ALBERT

Description: In this paper, we present the results obtained with a monitoring programme (23 days long) performed with Swift -XRT on the local Seyfert galaxy Mrk 915. The light-curve analysis shows a significant count rate variation (about a factor of 2–3) on a time-scale of a few days, while the X-ray colours show a change in the spectral curvature below 2 keV and the presence of two main spectral states. From the spectral analysis we find that the observed variations can be explained by the change of the intrinsic nuclear power (about a factor of 1.5) coupled with a change of the properties of an ionized absorber. The quality of the data prevents us from firmly establishing if the spectral variation is due to a change in the ionization state and/or in the covering factor of the absorbing medium. The latter scenario would imply a clumpy structure of the ionized medium. By combining the information provided by the light curve and the spectral analyses, we can derive some constraints on the location of the absorber under the hypotheses of either homogeneous or clumpy medium. In both cases, we find that the absorber should be located inside the outer edge of an extended torus and, in particular, under the clumpy hypothesis, it should be located near, or just outside, to the broad emission line region.

Description: We present results from a 90 ks Chandra ACIS-S observation of the X-ray luminous interacting galaxy system Arp 299 (NGC 3690/IC 694). We detect 25 discrete X-ray sources with luminosities above ~4.0 x 10 38 erg s –1 covering the entire Ultra Luminous X-ray source (ULX) regime. Based on the hard X-ray spectra of the non-nuclear discrete sources identified in Arp 299, and their association with young, actively star-forming region of Arp 299 we identify them as HMXBs. We find in total 20 off-nuclear sources with luminosities above the ULX limit, 14 of which are point-like sources. Furthermore we observe a marginally significant deficit in the number of ULXs, with respect to the number expected from scaling relations of X-ray binaries with the star formation rate (SFR). Although the high metallicity of the galaxy could result in lower ULX numbers, the good agreement between the observed total X-ray luminosity of ULXs, and that expected from the relevant scaling relation indicates that this deficit could be the result of confusion effects. The integrated spectrum of the galaxy shows the presence of a hot gaseous component with kT = 0.72 ± 0.03 keV, contributing ~20 per cent of the soft (0.1-2.0 keV) unabsorbed luminosity of the galaxy. A plume of soft X-ray emission in the west of the galaxy indicates a large scale outflow. We find that the AGN in NGC 3690 contributes only 22 per cent of the observed broad-band X-ray luminosity of Arp 299.

Description: We investigate the mid-infrared (mid-IR) 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 . 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 important contribution to the observed mid-IR flux in particular at the longest wavelengths ( W 3, at 12 μm, and W 4, at 22 μm). In about half of the sources (22 objects), we observe a very red mid-IR colour ( W 4 – W 3 〉 2.5) that can be explained only using a starburst galaxy template (M82). Using the 22 μm luminosities, corrected for the AGN contribution, we have then estimated the star formation rate (SFR) for 20 of these ‘red’ RL NLS1, finding values ranging from 10 to 500 M yr –1 . For the RL NLS1 showing bluer colours, instead, we cannot exclude the presence of a star-forming (SF) host galaxy although, on average, we expect a lower SFR. Studying the radio (1.4 GHz) to mid-IR (22 μm) flux ratios of the RL NLS1 in the sample, we found that in ~10 objects the SF 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 SF activity.

Description: In this paper, we present the results obtained with a monitoring programme (23 days long) performed with Swift -XRT on the local Seyfert galaxy Mrk 915. The light-curve analysis shows a significant count rate variation (about a factor of 2–3) on a time-scale of a few days, while the X-ray colours show a change in the spectral curvature below 2 keV and the presence of two main spectral states. From the spectral analysis we find that the observed variations can be explained by the change of the intrinsic nuclear power (about a factor of 1.5) coupled with a change of the properties of an ionized absorber. The quality of the data prevents us from firmly establishing if the spectral variation is due to a change in the ionization state and/or in the covering factor of the absorbing medium. The latter scenario would imply a clumpy structure of the ionized medium. By combining the information provided by the light curve and the spectral analyses, we can derive some constraints on the location of the absorber under the hypotheses of either homogeneous or clumpy medium. In both cases, we find that the absorber should be located inside the outer edge of an extended torus and, in particular, under the clumpy hypothesis, it should be located near, or just outside, to the broad emission line region.

Description: We present SDSS J143244.91+301435.3, a new case of a radio-loud narrow-line Seyfert 1 (RL NLS1) with a relatively high radio power ( P 1.4 GHz = 2.1 10 25  W Hz –1 ) and large radio-loudness parameter ( R 1.4 = 600 ± 100). The radio source is compact with a linear size below ~1.4 kpc but, in contrast to most of the RL NLS1 discovered so far with such a high R 1.4 , its radio spectrum is very steep (α = 0.93, S    –α ) and does not support a ‘blazar-like’ nature. Both the small mass of the central supermassive black hole and the high accretion rate relative to the Eddington limit estimated for this object (3.2 10 7  M and 0.27, respectively, with a formal error of ~0.4 dex for both quantities) are typical of the NLS1 class. Through modelling the spectral energy distribution of the source, we have found that the galaxy hosting SDSS J143244.91+301435.3 is undergoing quite intense star formation (SFR = 50 M  yr –1 ), which, however, is expected to contribute only marginally (~1 per cent) to the observed radio emission. The radio properties of SDSS J143244.91+301435.3 are remarkably similar to those of compact steep-spectrum (CSS) radio sources, a class of active galactic nuclei (AGN) mostly composed of young radio galaxies. This may suggest a direct link between these two classes of AGN, with CSS sources possibly representing the misaligned version (the so-called ‘parent population’) of RL NLS1 showing blazar characteristics.

Description: Although absorbed quasars are extremely important for our understanding of the energetics of the Universe, the main physical parameters of their central engines are still poorly known. In this work, we present and study a complete sample of 14 quasars (QSOs) that are absorbed in the X-rays (column density N H 〉 4 x 10 21 cm –2 and X-ray luminosity L 2-10 keV 〉 10 44 ergs –1 ; XQSO2) belonging to the XMM – Newton Bright Serendipitous Survey (XBS). From the analysis of their ultraviolet-to-mid-infrared spectral energy distribution, we can separate the nuclear emission from the host galaxy contribution, obtaining a measurement of the fundamental nuclear parameters, like the mass of the central supermassive black hole and the value of Eddington ratio, Edd . Comparing the properties of XQSO2s with those previously obtained for the X-ray unabsorbed QSOs in the XBS, we do not find any evidence that the two samples are drawn from different populations. In particular, the two samples span the same range in Eddington ratios, up to Edd ~ 0.5; this implies that our XQSO2s populate the ‘forbidden region’ in the so-called ‘effective Eddington limit paradigm’. A combination of low grain abundance, presence of stars inwards of the absorber, and/or anisotropy of the disc emission can explain this result.

Description: The cosmic history of the growth of supermassive black holes in galactic centres parallels that of star formation in the Universe. However, an important fraction of this growth occurs inconspicuously in obscured objects, where ultraviolet/optical/near-infrared emission is heavily obscured by dust. Since the X-ray flux is less attenuated, a high X-ray-to-optical flux ratio ( f x / f o ) is expected to be an efficient tool to find out these obscured accreting sources. We explore here via optical spectroscopy, X-ray spectroscopy and infrared photometry the most extreme cases of this population (those with f x / f o  〉 50, EXO50 sources hereafter), using a well-defined sample of seven X-ray sources extracted from the 2XMM catalogue. Five EXO50 sources (~70 per cent of the sample) in the bright flux regime explored by our survey ( f (2–10 keV)  ≥ 1.5 10 –13 erg cm –2 s –1 ) are associated with obscured AGN ( N H  〉 10 22  cm –2 ), spanning a redshift range between 0.75 and 1 and characterized by 2–10 keV intrinsic luminosities in the QSO regime (e.g. well in excess to 10 44 erg s –1 ). We did not find compelling evidence of Compton thick active galacic nuclei (AGN). Overall, the EXO50 type 2 QSOs do not seem to be different from standard X-ray-selected type 2 QSOs in terms of nuclear absorption; a very high AGN/host galaxy ratio seems to play a major role in explaining their extreme properties. Interestingly, three out of five EXO50 type 2 QSO objects can be classified as extreme dust-obscured galaxies (EDOGs, f 24 μm /f R ≥ 2000), suggesting that a very high AGN/host ratios (along with the large amount of dust absorption) could be the natural explanation also for a part of the EDOG population. The remaining two EXO50 sources are classified as BL Lac objects, having rather extreme properties, and which are good candidates for TeV emission.

Description: We present very long baseline interferometry (VLBI) observations, carried out with the European Very Long Baseline Interferometry Network (EVN), of SDSSJ143244.91+301435.3, a radio-loud narrow-line Seyfert 1 (RL NLS1) characterized by a steep radio spectrum. The source, compact at Very Large Array resolution, is resolved on the milliarcsec scale, showing a central region plus two extended structures. The relatively high brightness temperature of all components (5 x 10 6 –1.3 x 10 8  K) supports the hypothesis that the radio emission is non-thermal and likely produced by a relativistic jet and/or small radio lobes. The observed radio morphology, the lack of a significant core, and the presence of a low frequency (230 MHz) spectral turnover are reminiscent of the Compact Steep-Spectrum (CSS) sources. However, the linear size of the source (~0.5 kpc) measured from the EVN map is lower than the value predicted using the turnover/size relation valid for CSS sources (~6 kpc). This discrepancy can be explained by an additional component not detected in our observations, accounting for about a quarter of the total source flux density, combined to projection effects. The low core dominance of the source (CD 〈 0.29) confirms that SDSSJ143244.91+301435.3 is not a blazar, i.e. the relativistic jet is not pointing towards the observer. This supports the idea that SDSSJ143244.91+301435.3 may belong to the ‘parent population’ of flat-spectrum RL NLS1 and favours the hypothesis of a direct link between RL NLS1 and compact, possibly young, radio galaxies.

Description: In this work, the analysis of multi-epoch (1995–2010) X-ray observations of the Seyfert 1 galaxy H0557-385 is presented. The wealth of data presented in this analysis show that the source exhibits dramatic spectral variability, from a typical unabsorbed Seyfert 1 type spectrum to a Compton-thin absorbed state, on time-scales of ~5 yr. This extreme change in spectral shape can be attributed to variations in the column density and covering fraction of a neutral absorbing medium attenuating the emission from the central continuum source. Evidence for Compton reflection of the intrinsic nuclear emission is present in each of the spectra, though this feature is most prominent in the low-state spectra, where the associated Fe emission line complex is clearly visible. In addition to the variable absorbing medium, a warm absorber component has been detected in each spectral state. Optical spectroscopy concurrent with the 2010 XMM–Newton observation campaign has detected the presence of broad optical emission lines during an X-ray absorption event. From the analysis of both X-ray and optical spectroscopic data, it has been inferred that the X-ray spectral variability is a result of obscuration of the central emission region by a clumpy absorber covering ≥ 80 per cent of the source with an average column density of N H  ~ 7 x 10 23  cm –2 , and which is located outside the broad line region at a distance from the central source consistent with the dust sublimation radius of the AGN.