Search

Through an optical campaign performed at 5 telescopes located in the northern and the southern hemispheres, plus archival data from two on line sky surveys, we have obtained optical spectroscopy for 17 counterparts of suspected or poorly studied hard X-ray emitting active galactic nuclei (AGNs) detected with Swift/BAT in order to determine or better classify their nature. We find that 7 sources of our sample are type 1 AGNs, 9 are type 2 AGNs, and 1 object is an X-ray bright optically normal galaxy; the redshifts of these objects lie in a range between 0.012 and 0.286. For all these sources, X-ray data analysis was also performed to estimate their absorption column and to search for possible Compton thick candidates. Among our type 2 objects, we did not find any clear Compton thick AGN, but at least 6 out of 9 of them are highly absorbed (NH> 1023cm-2), while one does not require intrinsic absorption; i.e., it appears to be a naked Seyfert 2 galaxy.

Within the framework of our program of assessment of the nature of unidentified or poorly known INTEGRALsources, we present here spectroscopy of optical objects, selected through positional cross-correlation with soft X-ray detections (afforded with satellites such as Swift, ROSAT, Chandraand/or XMM-Newton) as putative counterparts of hard X-ray sources detected with the IBIS instrument onboard INTEGRAL. Using 6 telescopes of various sizes and archival data from two on-line spectroscopic surveys we are able to identify, either for the first time or independent of other groups, the nature of 20 INTEGRALhard X-ray sources. Our results indicate that: 11 of these objects are active galactic nuclei (AGNs) at redshifts between 0.014 and 0.978, 7 of which display broad emission lines, 2 show narrow emission lines only, and 2 have unremarkable or no emission lines (thus are likely Compton thick AGNs); 5 are cataclysmic variables (CVs), 4 of which are (possibly magnetic) dwarf novae and one is a symbiotic star; and 4 are Galactic X-ray binaries (3 with high-mass companions and one with a low-mass secondary). It is thus again found that the majority of these sources are AGNs or magnetic CVs, confirming our previous findings. When possible, the main physical parameters for these hard X-ray sources are also computed using the multiwavelength information available in the literature. These identifications support the importance of INTEGRALin the study of the hard X-ray spectrum 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 unidentified hard X-ray sources.

Context. The fast X-ray transient IGR J16479-4514 is known to display flares typically lasting a few hours. Recently, its counterpart has been identified with a supergiant star, therefore the source can be classified as a member of the newly discovered class of Supergiant Fast X-ray Transients (SFXTs); specifically, it is the one with the highest duty cycle.

Aims. We present a 0.2-200 keV broadband study of absorbed Active Galactic Nuclei (AGN) observed with INTEGRAL, XMM-Newton, Chandra, and ASCAto investigate the continuum shape and the absorbing/reflecting medium properties.

Aims. 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.

We report on the high-redshift blazar identification of a new gamma–ray source, Swift J1656.3-3302, detected with the BAT imager onboard the Swiftsatellite and the IBIS instrument on the INTEGRALsatellite. Follow-up optical spectroscopy has allowed us to identify the counterpart as an $R\sim 19$mag source that shows broad Lyman-α, Si iv, He ii, C iv, and C iii] emission lines at redshift $z = 2.40 \pm 0.01$. Spectral evolution is observed in X-rays when the INTEGRAL/IBIS data are compared to the Swift/BAT results, with the spectrum steepening when the source gets fainter. The 0.7–200 keV X-ray continuum, observed with Swift/XRT and INTEGRAL/IBIS, shows the power law shape typical of radio loud (broad emission line) active galactic nuclei (with a photon index $\Gamma \sim 1.6$) and a hint of spectral curvature below ~2 keV, possibly due to intrinsic absorption ($N_{\rm H} \sim 7\times 10 ^{22}$cm-2) local to the source. Alternatively, a slope change ($\Delta \Gamma \sim 1$) around 2.7 keV can describe the X-ray spectrum equally well. At this redshift, the observed 20–100 keV luminosity of the source is ~1048erg s-1(assuming isotropic emission), making Swift J1656.3-3302 one of the most X-ray luminous blazars. This source is yet another example of a distant gamma-ray loud quasar discovered above 20 keV. It is also the farthest object, among the previously unidentified INTEGRALsources, whose nature has been determined a posteriori through optical spectroscopy.

Context.The transient hard X-ray source IGR J11321-5311 was discovered by INTEGRAL on June 2005, during observations of the Crux spiral arm. To date, this is the only detection of the source to be reported by any X/γ-ray mission.

We present the results of the correlation between the nuclear 2–10 keV X-ray and radio (at 2 cm, 6 cm, and 20 cm) 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 LLRG 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, LX$\propto$$L_{\rm 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, $L_{2-10~{\rm keV}}$/LEdd~ 10-8, does not support the idea that the origin of the radio loudness is due to a switch in the accretion mode.

Optical spectroscopic identification of the nature of 21 unidentified southern hard X-ray objects is reported here in the framework of our campaign aimed at determining the nature of newly-discovered and/or unidentified sources detected by INTEGRAL. Our results show that 5 of these objects are magnetic Cataclysmic Variables (CVs), 4 are High-Mass X-ray Binaries (HMXBs; one of which is in the Large Magellanic Cloud) and 12 are Active Galactic Nuclei (AGNs). When feasible, the main physical parameters for these hard X-ray sources are also computed using the multiwavelength information available in the literature. These identifications further underscore the importance of INTEGRALin the study of the hard X-ray spectrum of AGNs, HMXBs and CVs, and the usefulness of a strategy of catalogues cross-correlation plus optical spectroscopy to securely pinpoint the actual nature of the X-ray sources detected with INTEGRAL.

Context.The microquasar 1E 1740.7-2942 is a source located in the direction of the Galactic Center. It has been detected at X-rays, soft gamma-rays, and in the radio band, showing an extended radio component in the form of a double-sided jet. Although no optical counterpart has been found so far for 1E 1740.7-2942, its X-ray activity strongly points to a galactic nature.

We investigate the relation between X-ray nuclear emission, optical emission line luminosities and black hole masses for a sample of 47 Seyfert galaxies. The sample, which has been selected from the Palomar optical spectroscopic survey of nearby galaxies (Ho et al. 1997a, ApJS, 112, 315), covers a wide range of nuclear powers, from $L_{2-10\,{\rm keV}}$~ 1043erg/s down to very low luminosities ($L_{2-10 \,{\rm keV}}$~ 1038erg/s). Best available data from Chandra, XMM-Newton and, in a few cases, ASCA observations have been considered. Thanks to the good spatial resolution available from these observations and a proper modeling of the various spectral components, it has been possible to obtain accurate nuclear X-ray luminosities not contaminated by off-nuclear sources and/or diffuse emission. X-ray luminosities have then been corrected taking into account the likely candidate Compton thick sources, which are a high fraction (>30%) among type 2 Seyferts in our sample. The main result of this study is that we confirm strong linear correlations between 2–10 keV, [OIII]λ5007, Hαluminosities which show the same slope as quasars and luminous Seyfert galaxies, independent of the level of nuclear activity displayed. Moreover, despite the wide range of Eddington ratios ($L/L_{\rm Edd}$) tested here (six orders of magnitude, from 0.1 down to ~10-7), no correlation is found between the X-ray or optical emission line luminosities and the black hole mass. Our results suggest that Seyfert nuclei in our sample are consistent with being a scaled-down version of more luminous AGN.

Context.During the first year in operation, INTEGRAL, the European Space Agency's γ-ray observatory, has detected more than 28 new bright sources in the galactic plane which emit the bulk of their emission above 10 keV.

Results obtained from an X-ray spectral survey of nearby Seyfert galaxies using XMM–Newtonare reported. The sample was optically selected, well defined, complete in Bmagnitude, and distance limited: it consists of the nearest ($D \la22$Mpc) 27 Seyfert galaxies (9 of type 1, 18 of type 2) taken from the Ho et al. (1997a, ApJS, 112, 315) sample. This is one of the largest atlases of hard X-ray spectra of low-luminosity active galaxies ever assembled. All nuclear sources except two Seyfert 2s are detected between 2 and 10 keV, half for the first time ever, and average spectra are obtained for all of them. Nuclear luminosities reach values down to 1038erg s-1. The shape of the distribution of X-ray parameters is affected by the presence of Compton-thick objects ($\ga$30% among type 2s). The latter have been identified either directly from their intense FeK line and flat X-ray spectra, or indirectly with flux diagnostic diagrams which use isotropic indicators. After taking into account these highly absorbed sources, we find that (i) the intrinsic X-ray spectral properties (i.e., spectral shapes and luminosities above 2 keV) are consistent between type 1 and type 2 Seyferts, as expected from “unified models”; (ii) Seyfert galaxies as a whole are distributed fairly continuously over the entire range of NH, between 1020and 1025cm-2; and (iii) while Seyfert 1s tend to have lower NHand Seyfert 2s tend to have the highest, we find 30% and 10% exceptions, respectively. Overall the sample is of sufficient quality to well represent the average intrinsic X-ray spectral properties of nearby active galactic nuclei, including a proper estimate of the distribution of their absorbing columns. Finally, we conclude that, with the exception of a few cases, the present study agrees with predictions of unified models of Seyfert galaxies, and extends their validity down to very low luminosities.

The second IBIS/ISGRI survey has produced a catalogue containing 209 hard X-ray sources visible down to a flux limit of around 1 milliCrab. The point source location accuracy of typically 1–3 arcmin has allowed the counterparts for most of these sources to be found at other wavelengths. In order to help identify the remaining objects, we have used the cross-correlation recently found between the ISGRI catalogue and the ROSAT All Sky Survey Bright Source Catalogue. In this way, for ISGRI sources which have a counterpart in soft X-rays, we can use the much smaller ROSAT error box to search for identifications. For this second survey, we find 114 associations with the number expected by chance to be ~2. Of these sources, 8 are in the list of unidentified objects and, using the smaller ROSAT error boxes, we can find tentative counterparts for five of them. We have performed the same analysis for the ROSAT Faint Source Catalogue, finding a further nine associations with ISGRI unidentified sources from a total of 29 correlations, and, notwithstanding the poorer location accuracy of these sources and higher chance coincidence possibility, we have managed to find a counterpart for another source. Finally, we have used the ROSAT HRI catalogue to search the ISGRI error boxes and find 5 more X-ray objects, of which two are neither in the bright nor faint source catalogues, and for which we have managed to find optical/near infrared associations. This makes a total of 19 objects with X-ray counterparts for which we have found possible identifications for nine, most of which are extragalactic.

We present results on approximately one year of INTEGRALobservations of six AGN detected during the regular scans of the Galactic Plane. The sample is composed by five Seyfert 2 objects (MCG –05–23–16, NGC 4945, the Circinus galaxy, NGC 6300, ESO 103–G35) and the radio galaxy Centaurus A. The continuum emission of each of these sources is well represented by a highly absorbed ($N_{\rm H}>10^{22} \, \rm cm^{-2}$) power law, with average spectral index $\Gamma = 1.9 \pm 0.3$. A high energy exponential cut-off at $E_{\rm c} \sim 50 \rm \,~keV$is required to fit the spectrum of the Circinus galaxy, whereas a lower limit of 130 keV has been found for NGC 4945 and no cut-off has been detected for NGC 6300 in the energy range covered by these INTEGRALdata. The flux of Centaurus A was found to vary by a factor of ~2 in 10 months, showing a spectral change between the high and low state, which can be modelled equally well by a change in the absorption (NHfrom 17 to $33 \times 10^{22} \rm \, cm^{-2}$) or by the presence of a cut-off at $\ga$120 keV in the low state spectrum. A comparison with recently reprocessed BeppoSAX/PDS data shows a general agreement with INTEGRALresults. The high energy cut-off in the hard X-ray spectra appears to be a common but not universal characteristic of Seyfert 2 and to span a wide range of energies.

INTEGRAL is the first gamma-ray astronomy mission with a sufficient sensitivity and angular resolution combination appropriate to the detection and identification of considerable numbers of gamma-ray emitting sources. The large field of view (~30° zero response FWHM) enables INTEGRAL to survey the galactic plane on a regular (~weekly) basis as part of the core programme. The first source catalogue, based on the 1st year of core programme data (~5 Ms) has been completed and published (Bird et al. 2004, ApJ, 607, L33). It contained 123 γ-ray sources (24 HMXB, 54 LMXB, 28 “unknown”, plus 17 others) – sufficient numbers for a reasonable statistical analysis of their global properties. These were located to a positional accuracy of typically 0.72 arcmin. The detection of previously unknown γ-ray emitting sources generally exhibiting high intrinsic absorption, which do not have readily identifiable counterparts at other wavelengths, is intriguing. The substantial fraction (roughly 20% of the total number) of unclassified γ-ray sources suggests they must constitute a significant family of objects. In this paper we review the global characteristics of the known galactic sources as well as the unclassified objects with the twin aims of investigating how the unclassified set may fit into stellar evolution and improving our understanding of known X-ray binary systems through the non-thermal γ-ray channel. In the context of the known systems we are very conscious that they constitute a γ-ray selected set, and may exhibit subtle generic differences to the rest of the class. We present Log(N)–Log(S) distributions, angular distributions, and for systems with reliable distance estimates the spatial distributions within the Galaxy and luminosity functions. For the unknown sources, this statistical analysis has shown that they are most likely to be HMXBs containing a highly magnetised neutron star. The lack of X-ray counterparts for these sources indicates a high degree of intrinsic obscuration.

At a flux limit of ~10-11erg cm-2s-1in the 20–100 keV band, the PDS instrument on-board BeppoSAX offers the opportunity to study the extragalactic sky with an unprecedented sensitivity. In this work we report on the results of a search in the BeppoSAX archive for serendipitous high energy sources at high galactic latitudes ($\vert b \vert\geq13^{\circ}$). We have defined a set of twelve regions in which the PDS/MECS cross-calibration constant is higher than the nominal value. We attribute this mismatch to the presence of a serendipitous source in the PDS field of view. In four cases the likely high energy emitter is also present in the MECS field of view. In these cases, we have performed a broad band spectral analysis (1.5–100 keV) to understand the source spectral behaviour and compare it with previous BeppoSAX observations when available. In eight cases the identification of the source likely to provide the PDS spectrum is based on indirect evidence (extrapolation to lower energies and/or comparison with previous observations). This approach led to the discovery of six new hard X-ray emitting objects (PKS 2356–611, 2MASX J14585116–1652223, NGC 1566, NGC 7319, PKS 0101–649 and ESO 025–G002) and to the presentation the PDS spectrum of NGC 3227 for the first time. In the remaining five cases we provide extra BeppoSAX observations that can be compared with measurements already published and/or in the archive.

In this paper we present a broad-band study of the X-ray emission of the blazar PKS 1830-211 based on Chandra and INTEGRAL observations. Notwithstanding the high redshift ($z=2.507$), it is a bright X-ray source (F(2–10 keV) $\simeq 10^{-11}$erg cm-2s-1), due to gravitational lensing by an intervening galaxy at $z=0.89$. Previous X-ray observations attribute the observed absorption at $E<2$keV to the lensing galaxy. Our analysis, although not in contrast with this hypothesis, suggests also the possibility of an intrinsic (ionized) absorption, taking place at the front side of the jet. This scenario is also supported by some evidence, in the same data, of a feature observed at 2.15 keV which can be interpreted as a blueshifted iron line ($v/c\simeq 0.18$). The SED of PKS 1830-211 can be well modelled by combining a Synchrotron Self-Compton component and an external source of photons to be scattered up to γ-ray energies by relativistic electrons moving outward in the jet. The main source of low energy photons is a dust torus at the temperature of 103K as expected in MeV blazars.

The IBIS/ISGRI first year galactic plane survey has produced a catalogue containing 123 hard X-ray sources visible down to a flux limit of a few milliCrabs. The point source location accuracy of typically 1–3 arcmin has allowed the counterparts for 95 of these sources to be found at other wavelengths. In order to identify the remaining 28 objects, we have cross-correlated the ISGRI catalogue with the ROSAT All Sky Survey Bright Source Catalogue. In this way, for ISGRI sources which have a counterpart in soft X-rays, we can use the, much smaller, ROSAT error box to search for identifications. As expected, we find a strong correlation between the two catalogues and calculate that there are 75 associations with the number expected by chance to be almost zero. Of these 75 sources, ten are in the list of unidentified objects. Using the ROSAT error boxes we provide tentative associations for 8 of these.

The Third EGRET Catalog (3EG) lists 66 high-confidence identifications of sources with Active Galactic Nuclei (AGN). All are classified as belonging to the blazar class, with the only exception of the nearby radio galaxy Centaurus A. We report and strengthen the association of another radio galaxy, 3C 111, with the EGRET source 3EG J0416+3650. At the time of the compilation of the 3EG catalogue, 3C 111 has been considered as a low-confidence counterpart of 3EG J0416+3650, being located outside the 99% γ-ray probability contour. Since this first suggestion, no other counterparts have been reported nor the EGRET error box has been searched for likely candidates. 3C 111 has never been considerated or cited in literature as a radiogalaxy counterpart of an EGRET source. We report a detailed multiwavelength study of the EGRET error box as well as for the first time the overall spectral energy distribution of 3C 111, which appears to be intriguingly similar to those of blazars, suggesting that the radiogalaxy 3C 111 is the likely counterpart of 3EG J0416+3650.

The results of an optical spectroscopy campaign performed at the Astronomical Observatory of Bologna in Loiano (Italy) on three hard X-ray sources detected by INTEGRAL(IGR J17303-0601, IGR J18027-1455 and IGR J21247+5058) are presented. These data have allowed a determination of the nature for two of them, with IGR J17303-0601 being a low mass X-ray binary in the Galaxy and IGR J18027-1455 a background type 1 Seyfert galaxy at redshift z= 0.035. IGR J21247+5058, instead, has a quite puzzling spectroscopic appearance, with a broad, redshifted Hαcomplex superimposed onto a “normal” F/G-type Galactic star continuum: these features, together with the spatially coincident extended radio emission, might suggest a chance alignment between a relatively nearby star and a background radio galaxy. These results underline the still non-negligible importance of smaller telescopes in modern astrophysics.

We report the discovery of a Compton-thick AGN and of intense star-formation activity in the nucleus and disk, respectively, of the nearly edge-on superwind galaxy NGC 4666. Spatially unresolved emission is detected by BeppoSAXonly at energies <10 keV, whereas spatially resolved emission from the whole disk is detected by XMM-Newton. A prominent ($EW \sim 1{-}2$keV) emission line at ~6.4 keV is detected by both instruments. From the XMM-Newtondata alone the line is spectrally localized at $E \simeq 6.42 \pm 0.03$keV, and seems to be spatially concentrated in the nuclear region of NGC 4666. This, together with the presence of a flat ($\Gamma\sim 1.3$) continuum in the nuclear region, suggests the existence of a strongly absorbed (i.e., Compton-thick) AGN, whose intrinsic 2–10 keV luminosity is estimated to be $L_{2{-}10} \ga2 \times 10^{41}$erg s-1. At energies $\la$1 keV the integrated (BeppoSAX) spectrum is dominated by a ~0.25 keV thermal gas component distributed throughout the disk (resolved by XMM-Newton). At energies ~2–10 keV, the integrated spectrum is dominated by a steep ($\Gamma\ga2$) power-law (PL) component. The latter emission is likely due to unresolved sources with luminosity $L \sim 10^{38}{-}10^{39}$erg s-1that are most likely accreting binaries (with BH masses ≤8 $M_\odot$). Such binaries, which are known to dominate the X-ray point-source luminosity in nearby star-forming galaxies, have $\Gamma\sim 2$PL spectra in the relevant energy range. A $\Gamma\sim 1.8$PL contribution from Compton scattering of (the radio-emitting) relativistic electrons by the ambient FIR photons may add a truly diffuse component to the 2–10 keV emission.

We discuss XMM-Newtonand BeppoSAX observations of MKN 231, the lowest-redshift Broad Absorption Line (BAL) QSO known so far and one of the best-studied Ultra Luminous Infrared Galaxies. By combining the XMM-Newtonspectral resolution and the high-energy bandpass of BeppoSAX we have been able to study in more detail than previously possible its 0.2–50 keV spectral properties. The BeppoSAX PDS data unveiled, for the first time, a highly absorbed ($N_{\rm H}\sim 2\times 10^{24}$cm-2) power-law component. We find that: a) below 10 keV we are seeing only reprocessed radiation through reflection and/or scattering; b) the intrinsic 2–10 keV luminosity of MKN 231 is $ 1^{+1.0}_{-0.5} \times 10^{44}$erg s-1, i.e. more than an order of magnitude greater than previous measurements; c) the starburst activity significantly contributes to the soft ($E<2$keV) X-ray emission.

We report on the association of an X-ray source (WGA J2025.1+3342), serendipitously found with BeppoSAX in two separate observations, with the unidentified EGRET source 3EG J2027+3429. The source is detected from 1 keV up to about 100 keV, has a flat ($\Gamma=0.6{-}1.5$) spectrum and is highly variable both in intensity and shape. The data indicate marginal evidence for an iron line in the source rest frame. The overall X-ray luminosity is ${\sim}4 \times10^{45}$erg s-1, typical of a quasar. The X-ray source is coincident in radio wavelengths with a bright object characterized by a flat spectrum over the band 0.3-10 GHz while in the optical it is identified with a quasar at redshift 0.22. All available data indicate a SED compatible with a low frequency peaked or red blazar type object. This identification is interesting because this is the second blazar found behind the galactic plane in the direction of the Cygnus region.

We report on the spectral properties of a sample of 90 hard X-ray selected serendipitous sources detected in 12 XMM–Newtonobservations with $1 \la{F_{2-10}}\la80 \times 10^{-14}$erg cm-2s-1. Approximately 40% of the sources are optically identified with $0.1 \la\ z\la2$and most of them are classified as broad line AGNs. A simple model consisting of power law modified by Galactic absorption offers an acceptable fit to ~65% of the source spectra. This fit yields an average photon index of $\langle\Gamma\rangle \approx 1.55$over the whole sample. We also find that the mean slope of the QSOs in our sample turns out to remain nearly constant ($\langle\Gamma\rangle \approx 1.8{-}1.9$) between $0 \la\ z\la2$, with no hints of particular trends emerging along z. An additional cold absorption component with $10^{21}\la{N_{\rm H}}\la10^{23}$cm-2is required in ~30% of the sources. Considering only subsamples that are complete in flux, we find that the observed fraction of absorbed sources (i.e. with ${N_{\rm H}}\ga\ 10^{22}$cm-2) is ~30%, with little evolution in the range $2 \la{F_{2-10}}\la\ 80 \times 10^{-14}$erg cm-2s-1. Interestingly, this value is a factor ~2 lower than predicted by the synthesis models of the CXB. This finding, detected for the first time in this survey, therefore suggests that most of the heavily obscured objects which make up the bulk of the CXB will be found at lower fluxes (${F_{2-10}}< 10^{-14}$erg cm-2s-1). This mismatch together with other recent observational evidences which contrast with CXB model predictions suggest that one (or more) of the assumptions usually included in these models need to be revised.

The PICsIT instrument is the high-energy imaging detector of IBIS on board INTEGRAL and comprises 4096 individual scintillator elements each working in the energy range from about 175 keV to 10 MeV. Images of the sky are created using the coded aperture technique wherein each point in the detection plane contributes to the final image. For this reason the sensitivity at any point in the image is highly dependent on both the total background and its spatial and temporal uniformity. Herein we describe the PICsIT in-flight background, for the principal modes of operation, from the point of view of total count rate and spectrum, and discuss both the spatial and temporal stability.

In this work we present the first of two papers devoted to the study of the X-ray spectral characteristics of Seyfert 1 galaxies in the Piccinotti sample. In particular we analyse here the BeppoSAX broad band (0.1–100 keV) data of 4 objects which, despite their X-ray brightness, have been historically poorly studied due to their late identification with an AGN; these are H0111-149 (MKN 1152), H0235-525 (ESO 198-G24), H0557-385 (IRAS F05563-3820) and H1846-786 (IRAS F18389-7834). We have assumed for all the sources a baseline model which includes a power law with an exponential cut-off plus a reflection component and an iron Kαline; we have also searched for the presence of intrinsic absorption and/or a soft excess component. Our analysis indicates the presence of complex absorption in two objects (H0557-385 and H0111-149) best described by a combination of two uniform absorbers, one cold and one warm. Only in one source, H0557-385, a soft excess component has been measured. The primary continuum is best described by a canonical power law ($\Gamma=1.7{-}2$) with a high energy cut-off in the range 40–130 keV. A cold reflection component is likely present in all sources with values ranging from less than 0.6 to higher than 2. In 3 out of 4 objects we find a cold iron line having equivalent width typical of Seyfert 1s (100–200 eV).

We have used the BeppoSAX satellite to study the broad band (0.5–100 keV) X-ray spectrum of the Seyfert 1.5 galaxy MKN6. The source is characterized by a power law of $\Gamma =1.7 ^{+0.08}_{-0.07}$and there is no strong evidence for either a reflection bump or a high energy cut-off. We have detected a narrow iron line at 6.4 keV (rest frame) with an equivalent width of 98$^{+33}_{-35}$eV. MKN6 also exhibits strong and complex absorption. At least two components ($N_{\rm H_{1}} =1.34 ^{+0.4}_{-0.4} \times 10 ^{22}$cm-2and $N_{\rm H_{2}} =4.18 ^{+2.2}_{-1.3} \times 10 ^{22}$cm-2) are present and they both partially cover the source with covering fractions of ~90% and ~50% respectively. Comparison with a previous ASCA observation indicates that in both absorbing columns the NHis variable over a 2 year timescale, while the covering fractions are constant over the same amount of time. The state of each absorber is cold or mildly photoionized. The Broad Line Region (BLR) is suggested as the possible location for this complex absorption.

Lo scopo di questo studio è stato valutare le caratteristiche, le alterazioni morfostrutturali e le conseguenze disfunzionali dell’articolazione temporomandibolare (ATM) in pazienti affetti da artrite idiopatica giovanile (AIG).

We present the XMM-Newtonobservation of the merging system IRAS 19254-7245, also known as The Superantennae, whose southern nucleus is classified as a Seyfert 2 galaxy. The XMM-Newtondata have allowed us to perform a detailed X-ray imaging and spectral analysis of this system. We clearly detect, for the first time in this system, a strong ($EW \sim 1.4$keV) Fe emission line at $6.49\pm 0.1$keV (rest-frame). The X-ray spectrum requires a soft thermal component ($kT\sim0.9$keV; $L_{0.5-2}\sim 4\times10^{41}$erg s-1), likely associated with the starburst, and a hard power-law continuum above 2 keV (observed $L_{2-10}\sim 4\times10^{42}$erg s-1). We confirm the flatness of this latter component, already noted in previous ASCA data. This flatness, together with the detection of the strong Fe-Kaline and other broad band indicators, suggest the presence of a Compton-thick AGN with intrinsic luminosity ?1044erg s-1. We show that a Compton-thick model can perfectly reproduce the X-ray spectral properties of this object.

We present a sample of 17 type 2 Seyfert galaxies which have an X-ray column density lower than 1022cm-2. The Compton thin nature of these sources is strongly suggested by isotropic indicators. We estimate the fraction of these sources to be in the range of 10%–30% of the population of type 2 Seyfert galaxies. Furthermore, this fraction appears to increase progressively at lower luminosities. The simple formulation of the Unified Model for Seyfert galaxies is not applicable in such sources since the pc-scale molecular torus is not likely to be responsible for the low column density observed; instead the absorption observed is likely to originate at larger scales. According to this hypothesis, in these objects the broad line regions are covered by some dusty obscuring material. In particular, this could occur in objects with dust lanes, patches or HII regions. However, we cannot rule out that in the lowest luminosity sources the BLR is weak, absent or has faded away. This last scenario is consistent with the predictions of some recent theoretical models for low luminosity AGNs.

High energy emission has been discovered serendipitously by the BeppoSAX/PDS telescope in the ~1.3° field of view around the Piccinotti source H0917-074. A re-pointing of BeppoSAX/NFI has allowed the association of this emission with the Seyfert 2 galaxy MCG-1-24-12  which lies within the original HEAO1/A2 error box of H0917-074. This is the first PDS serendipitous discovery of a Seyfert 2 galaxy and the first detection of MCG-1-24-12  in the X-ray domain. The measured 2–10 keV flux of MCG-1-24-12  is ~1 $\times$10-11erg cm-2s-1compatible with the Piccinotti HEAO-1/A2 observation. This is a factor of ~6 greater than that observed from EXO0917.3-0722, originally suggested as the counterpart of the Piccinotti source. The 2–10 keV spectrum of MCG-1-24-12  shows the presence of Fe Kαemission together with an absorption feature at ~8.7 keV. At high energies, the Seyfert 2 still dominates and the observed 20–100 keV flux is ~4 $\times$10-11erg cm-2s-1.

We present a spectroscopic study of 41 hard X-ray sources detected serendipitously with high significance (>5σin the 2–10 keV band) in seven EPICperformance/verification phase observations. The large collecting area of EPICallows us to explore the spectral properties of these faint hard X-ray sources with 2 < F2-10< 80 $\times$10-14erg cm-2s-1even though the length of the exposures are modest (~20 ks). Optical identifications are available for 21 sources of our sample. Using a simple power law plus Galactic absorption model we find an average value of the photon index Γ~ 1.6–1.7, broadly consistent with recent measurements made at similar fluxes with ASCAand with Chandrastacked spectral analyses. We find that 31 out of 41 sources are well fitted by this simple model and only eight sources require absorption in excess of the Galactic value. Interestingly enough, one third of these absorbed sources are broad line objects, though with moderate column densities. Two sources in the sample are X-ray bright optically quiet galaxies and show flat X-ray spectra. Comparing our observational results with those expected from standard synthesis models of the cosmic X-ray background (CXB) we find a fraction of unabsorbed to absorbed sources larger than predicted by theoretical models at our completeness limit of F2-10~ 5 $\times$10-14erg cm-2s-1. The results presented here illustrate well how wide-angle surveys performed with EPICon board XMM-Newtonallow population studies of interesting and unusual sources to be made as well as enabling constraints to be placed on some input parameters for synthesis models of the CXB.

An XMM–Newtonstudy of ultraluminous X–ray sources (ULX) has been performed in a sample of 10 nearby Seyfert galaxies. Eighteen ULX have been found with positional uncertainty of about $4''$. The large collecting area of XMM–Newtonmakes the statistics sufficient to perform spectral fitting with simple models in 8 cases. The main results of the present minisurvey strengthen the theory that the ULX could be accreting black holes in hard or soft state. In some cases, the contribution of the ULX to the overall X–ray flux appears to be dominant with respect to that of the active nucleus. In addition, 6 ULX present probable counterparts at other wavelengths (optical/infrared, radio). A multiwavelength observing strategy is required to better assess the nature of these sources.

In this work we present the observation of the Mkn 463 field performed with the MECS instrument on-board BeppoSAX in the 1.8-10.5 keV band. The Mkn 463 field is an example of an extragalactic field crowded with absorbed X-ray sources: apart from the Seyfert 2 galaxy Mkn 463 and the well known QSO PG 1352+183 (the only object showing no absorption), two other objects are detected with a column density in excess of the galactic value. The first 1SAX J1353.9+1820 is a red QSO from the BeppoSAX High Energy Large Area Survey (HELLAS). The second 1SAX J1355.4+1815 is optically unidentified, but its X-ray spectral characteristics indicate that it too is an AGN hidden behind a large column density.

In the present work we report the BeppoSAX observation of the Seyfert 1.9 galaxy NGC 526A in the band 0.1-150 keV. The high energy instrument onboard, PDS, has succeeded in measuring for the first time the spectrum of this source in the 13-150 keV range. The combined analysis of all Narrow Field Instruments provides a power law spectral index of $\simeq$1.6 and confirms the flat spectral nature of this source. Although NGC 526A varies strongly in the 2-10 keV range over a period of months/years, its spectral shape remains constant over these timescales. An FeK \alphaline, characterized by a complex structure, has been detected in the 6-7 keV range. The line, which has an equivalent width of 120 eV, is not compatible with being produced in an absorbing medium with NH~ 1022cm-2, but most likely originates by reflection in an accretion disk viewed at an intermediate inclination angle of ~42°. The reflection component is however small ($R \leq 0.7$) and so it is not sufficient to steepen the spectrum to photon index values more typical of AGNs. Instead, we find that the data are more consistent with a flat power law spectrum cut-off at around 100 keV plus a small reflection component which could explain the observed iron line. Thus NGC 526A is the only bona-fide Seyfert 2 galaxy which maintains a "flat spectrum" even when broad band data are considered: in this sense its properties, with respect to the general class of Seyfert 2's, are analogous to those of NGC 4151 with respect to the vast majority of Seyfert 1's.

We discuss BeppoSAX observations and archive ASCA data of NGC 7679, a nearby, nearly face-on SB0 galaxy in which starburst and AGN activities coexist. The X-ray observations reveal a bright ($L_{0.1-50 \rm keV} \sim 2.9 \times 10^{43}$erg s-1) and variable source having a minimum observed doubling/halving time scale of ~10-20 ksec. A simple power law with photon index of $\Gamma \sim 1.75$and small absorption ($N_{\rm H} < 4\times 10^{20}$cm-2) can reproduce the NGC 7679 spectrum from 0.1 up to 50 keV. These X-ray properties are unambiguous signs of Seyfert 1 activity in the nucleus of NGC 7679. The starburst activity, revealed by the IR emission, optical spectroscopy and Hαimaging, and dominating in the optical and IR bands, is clearly overwhelmed by the AGN in the X-ray band. Although, at first glance, this is similar to what is observed in other starburst-AGN galaxies (e.g. NGC 6240, NGC 4945), most strikingly here and at odds with the above examples, the X-ray spectrum of NGC 7679 does not appear to be highly absorbed. The main peculiarity of objects like NGC 7679 is not the strength of their starburst but the apparent optical weakness of the Seyfert 1 nucleus when compared with its X-ray luminosity. To date NGC 7679 is one of the few Seyfert 1/Starburst composites for which the broad-band X-ray properties have been investigated in detail. The results presented here imply that optical and infrared spectroscopy could be highly inefficient in revealing the presence of an AGN in these kinds of objects, which instead is clearly revealed from X-ray spectroscopic and variability investigations.

The Seyfert 2 Galaxy NGC 7172 was observed twice by BeppoSAX narrow field instruments approximately one year apart. As found in previous observations, the source is variable on short time scales (hours) by a factor of ~30%, confirming the presence of a type 1 nucleus at the center. A strong flux variability (by a factor of 2) on a longer time scale was observed between the two observations. Indeed, in November 1997, the lowest flux ever recorded was detected by BeppoSAX. The broad band spectra obtained with the BeppoSAX narrow field instruments show marginal evidence of a reflection component. This structure could explain the very flat spectra previously observed in the 2-10 keV band. An FeKαline was also detected in both observations. The line intensity appears to remain almost constant between the two observations even if the associated large errors cannot exclude some variability. In order to understand the problem of the origin of the line, data from previous observations, performed with other satellites, were also used. The scenario favored is one where the line is produced at a distance of approximatively 8 light years from the continuum source region, rather than having its origin in the accretion disk. In the framework of the standard unified models for AGN, this suggests that its origin is located in the molecular torus.

Neurofibromatosis type 2 (NF2) is an autosomal dominant syndrome with a prevalence of approximately 1 in 30,000. NF 2 is characterized by bilateral vestibular schwannomas, as well as meningiomas, ependymomas and gliomas. Currently, surgical resection and radiotherapy represent the mainstay of treatment, although new studies suggest a role for certain chemotherapeutic agents. Intravenous administration of Bevacizumab (Avastin, Genetech Pharmaceuticals) has been shown to be active in the treatment of vestibular schwannomas. The IV route of administration, however, carries a risk of known systemic side-effects such as bowel perforation, wound dehiscence and pulmonary embolism. In addition, the percentage of drug that reaches the tumor site may be restricted by the blood tumor barrier. This report describes the super-selective intra-arterial infusion of Bevacizumab following blood brain barrier disruption for the treatment of vestibular schwannomas in three patients with Neurofibromatosis type 2. It represents the first time such a technique has been performed for this disease. Additionally, this method of drug delivery may have important implications in the treatment of patients with vestibular schwannomas associated with Neurofibromatosis type 2.

Context. The fast X-ray transient IGR?J16479-4514 is known to display flares typically lasting a few hours. Recently, its counterpart has been identified with a supergiant star, therefore the source can be classified as a member of the newly discovered class of Supergiant Fast X-ray Transients (SFXTs); specifically, it is the one with the highest duty cycle.Aims. Characterize the quiescent X-ray behaviour of the source and compare its broad band spectrum to those during fast X-ray flares.Methods. We analysed IBIS and JEM-X data with OSA?5.1, along with archival Swift/XRT data.Results. We present results from a long-term monitoring of IGR?J16479-4514 with detailed spectral and timing information on 19?bright fast X-ray flares, 10 of which are newly discovered. We also report the first results on the quiescent X-ray emission. The typical luminosity value (~1034?erg?s-1) is about?2?orders of magnitude greater than what is typical of SFXTs, while its broad band X-ray spectrum has a shape very similar to the shape during fast X-ray transient activity, i.e. a rather steep power law with ??2.6.Conclusions. IGR?J16479-4514 is characterised by a quiescent X-ray luminosity higher than what is typical of other known SFXTs but lower than persistent emission from classical SGXBs. We suggest that this source is a kind of transition object between these two systems, supporting the idea that there is a continuum of behaviour between the class of SFXTs and that of classical persistent?SGXBs.

Aims. 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.Methods. 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.Results. 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 (???= 1.7 ?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 ? (~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.

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.

We report the identification of the optical and radio counterparts of the ultraluminous X-ray (ULX) source XMMU J124825.9+083020 (NGC 4698-ULX1). The optical spectrum taken with the VLT yields a redshift of $z=0.43$, which implies that the ULX is not associated with the nearby galaxy NGC 4698. The spectral energy distribution calculated from the available data indicates that the source is likely to be a BL Lac object. The possible synchrotron peak at X-ray energies suggests that this source may be a $\gamma$-ray emitter.

Abstract: Observational features in the low energy γ-ray spectra of Seyfert galaxies are interpreted in terms of broad and blueshifted annihilation radiation. The possibility that this ‘line’ emission is the underlying source of the bump in the cosmic diffuse γ-ray background is investigated. The observational data available in the literature are then used to estimate the maximum temperature of the electron positron plasma and the average positron annihilation rate for Seyfert galaxies. The assumption that other active nuclei, namely radio galaxies and quasars, are powered by the same annihilation mechanism is used to set limits on their contribution to the cosmic diffuse γ-ray background.

Light curves at X-ray, ultraviolet, optical and infrared wavelengths of NGC 4151 over the period 1977–1980 are presented together with a summary of the large amount of observational data relating to this Seyfert galaxy. Intensity variations in different wavebands are discussed and compared with recent low energy γ-ray observations of this object. The positive measurement of gamma-radiation in May 1977 is shown to have been characterised by a high optical state and a possible infrared maximum. The data presented are compared with the predictions of some emission mechanisms, which have been proposed to account for the gamma-radiation. In particular, a synchrotron self-Compton model, which relates the infrared/optical emission to the X-ray/low energy γ-ray emission is discussed.

During a balloon flight of the MISO telescope on the 30th September 1979, the Seyfert galaxies NGC 4151 and MGC 8-11-11 were studied in the hard X-ray range (EX > 20 keV) and low-energy γ-ray range up to 19 MeV. An emission at the 4.5 σ level above 20 keV (4 σ above 260 keV) was detected in the direction of NGC 4151. γ-ray emission at the 3.9 σ level above 90 keV was also observed from the direction of MCG 8-11-11. The emission photon spectrum shows a high-energy cutoff at about 3 MeV. A large amount of the observed low-energy γ-ray diffuse background could be produced by a few percent of the X-ray emitting Seyfert galaxies having a γ-ray luminosity comparable to that observed from the regions of NGC 4151 or MCG 8-11-11.

During a balloon flight in September 1979 of the MISO low-energy ?-ray telescope, the BL Lac-object MkN 501 was studied in the hard X-ray range above 30 keV and in the low energy ?-ray range up to 19 MeV. No statistically significant X- and ?-ray fluxes were detected. The implications of the upper limits obtained are discussed in the light of the relativistic jet theories recently proposed.

Three active galaxies, generally classified as Seyferts, have been discovered recently to be powerful, low energy γ-ray sources. The similarity between their spectral characteristics and those of the cosmic background at γ-ray energies suggests that these objects could make a significant contribution to this diffuse flux. This contribution has been assessed using two different number densities of γ-ray-emitting Seyfert galaxies based on optical and X-ray data. The comparison of the estimated and measured diffuse γ-ray background intensities is used to gain a deeper understanding of the metabolism of Seyfert galaxies.