1,720,960 research outputs found
Limits on Hot Galactic Halo Gas from X-ray Absorption Lines
No full textAlthough the existence of large-scale hot gaseous halos around massive disk galaxies has been theorized for a long time, there is yet very little observational evidence. We report the Chandra and XMM-Newton grating spectral detection of O VII and Ne IX Kα absorption lines along the sight line of 4U 1957+11. The line absorption is consistent with the interstellar medium in origin. Attributing these line absorptions to the hot gas associated with the Galactic disk, we search for the gaseous halo around the Milky Way by comparing this sight line with more distant ones (toward the X-ray binary LMC X-3 and the active galactic nucleus Mrk 421). We find that all the line absorptions along the LMC X-3 and Mrk 421 sight lines are attributable to the hot gas in a thick Galactic disk, as traced by the absorption lines in the spectra of 4U 1957+11 after a Galactic latitude-dependent correction. We constrain the O VII column density through the halo to be N[subscript O VII] < 5 × 10[superscript 15] cm[superscript −2] (95% confidence limit) and conclude that the hot gas contribution to the metal line absorptions, if existing, is negligible.United States. National Aeronautics and Space Administration. (Smithsonian Astrophysical Observatory) (Contract Number SV3- 73016)United States. National Aeronautics and Space Administration. (Smithsonian Astrophysical Observatory) (Contract Number NAS 08-03060)Smithsonian Astrophysical Observatory (Chandra X-ray Center (U.S.)) (Grant Number AR6-7023)Smithsonian Astrophysical Observatory (Chandra X-ray Center (U.S.)) (Grant Number AR7-8014
Disk-dominated States of 4U 1957+11: Chandra, XMM-Newton, and RXTE Observations of Ostensibly the Most Rapidly Spinning Galactic Black Hole
No full textWe present simultaneous Chandra High-Energy Transmission Gratings (HETG) and Rossi X-ray Timing Explorer (RXTE) observations of a "soft state" of the black hole candidate 4U 1957+11. These spectra, having limited hard X-ray excess, are an excellent test of disk atmosphere models that include effects of black hole spin. The HETG data show, by modeling the broadband continuum and direct fitting of absorption edges, that the disk spectrum is only very mildly absorbed, with N[subscript H] = (1–2) × 10[superscript 21] cm−[superscript 2]. These data additionally reveal λλ13.449 Ne IX absorption consistent with the warm/hot phase of the interstellar medium. The fitted disk model implies an inclined disk around a low-mass black hole rotating with normalized spin a* ≈ 1. We show, however, that pure Schwarzschild models describe the data extremely well, albeit with large disk atmosphere ``color-correction'' factors. Standard correction factors can be attained if one incorporates mild Comptonization. We find that the Chandra observations do not uniquely determine spin, even with this otherwise extremely well-measured, nearly pure disk spectrum. XMM-Newton RXTE observations, taken only six weeks later, are equally unconstraining. This lack of constraint is partly driven by the unknown mass and distance of 4U 1957+11; however, it is also driven by the limited Chandra and XMM-Newton bandpasses. We therefore present a series of 48 RXTE observations taken at different brightness/hardness levels. These data prefer a spin of a* ≈ 1, even when including a mild Comptonization component; however, they also show evolution of the color-correction factors. If the rapid-spin models with standard correction factors are to be believed, then the RXTE observations predict that 4U 1957+11 can range from a 3 M[sun] black hole at 10 kpc with a* ≈ 0.83 to a 16 M[sun] black hole at 22 kpc with a* ≈ 1.United States. National Aeronautics and Space Administration (Grant Number SV3-73016)German Aerospace Center (DLR) (Grant Number 50OR0701
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
Confirming the Detection of an Intergalactic X-Ray Absorber toward PKS 2155–304
No full textWe present new observations of PKS 2155-304 with the Chandra Low Energy Transmission Grating (LETG), using the Advanced CCD Imaging Spectrometer (ACIS). We confirm the detection of an absorption line plausibly identified as O VIII Lyα from a warm-hot intergalactic medium associated with a small group of galaxies along the line of sight, as originally reported by Fang and coworkers. Combining the previous observations by Fang and coworkers with five new long observations on the same target, we increase the total exposure time by a factor of 3 and the total counts per resolution element by a factor of 5. The measured line equivalent width is smaller than that observed by Fang and coworkers, but still consistent at 90% confidence. We also analyze the XMM-Newton observations on the same target, as well as observations using the combination of the Chandra LETG and the High Resolution Camera (HRC). These observations have been used to challenge our reported detection. While no line is seen in either the XMM-Newton or the Chandra LETG+HRC data, we find that our result is consistent with the upper limits from both data sets. We attribute the nondetection to (1) the higher quality of the Chandra LETG+ACIS spectrum and (2) the rather extended wings of the line-spread functions of both the XMM-Newton Reflection Grating Spectrometer (RGS) and the Chandra LETG+HRC. We discuss the implication of our observation on the temperature and density of the absorber. We also confirm the detection of z ~ 0 O VII absorption, and, comparing with previous Chandra analysis, we obtain much tighter constraints on the line properties
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
- …
