X-ray variability with WFXT: AGNs, transients and more

The Wide Field X-ray Telescope (WFXT) is a proposed mission with a high survey speed, due to the combination of large field of view (FOV) and effective area, i.e. grasp, and sharp PSF across the whole FOV. These characteristics make it suitable to detect a large number of variable and transient X-ray sources during its operating lifetime. Here we present estimates of the WFXT capabilities in the time domain, allowing to study the variability of thousand of AGNs with significant detail, as well as to constrain the rates and properties of hundreds of distant, faint and/or rare objects such as X-ray Flashes/faint GRBs, Tidal Disruption Events, ULXs, Type-I bursts etc. The planned WFXT extragalactic surveys will thus allow to trace variable and transient X-ray populations over large cosmological volumes.Comment: Proceedings of "The Wide Field X-ray Telescope Workshop", held in Bologna, Italy, Nov. 25-26 2009 (arXiv:1010.5889). To appear in Memorie della Societ\`a Astronomica Italiana 2010 - Minor corrections to text

Demography of obscured and unobscured AGN: prospects for a Wide Field X-ray Telescope

We discuss some of the main open issues in the evolution of Active Galactic Nuclei which can be solved by the sensitive, wide area surveys to be performed by the proposed Wide Field X-ray Telescope mission.Comment: Proceedings of "The Wide Field X-ray Telescope Workshop", held in Bologna, Italy, Nov. 25-26 2009. To appear in Memorie della Societa' Astronomica Italiana 2010 (arXiv:1010.5889

Official food safety audits in large scale retail trades in the time of COVID: system control experiences supported by an innovative approach

This work describes a new methodology used in large scale retail trades in official food safety auditing processes developed during COVID19 emergency. The aim is to evaluate Food Business Operators’ (FBOs) Food Safety Management System and its dynamic implementation and to understand the FBO’s level of cultural maturity about food safety according to EU Regulation 2021/382. The innovation mainly consists of: a) a pre-audit phase when auditors analyse food business operator’s (FBO) selfchecked plan and further documents to identify “markers” and useful evidences (that would be collected in on-site inspections) to evaluate the application of plan by FBO’s workers; b) an audit phase consisted of both a check of the company procedures and documents performed by the auditors via web conference and of contextually onsite inspections in a sample of company’s supermarkets performed by inspectors teams. The audit methodology here described may be useful, even though it is expensive in terms of time and energy used, for both Competent Authority (CA) and FBOs, regardless of the period of the COVID emergency. The so-structured official control allows the auditors to collect both documentary and on-site evidence at the same time, reaching a broader vision of auditees (not limited to single supermarkets) and a compliant with reality FBOs risk classification. The new approach may give advantages to both audit actors, CA as well as FBO, who may collect “markers” and evidence of the self-checked plan useful to improve FBO’s food safety system on the basis of the critical aspects detected during auditing process

High-redshift AGN in the Chandra Deep Fields: the obscured fraction and space density of the sub-L∗ population

This article investigates the population of high-redshift (3≤z<6) active galactic nuclei (AGN) selected in the two deepest X-ray surveys, the 7 Ms Chandra Deep Field-South and 2 Ms Chandra Deep Field-North

X-Ray Spectral Analyses of AGNs from the 7Ms Chandra Deep Field-South Survey: The Distribution, Variability, and Evolutions of AGN Obscuration

We present a detailed spectral analysis of the brightest active galactic nuclei (AGNs) identified in the 7Ms Chandra Deep Field-South (CDF-S) survey over a time span of 16 years. Using a model of an intrinsically absorbed power-law plus reflection, with possible soft excess and narrow Fe Kα line, we perform a systematic X-ray spectral analysis, both on the total 7Ms exposure and in four different periods with lengths of 2–21 months. With this approach, we not only present the power-law slopes, column densities ${N}_{{\rm{H}}}$, observed fluxes, and absorption-corrected 2–10 keV luminosities L X for our sample of AGNs, but also identify significant spectral variabilities among them on timescales of years. We find that the ${N}_{{\rm{H}}}$ variabilities can be ascribed to two different types of mechanisms, either flux-driven or flux-independent. We also find that the correlation between the narrow Fe line EW and ${N}_{{\rm{H}}}$ can be well explained by the continuum suppression with increasing ${N}_{{\rm{H}}}$. Accounting for the sample incompleteness and bias, we measure the intrinsic distribution of ${N}_{{\rm{H}}}$ for the CDF-S AGN population and present reselected subsamples that are complete with respect to ${N}_{{\rm{H}}}$. The ${N}_{{\rm{H}}}$-complete subsamples enable us to decouple the dependences of ${N}_{{\rm{H}}}$ on L X and on redshift. Combining our data with those from C-COSMOS, we confirm the anticorrelation between the average ${N}_{{\rm{H}}}$ and L X of AGN, and find a significant increase of the AGN-obscured fraction with redshift at any luminosity. The obscured fraction can be described as ${f}_{\mathrm{obscured}}\approx 0.42\ {(1+z)}^{0.60}$

The XMM-SERVS Survey: XMM-Newton Point-source Catalogs for the W-CDF-S and ELAIS-S1 Fields

We present the X-ray point-source catalogs in two of the XMM-Spitzer Extragalactic Representative Volume Survey (XMM-SERVS) fields, W-CDF-S (4.6 deg2) and ELAIS-S1 (3.2 deg2), aiming to fill the gap between deep pencil-beam X-ray surveys and shallow X-ray surveys over large areas. The W-CDF-S and ELAIS-S1 regions were targeted with 2.3 and 1.0 Ms of XMM-Newton observations, respectively; 1.8 and 0.9 Ms exposures remain after flare filtering. The survey in W-CDF-S has a flux limit of 1.0 × 10−14 erg cm−2 s−1 over 90% of its area in the 0.5–10 keV band; 4053 sources are detected in total. The survey in ELAIS-S1 has a flux limit of 1.3 × 10−14 erg cm−2 s−1 over 90% of its area in the 0.5–10 keV band; 2630 sources are detected in total. Reliable optical-to-IR multiwavelength counterpart candidates are identified for ≈89% of the sources in W-CDF-S and ≈87% of the sources in ELAIS-S1. A total of 3129 sources in W-CDF-S and 1957 sources in ELAIS-S1 are classified as active galactic nuclei (AGNs). We also provide photometric redshifts for X-ray sources; ≈84% of the 3319/2001 sources in W-CDF-S/ELAIS-S1 with optical-to-near-IR forced photometry available have either spectroscopic redshifts or high-quality photometric redshifts. The completion of the XMM-Newton observations in the W-CDF-S and ELAIS-S1 fields marks the end of the XMM-SERVS survey data gathering. The ≈12,000 pointlike X-ray sources detected in the whole ≈13 deg2 XMM-SERVS survey will benefit future large-sample AGN studies

VizieR Online Data Catalog: Chandra Deep Field-South survey: 7Ms sources (Luo+, 2017)

The 7Ms CDF-S contains 102 Chandra ACIS-I observations, with a total cleaned exposure time of 6.727Ms, taken in four separate epochs of time. The basic information on these observations is listed in Table 1. There were 48 recent observations acquired between 2014 June 9 and 2016 March 24, which constitute the last 3Ms of exposure of the 7Ms CDF-S. The first 1Ms of exposure consists of 11 observations taken between 1999 and 2000 (Giacconi+ 2002, J/ApJS/139/369; Rosati+ 2002ApJ...566..667R; Alexander+ 2003, J/AJ/126/539), the next 1Ms of exposure consists of 12 observations taken in 2007 (Luo+ 2008, J/ApJS/179/19), and another 2Ms of exposure includes 31 observations in 2010 (Xue+ 2011, J/ApJS/195/10). The total area covered by the 7Ms CDF-S is 484.2arcmin2. (3 data files)

Proceedings of the Wide Field X-ray Telescope Workshop

We list here the contents of the Proceedings of the "Wide Field X-ray Telescope" conference held in Bologna, Italy on 25-26 Nov 2009. The conference highlighted the scientific potential and discovery space provided by an X-ray mission concept characterized by a wide field-of-view (1 sq.deg.), large effective area (1 sq.mt.) and approximately constant PSF (~5 arcsec HEW) across the whole FOV. The index is in html form with clickable links to the individual contributions

The Wide Field X-ray Telescope

Proceedings of the "Wide Field X-ray Telescope" conference held in Bologna, Italy on 25-26 Nov 2009. The conference highlighted the scientific potential and discovery space provided by an X-ray mission concept characterized by a wide field-of-view (1 sq.deg.), large effective area (1 sq.mt.) and approximately constant PSF (~5 arcsec HEW) across the whole FOV