1,721,391 research outputs found
Hard X-rays from Type II bursts of the Rapid Burster and its transition toward quiescence
No full textWe report on 4 BeppoSAX Target Of Opportunity observations of MXB 1730-335, the Rapid Burster (RB), made during the 1998 February-March outburst. In the first observation, approximately 20 days after the outburst peak, the X-ray light curve showed Type II bursts at a rate of 43 hr-1. Nine days later, during the second BeppoSAX pointing, only 5 Type II bursts were detected at the beginning of the observation. During the third pointing no X-ray bursts were detected and in the fourth and final observation the RB was not detected at all. Persistent emission from the RB was detected up to 10 keV during the first three pointings. The spectra of the persistent and bursting emissions below 10 keV were best fit with a model consisting of two blackbodies. An additional component (a power law) was needed to describe the 1-100 keV bursting spectrum when the persistent emission was subtracted. To our knowledge, this is the first detection of the RB beyond 20 keV. We discuss the evolution of the spectral parameters for the bursting and persistent emission during the outburst decay. The light curve, after the second BeppoSAX pointing, showed a steepening of the previous decay trend, and a sharper decay rate leading to quiescence was observed with BeppoSAX in the two subsequent observations. We interpret this behaviour as caused by the onset of the propeller effect. Finally, we infer a neutron star magnetic field B ~ 4 x 108 Gauss
The x-ray source 1rxs J180431.1-273932: The importance of being pinpointed
No full textWe report on the optical follow-up observation of the X-ray source 1RXS J180431.1-273932 which was previously recognized as a Symbiotic X-ray Binary. With the new analysis, we found that the brightest optical source inside the 90% X-ray positional error circle is spectroscopically identified as a magnetic cataclysmic variable (CV), most likely of Intermediate Polar type, hosting an accreting white dwarf with mass ≃ 0.8 M⊙
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
Optical identification of X-ray source 1RXS J180431.1-273932 as a magnetic cataclysmic variable
No full textThe X-ray source 1RXS J180431.1-273932 has been proposed as a new member of the symbiotic X-ray binary (SyXB) class of systems, which are composed of a late-type giant that loses matter to an extremely compact object, most likely a neutron star. In this paper, we present an optical campaign of imaging plus spectroscopy on selected candidate counterparts of this object. We also reanalyzed the available archival X-ray data collected with XMM-Newton. We find that the brightest optical source inside the 90% X-ray positional error circle is spectroscopically identified as a magnetic cataclysmic variable (CV), most likely of intermediate polar type, through the detection of prominent Balmer, He i, He ii, and Bowen blend emissions. On either spectroscopic or statistical grounds, we discard as counterparts of the X-ray source the other optical objects in the XMM-Newton error circle. A red giant star of spectral type M5 III is found lying just outside the X-ray position: we consider this latter object as a fore-/background one and likewise rule it out as a counterpart of 1RXS J180431.1-273932. The description of the X-ray spectrum of the source using a bremsstrahlung plus black-body model gives temperatures of kTbr ~ 40 keV and kTbb ~ 0.1 keV for these two components. We estimate a distance of d ~ 450 pc and a 0.2-10 keV X-ray luminosity of LX ~ 1.7 × 1032 erg s-1 for this system and, using the information obtained from the X-ray spectral analysis, a mass MWD ~ 0.8 Msun for the accreting white dwarf (WD). We also confirm an X-ray periodicity of 494 s for this source, which we interpret as the spin period of the WD. In summary, 1RXS J180431.1-273932 is identified as a magnetic CV and its SyXB nature is excluded.
Partly based on observations collected at the Italian Telescopio Nazionale Galileo, located at the Observatorio del Roque de los Muchachos (Canary Islands, Spain).Reduced data used for imaging and spectra is only available at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/544/A11
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe 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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