Variability and the X-ray/UV ratio of Active Galactic Nuclei

The observed relation between the X-ray radiation from AGNs, originating in the corona, and the optical/UV radiation from the disk is usually described by the anticorrelation between the UV to X-ray slope alpha_ox and the UV luminosity. Many factors can affect this relation, including: enhanced X-ray emission associated with the jets of radio-loud AGNs; X-ray absorption associated with the UV Broad Absorption Line (BAL) outflows; other X-ray absorption not associated with BALs; intrinsic X-ray weakness; UV and X-ray variability, and non-simultaneity of UV and X-ray observations. The separation of these effects provides information about the intrinsic alpha_ox-L_UV relation and its dispersion, constraining models of disk-corona coupling. We extract simultaneous data from the second XMM-Newton serendipitous source catalogue and the XMM-Newton Optical Monitor Serendipitous UV Source Survey Catalog, and derive the single-epoch alpha_ox indices. We use ensemble structure functions to analyse multi-epoch data. We confirm the anticorrelation of alpha_ox with L_UV, and do not find any evidence of a dependence of alpha_ox on z. The dispersion in our simultaneous data (0.12) is not significantly smaller than in previous non-simultaneous studies, suggesting that "artificial alpha_ox variability" introduced by non-simultaneity is not the main cause of dispersion. "Intrinsic alpha_ox variability", i.e., the true variability of the X-ray to optical ratio, is instead important, and accounts for ~30% of the total variance, or more. "Inter-source dispersion", due to intrinsic differences in the average alpha_ox values from source to source, is also important. The dispersion introduced by variability is mostly caused by the long timescale variations, which are expected to be driven by the optical variations.Comment: 16 pages, 10 figures, 1 table. Final version equal to the published on

MOJAVE: Monitoring of Jets in AGN with VLBA Experiments. IV. The Parent Luminosity Function of Radio-Loud Blazars

(Abridged) We use a complete sample of active galactic nuclei (AGN) selected on the basis of relativistically beamed 15 GHz radio flux density to derive the parent radio luminosity function (RLF) of bright radio-selected blazar cores. We use a maximum likelihood method to fit a beamed RLF to the observed data and thereby recover the parameters of the intrinsic (unbeamed) RLF. We analyze two subsamples of the MOJAVE sample: the first contains only objects of known FR II class, with a total of 103 sources, and the second subsample adds 24 objects of uncertain FR class for a total of 127 sources. Both subsamples exclude four known FR I radio galaxies and two gigahertz-peaked spectrum sources. We obtain good fits to both subsamples using a single power law intrinsic RLF with pure density evolution function. We find that a previously reported break in the observed MOJAVE RLF actually arises from using incomplete bins (because of the luminosity cutoff) across a steep and strongly evolving RLF, and does not reflect a break in the intrinsic RLF. The derived space density of the parent population of the FR II sources from the MOJAVE sample (with L>1.3e25 W/Hz) is approximately 1600/Gpc^3.Comment: 31 pages, 7 figures and 2 tables. Accepted for publication in ApJ. Changes: classification of sources based on radio morphology instead of optical classes; added the parameters of the RLF of the FR II sources; added more explanations; added a table listing the sample sources; added 2 extra figures related to the observed break in the RLF; updated reference

Variability and the X-ray/UV ratio of active galactic nuclei. II. Analysis of a low-redshift Swift sample

Variability, both in X-ray and optical/UV, affects the well-known anti-correlation between the $\alpha_{ox}$ spectral index and the UV luminosity of active galactic nuclei, contributing part of the dispersion around the average correlation ("intra-source dispersion"), in addition to the differences among the time-average $\alpha_{ox}$ values from source to source ("inter-source dispersion"). We want to evaluate the intrinsic $\alpha_{ox}$ variations in individual objects, and their effect on the dispersion of the $\alpha_{ox}-L_{UV}$ anti-correlation. We use simultaneous UV/X-ray data from Swift observations of a low-redshift sample, to derive the epoch-dependent $\alpha_{ox}(t)$ indices. We correct for the host galaxy contribution by a spectral fit of the optical/UV data. We compute ensemble structure functions to analyse variability of multi-epoch data. We find a strong "intrinsic $\alpha_{ox}$ variability", which makes an important contribution ($\sim40$ of the total variance) to the dispersion of the $\alpha_{ox}-L_{UV}$ anti-correlation ("intra-source dispersion"). The strong X-ray variability and weaker UV variability of this sample are comparable to other samples of low-z AGNs, and are neither due to the high fraction of strongly variable NLS1s, nor to dilution of the optical variability by the host galaxies. Dilution affects instead the slope of the anti-correlation, which steepens, once corrected, becoming similar to higher luminosity sources. The structure function of $\alpha_{ox}$ increases with the time lag up to $\sim$1 month. This indicates the important contribution of the intermediate-long timescale variations, possibly generated in the outer parts of the accretion disk

Evaluation of Italian Judicial System

Italy is frequently reprimanded by the European Court of Human Rights (ECtHR) over the amount of time it takes Italian courts to reach verdicts. European Court decisions have lead to calls for an urgent intervention in order to save time and costs in Italian judicial system. Efficiency and effectiveness are key targets for managing justice in Italy. Nevertheless they are not easy to achieve. In this paper, using a Stochastic Frontier Model (SFM) we compare the Italian courts efficiency to identify strong and weak points

Developing a Framework to Understand Student Engagement, Team Dynamics, and Learning Outcomes Using ERPsim

The value of enterprise resource planning (ERP) systems to business organizations has long been recognized with their use being integrated into educational business curricula and training. ERPsim games incorporate live business simulations that enable students to learn about ERP concepts firsthand by working in teams and managing their own companies using SAP ERP software. Prior research has examined the use of ERPsim and learning outcomes, yet to date, there is little if any research that has explored the association of learning outcomes with student engagement and team dynamics, two areas that have continued to grow in importance in many business school programs. This research develops and tests a model to examine these relationships. Validated constructs and a validated survey instrument are created and verified. Study results indicate a positive association between student engagement, team dynamics, and learning outcomes. Results and implications are discussed, and recommendations for further research are presented

The Phoenix galaxy: UGC4203 re-birth from its ashes?

We report on a dramatic transition between a Compton-thick, reflection-dominated state and a Compton-thin state in the Seyfert 2 galaxy UGC4203, discovered by comparing a recent (May 2001) XMM-Newton observation with ASCA observations performed about six years earlier. This transition can be explained either as a change in the column density of the absorber, maybe due to moving clouds in a clumpy torus, or as the revival of a transient active nucleus, which was in a phase of very low activity when observed by ASCA. If the latter explanation is correct, spectral transitions of this kind provide observational support to the idea that Compton-thick and Compton-thin regions coexist in the same source, the former likely to be identified with the "torus", the latter with dust lanes on much larger scales.Comment: 6 Latex pages, 5 figures, To appear in Astronomy & Astrophysic

Further insights on predictors of environmental tobacco smoke exposure during the pediatric age

Background: The smoking ban in public places has reduced Environmental Tobacco Smoke (ETS) exposure for non-smokers, but despite this, domestic environments still remain places at high risk of exposure, and, today, about 40% of children worldwide are exposed to ETS at home. The aims of the study are to investigate the contribution of several factors on ETS exposure among a group of Italian children and to evaluate the changes in smoking precautions adopted at home when the smoker is the mother, the father, or both parents, respectively. Methods: A cross-sectional study was performed on a sample of 519 Italian schoolchildren. Information was collected via a questionnaire. Results: 41.4% of the participants lived with at least one smoker. Almost half of the children exposed to ETS lived with one or more smokers who do not observe any home smoking ban. Lower maternal or paternal educational levels significantly increase the risk of ETS exposure at home and the “worst case” is represented by both parents who smoke. Conclusions: More effective preventive interventions are needed to protect children from ETS exposure. Some interventions should be specifically dedicated to smokers with a low educational level and to mothers that smoke

Dust Emission from Active Galactic Nuclei

Unified schemes of active galactic nuclei (AGN) require an obscuring dusty torus around the central source, giving rise to Seyfert 1 line spectrum for pole-on viewing and Seyfert 2 characteristics in edge-on sources. Although the observed IR is in broad agreement with this scheme, the behavior of the 10 micron silicate feature and the width of the far-IR emission peak remained serious problems in all previous modeling efforts. We show that these problems find a natural explanation if the dust is contained in about 5-10 clouds along radial rays through the torus. The spectral energy distributions (SED) of both type 1 and type 2 sources are properly reproduced from different viewpoints of the same object if the visual optical depth of each cloud is larger than about 60 and the clouds' mean free path increases roughly in proportion to radial distance.Comment: 11 pages, submitted to ApJ Letter

The Transverse Proximity Effect: A Probe to the Environment, Anisotropy, and Megayear Variability of QSOs

The transverse proximity effect is the expected decrease in the strength of the Lya forest absorption in a QSO spectrum when another QSO lying close to the line of sight enhances the photoionization rate above that due to the average cosmic ionizing background. We select three QSOs from the Early Data Release of the Sloan Digital Sky Survey that have nearby foreground QSOs, with proper line of sight tangential separations of 0.50, 0.82, and 1.10 h^{-1} Mpc. We estimate that the ionizing flux from the foreground QSO should increase the photoionization rate by a factor (94, 13, 13) in these three cases, which would be clearly detectable in the first QSO and marginally so in the other two. We do not detect the transverse proximity effect. Three possible explanations are provided: an increase of the gas density in the vicinity of QSOs, time variability, and anisotropy of the QSO emission. We find that the increase of gas density near QSOs can be important if they are located in the most massive halos present at high redshift, but is not enough to fully explain the absence of the transverse proximity effect. Anisotropy requires an unrealistically small opening angle of the QSO emission. Variability demands that the luminosity of the QSO with the largest predicted effect was much lower 10^6 years ago, whereas the transverse proximity effect observed in the HeII Lya absorption in QSO 0302-003 by Jakobsen et al. (2003) implies a lifetime longer than 10^7 years. A combination of all three effects may better explain the lack of Lya absorption reduction. A larger sample of QSO pairs may be used to diagnose the environment, anisotropy and lifetime distribution of QSOs.Comment: 27 pages, 13 figures, accepted by Ap