Ensemble spectral variability study of Active Galactic Nuclei from the XMM-Newton serendipitous source catalogue

The variability of the X-ray spectra of active galactic nuclei (AGN) usually includes a change of the spectral slope. This has been investigated for a small sample of local AGNs by Sobolewska and Papadakis, who found that slope variations are well correlated with flux variations, and that spectra are typically steeper in the bright phase (softer when brighter behaviour). Not much information is available for the spectral variability of high-luminosity AGNs and quasars. In order to investigate this phenomenon, we use data from the XMM-Newton Serendipitous Source Catalogue, Data Release 5, which contains X-ray observations for a large number of active galactic nuclei in a wide luminosity and redshift range, for several different epochs. This allows to perform an ensemble analysis of the spectral variability for a large sample of quasars. We quantify the spectral variability through the spectral variability parameter $\beta$, defined as the ratio between the change in spectral slope and the corresponding logarithmic flux variation. We find that the spectral variability of quasars has a softer when brighter behaviour, similarly to local AGNs.Comment: 5 pages, 2 figures. Prepared for the proceedings of the 6th Young Researchers Meeting, L'Aquil

The MEXSAS2 Sample and the Ensemble X-ray Variability of Quasars

We present the second Multi-Epoch X-ray Serendipitous AGN Sample (MEXSAS2), extracted from the 6th release of the XMM Serendipitous Source Catalogue (XMMSSC-DR6), cross-matched with Sloan Digital Sky Survey quasar catalogues DR7Q and DR12Q. Our sample also includes the available measurements for masses, bolometric luminosities, and Eddington ratios. Analyses of the ensemble structure function and spectral variability are presented, together with their dependences on such parameters. We confirm a decrease of the structure function with the X-ray luminosity, and find a weak dependence on the black hole mass. We introduce a new spectral variability estimator, taking errors on both fluxes and spectral indices into account. We confirm an ensemble softer when brighter trend, with no dependence of such estimator on black hole mass, Eddington ratio, redshift, X-ray and bolometric luminosity.Comment: 6 pages, 3 figures, to appear in Frontiers in Astronomy and Space Science

The NuSTAR view of the Seyfert Galaxy HE 0436-4717

We present the multi epoch spectral analysis of HE 0436-4717, a bright Seyfert 1 galaxy serendipitously observed by the high energy satellite NuSTAR four times between December 2014 and December 2015. The source flux shows modest variability within each pointing and among the four observations. Spectra are well modelled in terms of a weakly variable primary power law with constant photon index ($\Gamma$=2.01$\pm$0.08). A constant narrow \ion{Fe} K$\alpha$ emission line suggests that this feature has an origin far from the central black hole, while a broad relativistic component is not required by the data. The Compton reflection component is also constant in flux with a corresponding reflection fraction R=0.7$^{+0.2}_{-0.3}$. The iron abundance is compatible with being Solar (A$_{Fe}$=1.2$^{+1.4}_{-0.4}$), and a lower limit for the high energy cut-off E$_c$>280 keV is obtained. Adopting a self-consistent model accounting for a primary Comptonized continuum, we obtain a lower limit for the hot corona electron temperature kT$_e$>65 keV and a corresponding upper limit for the coronal optical depth of $\tau_e$<1.3. The results of the present analysis are consistent with the locus of local Seyfert galaxies in the kT$_e$-$\tau_e$ and temperature-compactness diagrams.Comment: accepted for publication in A&

Individual optical variability of Active Galactic Nuclei from the MEXSAS2 sample

Most of the variability studies of active galactic nuclei (AGNs) are based on ensemble analyses. Nevertheless, it is interesting to provide estimates of the individual variability properties of each AGN, in order to relate them with intrinsic physical quantities. A useful dataset is provided by the Catalina Surveys Data Release 2 (CSDR2), which encompasses almost a decade of photometric measurements of $\sim500$ million objects repeatedly observed hundreds of times. We aim to investigate the individual optical variability properties of 795 AGNs originally included in the Multi-Epoch XMM Serendipitous AGN Sample 2 (MEXSAS2). Our goals consist in: (i) searching for correlations between variability and AGN physical quantities; (ii) extending our knowledge of the variability features of MEXSAS2 from the X-ray to the optical. We use the structure function (SF) to analyse AGN flux variations. We model the SF as a power-law, $\text{SF}(\tau)=A\,(\tau/\tau_0)^\gamma$, and we compute its variability parameters. We introduce the V-correction as a simple tool to correctly quantify the amount of variability in the rest frame of each source. We find a significant decrease of variability amplitude with increasing bolometric, optical and X-ray luminosity. We obtain the indication of an intrinsically weak positive correlation between variability amplitude and redshift, $z$. Variability amplitude is also positively correlated with $\alpha_\text{ox}$. The slope of the SF, $\gamma$, is weakly correlated with the bolometric luminosity $L_\text{bol}$ and/or with the black hole mass $M_\text{BH}$. When comparing optical to X-ray variability properties, we find that X-ray variability amplitude is approximately the same for those AGNs with larger or smaller variability amplitude in the optical. On the contrary, AGNs with steeper SF in the optical do present steeper SF in the X-ray, and vice versa.Comment: 13 pages, 14 figures, 3 tables, accepted for publication in MNRA

Nomi di frutti e di piante nel dialetto di Nemi, tra conservazione e innovazione

Items of food lexicon, particularly relevant to fruit names, observed in the dialect spoken in Nemi, in the Castelli Romani area, are characterized by survival of the neutral gender. Materials, collected through dialectal inquiries, are analyzed from both etymological and morphological points of view and grouped according to their plural endings: -a, -ora, -i, and -e. A marked vitality is shown by the class of nouns with –a ending in the plural, such as u melu / e mela (eng. ‘the apple, the apples’). This morpheme is also found in other sectors of the lexicon and in toponymy. An insight is also given regarding the sociolinguistic use of those forms, that reveals the variable vitality of the dialect among people of different age ranges. This specific type of morphological analysis applied to a specific set of lexical items confirms the picture of extraordinary variety of the Median dialects of Italy, which the dialect of Nemi including those of the Castelli Romani area, belongs to

Wavelength Dependences of the Optical/UV and X-ray Luminosity Correlations of Quasars

The inter-band correlations between optical/UV and X-ray luminosities of active galactic nuclei (AGN) are important for understanding the disc-coronal connection, as well as using AGN as standard candles for cosmology. It is conventional to measure the X-ray luminosity at rest frame 2 keV and compare to the UV luminosity at the rest-frame 2500 \AA, but the wavelength-dependence was never well explored. In this work, we adopt a well-defined sample of 1169 unobscured quasars in the redshift range 0.13 - 4.51, and apply the direct-correlation method to explore how the correlation with the 2 keV luminosity changes at different optical/UV wavelengths, from 1280 - 5550 \AA\ where the spectral quality is high. We find that the luminosity at all UV continuum wavelengths correlates with the X-ray luminosity similarly to that at 2500 \AA, and that these correlations are better than at the optical wavelengths. Strong self-correlation is also found in the broadband optical/UV continuum, supporting the scenario that it is dominated by the disc emission. Correlations of various emission lines are also investigated (e.g. C IV, C III], Mg II, H$\beta$, [O III]$\lambda\lambda 4959/5007$), including the Baldwin effect and correlations involving line-widths. We find the forms of these line correlations are different, and they are also different from their underlying continua, suggesting various complexities in the line-generation process. We discuss these results in the disc-wind scenario. Our study confirms that the rest-frame 2500 \AA\ is a good wavelength to represent the optical/UV continual properties of quasars, and shows the advantages of the direct-correlation method.Comment: 18 pages, 15 figures, accepted for publication in MNRA

HST unveils a compact mildly relativistic Broad Line Region in the candidate true type 2 NGC 3147

NGC 3147 has been considered the best case of a true type 2 AGN: an unobscured AGN, based on the unabsorbed compact X-ray continuum, which lacks a broad line region (BLR). However, the very low luminosity of NGC 3147 implies a compact BLR, which produces very broad lines, hard to detect against the dominant background host galaxy. Narrow (0.1"x0.1") slit HST spectroscopy allowed us to exclude most of the host galaxy light, and revealed an H$\alpha$ line with an extremely broad base (FWZI$\sim27\,000$ km s$^{-1}$). The line profile shows a steep cutoff blue wing and an extended red wing, which match the signature of a mildly relativistic thin accretion disk line profile. It is indeed well fit with a nearly face on thin disk, at $i\sim23^\circ$, with an inner radius at $77\pm15$ r$_g$, which matches the prediction of $62^{+18}_{-14}$ r$_g$ from the $R_{\rm BLR} \sim L^{1/2}$ relation. This result questions the very existence of true type 2 AGN. Moreover, the detection of a thin disk, which extends below 100 r$_g$ in an $L/L_{\rm Edd}\sim10^{-4}$ system, contradicts the current view of the accretion flow configuration at extremely low accretion rates.Comment: 6 pages, 3 figures, accepted for publication in MNRAS Letter

X-HESS: a large sample of highly accreting serendipitous AGN under the XMM-Newton microscope

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 Nachrichte

Electrophysiology of glioma: a Rho GTPase-activating protein reduces tumor growth and spares neuron structure and function

Background. Glioblastomas are the most aggressive type of brain tumor. A successful treatment should aim at halting tumor growth and protecting neuronal cells to prevent functional deficits and cognitive deterioration. Here, we exploited a Rho GTPase-activating bacterial protein toxin, cytotoxic necrotizing factor 1 (CNF1), to interfere with glioma cell growth in vitro and vivo. We also investigated whether this toxin spares neuron structure and function in peritumoral areas. Methods. We performed a microarray transcriptomic and in-depth proteomic analysis to characterize the molecular changes triggered by CNF1 in glioma cells. We also examined tumor cell senescence and growth in vehicle-and CNF1-treated glioma-bearing mice. Electrophysiological and morphological techniques were used to investigate neuronal alterations in peritumoral cortical areas. Results. Administration of CNF1 triggered molecular and morphological hallmarks of senescence in mouse and human glioma cells in vitro. CNF1 treatment in vivo induced glioma cell senescence and potently reduced tumor volumes. In peritumoral areas of glioma-bearing mice, neurons showed a shrunken dendritic arbor and severe functional alterations such as increased spontaneous activity and reduced visual responsiveness. CNF1 treatment enhanced dendritic length and improved several physiological properties of pyramidal neurons, demonstrating functional preservation of the cortical network. Conclusions. Our findings demonstrate that CNF1 reduces glioma volume while at the same time maintaining the physiological and structural properties of peritumoral neurons. These data indicate a promising strategy for the development of more effective antiglioma therapies

The lively accretion disk in NGC 2992. I. Transient iron K emission lines in the high flux state

We report on one of the brightest flux levels of the Seyfert 2 galaxy NGC 2992 ever observed in X-rays, on May 2019. The source has been monitored every few days from March 26, 2019 to December 14, 2019 by Swift-XRT, and simultaneous XMM-Newton (250 ks) and NuSTAR (120 ks) observations were triggered on May 6, 2019. The high count rate of the source (its 2-10 keV flux ranged between 0.7 and $1.0\times10^{-10}$ erg cm$^{-2}$ s$^{-1}$) allows us to perform a time-resolved spectroscopy, probing spatial scales of tens of gravitational radii from the central black hole. By constructing a map of the excess emission over the primary continuum, we find several emission structures in the 5.0-7.2 keV energy band. From fitting the 50 EPIC pn spectral slices of $\sim$5 ks duration, we interpret them as a constant narrow iron K$\alpha$ line and three variable components in the iron K complex. When a self-consistent model accounting for the accretion disk emission is considered (KYNrline), two of these features (in the 5.0-5.8 keV and 6.8-7.2 keV bands) can be ascribed to a flaring region of the accretion disk located at ${r_{in}}\simeq15$-40 r$_{g\rm }$ from the black hole. The third one (6.5-6.8 keV) is likely produced at much larger radii ($r_{in}>50$ r$_{g\rm }$). The inner radius and the azimuthal extension retrieved from the coadded spectra of the flaring states are ${ r_{in}}=15\pm3$ r$_{g\rm }$ and $\phi=165^{\circ}-330^{\circ}$, suggesting that the emitting region responsible for the broad iron K component is a relatively compact annular sector within the disk. Our findings support a physical scenario in which the accretion disk in NGC 2992 becomes more active at high accretion rates ($L_{\rm bol}/L_{\rm Edd}\geq4\%$).Comment: 12 pages, 12 figures, 1 table. Accepted for publication in MNRA