1,721,084 research outputs found
X-ray eclipse mapping constrains the binary inclination and mass ratio of swift J1858.6-0814
No full textX-ray eclipse mapping is a promising modelling technique, capable of constraining the mass and/or radius of neutron stars (NSs) or blackholes (BHs) in eclipsing binaries and probing any structure surrounding the companion star. In eclipsing systems, the binary inclination, , and mass ratio, relate via the duration of totality, . The degeneracy between and can then be broken through detailed modelling of the eclipse profile. Here we model the eclipses of the NS low-mass X-ray binary Swift J1858.60814 utilising archival NICER observations taken while the source was in outburst. Analogous to EXO0748676, we find evidence for irradiation driven ablation of the companion's surface by requiring a layer of stellar material to surround the companion star in our modelling. This material layer extends km from the companion's surface and is likely the cause of the extended, energy-dependent and asymmetric ingress and egress that we observe. Our fits return an inclination of and a mass ratio . Using Kepler's law to relate the mass and radius of the companion star via the orbital period ( 21.3 hrs), we subsequently determine the companion to have a low mass in the range and a large radius in the range . Our results, combined with future radial velocity amplitudes measured from stellar absorption/emission lines, can place precise constraints on the component masses in this system
Eclipse mapping of EXO 0748-676: evidence for a massive neutron star
No full textDetermining the maximum possible neutron star (NS) mass places limits on the equation of state (EoS) of ultra-dense matter. The mass of NSs in low-mass X-ray binaries can be determined from the binary mass function, providing independent constraints are placed on both the binary inclination and mass ratio. In eclipsing systems, they relate via the totality duration. EXO 0748–676 is an eclipsing NS low-mass X-ray binary with a binary mass function estimated using stellar emission lines from the irradiated face of the companion. The NS mass is thus known as a function of mass ratio. Here, we model the X-ray eclipses in several energy bands, utilizing archival XMM–Newton data. We find a narrow region of absorbing material surrounding the companion star is required to explain the energy-dependent eclipses. Therefore, we suggest the companion may be experiencing ablation of its outer layers and that the system could transition into a redback millisecond pulsar. Our fit returns a mass ratio of q=0.222+0.07−0.08 and an inclination i=76.5±1.41.1. Combining these with the previously measured radial velocity of 410 ± 5 km s−1, derived from Doppler mapping analysis of H α emission during quiescence, returns an NS mass of ∼2 M⊙ even if the line originates as far from the NS as physically possible, favouring hard EoS. The inferred mass increases for a more realistic emission point. However, a ∼1.4 M⊙ canonical NS mass is possible when considering radial velocity values derived from other emission lines observed both during outburst and quiescence
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
The Luminous, Hard State Can't Be MAD
Full text linkWe present a straightforward argument for why the luminous, hard state of
black hole X-ray binaries (BHXRBs) cannot always be associated with a
magnetically arrested accretion disc (MAD). It relies on three core premises:
1) that the type-C quasi-periodic oscillation (QPO) is best explained by
Lense-Thirring (LT) precession of a tilted, inner, hot flow; 2) that observed
optical and infrared (IR) QPOs with the same or lower frequency as the type-C
QPO suggest the jet, too, must precess in these systems; and 3) that numerical
simulations of MADs show that their strong magnetic fields promote alignment of
the disc with the black hole and, thereby, suppress LT precession. If all three
premises hold true, then, at least whenever the optical and IR QPOs are
observed alongside the type-C QPO, these systems cannot be in the MAD state.
Extending the argument further, if the type-C QPO is always associated with LT
precession, then it would rule out MADs anytime this timing feature is seen,
which covers nearly all BHXRBs when they are in the luminous, hard and
hard-intermediate states.Comment: 5 pages, 2 figures, accepted to MNRA
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
Predicting the self-lensing population in optical surveys
No full textThe vast majority of binaries containing a compact object and a regular star spend most of their time in a quiescent state where no strong interactions occur between components. Detection of these binaries is extremely challenging and only few candidates have been detected through optical spectroscopy. Self-lensing represents a new means of detecting compact objects in binaries, where gravitational lensing of the light from the visible component by the compact object produces periodic optical flares. Here we show that current and planned large-area optical surveys can detect a significant number (∼100–10,000s) of these self-lensing binaries and provide insights into the properties of the compact lenses. We show that many of the predicted population of observable self-lensing binaries will be observed with multiple self-lensing flares; this both improves the chances of detection and also immediately distinguishes them from chance-alignment micro-lensing events. Through self-lensing we can investigate long – but previously hidden – stages of binary evolution and consequently provide new constraints on evolutionary models which impact on the number and nature of double compact object mergers
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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