A
bstract
We investigate the possibility of using quasi-normal modes (QNMs) to probe the microscopic structure of two-dimensional (2D) anti-de Sitter (AdS
2
) dilatonic black holes. We first extend ...previous results on the QNMs spectrum, found for external massless scalar perturbations, to the case of massive scalar perturbations. We find that the quasi-normal frequencies are purely imaginary and scale linearly with the overtone number. Motivated by this and extending previous results regarding Schwarzschild black holes, we propose a microscopic description of the 2D black hole in terms of a coherent state of
N
massless particles quantized on a circle, with occupation numbers sharply peaked on the characteristic QNMs frequency
ω
̂
. We further model the black hole as a statistical ensemble of
N
decoupled quantum oscillators of frequency
ω
̂
. This allows us to recover the Bekenstein-Hawking (BH) entropy
S
of the hole as the leading contribution to the Gibbs entropy for the set of oscillators, in the high-temperature regime, and to show that
S
=
N
. Additionally, we find sub-leading logarithmic corrections to the BH entropy. We further corroborate this microscopic description by outlining a holographic correspondence between QNMs in the AdS
2
bulk and the de Alfaro-Fubini-Furlan conformally invariant quantum mechanics. Our results strongly suggest that modelling a black hole as a coherent state of particles and as a statistical ensemble of decoupled harmonic oscillators is always a good approximation in the large black-hole mass, large overtone number limit.
ABSTRACT
MAXI J1820+070, a black hole candidate first detected in early 2018 March, was observed by XMM–Newton during the outburst rise. In this letter we report on the spectral and timing analysis ...of the XMM–Newton X-ray and UV data, as well as contemporaneous X-ray data from the Swift satellite. The X-ray spectrum is well described by a hard thermal Comptonization continuum. The XMM–Newton X-ray light curve shows a pronounced dipping interval, and spectral analysis indicates that it is caused by a moderately ionized partial covering absorber. The XMM–Newton/OM U-filter data do not reveal any signs of the 17 h orbital modulation that was seen later on during the outburst decay. The UV/X-ray cross-correlation function shows a complex shape, with a peak at positive lags of about 4 s and a precognition dip at negative lags, which is absent during the X-ray dipping episode. Such shape could arise if the UV emission comes partially from synchrotron self-Compton emission near the black hole, as well as from reprocessing of the X-rays in the colder accretion disc further out.
IRAS 16293-2422 is a very well-studied young stellar system seen in projection towards the L1689N cloud in the Ophiuchus complex. However, its distance is still uncertain; there is a range of values ...from 120 pc to 180 pc. Our goal is to measure the trigonometric parallax of this young star by means of H2O maser emission. We use archival data from 15 epochs of VLBA observations of the 22.2 GHz water maser line. By modeling the displacement on the sky of the H2O maser spots, we derived a trigonometric parallax of 7.1 ± 1.3 mas, corresponding to a distance of 141−21+30 pc. This new distance is in good agreement with recent values obtained for other magnetically active young stars in the L1689 cloud. We relate the kinematics of these masers with the outflows and the recent ejections powered by source A in the system.
Over 100 trigonometric parallaxes and proper motions for masers associated with young, high-mass stars have been measured with the Bar and Spiral Structure Legacy Survey, a Very Long Baseline Array ...key science project, the European VLBI Network, and the Japanese VLBI Exploration of Radio Astrometry project. These measurements provide strong evidence for the existence of spiral arms in the MilkyWay, accurately locatingmany arm segments and yielding spiral pitch angles ranging from about 7degrees to 20degrees. Assuming a "universal" spiral galaxy form for the rotation curve, we estimate the thin disk scale length to be 2.44 + or - 0.16 kpc. With this large data set, the parameters R sub(0) and Theta sub(0) are no longer highly correlated and are relatively insensitive to different forms of the rotation curve.
We report four trigonometric parallaxes for high-mass star-forming regions within 4 kpc of the Galactic center. These measurements were made with the Very Long Baseline Array as part of the BeSSeL ...Survey. By associating these sources kinematically with large-scale features in CO and HI longitude-velocity diagrams, we begin to outline some major features of the inner Milky Way: the Connecting arm, the near and far 3 kpc arms, and the Norma arm. The Connecting arm in the first Galactic quadrant lies closer to the Galactic center than the far 3 kpc arm and is offset by the long-bar's major axis near its leading edge, supporting the presence of an inner Lindblad resonance. Assuming the 3 kpc arms are a continuous physical structure, the relative Galactocentric distance of its near and far sides suggests highly elliptical streamlines of gas around the barfs) and a bar corotation radius, r sub(CR) gap 3.6 kpc. At a Galactic longitude near 10degrees and a heliocentric distance of about 5 kpc, the near 3 kpc arm and the Norma arm intersect on a face-on view of our Galaxy, while passing at different Galactic latitudes. We provide an accurate distance measurement to the W 31 star-forming complex of 4.95 super(+0.51) sub(-0.43) kpc from the Sun, which associates it with a bright CO feature belonging to the near 3 kpc arm.
Studies on the determinants of plant–herbivore and herbivore–parasitoid associations provide important insights into the origin and maintenance of global and local species richness. If parasitoids ...are specialists on herbivore niches rather than on herbivore taxa, then alternating escape of herbivores into novel niches and delayed resource tracking by parasitoids could fuel diversification at both trophic levels. We used DNA barcoding to identify parasitoids that attack larvae of seven Pontania sawfly species that induce leaf galls on eight willow species growing in subarctic and arctic–alpine habitats in three geographic locations in northern Fennoscandia, and then applied distance‐ and model‐based multivariate analyses and phylogenetic regression methods to evaluate the hierarchical importance of location, phylogeny and different galler niche dimensions on parasitoid host use. We found statistically significant variation in parasitoid communities across geographic locations and willow host species, but the differences were mainly quantitative due to extensive sharing of enemies among gallers within habitat types. By contrast, the divide between habitats defined two qualitatively different network compartments, because many common parasitoids exhibited strong habitat preference. Galler and parasitoid phylogenies did not explain associations, because distantly related arctic–alpine gallers were attacked by a species‐poor enemy community dominated by two parasitoid species that most likely have independently tracked the gallers’ evolutionary shifts into the novel habitat. Our results indicate that barcode‐ and phylogeny‐based analyses of food webs that span forested vs. tundra or grassland environments could improve our understanding of vertical diversification effects in complex plant–herbivore–parasitoid networks.
Vascular risk factors (VRFs) may act synergistically, and clinical decision support tools (CDSTs) have been developed that present vascular risk as a summarized score. Because VRFs are a major issue ...in patients with idiopathic normal pressure hydrocephalus (INPH), a CDST may be useful in the diagnostic workup. The objective was to compare 4 CDSTs to determine which one most accurately predicts short-term outcome and 10-year mortality after CSF shunt surgery in INPH patients.
One-hundred forty INPH patients who underwent CSF shunt surgery were included. For each patient, 4 CDST scores (Systematic Coronary Risk Evaluation-Older Persons SCORE-OP, Framingham Risk Score FRS, Revised Framingham Stroke Risk Profile, and Kiefer's Comorbidity Index KCI) were estimated. Short-term outcome (3 months after CSF shunt surgery) was defined on the basis of improvements in gait, Mini-Mental State Examination score, and modified Rankin Scale score. The 10-year mortality rate after surgery was noted. The CDSTs were compared by using Cox regression analysis, receiver operating characteristic curve analysis, and the chi-square test.
For 3 CDSTs, increased score was associated with increased risk of 10-year mortality. A 1-point increase in the FRS indicated a 2% higher risk of death within 10 years (HR 1.02, 95% CI 1.003-1.035, p = 0.021); SCORE-OP, 5% (HR 1.05, 95% CI 1.019-1.087, p = 0.002); and KCI, 12% (HR 1.12, 95% CI 1.03-1.219, p = 0.008). FRS predicted short-term outcome of surgery (p = 0.024). When the cutoff value was set to 32.5%, the positive predictive value was 80% and the negative predictive value was 48% (p = 0.012).
The authors recommend using FRS to predict short-term outcome and 10-year risk of mortality in INPH patients. The study indicated that extensive treatment of the risk factors of INPH may decrease risk of mortality. Clinical trial registration no.: NCT01850914 (ClinicalTrials.gov).
Abstract
The black hole (BH) binary V404 Cyg entered the outburst phase in 2015 June after 26 yr of X-ray quiescence, and with its behaviour broke the outburst evolution pattern typical of most BH ...binaries. We observed the entire outburst with the Swift satellite and performed time-resolved spectroscopy of its most active phase, obtaining over a thousand spectra with exposures from tens to hundreds of seconds. All the spectra can be fitted with an absorbed power-law model, which most of the time required the presence of a partial covering. A blueshifted iron-Kα line appears in 10 per cent of the spectra together with the signature of high column densities, and about 20 per cent of the spectra seem to show signatures of reflection. None of the spectra showed the unambiguous presence of soft disc–blackbody emission, while the observed bolometric flux exceeded the Eddington value in 3 per cent of the spectra. Our results can be explained assuming that the inner part of the accretion flow is inflated into a slim disc that both hides the innermost (and brightest) regions of the flow, and produces a cold, clumpy, high-density outflow that introduces the high absorption and fast spectral variability observed. We argue that the BH in V404 Cyg might have been accreting erratically or even continuously at Eddington/super-Eddington rates – thus sustaining a surrounding slim disc – while being partly or completely obscured by the inflated disc and its outflow. Hence, the largest flares produced by the source might not be accretion-driven events, but instead the effects of the unveiling of the extremely bright source hidden within the system.
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