1 Seyfert galaxies. At lower energies there is clear evidence of a soft component (reproduced with a thermal and/or scattering model), in six objects.

astro-ph↗

arXiv2007

NGC3147: a "true" Seyfert 2 without the broad-line region

We report on simultaneous optical and X-ray observations of the Seyfert galaxy, NGC3147. The XMM-Newton spectrum shows that the source is unabsorbed in the X-rays ($N_H<5\times10^{20}$ cm$^{-2}$). On the other hand, no broad lines are present in the optical spectrum. The origin of this optical/X-rays misclassification (with respect to the Unification Model) cannot be attributed to variability, since the observations in the two bands are simultaneous. Moreover, a Compton-thick nature of the object can be rejected on the basis of the low equivalent width of the iron K$α$ line ($\simeq130$ eV) and the large ratio between the 2-10 keV and the [OIII] fluxes. It seems therefore inescapable to conclude that NGC3147 intrinsically lacks the Broad Line Region (BLR), making it the first "true" Seyfert 2.

astro-ph↗

arXiv2007

The XMM-Newton Serendipitous Survey V. Optical identification of the XMM-Newton Medium sensitivity Survey (XMS)

We present the XMM-Newton Medium sensitivity Survey (XMS), including a total of 318 X-ray sources found among the serendipitous content of 25 XMM-Newton target fields. The XMS comprises four largely overlapping source samples selected at soft (0.5-2 keV), intermediate (0.5-4.5 keV), hard (2-10 keV) and ultra-hard (4.5-7.5 keV) bands, the first three of them being flux-limited. We report on the optical identification of the XMS samples, complete to 85-95%. At the intermediate flux levels sampled by the XMS we find that the X-ray sky is largely dominated by Active Galactic Nuclei. The fraction of stars in soft X-ray selected samples is below 10%, and only a few per cent for hard selected samples. We find that the fraction of optically obscured objects in the AGN population stays constant at around 15-20% for soft and intermediate band selected X-ray sources, over 2 decades of flux. The fraction of obscured objects amongst the AGN population is larger (~35-45%) in the hard or ultra-hard selected samples, and constant across a similarly wide flux range. The distribution in X-ray-to-optical flux ratio is a strong function of the selection band, with a larger fraction of sources with high values in hard selected samples. Sources with X-ray-to-optical flux ratios in excess of 10 are dominated by obscured AGN, but with a significant contribution from unobscured AGN.

astro-ph↗

arXiv2007

Broadband X-ray spectrum of the newly discovered broad line radio galaxy IGR J21247+5058

In this paper we present radio and high energy observations of the INTEGRAL source IGR J21247+5058, a broad line emitting galaxy obscured by the Galactic plane. Archival VLA radio data indicate that IGR J21247+5058 can be classified as an FRII Broad Line Radio Galaxy. The spectrum between 610 MHz and 15 GHz is typical of synchrotron self-absorbed radiation with a peak at 8 GHz and a low energy turnover; the core fraction is 0.1 suggestive of a moderate Doppler boosting of the base of the jet. The high energy broad-band spectrum was obtained by combining XMM-Newton and Swift/XRT observation with INTEGRAL/IBIS data. The 0.4-100 keV spectrum is well described by a power law, with slope $Γ$=1.5, characterised by complex absorption due to two layers of material partially covering the source and a high energy cut-off around 70-80 keV. Features such as a narrow iron line and a Compton reflection component, if present, are weak, suggesting that reprocessing of the power law photons in the accretion disk plays a negligible role in the source.

astro-ph↗

arXiv2007

An XMM-Newton study of Hyper-Luminous Infrared Galaxies

Hyper-Luminous Infrared Galaxies (HLIRGs) are the most luminous persistent objects in the Universe. They exhibit extremely high star formation rates, and most of them seem to harbour an AGN. They are unique laboratories to investigate utmost star formation, and its connection to super-massive black hole growth. X-ray studies of HLIRGs have the potential to unravel the AGN contribution to the bolometric output from these bright objects. We have selected a sample of 14 HLIRGs observed by XMM-Newton (type 1, type 2 AGN and starburst), 5 of which are candidates to be Compton-thick objects. This is the first time that a systematic study of this type of objects is carried out in the X-ray spectral band. Their X-ray spectral properties have been correlated with their IR luminosities, estimated by IRAS, ISO and sub-mm data. The X-ray spectra of HLIRGs present heterogeneous properties. All our X-ray detected HLIRGs (10) have AGN-dominated X-ray spectra. The hard X-ray luminosity of 8 of them is consistent with a pure AGN contribution, while in the remaining 2 sources both an AGN and a starburst seem to contribute to the overall emission. We found soft excess emission in 5 sources. In one of them it is consistent with a pure starburst origin, while in the other 4 sources it is consistent with an AGN origin. The observed X-ray emission is systematically below the one expected for a standard local QSO of the same IR luminosity, suggesting the possible presence of absorption in type 2 objects and/or a departure from a standard spectral energy distribution of QSO. The X-ray-to-IR-luminosity ratio is constant with redshift, indicating similar evolutions for the AGN and starburst component, and that their respective power sources could be physically related.

astro-ph↗

arXiv2007

The X-ray and Radio Connection in Low-luminosity Active Nuclei

We present the results of the correlation between the nuclear 2-10 keV X-ray and radio (at 2cm, 6cm and 20cm) luminosities for a well defined sample of local Seyfert galaxies. We use a sample of low luminosity radio galaxies (LLRGs) for comparison. In both Seyfert and LLRGs samples, X-ray and radio luminosities are significantly correlated over 8 orders of magnitude, indicating that the X-ray and radio emission sources are strongly coupled. Moreover, both samples show a similar regression slope, L(X)$\propto$ L(R)^(0.97), but Seyfert galaxies are three orders of magnitude less luminous in the radio band than LLRGs. This suggests that either similar physical mechanisms are responsible for the observed emission or a combination of different mechanisms ends up producing a similar correlation slope. Indeed, the common belief for LLRG is that both the X-ray and radio emission are likely dominated by a relativistic jet component, while in Seyfert galaxies the X-ray emission probably arises from a disk-corona system and the radio emission is attributed to a jet/outflow component. We investigate the radio loudness issue in the two samples and find that the Seyfert galaxies and the LLRGs show a different distribution of the radio loudness parameters. No correlation is found between the luminosity and the radio loudness, however the latter is related to the black hole mass and anti-correlated with the Eddington ratio. The dichotomy in the radio loudness between Seyfert and LLRG observed down to low Eddington ratios, L(2-10)/L(Edd) $\sim$ 10^(-8), does not support the idea that the origin of the radio loudness is due to a switch in the accretion mode.

astro-ph↗

arXiv2006

Multi-wavelength and black hole mass properties of Low Luminosity Active Nuclei

We investigate the relation between the X-ray nuclear emission, optical emission line, radio luminosity and black hole mass for a sample of nearby Seyfert galaxies. Strong linear correlations between the 2-10 keV and [OIII], radio luminosities have been found, showing the same slopes found in quasars and luminous Seyfert galaxies, thus implying independence from the level of nuclear activity displayed by the sources. Moreover, despite the wide range of Eddington ratios (L/L(Edd)) tested here (six orders of magnitude, from 0.1 down to 10^(-7), no correlation is found between the X-ray, optical emission lines, radio luminosities and the black hole mass. These results suggest that low luminosity Seyfert galaxies are a scaled down version of luminous AGN and probably are powered by the same physical processes.

astro-ph↗