322,848 research outputs found
A changing inner radius in the accretion disc of Q0056-363? RID B-4804-2010
No full textQ0056-363 is the most powerful X-ray quasar known to exhibit a broad, likely relativistic iron line (Porquet & Reeves 2003, A&A, 408, 119). It has been observed twice by XMM-Newton, three and half years apart ( July 2000 and December 2003). In the second observation, the UV and soft X-ray fluxes were fainter, the hard X-ray power law flatter, and the iron line equivalent width (EW) smaller than in the 2000 observation. These variations can all be explained, at least qualitatively, if the disc is truncated in the second observation. We report also on the possible detection of a transient, redshifted iron absorption line during the 2003 observation
The XMM deep survey in the CDF-S: VIII. X-ray properties of the two brightest sources
No full textWe present results from the deep XMM-Newton observations of the two brightest X-ray sources in the Chandra Deep Field South (CDFS), PID 203 (z = 0.544) and PID 319 (z = 0.742). The long exposure of 2.5 Ms over a 10 year period (net 4 yr with a 6 yr gap) makes it possible to obtain high quality X-ray spectra of these two Type I AGN with X-ray luminosity of 1044 erg/s, which is the typical luminosity for low-redshift PG quasars, and track their X-ray variability both in flux and spectral shape. Both sources showed X-ray flux variability of ~10-20% in rms, which is similar in the soft (0.5-2 keV) and hard (2-7 keV) bands. PID 203, which has evidence for optical extinction, shows modest amount of absorption (NH ≤ 1×10^21 cm-2) in the X-ray spectrum. Fe K emission is strongly detected in both objects with EW~0.2 keV. The lines in both objects are moderately broad and exhibit marginal evidence for variability in shape and flux, indicating that the bulk of the line emission comes from their accretion disks rather than distant tori
Diffusive author(s), cohesive author: Analysis of S/N (1994)
No full textThis study indicates the ways in which various aspects of the author(s) are brought forth in Dumb type’s performance art, the S/N production. Previous research has suggested a non-hierarchical organization of Dumb type and the absence of a “privileged author” in Dumb type’s collaborative work, S/N. However, the results that I have investigated from member’s interviews on the creative process of S/N along with my analysis of the recorded images of S/N, indicate a different aspect of the author(s). First, S/N was created through, so to speak, the collective ideas of the members of Dumb type. Further, S/N has at least nine quotations from previous performances, installations, and printed writings, besides the work-in-progress technique. Explicating one of the “author functions” as given by Michel Foucault, each text has plural subjects of the author. However, it has been revealed from members’ interviews that Teiji Furuhashi had a decision-making role in selecting the members’ ideas within the performance. Since then, S/N has had plural subjects of creation; however, Furuhashi is one of the subjects of creation along with the “privileged author.” S/N has plural authors (diffusive authors) yet at the same time, it has a “privileged author,” Teiji Furuhashi (cohesive author)
Going Beyond Counting First Authors in Author Co-citation Analysis
No full textThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
The XMM deep survey in the CDF-S VIII. X-ray properties of the two brightest sources
No full textWe present results from the deep XMM-Newton observations of the two brightest X-ray sources in the Chandra Deep Field South (CDFS), PID 203 (z = 0.544) and PID 319 (z = 0.742). The long exposure of 2.5 Ms over a 10 year period (net 4 yr with a 6 yr gap) makes it possible to obtain high quality X-ray spectra of these two Type I AGN with X-ray luminosity of 1044 ergs−1, typical luminosity for low-redshift PG quasars, track their X-ray variability both in flux and spectral shape. Both sources showed X-ray flux variability of ∼10-20 % in rms which is similar in the soft (0.5-2 keV) and hard (2-7 keV) bands. PID 203, which has evidence for optical extinction, shows modest amount of absorption (NH≤ 1×1021 cm−2) in the X-ray spectrum. Fe K emission is strongly detected in both objects with EW∼ 0.2 keV. The lines in both objects are moderately broad and exhibit marginal evidence for variability in shape and flux, indicating that the bulk of the line emission come from their accretion disks rather than distant tori
Serching for AGNs with VST: optical variability in the COSMOS and CDFS regions
No full textActive Galactic Nuclei (AGN) are characterised by strong variability at all wavelengths. We exploited 3 years of VST monitoring observations of the COSMOS and CDFS regions, performed within the SUDARE/VOICE surveys, to assemble a sample of AGN candidates based on variability. Variability selection does not make strong a-priori assumptions about the properties of the sources and can thus integrate and complete samples selected by other techniques. We investigate the effectiveness and reliability of this selection method by comparing it with spectroscopic, X-ray and IR selected samples, showing that variability-selection can yield extremely pure samples, with completeness 〉50% with respect of X-ray and IR selections. We explore the dependence of variability from obscuration, mass and accretion rate, and predict the performance that can be expected by future monitoring surveys such as LSST
Dispelling the Myths Behind First-author Citation Counts
No full textWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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