arXiv subjects

T. Maccacaro

Publications and source records attributed to T. Maccacaro.

At least 19 recordsLinked to original sources

arXiv2019

Te-REX: a sample of extragalactic TeV-emitting candidates

The REX (Radio-Emitting X-ray sources) is a catalogue produced by cross-matching X-ray data from the ROSAT-PSPC archive of pointed observations and radio data from the NRAO VLA Sky Survey, aimed at the selection of blazars. From the REX catalogue, we select a well defined and statistically complete sample of high-energy peaked BL Lac (HBL). HBL are expected to be the most numerous class of extragalactic TeV emitting sources. Specifically, we have considered only the REX sources in the currently planned CTA extragalactic survey area satisfying specific criteria and with an optical spectroscopic confirmation. We obtain 46 HBL candidates that we called Te-REX (TeV-emitting REX). We estimate the very high-energy gamma-ray emission, in the TeV domain, using an empirical approach i.e. using specific statistical relations between gamma-rays (at GeV energies) and radio/X-rays properties observed in bright HBL from the literature. We compare the spectral energy distributions (SEDs) with the sensitivities of current and upcoming Cherenkov telescopes and we predict that 14 Te-REX could be detectable with 50 hours of observations of CTA and 7 of them also with current Cherenkov facilities in 50 hours. By extrapolating these numbers on the total extragalactic sky, we predict that about 800 HBL could be visible in pointed CTA observations and about 400 with current Cherenkov telescopes in 50 hours. Interestingly, our predictions show that a non-negligible fraction (about 30%) of the HBL that will be detectable by CTA is composed of relatively weak objects whose optical nuclear emission is swamped by the host-galaxy light and not (yet) detected by Fermi-LAT.

astro-ph.HE↗

arXiv2015

WISE colours and star-formation in the host galaxies of radio-loud narrow-line Seyfert 1

We investigate the mid-infrared properties of the largest (42 objects) sample of radio-loud narrow-line Seyfert 1 (RL NLS1) collected to date, using data from the Wide-field Infrared Survey Explorer (WISE). We analyse the mid-IR colours of these objects and compare them to what is expected from different combinations of AGN and galaxy templates. We find that, in general, the host-galaxy emission gives an importan contribution to the observed mid-IR flux in particular at the longest wavelengths (W3, at 12micron, and W4, at 22micron). In about half of the sources (22 objects) we observe a very red mid-IR colour (W4-W3>2.5) that can be explained only using a starburst galaxy template (M82). Using the 22micron luminosities, corrected for the AGN contribution, we have then estimated the star-formation rate for 20 of these "red" RL NLS1, finding values ranging from 10 to 500 Msun/y. For the RL NLS1 showing bluer colours, instead, we cannot exclude the presence of a star-forming host galaxy although, on average, we expect a lower star-formation rate. Studying the radio (1.4GHz) to mid-IR (22micron) flux ratios of the RL NLS1 in the sample we found that in ~10 objects the star-forming activity could represent the most important component also at radio frequencies, in addition (or in alternative) to the relativistic jet. We conclude that both the mid-IR and the radio emission of RL NLS1 are a mixture of different components, including the relativistic jet, the dusty torus and an intense star-forming activity.

astro-ph.GA↗

arXiv2014

SDSSJ143244.91+301435.3: a link between radio-loud narrow-line Seyfert 1 galaxies and compact steep-spectrum radio sources?

We present SDSSJ143244.91+301435.3, a new case of radio-loud narrow line Seyfert 1 (RL NLS1) with a relatively high radio power (P1.4GHz=2.1x10^25 W Hz^-1) and large radioloudness parameter (R1.4=600+/-100). The radio source is compact with a linear size below ~1.4 kpc but, contrary to most of the RL NLS1 discovered so far with such a high R1.4, its radio spectrum is very steep (alpha=0.93) and not supporting a 'blazar-like' nature. Both the small mass of the central super-massive black-hole and the high accretion rate relative to the Eddington limit estimated for this object (3.2x10^7 Msun and 0.27, respectively, with a formal error of ~0.4 dex on both quantities) are typical of the class of NLS1. Through a modeling of the spectral energy distribution of the source we have found that the galaxy hosting SDSSJ143244.91+301435.3 is undergoing a quite intense star-formation (SFR=50 Msun y^-1) which, however, is expected to contribute only marginally (~1 per cent) to the observed radio emission. The radio properties of SDSSJ143244.91+301435.3 are remarkably similar to those of compact steep spectrum (CSS) radio sources, a class of AGN mostly composed by young radio galaxies. This may suggest a direct link between these two classes of AGN, with the CSS sources possibly representing the misaligned version (the so-called parent population) of RL NLS1 showing blazar characteristics.

astro-ph.GA↗

arXiv2008

The XMM-Newton Serendipitous Survey. V. The Second XMM-Newton Serendipitous Source Catalogue

Aims: Pointed observations with XMM-Newton provide the basis for creating catalogues of X-ray sources detected serendipitously in each field. This paper describes the creation and characteristics of the 2XMM catalogue. Methods: The 2XMM catalogue has been compiled from a new processing of the XMM-Newton EPIC camera data. The main features of the processing pipeline are described in detail. Results: The catalogue, the largest ever made at X-ray wavelengths, contains 246,897 detections drawn from 3491 public XMM-Newton observations over a 7-year interval, which relate to 191,870 unique sources. The catalogue fields cover a sky area of more than 500 sq.deg. The non-overlapping sky area is ~360 sq.deg. (~1% of the sky) as many regions of the sky are observed more than once by XMM-Newton. The catalogue probes a large sky area at the flux limit where the bulk of the objects that contribute to the X-ray background lie and provides a major resource for generating large, well-defined X-ray selected source samples, studying the X-ray source population and identifying rare object types. The main characteristics of the catalogue are presented, including its photometric and astrometric properties .

astro-ph↗

arXiv2008

The cosmological properties of AGN in the XMM-Newton Hard Bright Survey

(ABRIDGED) We investigate here the XLF of absorbed (Nh between 4E21 and E24 cm-2) and unabsorbed (Nh < 4E21 cm-2) AGN, the fraction of absorbed AGN as a function of Lx (and z), the intrinsic Nh distribution of the AGN population, and the XLF of Compton Thick (Nh > E24 cm-2) AGN. To carry out this investigation we have used the XMM-Newton Hard Bright Serendipitous Sample (HBSS) a complete sample of bright X-ray sources (fx > 7E-14 cgs) at high galactic latitude (|b| > 20 deg) selected in the 4.5-7.5 keV energy band. The HBSS sample is now almost completely identified (97% spectroscopic ID) and it can be safely used for a statistical investigation. The HBSS contains 62 AGN out of which 40 are unabsorbed (or marginally absorbed; Nh < 4E21 cm-2) and 22 are absorbed (Nh between 4E21 and E24 cm-2). Absorbed and unabsorbed AGN are characterized by two different XLF with the absorbed AGN population being described by a steeper XLF, if compared with the unabsorbed ones, at all luminosities. The intrinsic fraction F of absorbed AGN with L(2-10 keV) > 3E42 cgs is 0.57+/-0.11; we find that F decreases with the intrinsic luminosity, and probably, increases with the redshift. Our data are consistent with a flat Log Nh distribution for Nh between E20 and E24 cm-2. Finally, by comparing the results obtained here with those obtained using an optically selected sample of AGN we derive, in an indirect way, the XLF of Compton Thick AGN. The density ratio between Compton Thick AGN (Nh > E24 cm-2) and Compton Thin AGN (Nh < E24 cm-2) decreases from 1.08+/-0.44 at Lx E43 cgs to 0.23+/-0.15 at Lx E45 cgs.

astro-ph↗

arXiv2007

The XMM-Newton bright serendipitous survey. Identification and optical spectral properties

AIMS: We present the optical classification and redshift of 348 X-ray selected sources from the XMM-Newton Bright Serendipitous Survey (XBS) which contains a total of 400 objects (identification level = 87%). About 240 are new identifications. In particular, we discuss in detail the classification criteria adopted for the Active Galactic Nuclei population. METHODS: By means of systematic spectroscopic campaigns and through the literature search we have collected an optical spectrum for the large majority of the sources in the XBS survey and applied a well-defined classification ``flow-chart''. RESULTS: We find that the AGN represent the most numerous population at the flux limit of the XBS survey (~10^-13 erg cm^-2 s^-1) constituting 80% of the XBS sources selected in the 0.5-4.5 keV energy band and 95% of the ``hard'' (4.5-7.5 keV) selected objects. Galactic sources populate significantly the 0.5-4.5 keV sample (17%) and only marginally (3%) the 4.5-7.5 keV sample. The remaining sources in both samples are clusters/groups of galaxies and normal galaxies (i.e. probably not powered by an AGN). Furthermore, the percentage of type2 AGN (i.e. optically absorbed AGNs with A_V>2mag) dramatically increases going from the 0.5-4.5 keV sample (f=N_AGN2/N_AGN=7%) to the 4.5-7.5 keV sample (f=32%). We finally propose two simple diagnostic plots that can be easily used to obtain the spectral classification for relatively low redshift AGNs even if the quality of the spectrum is not good.

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

Elusive AGN in the XMM-Newton bright serendipitous survey

AIMS: We investigate here the nature of all the sources (35 in total) in the XBS survey (which is 86% optically identified) showing an optical spectrum dominated by the light from the host galaxy with no evidence (or little evidence) for the presence of an AGN. METHODS: We use the X-ray spectral analysis to assess the presence of an AGN in these sources and to characterize its properties. RESULTS: We detect AGN activity in 33 out of 35 sources. The remaining 2 sources are the ones with the lowest X-ray luminosity in the sample (L[2-10keV]<10^41 erg s^-1) and their X-ray emission could be produced within the host galaxy. We find that the ``recognition problem'' for AGN is very critical in the low-luminosity regime (at least 60% of the AGN with L[2-10keV]<10^43 erg s^-1 are elusive) becoming negligible for high X-ray luminosities (~1.5% of elusive AGN with L[2-10keV]>10^44 erg s^-1). This problem affects mostly absorbed AGN (~40% of type~2 AGN in the survey are elusive) but also a significant fraction of unabsorbed AGN (8%). CONCLUSIONS: We find that the simplest explanations of why these 33 (or most of them) AGNs are elusive are two: at low X-ray luminosities (<10^43 erg s^-1) the most important reason is the intrinsically low AGN/galaxy contrast (optical dilution) while at high luminosities (>10^44 erg s^-1) it is due to the optical absorption (in the Compton-thin regime, i.e. NH<10^24 cm^-2). Alternative hypotheses, like the presence of Compton-thick sources, BL Lac objects or ``non-standard'' AGN (e.g. with alpha_OX<1 or with weak/absorbed Narrow Line Region) are not supported by the data although we cannot exclude the presence in the sample of a few sources of these types.

astro-ph↗

arXiv2007

The XMM-Newton serendipitous survey IV. The AXIS X-ray source counts and angular clustering

AXIS (An XMM-Newton International Survey) is a survey of 36 high Galactic latitude XMM-Newton observations covering 4.8 deg2 and containing 1433 serendipitous X-ray sources detected with 5-sigma significance. We have studied the X-ray source counts in four energy bands soft (0.5-2 keV), hard (2-10 keV), XID (0.5-4.5 keV) and ultra-hard (4.5-7.5 keV). We have combined this survey with shallower and deeper surveys. Our source counts results are compatible with most previous samples in the soft, XID, ultra-hard and hard bands. The fractions of the XRB resolved in the surveys used in this work are 87%, 85%, 60% and 25% in the soft, hard, XID and ultra-hard bands, respectively. Extrapolation of our source counts to zero flux are not enough to saturate the XRB intensity. Only galaxies and/or absorbed AGN may be able contribute the remaining unresolved XRB intensity. Our results are compatible, within the errors, with recent revisions of the XRB intensity in the soft and hard bands. The maximum fractional contribution to the XRB comes from fluxes within about a decade of the break in the source counts (~1e-14 cgs), reaching ~50% of the total in the soft and hard bands. Using only AXIS sources, we have studied the angular correlation in those bands using a novel robust technique. Angular clustering (widely distributed over the sky and not confined to a few deep fields) is detected at 99-99.9% significance in the soft and XID bands, with no detection in the hard and ultra-hard band (probably due to the smaller number of sources). We cannot confirm the detection of significantly stronger clustering in the hard-spectrum hard sources. Medium depth surveys such as AXIS are essential to determine the evolution of the X-ray emission in the Universe below 10 keV.

astro-ph↗

arXiv2006

An X-ray bright ERO hosting a type 2 QSO

We present the XMM-Newton and the optical-VLT spectra along with the optical and the near-infrared photometric data of one of the brightest X-ray (F(2-10 keV)~1e-13 erg/s cm^2) extremely red objects (R-K>=5) discovered so far. The source, XBSJ0216-0435, belongs to the XMM-Newton Bright Serendipitous Survey and it has extreme X-ray-to-optical (~220) and X-ray-to-near-infrared (~60) flux ratios. Thanks to its brightness, the X-ray statistics are good enough for an accurate spectral analysis by which the presence of an X-ray obscured (NH>1e22 cm^-2) QSO (L(2-10 keV)=4e45 erg/s) is determined. A statistically significant (~99%) excess around 2 keV in the observed-frame suggests the presence of an emission line. By assuming that this feature corresponds to the iron Kalpha line at 6.4 keV, a first estimate of the redshift of the source is derived (z_x~2). The presence of a high redshift QSO2 has been finally confirmed through dedicated VLT optical spectroscopic observations (z_o=1.985+/-0.002). This result yields to an optical validation of a new X-ray Line Emitting Object (XLEO) for which the redshift has been firstly derived from the X-ray data. XBSJ0216-0435 can be considered one of the few examples of X-ray obscured QSO2 at high redshift for which a detailed X-ray and optical spectral analysis has been possible. The spectral energy distribution from radio to X-rays is also presented. Finally from the near-infrared data the luminosity and the stellar mass of the host galaxy has been estimated finding a new example of the coexistence at high-z between massive galaxies and powerful QSOs.

astro-ph↗

arXiv2005

The Bright Side of the Hard X-ray Sky: The XMM-Newton Bright Survey

We discuss here the main goals and some interesting results of the "XMM-Newton Bright Serendipitous Survey", a research program conducted by the XMM-Newton Survey Science Center in two complementary energy bands (0.5-4.5 keV and 4.5-7.5 keV) in the bright (>~7E-14) flux regime. The very high identification rate (96%) for the X-ray source sample selected in the 4.5-7.5 keV band is used here to have, in this energy range, an "unbiased" view of the extragalactic hard X-ray sky at bright fluxes.

astro-ph↗

arXiv2005

The XMM-Newton view of the relativistic spectral features in AXJ0447-0627

The XMM-Newton observation of the optically Type 1 AGN AXJ0447-0627 (z=0.214) unambiguously reveals a complex, bright and prominent set of lines in the 4-8 keV rest frame energy range. Although, from a phenomenological point of view, the observed properties can be described by a simple power law model plus 5 narrow Gaussian lines (at rest frame energies of nearly 4.49, 5.55, 6.39, 7.02 and 7.85 keV), we find that a model comprising a power law (Gamma of the order of 2.2), a reflected relativistic continuum, a narrow Fe I Kalpha line from neutral material as well as a broad Fe Kalpha relativistic line from a ionized accretion disk represents a good physical description of the data. The ''double horned'' profile of the relativistic line implies an inclination of the accretion disk of the order of 45 degree, and an origin in a narrow region of the disk, from R_in of the order of 19 GM/c^2 to R_out of the order of 30 GM/c^2. The narrow Fe I Kalpha line from neutral material is probably produced far from the central black hole, most likely in the putative molecular torus. Although some of these properties have been already found in other Type 1 AGN and discussed in the literature, at odd with the objects reported so far we measure high equivalent widths (EWs) of the observed lines: nearly 1.4 keV for the ``double horned'' relativistic line and nearly 0.4 keV for the narrow line.

astro-ph↗

arXiv2005

The first optical validation of an XLEO: a detection in the XMM-Newton observation of the CDFS

We present the first optical validation of an X-ray Line-Emitting Object (XLEO) discovered in the XMM-Newton observation of the Chandra Deep Field South. The object is an AGN at z_x ~ 0.66. An optical spectrum of the source indeed confirms and refines (z_o = 0.665) the redshift obtained from the X-ray line. The X-ray and optical properties of the source are presented and discussed.

astro-ph↗

arXiv2004

X-ray spectra of XMM-Newton serendipitous medium flux sources

We report on the results of a detailed analysis of the X-ray spectral properties of a large sample of sources detected serendipitously with the XMM-Newton observatory in 25 selected fields. The survey covers a total solid angle of ~3.5 deg2 and contains 1137 sources with ~10E-15 < S0.5-10 < 10E-12 erg cm-2 s-1. We find evidence for hardening of the average X-ray spectra of the sources towards fainter fluxes. We interpret this as indicating a higher degree of photoelectric absorption amongst the fainter population. Absorption is detected at 95% confidence in 20% of the sources, but it could certainly be present in many other sources below our detection capabilities. For Broad Line AGNs (BLAGNs), we detect absorption in ~10% of the sources with column densities in the range 10E21 - 10E22 cm-2. The fraction of absorbed Narrow Emission Line galaxies (NELGs, most with intrinsic X-ray luminosities >10E43 erg s-1, and therefore classified as type 2 AGNs) is significantly higher (40%), with a hint of moderately higher columns. We do not find evidence for a redshift evolution of the underlying power law index of BLAGNs, which stays roughly constant at Gamma ~1.9, with intrinsic dispersion of 0.4. A small fraction (~7%) of BLAGNs and NELGs require the presence of a soft excess, that we model as a black body with temperature ranging from 0.1 to 0.3 keV. Comparing our results on absorption to popular X-ray background synthesis models, we find absorption in only ~40% of the sources expected. This is due to a deficiency of heavily absorbed sources (with NH ~10E22 - 10E24 cm-2) in our sample in comparison with the models. We therefore conclude that the synthesis models require some revision in their specific parameters.

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arXiv2004

X-ray Line Emitting Objects in XMM-Newton Observations: the Tip of the Iceberg

We present preliminary results from a novel search for X-ray Line Emitting Objects (XLEOs) in XMM-Newton images. Three sources have been detected in a test-run analysis of 13 XMM-Newton observations. The three objects found are most likely extremely absorbed AGN characterized by a column density NH~10^24cm^-2. Their redshift has been directly determined from the X-ray data, by interpreting the detected emission line as the 6.4 keV Fe line. The measured equivalent width of the X-ray line is, in all three cases, several keV. This pilot study demonstrates the success of our search method and implies that a large sample of XLEOs can be obtained from the public XMM-Newton data archive.

astro-ph↗

arXiv2004

XMM-Newton spectroscopy of an X-ray selected sample of RL AGNs

This paper presents the X-ray spectroscopy of an X-ray selected sample of 25 radio-loud (RL) AGNs extracted from the XBSS sample. The main goal is to study the origin of the X-ray spectral differences usually observed between radio-loud and radio-quiet (RQ) AGNs. To this end, a comparison sample of 53 RQ AGNs has been also extracted from the same XBSS sample and studied together with the sample of RL AGNs. We have focused the analysis on the distribution of the X-ray spectral indices of the power-law component that models the large majority of the spectra in both samples. We find that the mean X-ray energy spectral index is very similar in the 2 samples and close to alpha_X~1. However, the intrinsic distribution of the spectral indices is significantly broader in the sample of RL AGNs. In order to investigate the origin of this difference, we have divided the RL AGNs into blazars and ``non-blazars'', on the basis of the available optical and radio information. We find strong evidence that the broad distribution observed in the RL AGN sample is mainly due to the presence of the blazars. Furthermore, within the blazar class we have found a link between the X-ray spectral index and the value of the radio-to-X-ray spectral index suggesting that the observed X-ray emission is directly connected to the emission of the relativistic jet. This trend is not observed among the ``non-blazars'' RL AGNs. This favours the hypothesis that, in these latter sources, the X-ray emission is not significantly influenced by the jet emission and it has probably an origin similar to the RQ AGNs. Overall, the results presented here indicate that the observed distribution of the X-ray spectral indices in a given sample of RL AGNs is strongly dependent on the amount of relativistic beaming present in the selected sources.

astro-ph↗

arXiv2004

Exploring the X-ray Sky with the XMM-Newton Bright Serendipitous Survey

ABRIDGED. We present "The XMM-Newton Bright Serendipitous Survey", two flux-limited samples with flux limit fx ~7E-14 cgs in the 0.5-4.5 keV (BSS) and 4.5-7.5 keV (HBSS) energy band, respectively. After discussing the survey strategy, we present the basic data on a complete sample of 400 X-ray sources derived from the analysis of 237 XMM-Newton fields. The survey covers an area of 28.10 (25.17 for the HBSS) sq. deg. Up to now ~71% (~90%) of the sources have been spectroscopically identified making the BSS (HBSS) the sample with the highest number of identified XMM-Newton sources published so far. We find that: a) the optical counterpart in the majority (~90%) of cases has a magnitude brighter than the POSS II limit; b) the majority of the objects identified so far are broad line AGN. No obvious trend of the source spectra (as deduced from the Hardness Ratios analysis) as a function of the count rate is seen and the average spectra of the "extragalactic" population corresponds to an X-ray energy spectral index of ~0.8 (~0.64) for the BSS (HBSS) sample. About 13% (40%) of the sources are described by an energy spectral index flatter than that of the CXB. We measure a surface density of optically type 1 and type 2 AGN of 1.63+/-0.25 deg-2 and 0.83+/-0.18$ deg-2, respectively; optically type 2 AGN represent 34+/-9% of the total AGN population. Finally, we find a clear separation, in the hardness ratio diagram and in the (hardness ratio) vs. (X-ray to optical flux ratio) diagram, between "coronal emitting" stars and extragalactic sources.

astro-ph↗

arXiv2004

The broad-band properties of the XMM-Newton Bright Serendipitous Sources

We present here "The XMM-Newton Bright Serendipitous Survey", a survey program conducted by the XMM-Newton Survey Science Center. In particular we discuss the main goals of this project, we present the sample(s) and the current optical breakdown and we discuss some broad band spectral properties as derived from an hardness ratio analysis of the single sources. Finally we report the 4.5--7.5 keV Log(N$>$S)-LogS for type 1 and type 2 AGN.

astro-ph↗