Compton-thick AGN in the NuSTAR era II: A deep NuSTAR and XMM-Newton view of the candidate Compton thick AGN in NGC 1358

We present the combined NuSTATR and XMM-Newton 0.6-79 keV spectral analysis of a Seyfert 2 galaxy, NGC 1358, which we selected as a candidate Compton thick (CT-) active galactic nucleus (AGN) on the basis of previous Swift/BAT and Chandra studies. According to our analysis, NGC 1358 is confirmed to be a CT-AGN using physical motivated models, at >3 $\sigma$ confidence level. Our best-fit shows that the column density along the 'line-of-sight' of the obscuring material surrounding the accreting super-massive black hole is N$\rm _H$ = [1.96--2.80] $\times$ 10$^{24}$ cm$^{-2}$. The high-quality data from NuSTAR gives the best constraints on the spectral shape above $\sim$10 keV to date on NGC 1358. Moreover, by combining NuSTAR and XMM-Newton data, we find that the obscuring torus has a low covering factor ($f_c$ <0.17), and the obscuring material is distributed in clumps, rather than uniformly. We also derive an estimate of NGC 1358's Eddington ratio, finding it to be $\lambda_{\rm Edd}$ $\sim$$4.7_{-0.3}^{+0.3}$ $\times$ 10$^{-2}$, which is in acceptable agreement with previous measurements. Finally, we find no evidence of short-term variability, over a $\sim$100 ks time-span, in terms of both 'line-of-sight' column density and flux.Comment: 12 pages, 6 figure

Heavily obscured AGN in the local Universe

We present here a new powerful diagnostic plot to select heavily obscured AGN in the local universe by combining infrared (Spitzer, IRAS) and X-ray (XMM) information. On the basis of this plot, we selected a sample of X-ray obscured sources in the 2XMM catalogue and found seven newly discovered Compton-thick AGN candidates.Comment: 2 pages, 2 figures, To appear in refereed Proceedings of "X-ray Astronomy 2009: Present Status, Multi-Wavelength Approach and Future Perspectives", Bologna, Italy, September 7-11, 2009, AIP, eds. A. Comastri, M. Cappi, and L. Angelin

The space density of Compton-thick AGN at z~0.8 in the zCOSMOS-Bright Survey

The obscured accretion phase in BH growth is a key ingredient in many models linking the AGN activity with the evolution of their host galaxy. At present, a complete census of obscured AGN is still missing. The purpose of this work is to assess the reliability of the [NeV] emission line at 3426 A to pick up obscured AGN up to z~1 by assuming that [NeV] is a reliable proxy of the intrinsic AGN luminosity and using moderately deep X-ray data to characterize the amount of obscuration. A sample of 69 narrow-line (Type 2) AGN at z=0.65-1.20 were selected from the 20k-zCOSMOS Bright galaxy sample on the basis of the presence of the [NeV] emission. The X-ray properties of these galaxies were then derived using the Chandra-COSMOS coverage of the field; the X-ray-to-[NeV] flux ratio, coupled with X-ray spectral and stacking analyses, was then used to infer whether Compton-thin or Compton-thick absorption were present in these sources. Then the [NeV] luminosity function was computed to estimate the space density of Compton-thick (CT) AGN at z~0.8. Twenty-three sources were detected by Chandra, and their properties are consistent with moderate obscuration (on average, ~a few 10^{22} cm^-2). The X-ray properties of the remaining 46 X-ray undetected Type 2 AGN were derived using X-ray stacking analysis. Current data indicate that a fraction as high as ~40% of the present sample is likely to be CT. The space density of CT AGN with logL_2-10keV>43.5 at z=0.83 is (9.1+/-2.1) 10^{-6} Mpc^{-3}, in good agreement with both XRB model expectations and the previously measured space density for objects in a similar redshift and luminosity range. We regard our selection technique for CT AGN as clean but not complete, since even a mild extinction in the NLR can suppress [NeV] emission. Therefore, our estimate of their space density should be considered as a lower limit.Comment: 10 pages, 7 figures, 2 tables, A&A, in pres

The structure of the X-ray absorber in Mrk 915 revealed by Swift

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.Comment: 8 pages, 6 figures, 1 table. Accepted for publication on MNRA

The X-ray emission of z>2.5 active galactic nuclei can be obscured by their host galaxies

We present a multi-wavelength study of seven AGN at spectroscopic redshift >2.5 in the 7 Ms Chandra Deep Field South, selected to have good FIR/sub-mm detections. Our aim is to investigate the possibility that the obscuration observed in the X-rays can be produced by the interstellar medium (ISM) of the host galaxy. Based on the 7 Ms Chandra spectra, we measured obscuring column densities N$_{H, X}$ in excess of 7x10$^{22}$ cm$^{-2}$ and intrinsic X-ray luminosities L$_{X}$>10$^{44}$ erg s$^{-1}$ for our targets, as well as equivalent widths for the Fe K$\alpha$ emission line EW>0.5-1 keV. We built the UV-to-FIR spectral energy distributions by using broad-band photometry from CANDELS and Herschel catalogs. By means of an SED decomposition technique, we derived stellar masses (M$_{*}$~10$^{11}$ Msun), IR luminosities (L$_{IR}$>10$^{12}$ Lsun), star formation rates (SFR~190-1680 Msun yr$^{-1}$) and AGN bolometric luminosities (L$_{bol}$~10$^{46}$ erg s$^{-1}$) for our sample. We used an empirically-calibrated relation between gas masses and FIR/sub-mm luminosities and derived M$_{gas}$~0.8-5.4x10$^{10}$ Msun. High-resolution (0.3-0.7'') ALMA data (when available, CANDELS data otherwise) were used to estimate the galaxy size and hence the volume enclosing most of the ISM under simple geometrical assumptions. These measurements were then combined to derive the column density associated with the ISM of the host, on the order of N$_{H, ISM}$~10$^{23-24}$ cm$^{-2}$. The comparison between the ISM column densities and those measured from the X-ray spectral analysis shows that they are similar. This suggests that, at least at high redshift, significant absorption on kpc scales by the dense ISM in the host likely adds to or substitutes that produced by circumnuclear gas on pc scales (i.e., the torus of unified models). The lack of unobscured AGN among our ISM-rich targets supports this scenario.Comment: 15 pages, 3 figures. Accepted for publication in A&

XMM-Newton and NuSTAR joint observations of Mrk 915: a deep look into the X-ray properties

We report on the X-ray monitoring programme (covering slightly more than 11 days) carried out jointly by XMM-Newton and NuSTAR on the intermediate Seyfert galaxy Mrk 915. The light curves extracted in different energy ranges show a variation in intensity but not a significant change in spectral shape. The X-ray spectra reveal the presence of a two-phase warm absorber: a fully covering mildly ionized structure [log xi/(erg cm/s)~2.3, NH~1.3x10^21 cm-2] and a partial covering (~90 per cent) lower ionized one [log xi/(erg cm/s)~0.6, NH~2x10^22 cm-2]. A reflection component from distant matter is also present. Finally, a high-column density (NH~1.5x10^23 cm-2) distribution of neutral matter covering a small fraction of the central region is observed, almost constant, in all observations. Main driver of the variations observed between the datasets is a decrease in the intrinsic emission by a factor of ~1.5. Slight variations in the partial covering ionized absorber are detected, while the data are consistent with no variation of the total covering absorber. The most likely interpretation of the present data locates this complex absorber closer to the central source than the narrow line region, possibly in the broad line region, in the innermost part of the torus, or in between. The neutral obscurer may either be part of this same stratified structure or associated with the walls of the torus, grazed by (and partially intercepting) the line of sight.Comment: 14 pages, 10 figures, 4 tables. Accepted for publication in MNRA

Sustainable and Resistant Road Infrastructures: The Role of the Envision Framework as a Guide to a New Design Approach

In Italy, resilience and sustainability concepts are generally applied to road infrastructures (mainly in terms of pavements) in order to minimize the environmental impacts of their construction and maintenance. In this paper the Envision framework has been adopted to evaluate the sustain-ability of a road project, optimizing its resilience for both short-term and long-term impacts. The rating approach has been applied considering not only pavements analysis but also the complete project process. The authors have upgraded the original Envision framework to road infrastructures, in compliance with the Italian regulatory framework. Four scenarios have been considered. The first allowed us to understand which credits can be evaluated with the available project documentation. The second represents a snapshot of the state of the project. The third evaluates the effect of the improvement in the performance level obtained by analyzing the potential increases. Finally, the last considers also for “pending” credits

Bike Lane Design: the Context Sensitive Approach

In these days of increasing congestion on roads, bicycles continue to provide a valuable contribution to mobility in Europe. Their relatively small size and low cost enable them to blend efficiently into in the traffic flow while needing less space compared to other vehicles. However, cyclists form one of the most vulnerable groups of road users. So the design of safe infrastructures for all travellers categories, included the cyclists, becomes a primary requirement. To obtain these results, a Context Sensitive Design approach is a very useful tool. In this way, in fact, it is possible to examine a project or existing road, reporting its crash potential and safety performances and detecting its deficiencies, taking into consideration communities and lands which it passes through. In this paper the authors, starting from results collected on a bike lane placed in Rimini, provide useful results for designers, construction and maintenance contractors, in order to obtain safe bike lanes

Mining the XRT archive to probe the X-ray absorber structure in the AGN population

One of the key ingredients of the Unified Model of Active Galactic Nuclei (AGN) is the presence of a torus-like optically thick medium composed by dust and gas around the putative supermassive black hole. However, the structure, size and composition of this circumnuclear medium are still matter of debate. To this end, the search for column density variations through X-ray monitoring on different timescales (months, weeks and few days) is fundamental to constrain size, kinematics and location of the X-ray absorber(s). Here we describe our project of mining the Swift-XRT archive to assemble a sample of AGN with extreme column density variability and determining the physical properties of the X-ray absorber(s). We also present the results obtained from a daily-weekly Swift-XRT follow-up monitoring recently performed on one of the most interesting new candidates for variability discovered so far, Mrk 915.Comment: 6 pages, 3 figures. To appear in Proceedings of Science for the "Swift: 10 years of Discovery" meeting, held in Rome (2-5 December 2014

X-ray observation of ULAS J1120+0641, the most distant quasar at z=7.08

We aim at probing the emission mechanism of the accreting super massive black holes in the high redshift Universe. We study the X-ray spectrum of ULAS1120+0641, the highest redshift quasar detected so far at z=7.085, which has been deeply observed (340 ks) by XMM-Newton. Despite the long integration time the spectral analysis is limited by the poor statistics, with only 150 source counts being detected. We measured the spectrum in the 2-80 keV rest-frame (0.3-10 keV observed) energy band. Assuming a simple power law model we find a photon index of 2.0+/-0.3 and a luminosity of 6.7+/-0.3 10^44 erg/s in the 2-10 keV band, while the intrinsic absorbing column can be only loosely constrained (NH< 1E23 cm^-2). Combining our data with published data we calculate that the X-ray-to-optical spectral index alpha_OX is1.8+/-0.1, in agreement with the alpha_OX-UV luminosity correlation valid for lower redshift quasars. We expanded to high energies the coverage of the spectral energy distribution of ULAS1120+0641. This is the second time that a z >6 quasar has been investigated through a deep X-ray observation. In agreement with previous studies of z~6 AGN samples, we do not find any hint of evolution in the broadband energy distribution. Indeed from our dataset ULAS 1120+0641 is indistinguishable from the population of optically bright quasar at lower redshift.Comment: 5 pages, 4 figures, A&A in press; updated with the accepted versio