1,720,972 research outputs found
Spectral evolution of Scorpio X-1 along its color-color diagram
No full textWe analyze a large collection of RXTE archive data of the bright X-ray source Scorpius X-1 in order to study the broadband spectral evolution of the source for different values of the inferred mass accretion rate by selecting energy spectra from its Color-Color Diagram. We model the spectra with the combination of two absorbed components: a soft thermal component, which can be interpreted as thermal emission from an accretion disk, and a hybrid Comptonization component, which self-consistently includes the Fe K alpha fluorescence line and the Compton reflected continuum. The presence of hard emission in Scorpius X-1 has been previously reported, however, without a clear relation with the accretion rate. We show, for the first time, that there exists a common trend in the spectral evolution of the source, where the spectral parameters change in correlation with the position of the source in the CD. Using a hybrid thermal/non-thermal Comptonization model (EQPAIR code), we show that the ratio of the power supplied to the non-thermal distribution to the total power injected into the Comptonizing plasma correlates with the accretion rate, being the highest at the lowest accretion rates. We discuss the physical implications derived from the results of our analysis, with a particular emphasis on the hardest part of the X-ray emission and its possible origin. RI Iaria, Rosario/F-2520-201
Relativistic smearing detected in the spectrum of Cyg X-1 in hard state observed by BeppoSAX
No full textWe report on an observation of the black hole candidate Cyg X-1 performed by the Narrow Field Instruments on board BeppoSAX satellite. During the BeppoSAX observation Cyg X-1 was in its usual low (hard) state with a 0.1-200 keV luminosity of similar to 2.6 x 10(37) erg/s, adopting a distance of 2.5 kpc. The broad band spectrum (0.1-30 keV) is well fitted by an absorbed power-law partially reflected by cold matter and a soft excess. The reprocessed component is relativistically smeared and the inferred inner radius of the disc is 20 +/- 10 gravitational radii. This inner radius is much smaller than the prediction of the so called Advection Dominated Accretion Flow models: R-in > 200 R-g
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe 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
Full text link“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
Full text linkWe 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
Broadband Spectral Evolution of Scorpius X-1 along Its Color-Color Diagram
Full text linkWe analyze a large collection of RXTE archive data from 1997 April to 2003 August of the bright X-ray source Scorpius X-1 in order to study the broadband spectral evolution of the source for different values of the inferred mass accretion rate by studying energy spectra from selected regions in the Z track of its color-color diagram (CD). A two-component model, consisting of a soft thermal component interpreted as thermal emission from an accretion disk and a thermal Comptonization component, is unable to fit the whole 3-200 keV energy spectrum at low accretion rates. Strong residuals in the highest energy band of the spectrum require the addition of a third component that can be fitted with a power-law component, which could represent a second thermal Comptonization from a much hotter plasma, or a hybrid thermal/nonthermal Comptonization. The presence of this hard emission in Sco X-1 has been previously reported, however, without a clear relation with the accretion rate. We show, for the first time, that there exists a common trend in the spectral evolution of the source, where the spectral parameters change in correlation with the position of the source in the CD. In particular, using a hybrid Comptonization model, we show that the power supplied to the nonthermal distribution can be as high as half of the total hard power injected in heating the electron distribution. We discuss the physical implications derived from the results of our analysis, with a particular emphasis on the hardest part of the X-ray emission and its possible origins
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