1,721,039 research outputs found
"An X-ray review of MS 1054-0321: Hot or not?"
Get PDFXMM-Newton observations are presented for the z=0.83 cluster of galaxies MS 1054-0321, the highest redshift cluster in the Einstein Extended Medium Sensitivity Survey (EMSS). The temperature inferred by the XMM-Newton data, T=7.2+0.7-0.6 keV, is much lower than the temperature previously reported from ASCA data, T=12.3+3.1-2.2 keV (Donahue et al. 1998), and a little lower than the Chandra temperature, T=10.4+1.7-1.5 keV, determined by Jeltema et al. 2001. The discrepancy between the newly derived temperature and the previously derived temperatures is discussed in detail. If one allows the column density to be a free parameter, then the best fit temperature becomes T=8.6+1.2-1.1 keV, and the best fit column density becomes NH=1.33+0.15-0.14 ×1020 atoms cm-2. The iron line is well detected in the XMM-Newton spectrum with a value for the abundance of Z=0.33+0.19-0.18 Z⊙, in very good agreement with previous determinations. The derived XMM X-ray luminosity for the overall cluster in the 2-10 keV energy band is LX= (3.81±0.19) ×1044 h-2 erg s-1 while the bolometric luminosity is LBOL=(8.05±0.40) ×1044 h-2 erg s-1. The XMM-Newton data confirm the substructure in the cluster X-ray morphology already seen by ROSAT and in much more detail by Chandra. We find that only two of the three clumps detected in the weak lensing mass reconstruction image are visible in X-rays, as already noted by \cite{jel01}. The central weak lensing clump is coincident with the main cluster component and has a temperature T=8.1+1.3-1.2 keV. The western weak lensing clump coincides with the western X-ray component which is much cooler with a temperature T=5.6+0.8-0.6 keV. The optically measured velocity dispersion, obtained from 145 cluster redshifts, is consistent with the velocity dispersion expected from the σV-TX relationship once the XMM-Newton temperature is used. MS 1054-0321 fits well in the σ ∝ T1/2 correlation available in the literature and derived from information collected for all clusters at redshfits of z≤1.27 known today and with a measured X-ray temperature. The cluster temperature seems to be commensurate with the predictions from its X-ray luminosity from the LX-TX relation of local clusters. Given the newly determined temperature, MS 1054-0321 is no longer amongst the hottest clusters known.
Data presented here used the XMM-Newton facility
Variable X-ray absorption in mini-BAL QSOs
No full textWe present the results of X-ray spectral analysis of two mini-BAL QSOs, PG 1126-041 and PG 1351+640, aimed at getting insights into the physics of quasar outflows. We find strong X-ray spectral variability on timescales of years. These variations can be well reproduced by variations of physical properties as the covering factor and column density of ionized gas along the line of sight, compatible with radiatively-driven accretion disk wind models
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
Direct observation of an extended X-ray jet at
Get PDFWe report on the direct observation of an extended X-ray jet in the z = 6.1 radio-loud active galactic nucleus PSO J030947.49+271757.31 from a deep Chandra X-ray observation (128 ksec). This detection represents the most distant kiloparsec-scale off-nuclear emission resolved in X-rays to date. The angular distance of the emission is ∼4″ (corresponding to ∼20 kpc at z = 6.1), along the same direction of the jet observed at parsec scales in previous VLBA high-resolution radio observations. Moreover, the 0.5–7.0 keV isophotes coincide with the extended radio emission as imaged by the VLA Sky Survey at 3 GHz. The rest-frame 2–10 keV luminosity of the extended component is L2 − 10 keV = 5.9 × 1044 erg s−1, about 8% of the core: this makes it one of the most luminous jets resolved in X-rays so far. Through spectral energy distribution modelling we find that this emission can be explained by the inverse Compton interaction with the photons of the cosmic microwave background, assuming that the jet’s physical parameters are similar to those in the local Universe. At the same time, we find that the radiation produced by a putative population of high-energy electrons through the synchrotron process observed at low redshift is quenched at high redshift, hence becoming negligible
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
The z > 3 AGN population in the 4 Ms CDFS
No full textWe present results from a spectral analysis of a sample of 34 high-redshift (z > 3) X-ray selected AGN in the 4 Ms Chandra Deep Field South, the deepest X-ray survey to date. The intrinsic column density distribution, corrected for observational bi- ases using spectral simulations, and the source number counts down to flux F0.5−2keV∼ 4 × 10−17 erg s−1 cm−2 are compared with the expectations from X-ray background synthesis models. All the results are presented and discussed in Vito et al. (2013)
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe 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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