1,721,013 research outputs found
Turbulent accretion onto massive black holes
Get PDFTurbulent spherical accretion onto massive black holes (Mapprox.10/sup 6/--10/sup 9/ M/sub sun/) is considered. Temperatures of the order of 10/sup 9/--10/sup 10/ K are found in the inner zone where the synchrotron frequencies are 10/sup 13/--10/sup 14/ Hz. If the optical depth of the hole atmosphere is tauapprox.1, Comptonization can produce a power-law spectrum of index approx.1 from the synchrotron frequencies up to medium X-rays. If tau> or approx. =1, convection of radiation into the hole becomes important at small radii, reducing the efficiency of emission. The results are briefly compared with the observations
The origin of the iron lines in NGC 7213
No full textThe analysis of a simultaneous XMM-Newton/BeppoSAX plus three previous BeppoSAX observations revealed that NGC 7213 is a rather peculiar Seyfert 1. No significant Compton reflection component was observed, while an iron line complex, best explained in terms of three narrow lines, is clearly apparent in the data. Due to the absence of the reflection component, the neutral iron line is likely not produced in a Compton-thick material, but current data do not allow to choose between a Compton-thin torus and the BLR. The two ionized iron lines from \ion{Fe}{xxv} and \ion{Fe}{xxvi} may be produced in a photoionized gas with a column density of a few 1023 cm-2, in analogy with the case of NGC 5506
BeppoSAX HELLAS survey. VI
No full textWe present results of a complete radio follow-up obtained with the VLA and ATCA radio telescopes down to a 6-cm flux limit of about 0.3 mJy (3σ) of all the 147 X-ray sources detected in the BeppoSAX HELLAS survey. We found 53 X-ray/radio likely associations, corresponding to about one-third of the X-ray sample. Using the two-point spectral index αro=0.35 we divided all the HELLAS X-ray sources into radio-quiet and radio-loud. We have 26 sources classified as radio-loud objects, corresponding to 18 per cent of the HELLAS sample. In agreement with previous results, the identified radio-loud sources are associated mainly with Type 1 active galactic nuclei (AGNs) with L5-10kev>~1044erg/s, while all the identified Type 2 AGNs and emission-line galaxies are radio-quiet objects with L5-10kev<~1044erg/s
Simultaneous Exosat-IUE observations of NGC 4151
No full textNGC 4151 was observed four times in Nov. 83. The results indicate that: (1) there exists a correlation between the X-ray and UV fluxes on the long term; (2) the soft X-ray excess between 0.1 and 1 keV is probably steeper than expected from the leaky absorber model by Holt et al. (1980); (3) the spectral fit to the ME data, after correction for a soft component, yields α = 1.73±0.27, NH = (15.2±2.2)×1022cm-2, E.W.(Fe line) = 0.208±0.084 keV, and does not require a strong overabundance of Fe in the absorber. The relationship between NH and the strength of the broad emission lines is commented
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
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 recent X-ray history of NGC 5506
No full textWe present a detailed discussion of the spectral and spatial components
of NGC 5506, based on XMM–Newton, Chandra and BeppoSAX observations.
The overall picture consists of a nucleus absorbed by cold gas with column
density of ≈
1022 cm-2 and surrounded by a Compton-thick torus,
whose existence is inferred by a cold reflection component and an iron Kα
line. On a much larger scale, a photoionized gas extended on ≈
350 pc
reprocesses the nuclear radiation, producing a soft excess and ionized iron
lines. Noteworthy, we find no evidence for the presence of the accretion disc.
- …
