1,720,996 research outputs found
Broad-band reflection spectroscopy of MAXI J1535-571 using AstroSat: estimation of black hole mass and spin
Get PDFWe report the results from AstroSat observations of the transient Galactic black hole X-ray binary MAXI J1535–571 during its hard-intermediate state of the 2017 outburst. We systematically study the individual and joint spectra from two simultaneously observing AstroSat X-ray instruments, and probe and measure a number of parameter values of accretion disc, corona, and reflection from the disc in the system using models with generally increasing complexities. Using our broad-band (1.3–70 keV) X-ray spectrum, we clearly show that a soft X-ray instrument, which works below 10–12 keV, alone cannot correctly characterize the Comptonizing component from the corona, thus highlighting the importance of broad-band spectral analysis. By fitting the reflection spectrum with the latest version of the RELXILL family of relativistic reflection models, we constrain the black hole’s dimensionless spin parameter to be 0.67+0.16−0.04. We also jointly use the reflection spectral component (RELXILL) and a general relativistic thin disc component (Kerrbb), and estimate the black hole’s mass and distance to be 10.39+0.61−0.62 M⊙ and 5.4+1.8−1.1 kpc, respectivel
Unravelling the unusually curved X-ray spectrum of RGB J0710 + 591 using AstroSat observations
No full textWe report the analysis of simultaneous multiwavelength data of the high-energy-peaked blazar RGB J0710 + 591 from the Large Area X-ray Proportional Counters, Soft X-ray focusing Telescope, and Ultraviolet Imaging Telescope (UVIT) instruments onboard AstroSat. The wide band X-ray spectrum (0.35–30 keV) is modelled as synchrotron emission from a non-thermal distribution of high-energy electrons. The spectrum is unusually curved, with a curvature parameter βp ∼ 6.4 for a log parabola particle distribution, or a high-energy spectral index p2 > 4.5 for a broken power-law distribution. The spectrum shows more curvature than an earlier quasi-simultaneous analysis of Swift–XRT/NuSTAR data where the parameters were βp ∼ 2.2 or p2 ∼ 4. It has long been known that a power-law electron distribution can be produced from a region where particles are accelerated under Fermi process and the radiative losses in acceleration site decide the maximum attainable Lorentz factor, γmax. Consequently, this quantity decides the energy at which the spectrum curves steeply. We show that such a distribution provides a more natural explanation for the AstroSat data as well as the earlier XRT/NuSTAR observation, making this as the first well-constrained determination of the photon energy corresponding to γmax. This in turn provides an estimate of the acceleration time-scale as a function of magnetic field and Doppler factor. The UVIT observations are consistent with earlier optical/UV measurements and reconfirm that they plausibly correspond to a different radiative component than the one responsible for the X-ray emissio
Re-awakening of GRS 1716-249 after 23 yr, observed by Swift/XRT and NuSTAR
No full textIn this work, we present a spectral and temporal analysis of Swift/XRT and NuSTAR
observations of GRS 1716–249 during its recent 2016–2017 outburst. This low-mass X-ray
binary underwent an extraordinary outburst after a long quiescence of 23 yr, since its last major
outburst in 1993. The source was observed over two different epochs during 2017 April 7 and
10. The best-fitting joint spectral fitting in the energy range 0.5–79.0 keV indicates that the
spectrum is best described by relatively cold, weak disc blackbody emission, dominant thermal
Comptonization emission, and a relativistically broadened fluorescent iron K α emission line.
We observed a clear indication of a Compton hump around 30 keV. We also detected an excess
feature of 1.3 keV. Assuming a lamp-post geometry of the corona, we constrained the inner
disc radius for both observations to 11.92+8.62 −11.92 RISCO (i.e. an upper limit) and 10.39+9.51 −3.02 RISCO
(where RISCO ≡ radius of the innermost stable circular orbit) for the first epoch (E1) and
second epoch (E2), respectively. A significant (5σ) type C quasi-periodic oscillation (QPO) at
1.20 ± 0.04 Hz is detected for the first time for GRS 1716–249, which drifts to 1.55 ± 0.04 Hz
(6σ) at the end of the second observation. The derived spectral and temporal properties show
a positive correlation between the QPO frequency and the photon inde
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
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
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
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