Search

A complete demographic of active galactic nuclei (AGN) is essential to understand the evolution of the Universe. Optical surveys estimate the population of AGN in the local Universe to be of $\sim$ 4%. However, these results could be biased towards bright sources, not affected by the host galaxy attenuation. An alternative method for detecting these objects is through the X-ray emission. In this work, we aim to complement the AGN population of the optical CALIFA survey (941 sources), by using X-ray data from Chandra, which provides the best spatial resolution to date, essential to isolate the nuclear emission from the host galaxy. We study a total of 138 sources with available data. We find 34 new bonafide AGN and 23 AGN candidates, which could increase the AGN population to 7-10\% among the CALIFA survey. X-rays are particularly useful for low-luminosity AGN since they are excluded by the criterion of large equivalent width of the $H\alpha$ emission line when applied to optical selections. Indeed, placing such a restrictive criteria might cause a loss of up to 70% of AGN sources. X-ray detected sources are preferentially located in the right side of the [$OIII$]/$H\beta$ versus [$NII$]/$H\alpha$ diagram, suggesting that this diagram might be the most reliable at classifying AGN sources. Our results support the idea that multi-wavelength studies are the best way to obtain a complete AGN population., Comment: 18 pages, 8 figures, 7 tables, 5 pages of supplementary online material available. Accepted for publication in MNRAS

The European Space Agency is studying two large-class missions bound to operate in the decade of the 30s, and aiming at investigating the most energetic and violent phenomena in the Universe. $Athena$ is poised to study the physical conditions of baryons locked in large-scale structures from the epoch of their formation, as well as to yield an accurate census of accreting super-massive black holes down to the epoch of reionization; LISA will extend the hunt for Gravitational Wave (GW) events to the hitherto unexplored mHz regime. We discuss in this paper the science that their concurrent operation could yield, and present possible $Athena$ observational strategies. We focus on Super-Massive (M$\lesssim10^7\rm M_{\odot}$) Black Hole Mergers (SMBHMs), potentially accessible to $Athena$ up to $z\sim2$. The simultaneous measurement of their electro-magnetic (EM) and GW signals may enable unique experiments in the domains of astrophysics, fundamental physics, and cosmography, such as the magneto-hydrodynamics of fluid flows in a rapidly variable space-time, the formation of coronae and jets in Active Galactic Nuclei, and the measurement of the speed of GW, among others. Key to achieve these breakthrough results will be the LISA capability of locating a SMBHM event with an error box comparable to, or better than the field-of-view of the $Athena$ Wide Field Imager ($\simeq0.4\,$deg$^2$) and $Athena$ capability to slew fast to detect the source during the inspiral phase and the post-merger phase. Together, the two observatories will open in principle the exciting possibility of truly concurrent EM and GW studies of the SMBHMs, Comment: 17 pages, 8 figures. Accepted for publication in MNRAS

The bulk of X-ray spectroscopic studies of active galactic nuclei (AGN) are focused on local ($z < 0.1$) sources with low-to-moderate ($< 0.3$) Eddington ratio ($\lambda_\mathrm{Edd}$). It is then mandatory to overcome this limitation and improve our understanding of highly accreting AGN. In this work we present the preliminary results from the analysis of a sample of $\sim70$ high-$\lambda_\mathrm{Edd}$ radio-quiet AGN at $0.06 \leq z \leq 3.3$, based on the 10th release of the XMM-Newton serendipitous source catalogue, that we named as XMM-Newton High-Eddington Serendipitous AGN Sample (X-HESS). Almost $\sim35\%$ of the X-HESS AGN have multi-epoch archival observations and $\sim70\%$ of the sources can rely on simultaneous OM optical data. First results reveal sources showing signatures of ultra-fast outflows and remarkable long- and short-term X-ray flux variations. Indeed in J095847.88+690532.7 ($z \sim 1.3$), one of the most densely monitored objects hosting a $\sim$$10^9\,M_\odot$ supermassive black hole, we discovered a variation of the soft X-ray flux by a factor of > 2 over approximately one week (rest-frame). Large variations in the power-law continuum photon index $\Gamma$ are also observed, questioning expectations from previously reported $\Gamma - \lambda_\mathrm{Edd}$ relations, for which $\Gamma \geq 2$ would be a ubiquitous hallmark of AGN with $\lambda_\mathrm{Edd} \sim 1$., Comment: 7 pages, 5 figures, proceedings of the XMM-Newton Workshop 2022 "Black hole accretion under the X-ray microscope". Accepted for publication in Astronomische Nachrichten

We present a new X-ray spectroscopic study of $22$ luminous ($2\times10^{45}\lesssim L_{\rm bol}\rm /erg\,s^{-1} \lesssim 2\times10^{46}$) active galactic nuclei (AGNs) at intermediate-redshift ($0.1 \lesssim z \lesssim 0.4$), as part of the SUpermassive Black hole Winds in the x-rAYS (SUBWAYS) sample, mostly composed of quasars (QSOs) and type\,1 AGN. Here, 17 targets were observed with \textit{XMM-Newton} between 2019--2020 and the remaining 5 are from previous observations. The aim of this large campaign ($1.45\,\rm Ms$ duration) is to characterise the various manifestations of winds in the X-rays driven from supermassive black holes in AGN. In this paper we focus on the search and characterization of ultra-fast outflows (UFOs), which are typically detected through blueshifted absorption troughs in the Fe\,K band ($E>7\,\rm keV$). By following Monte Carlo procedures, we confirm the detection of absorption lines corresponding to highly ionised iron (e.g., Fe\,\textsc{xxv}\,H$\alpha$, Fe\,\textsc{xxvi}\,Ly$\alpha$) in 7/22 sources at the $\gtrsim95\%$ confidence level (for each individual line). The global combined probability of such absorption features in the sample is $>99.9\%$. The SUBWAYS campaign extends at higher luminosity and redshifts than previous local studies on Seyferts, obtained using \xmm and \suzaku observations. We find a UFO detection fraction of $\sim30\%$ on the total sample that is in agreement with the previous findings. This work independently provides further support for the existence of highly-ionised matter propagating at mildly relativistic speed ($\gtrsim0.1c$) in a considerable fraction of AGN over a broad range of luminosities, which is expected to play a key role in the self-regulated AGN feeding-feedback cycle, as also supported by hydrodynamical multiphase simulations., Comment: 30 pages, 10 figures, accepted for publication in A&A

We report on a long (250 ks) NuSTAR observation of the bright quasar RBS 1055 performed in March 2021, and archival XMM-Newton pointings (185 ks) taken in July 2014. An optical spectrum of the source taken with the Double Spectrograph at the Palomar Observatory, quasi-simultaneous with the NuSTAR observations, is also analyzed. We find that the two-coronae model, in which a warm and hot corona coexist, well reproduces its broad band spectrum, with temperatures kT$_e=0.12^{+0.08}_{-0.03}$ keV, kT$_e=30^{+40}_{-10}$ keV and Thomson optical depths $\tau$=30$_{-10}^{+15}$ and $\tau$=3.0$_{-1.4}^{+1.0}$ for the former and the latter component, respectively. We confirm the presence of an intense Fe K$\alpha$ emission line (EW=55$\pm$6 eV) and, when a toroidal model is considered for reproducing the Compton reflection, a Compton-thin solution with N$_{\rm H}=(3.2^{+0.9}_{-0.8})\times10^{23}$ cm$^{-2}$ for the circumnuclear reflector is found. The analysis of the optical spectrum reveals a likely peculiar configuration of our line of sight with respect to the nucleus, and the presence of a broad [O III] component, tracing outflows in the NLR, with a velocity shift $v=$1500$\pm100$ km s$^{-1}$, leading to a mass outflow rate $\dot{M}_{\rm out}=25.4\pm1.5$ M$_{\odot}$ yr$^{-1}$ and outflow kinetic power $\dot{E}_{\rm kin}$/L$_{\rm Bol}$ $\sim$0.33%. We estimate the BH mass to be in the range 2.8$\times$10$^{8}$-1.2$\times$10$^{9}$ M$_{\odot}$, according to different BLR emission lines, with an average value of =6.5$\times$10$^{8}$ M$_{\odot}$. With an Fe K$\alpha$ which is 3$\sigma$ above the value predicted from the EW-L$_{2-10\ \rm keV}$ relation and an extreme source brightness at 2 keV (a factor 10-15 higher than the one expected from the optical/UV), RBS 1055 confirms to be an outlier in the X-rays, compared to other objects in the same luminosity and redshift range., Comment: 11 pages, 10 figures, 4 tables. Accepted for publication in Astronomy & Astrophysics

The X-ray Integral Field Unit (X-IFU) is the high resolution X-ray spectrometer of ESA's Athena X-ray observatory. It will deliver X-ray data in the 0.2-12 keV band with an unprecedented spectral resolution of 2.5 eV up to 7 keV. During the observation of very bright X-ray sources, the X-IFU detectors will receive high photon rates. The count rate capability of the X-IFU will be improved by using the defocusing option, which will enable the observations of extremely bright sources with fluxes up to $\simeq 1$ Crab. In the defocused mode, the point spread function (PSF) of the telescope will be spread over a large number of pixels. In this case, each pixel receives a small fraction of the overall flux. Due to the energy dependence of the PSF, this mode will generate energy dependent artefacts increasing with count rate if not analysed properly. To account for the degradation of the energy resolution with pulse separation in a pixel, a grading scheme (here four grades) will be defined to affect the proper energy response to each event. This will create selection effects preventing the use of the nominal Auxiliary Response File (ARF) for all events. We present a new method for the reconstruction of the spectra obtained from observations performed with a PSF that varies as a function of energy. We apply our method to the case of the X-IFU spectra obtained during the defocused observations. We use the end-to-end SIXTE simulator to model defocused X-IFU observations. Then we estimate new ARF for each of the grades by calculating the effective area at the level of each pixel. Our method allows us to successfully reconstruct the spectra of bright sources when employed in the defocused mode, without any bias. Finally, we address how various sources of uncertainty related to our knowledge of the PSF as a function of energy affect our results., Comment: Accepted for publication in A&A

On behalf of the International Astronomical Consortium for High Energy Calibration (IACHEC), we present results from the cross-calibration campaigns in 2012 on 3C 273 and in 2013 on PKS 2155-304 between the then active X-ray observatories Chandra, NuSTAR, Suzaku, Swift and XMM-Newton. We compare measured fluxes between instrument pairs in two energy bands, 1-5 keV and 3-7 keV and calculate an average cross-normalization constant for each energy range. We review known cross-calibration features and provide a series of tables and figures to be used for evaluating cross-normalization constants obtained from other observations with the above mentioned observatories., Comment: Accepted for publication in the Astronomical Journal

IAU Symposium, 10 (313), ISSN:0074-1809, ISSN:1743-9213, Extragalactic jets from every angle, ISBN:978-1-107-07874-1

I will present XMM-Newton-RGS observations of the Seyfert 1 Galaxies Mrk 335 and NGC 4051 that unveiled an emission line-rich spectrum during a low flux state of the AGN continuum.Line ratio diagnostics from H-like and He-like ions indicate that the emission lines arise in X-ray photoionized plasma. The physical properties of the line emitting material were derived using the CLOUDY photoionization code. Although the properties of the plasma cannot be uniquely determined, we found that the density of the X-ray photoionized gas in Mrk 335 is constrained at 99% c.l. to 10^9-10^{11} cm^{-3}, placing the gas within the inner edge of the optical Broad Line Region. For NGC 4051, the density and the location of the plasma are instead consistent with outer region of the AGN. I will briefly present other Seyfert 1 sources where X-ray photoionized emission lines possibly arise in the Broad Line Region and I will review the implication of these findings in a broader context.

Context: By studying the optical brightness surface density of the globular cluster NGC 6388, it has been recently proposed that it harbors a central intermediate-mass black hole with mass ≃ 5.7×103 M⊙. Aims: We expect that the compact object in the center of NGC 6388 emits radiation in the X-ray band as a consequence of the accretion from the surrounding matter. We searched for XMM-Newton and Chandra observations towards NGC 6388 to test this hypothesis. Methods: We determine both the hardness ratios and luminosity with a minimum set of assumptions for each of the identified field sources. Results: The Chandra satellite disentangles several point-like X-ray sources, probably low mass X-ray binaries, well within the core radius of the globular cluster. However, three of them, coinciding with the cluster center of gravity, remain unresolved. Their total luminosity is L_X^Obs ≃ 2.7×1033 erg s-1. If one of these sources is the X-ray counterpart of the intermediate-mass black hole in NGC 6388, the corresponding upper limit on the accretion efficiency, with respect to the Eddington luminosity, is 3×10-9. This measurement could be tightened if moderately deep radio observations of the field were performed. Bi

We present preliminary results of BeppoSAX AO1 observations of 3C 273 performed in January 1997. We also present a close comparison with data obtained during the satellite SVP, in July 1996. On average, the AO1 flux is about a factor 2 higher than the flux detected during the SVP, and roughly on the middle of the historical X-ray flux range. Power law fits with galactic absorption to all observations yield spectral indices in the range 1.53-1.6, with the spectrum extending from 0.2 to at least up to 200 keV without any significant slope change. The broad band spectrum appears basically featureless, marking a clear difference from the SVP data, where an absorption feature at low energy and a fluorescence iron emission line are present. The lack of cold/warm matter signatures in our data may indicate that, at this "high" level of luminosity, the featureless continuum produced in a relativistic jet overwhelms any thermal and/or reprocessing component, while the two components were at least comparable during the "low" state of July 1996., Comment: 1+4 pages, 3 ps inlined figures, espcrc2.sty. Proc. of the Conf. "The Active X-Ray Sky: Results from BeppoSAX and Rossi-XTE", Rome 21-24 October 1997

We report on XMM-Newton observations of the black hole X-ray binary 4U 1630-47 during its 2012-2013 outburst. The first five observations monitor the source as its luminosity increases across the high-soft state of accretion. In the sixth observation the source has made a transition to an "anomalous" state, characterised by a significant contribution of electron scattering. A thermally/radiatively driven disc wind is present in the first four observations, which becomes more photoionised as the luminosity increases with time. In the fifth observation, the wind is not observed any more as a consequence of strong photoionisation and the low sensitivity of this observation. This overall trend is then consistent with a fully ionised wind causing the electron scattering characteristic of the anomalous state in the sixth observation. A broad iron emission line co-exists with the absorption features from the wind in the first four observations but is not visible in the last two observations. We find that the changes in the state of the wind as measured from modelling the absorption features with a self-consistent warm absorber model are correlated to the changes in the broad iron line. When the latter is modeled with a reflection component we find that the reflection fraction decreases as the illumination increases. We propose that the changes in both the absorption and broad emission lines are caused by the increasing luminosity and temperature of the accretion disc along the soft state. Such changes ultimately enable the transition to a state where the wind is fully ionised and consequently Comptonisation plays a significant role., Comment: Replacement: note added in proof. Accepted for publication in A&A. arXiv admin note: text overlap with arXiv:1204.5904

Validating our understanding of the innermost structure of Active Galactic Nuclei (AGN) would require resolving sub-parsec scales. Lacking adequate direct imaging, X-ray astronomy can still contribute to this undertaking through the study of spectral variability on time-scales from days to years. This bears information on the location of gaseous and dusty systems in the innermost regions around the accreting supermassive black hole. In this paper I discuss the application of this concept in two specific contexts: a) "fast" column density variations in heavily obscured AGN; b) reverberation of optically-thick reprocessing. These results lend support to a scenario where obscuration and optically thick reprocessing are due to a variety of different systems, ranging from the Broad Line Regions to a clumpy structure extended on larger scales up to hundreds of parsecs.

In this paper we describe the scientific goals and the experimental set-up of the projectPulsar search in M33. Its aim is the discovery of radio pulsars in the Scd spiral Galaxy M33 (NGC 598). A complete survey of the H a area of M33, with an exagonal grid somewhat less than one-half power of the Arecibo telescope at 1400 MHz, has been performed and about 100 observations over the 40% of the grid areas are now available. An improved version of the analysis procedure has been realized and is shortly described in the following. Some considerations about the detectability of pulsars eventually present in M33 are reported.

We have simulated, using a Monte Carlo method, time series representing the aperiodic variability typically observed in some X-ray sources. We have supposed that such red-noise features are generated by a shot noise process. The resulting time series have been analyzed by fast Fourier transform techniques. Using different sets of parameters we have been able to generate power spectra of different shapes. Some preliminary results of these simulations are discussed.

The International Astronomical Consortium for High‐Energy Calibration (IACHEC) aims to provide standards for high energy calibration and supervise cross‐calibration between different X‐ray and Gamma‐ray observatories. This goal is reached through Working Groups, involving around 40 astronomers worldwide. In these Groups, IACHEC members co‐operate to define calibration standards and procedures. Their scope is primarily a practical one: a set of astronomical sources, data and results (eventually published in refereed journals) will be the outcome of a co‐ordinated and standardized analysis of reference sources (“high‐energy standard candles”). We briefly describe here just two of the many studies undertaken by the IACHEC; a cross‐calibration analysis of O and Ne line fluxes from the thermal SNR 1E0102.2‐7219, and at higher energies a comparison study of a sample of cluster temperatures and fluxes. A more detailed picture of the activities of the IACHEC is available via the information portal at http://web.mit.edu/iachec/.

In this paper we present the differences and similarities found between Low Ionization Narrow Emission Regions (LINERs) and Seyfert 2s based on their X‐ray and optical emission. We have performed a careful study of the X‐ray nuclear properties of a sample of 82 of these LINERs [1, 2, 3]. Around 90% of our sample galaxies show evidences of hosting an AGN. However, the most important question remains still open: Why are they different to other AGN? One of the most important differences that we find is that a thermal component is needed in a high fraction of LINERs (90%). We also present here the preliminary results on a high‐resolution soft X‐ray (0.2–2 keV) spectroscopic study of a sample of 53 LINERs observed with the Reflection Grating Spectrometer (RGS) on board XMM‐Newton. We have found that, in most cases, the soft spectra actually result from the blending of emission lines, similarly to what is found in Seyfert galaxies [4]. Emission lines between 5–30Ȧ have been systematically fitted to obtain their...

We present initial results from a new 440-ks Chandra HETG GTO observation of the canonical Seyfert 2 galaxy NGC 1068. The proximity of NGC 1068, together with Chandra's superb spatial and spectral resolution, allow an unprecedented view of its nucleus and circumnuclear NLR. We perform the first spatially resolved high-resolution X-ray spectroscopy of the `ionization cone' in any AGN, and use the sensitive line diagnostics offered by the HETG to measure the ionization state, density, and temperature at discrete points along the ionized NLR. We argue that the NLR takes the form of outflowing photoionized gas, rather than gas that has been collisionally ionized by the small-scale radio jet in NGC 1068. We investigate evidence for any velocity gradients in the outflow, and describe our next steps in modeling the spatially resolved spectra as a function of distance from the nucleus.

High resolution spectroscopy is acquiring increasing importance in the study of AGNs. We discuss the results on three Seyfert galaxies (Mrk 335, NGC 4051, and NGC 1365).

While in Radio–Quiet (RQ) AGN warm gas photoionised by the nuclear engine has been well revealed and studied in X‐rays, it is still unclear whether a similar gaseous environment can survive in Radio–Loud (RL) objects. The exploration of the environment surrounding the nuclei of RL sources is an important point to be addressed. It can help to understand the physical link among accretion flows, winds and jet, and the influence that each component can have on the host galaxy. We report on the recent discovery of warm gas in RL AGN, indicating that relativistic collimated plasma (jet) and slower outflows of photoionised gas can coexist in the same source. The physical properties of this gas seem to be very similar to RQ ones, suggesting that RL and RQ AGN environment becomes indistinguishable at large distances from the central engine (e.g. the Narrow Line Region).

We present in this paper preliminary results of a spectroscopic study of a sample of isolated X-ray flares in Active Galactic Nuclei. The motivation of this study is to provide clues on the nature of X-ray variability in AGN. Although there is nowadays general consensus that the physical processes responsible for the often extreme X-ray variability observed in AGN occurs in the accretion flow onto the supermassive black holes, there is little consensus about its mechanism and the ultimate physical driver. The now almost twenty years old controversy between X-ray disk illumination and accretion flow instabilities is still basically unresolved ([4]), despite several multiwavelength monitoring programs ([3]). The recent discovery of “narrow” blue-shifted features in the X-ray spectra of nearby Seyfert Galaxies has revived the hypothesis of localized “flares” illuminating a small portion of the accretion flow, whose combination produce the observed overall X-ray variability ([2]), possibly in analogy to the shot noise observed in Galactic X-ray binaries ([1]). To address this issue, we have selected a sample of “isolated flares” detected in light curves of XMM-Newton observations of AGN. We have not attempted at an “objective” definition of what an isolated flare is. It suffices here to day that we consider hereafter events, where a trailing and leading edge above a constant quiescent level can be recognized.

XMM‐Newton data analysis of the bright galaxy 4U 1344‐60 is presented. The observed X‐ray spectrum is complex. The continuum emission can be described as a power law obscured by two neutral absorption components. Interestingly, 4U 1344‐60 exhibits a broad and skewed iron line at 6.4 keV most likely originated in a few gravitational radius from the black hole. Optical spectral analysis was also presented. On the basis of its results, we propose to classify 4U 1344‐60 as a Seyfert 1.5 galaxy located at z=0.012±0.001.

We present an overview of the set of celestial sources used for in-flight calibration of x-ray detectors by past and operational missions. We show the rationale behind their choice as a guideline for future missions aiming at optimizing the critical early phases of their science operations.

We present the analysis and the results of a 20 ks XMM-Newton observation of the extremely X-ray loud (L_X ~ 5 x 10^{47} erg/s) flat-spectrum radio quasar RBS 315 at a redshift of 2.69. This EPIC observation has allowed us to strongly constrain the slope of the continuum (Gamma = 1.23+/-0.01) as well as to discover the presence of a sharp drop below ~ 2 keV in its spectrum. Such a flat photon index and the huge luminosity suggest that the X-ray emission is due to the low energy tail of the Comptonized spectrum, produced from plasma in a relativistic jet oriented close to our line of sight. Even though the hypothesis of a break in the continuum cannot be completely discarded as an explanation of the soft X-ray cutoff, the presence of intrinsic absorption appears more plausible. Spectral fits with cold (Nh(z) = 1.62+/-0.09 x 10^{22} cm^{-2}) and lukewarm (Nh(z) = 2.2^{+0.9}_{-0.3} x 10^{22} cm^{-2}; xi = 15^{+38}_{-12} erg/cm^{2}/s) absorbers are statistically indistinguishable. Remarkably, our results are very similar to those reported so far for other absorbed high-z Blazars observed by XMM-Newton. The existence of this ``homogeneous'' class of jet-dominated superluminous obscured QSOs at high z therefore could be important in the context of the formation and cosmological evolution of radio-loud objects, Accepted by A&A Letters

Various X-ray satellites have used the Crab as a standard candle to perform their calibrations in the past. The calibration of XMM-Newton, however, is independent of the Crab nebula, because this object has not been used to adjust spectral calibration issues. In 2004 a number of special observations were performed to measure the spectral parameters and the absolute flux of the Crab with XMM-Newtons EPIC-pn CCD camera. We describe the results of the campaign in detail and compare them with data of four current missions (Integral, Swift, Chandra, RXTE) and numerous previous missions (ROSAT, EXOSAT, Beppo-SAX, ASCA, Ginga, Einstein, Mir-HEXE)., Comment: 12 pages, 7 figures

We analyzed the 2003 Target of Opportunity XMM‐Newton observation of IGR J16318‐4848, to derive the properties of the matter responsible for the obscuration and for the emission of Fe and Ni lines. The line of sight material has a column density of about 2×1024 cm−2 but, from the Fe Kα line EW and Compton Shoulder, we argue that the average column density is a few ×1023 cm−2, while the covering factor is about 0.1–0.2. The iron Kα line varies on time scales as short as 1000 s, implying a size of the emitting region less than 3×1013 cm. An ongoing XMM‐Newton/INTEGRAL monitoring campaign is confirming the non‐transient nature of the source.

We present preliminary results of a systematic analysis of the XMM-Newton spectra of nearby optically-bright QSOs. The objects have been optically selected from the Bright Quasar Survey sample. The goal of this project is to characterise the X-ray spectral properties of optically selected QSOs in the 0.3-12 keV energy band. A power law component accounts the hard band spectra with a average photon index of 2.0+/-0.2. No single model is able to account for the ubiquitous soft excess. We discuss several possibilities such single and multi-temperature black-body, power law and bremsstrahlung. We observed a X-ray Baldwin effect in our sample., Comment: 2 pages, 1 figure, to appear in the proceedings of the conference "Multiwavelength AGN Surveys", held in Cozumel, Mexico, December 2003

We present results from the analysis of a BeppoSAX observation of the Centaurus Cluster. The radial metal abundance profile shows evidence of a large enhancement in the core, where Ab $>$ 1 (sol. units). The temperature map indicates that the cluster is characterized by a gradient oriented in the NW/SE direction, with cooler gas in the NW and hotter gas in the SE (\Delta kT \sim 1 keV). In hard X-rays, where the PDS detects emission with a flux of $2.2 \times 10^{-11}$ erg/cm^2/s in the 20-200 keV band, the spectrum lies above the extrapolation of the cluster thermal emission. We discuss several possible interpretations for the hard excess finding that none is completely satisfactory., Comment: To appear in A&A

In this paper, a BeppoSAX observation of the bright Seyfert 2 galaxy NGC6300 is presented. The rapidly variable emission from the active nucleus is seen through a Compton-thin (NH ~ 3x10^23 atomoms/cm/cm) absorber. A Compton-reflection component with an unusually high reflection fraction (R ~ 4.2), and the comparison with a reflection-dominated spectrum measured by RXTE two and half years earlier suggest that NGC6300 belongs to the class of "transient" AGN, undergoing long and repeated periods of low-activity. The spectral transition provides support to the idea that Compton-thick and Compton-thin X-ray absorbers in Seyfert 2 galaxies are decoupled, the former being most likely associated with the "torus", whereas the latter is probably located at much larger distances., 5 Latex pages, 5 figures, To appear in Monthly Notices of the Royal Astronomical Society (Letters)

In the following paper, some first Beppo-SAX results on AGN are presented. Main on-flight calibration features and observational properties are discussed at the light of possible future AGN studies, 5 pages, Latex, 4 Postscript figures, `an-art.sty' included, to appear in Astronomische Nachrichten, vol.4, pag. 223

There is a great deal of evidence that the X-ray emission from High Mass X-Ray Binaries (HMXRB) is often associated with the accretion of matter from a “normal” companion to a degenerate (neutron) star. Provided the magnetic field in these systems is very high (B ~ 1012 — 1013 G), the accretion should occur via the formation of discrete “blobs” which should emit through bremsstrahlung process due to the sudden stop near the surface of the neutron star[2, 3, 5]. There are a number of detections of non-Poissonian aperiodic variations in the intensity of emitted radiation (often referred to as “flickering”) with a characteristic Power Spectrum Density (PSD) broad band feature (red noise)[4, 1]. We have made a detailed investigation the possible effects arising when coupling the coherent part (the pulsation) with the incoherent (the flickering).

The Crab Nebula and the Pulsar were observed from 31th to 1st of August and from 6th to 7th September 1996 with the Narrow Field Instruments (NFI's) on board of BeppoSAX, during the Science Verification Phase. The fine time resolution (15 μs) and the high statistic of the data provided phase histogram of very good quality and well suited for phase resolved spectroscopy over the entire energy band (0.1–300 keV) covered by BeppoSAX payload. We present some results of the phase resolved spectral analysis.

We present preliminary results from two observations of the radio galaxy Centaurus A performed by the BeppoSAX satellite. We did not detect any spectral variation of the nuclear continuum in spite of the long-term flux change (by a factor 1.3) between the two observations. At both epochs, the nuclear point-like emission was well fitted with a strongly absorbed power law with an exponential cutoff at high energies (E_cutoff>200 keV). We also observed a significant flux variation of the iron line between the two observations. The flux of the line and of the continuum changed in the opposite sense. The line is more intense at the first epoch, when the nuclear source was at the lower intensity level. The implied delay between the continuum and line variations strongly suggests that the cold material responsible for the iron line production is not located very near to the primary X-ray source. There is also evidence that the line profile changed between the two epochs, being broader and slightly blueshifted when the source was fainter. It is possible that the emission feature is a blend of cold and ionized iron lines produced in separate regions surrounding the nuclear source., 4 pages, 4 figures, accepted for publication in Advances in Space Research, proceedings of 32nd COSPAR Symposium (1998)

The broad-band 0.1–200 keV spectra of a selected sample of Seyfert 2 galaxies have been measured within the BeppoSAX Core Programme. Here we present the first results obtained for 3 objects, NGC 7172, MKN 3 and NGC 7674. The broad band BeppoSAX data illustrate the high spectral complexity often found in Seyfert 2 galaxies predicted by unified models: NGC 7172 is found to be a Compton-thin source in which the primary emission is seen through absorbing material; MKN 3 is a border line object where the emission is partly seen directly and partly reprocessed by the absorbing material; NGC 7674 is an example of a Compton-thick source where the primary emission is hidden and only reprocessed radiation is observed.

Context. By studying the optical brightness surface density of the globular cluster NGC 6388, it has been recently proposed that it harbors a central intermediate-mass black hole with mass ≃5.7 x 10 3 M ⊙ . Aims. We expect that the compact object in the center of NGC 6388 emits radiation in the X-ray band as a consequence of the accretion from the surrounding matter. We searched for XMM-Newton and Chandra observations towards NGC 6388 to test this hypothesis. Methods. We determine both the hardness ratios and luminosity with a minimum set of assumptions for each of the identified field sources. Results. The Chandra satellite disentangles several point-like X-ray sources, probably low mass X-ray binaries, well within the core radius of the globular cluster. However, three of them, coinciding with the cluster center of gravity, remain unresolved. Their total luminosity is L Obs X ≃ 2.7 x 10 33 erg s -1 . If one of these sources is the X-ray counterpart of the intermediate-mass black hole in NGC 6388, the corresponding upper limit on the accretion efficiency, with respect to the Eddington luminosity, is 3 x 10 -9 . This measurement could be tightened if moderately deep radio observations of the field were performed.

We present a deep (~5.8 days) 0.3-2 keV high-resolution spectrum of NGC1365, collected with the reflection grating spectrometer (RGS) on board XMM-Newton. The spectrum is dominated by strong recombination lines of He- and H-like transitions from carbon to silicon, as well as by L transitions from FeXVII. The continuum is strong, especially in the 10 to 20 Angstrom, range. Formal fits require two optically thin, collisionally ionised plasma components, with temperatures ~300 and ~640 eV. However, they leave the bulk of the forbidden components of the He-alpha OVII and NVI triplets unaccounted for. These features can be explained as being produced by photoionised gas. NGC1365 is therefore the first obscured AGN, whose high-resolution X-ray spectrum requires both collisional ionisation and photoionisation. The relative weakness of photoionisation does not stem from the intrinsic weakness of its AGN, whose X-ray luminosity is ~10^{42} erg/s. We suggest that it may instead come from the line-of-sight from the active nucleus to the NLR being blocked by optically thick matter in the broad line region, at the same time responsible for the large observed variation of the column density obscuring the X-ray active nucleus. Alternatively, NGC1365 could host a remarkably luminous nuclear starburst when compared to the AGN accretion power [abriged]., Comment: Accepted for publication in Astronomy & Astrophysics, 13 pages, 10 figures

The analysis of an INTEGRAL AO2 observation of the error contours of the EGRET source 3EG J1621+8203 is presented. The only source found inside the error contours for energies between 20 and 30 keV at 5 sigma detection significance is the FR I radio galaxy NGC 6251. This supports the identification of NGC 6251 with 3EG J1621+8203. The observed flux is higher and softer than observed in the past, but consistent with a variable blazar-like spectral energy distribution., 5 pages, 2 figures. Accepted for publication on A&A Main Journal