Modern problems in astronomical Bayesian inference require efficient methods for sampling from complex, high-dimensional, often multimodal probability distributions. Most popular methods, such as ...MCMC sampling, perform poorly on strongly multimodal probability distributions, rarely jumping between modes or settling on just one mode without finding others. Parallel tempering addresses this problem by sampling simultaneously with separate Markov chains from tempered versions of the target distribution with reduced contrast levels. Gaps between modes can be traversed at higher temperatures, while individual modes can be efficiently explored at lower temperatures. In this paper, we investigate how one might choose the ladder of temperatures to achieve more efficient sampling, as measured by the autocorrelation time of the sampler. In particular, we present a simple, easily implemented algorithm for dynamically adapting the temperature configuration of a sampler while sampling. This algorithm dynamically adjusts the temperature spacing to achieve a uniform rate of exchanges between chains at neighbouring temperatures. We compare the algorithm to conventional geometric temperature configurations on a number of test distributions and on an astrophysical inference problem, reporting efficiency gains by a factor of 1.2–2.5 over a well-chosen geometric temperature configuration and by a factor of 1.5–5 over a poorly chosen configuration. On all of these problems, a sampler using the dynamical adaptations to achieve uniform acceptance ratios between neighbouring chains outperforms one that does not.
All ten LIGO/Virgo binary black hole (BH-BH) coalescences reported following the O1/O2 runs have near-zero effective spins. There are only three potential explanations for this. If the BH spin ...magnitudes are large, then: (i) either both BH spin vectors must be nearly in the orbital plane or (ii) the spin angular momenta of the BHs must be oppositely directed and similar in magnitude. Then there is also the possibility that (iii) the BH spin magnitudes are small. We consider the third hypothesis within the framework of the classical isolated binary evolution scenario of the BH-BH merger formation. We test three models of angular momentum transport in massive stars: a mildly efficient transport by meridional currents (as employed in the Geneva code), an efficient transport by the Tayler-Spruit magnetic dynamo (as implemented in the MESA code), and a very-efficient transport (as proposed by Fuller et al.) to calculate natal BH spins. We allow for binary evolution to increase the BH spins through accretion and account for the potential spin-up of stars through tidal interactions. Additionally, we update the calculations of the stellar-origin BH masses, including revisions to the history of star formation and to the chemical evolution across cosmic time. We find that we can simultaneously match the observed BH-BH merger rate density and BH masses and BH-BH effective spins. Models with efficient angular momentum transport are favored. The updated stellar-mass weighted gas-phase metallicity evolution now used in our models appears to be key for obtaining an improved reproduction of the LIGO/Virgo merger rate estimate. Mass losses during the pair-instability pulsation supernova phase are likely to be overestimated if the merger GW170729 hosts a BH more massive than 50
M
⊙
. We also estimate rates of black hole-neutron star (BH-NS) mergers from recent LIGO/Virgo observations. If, in fact. angular momentum transport in massive stars is efficient, then any (electromagnetic or gravitational wave) observation of a rapidly spinning BH would indicate either a very effective tidal spin up of the progenitor star (homogeneous evolution, high-mass X-ray binary formation through case A mass transfer, or a spin- up of a Wolf-Rayet star in a close binary by a close companion), significant mass accretion by the hole, or a BH formation through the merger of two or more BHs (in a dense stellar cluster).
There have recently been several reports of apparently periodic variations in the light curves of quasars, e.g. PG 1302−102 by Graham et al. Any quasar showing periodic oscillations in brightness ...would be a strong candidate to be a close binary supermassive black hole and, in turn, a candidate for gravitational wave studies. However, normal quasars – powered by accretion on to a single, supermassive black hole – usually show stochastic variability over a wide range of time-scales. It is therefore important to carefully assess the methods for identifying periodic candidates from among a population dominated by stochastic variability. Using a Bayesian analysis of the light curve of PG 1302−102, we find that a simple stochastic process is preferred over a sinusoidal variation. We then discuss some of the problems one encounters when searching for rare, strictly periodic signals among a large number of irregularly sampled, stochastic time series, and use simulations of quasar light curves to illustrate these points. From a few thousand simulations of steep spectrum (‘red noise’) stochastic processes, we find many simulations that display few-cycle periodicity like that seen in PG 1302−102. We emphasize the importance of calibrating the false positive rate when the number of targets in a search is very large.
Abstract
We present observations of two strong-lensing galaxy clusters located within the 90 per cent credible sky localization maps released following LIGO–Virgo’s discovery of the binary black hole ...(BH–BH) gravitational wave (GW) source GW170814. Our objectives were (1) to search for candidate electromagnetic (EM) counterparts to GW170814 under the hypothesis that it was strongly lensed, and thus more distant and less massive than inferred by LIGO–Virgo, and (2) to demonstrate the feasibility of rapid target of opportunity observations to search for faint lensed transient point sources in crowded cluster cores located within GW sky localizations. Commencing 20 h after discovery, and continuing over 12 nights, we observed Abell 3084 (z = 0.22) and SMACS J0304.3 − 4401 (z = 0.46) with GMOS on the Gemini-South telescope, and Abell 3084 with MUSE on ESO’s Very Large Telescope. We detect no candidate EM counterparts in these data. Calibration of our photometric analysis methods using simulations yields 5σ detection limits for transients in difference images of the cores of these clusters of i = 25. This is the most sensitive photometric search to date for counterparts to GW sources, and rules out the possibility that GW170814 was lensed by these clusters with a kilonova-like EM counterpart. Based on the detector frame masses of the compact objects, and assuming that at least one neutron star (NS) is required in the merging system to produce a kilonova-like counterpart, implies that GW170814 was neither an NS–NS nor NS–BH merger at z > 8 lensed by either of these clusters. Also, in the first ever emission line search for counterparts to GW sources, we detected no lines down to a 5σ detection limit of $5\times 10^{-17}\, {\rm erg\, s^{-1}\, cm^{-2}}$.
ABSTRACT
Observations by LIGO–Virgo of binary black hole mergers suggest a possible anticorrelation between black hole mass ratio (q = m2/m1) and the effective inspiral spin parameter χeff, the ...mass-weighted spin projection on to the binary orbital angular momentum. We show that such an anticorrelation can arise for binary black holes assembled in active galactic nuclei (AGNs) due to spherical and planar symmetry-breaking effects. We describe a phenomenological model in which (1) heavier black holes live in the AGN disc and tend to spin-up into alignment with the disc; (2) lighter black holes with random spin orientations live in the nuclear spheroid; (3) the AGN disc is dense enough to rapidly capture a fraction of the spheroid component, but small in radial extent to limit the number of bulk disc mergers; (4) migration within the disc is non-uniform, likely disrupted by feedback from migrators or disc turbulence; (5) dynamical encounters in the disc are common and preferentially disrupt binaries that are retrograde around their centre of mass, particularly at stalling orbits, or traps. Comparisons of predictions in (q, χeff) parameter space for the different channels may allow us to distinguish their fractional contributions to the observed merger rates.
The solar analogues 16 Cyg A and B are excellent asteroseismic targets in the Kepler field of view and together with a red dwarf and a Jovian planet form an interesting system. For these more evolved ...Sun-like stars we cannot detect surface rotation with the current Kepler data but instead use the technique of asteroseimology to determine rotational properties of both 16 Cyg A and B. We find the rotation periods to be ... and ..., and the angles of inclination to be ... and ..., for A and B, respectively. Together with these results we use the published mass and age to suggest that, under the assumption of a solar-like rotation profile, 16 Cyg A could be used when calibrating gyrochronology relations. In addition, we discuss the known 16 Cyg B star-planet eccentricity and measured low obliquity which is consistent with Kozai cycling and tidal theory. (ProQuest: ... denotes formulae/symbols omitted.)
Abstract
Gravitational-wave (GW) detections are starting to reveal features in the mass distribution of double compact objects. The lower end of the black hole (BH) mass distribution is especially ...interesting as few formation channels contribute here and because it is more robust against variations in the cosmic star formation than the high-mass end. In this work we explore the stable mass transfer channel for the formation of GW sources with a focus on the low-mass end of the mass distribution. We conduct an extensive exploration of the uncertain physical processes that impact this channel. We note that, for fiducial assumptions, this channel reproduces the peak at ∼9
M
☉
in the GW-observed binary BH mass distribution remarkably well and predicts a cutoff mass that coincides with the upper edge of the purported neutron star–black hole (NS–BH) mass gap. The peak and cutoff mass are a consequence of the unique properties of this channel; namely (1) the requirement of stability during the mass transfer phases, and (2) the complex way in which the final compact object masses scale with the initial mass. We provide an analytical expression for the cutoff in the primary component mass and show that this adequately matches our numerical results. Our results imply that selection effects resulting from the formation channel alone can provide an explanation for the purported NS–BH mass gap in GW detections. This provides an alternative to the commonly adopted view that the gap emerges during BH formation.
We examine the performance of a variety of different estimators for the mass of galaxy groups, based on their galaxy distribution alone. We draw galaxies from the Sloan Digital Sky Survey for a set ...of groups and clusters for which hydrostatic mass estimates based on high-quality Chandra X-ray data are available. These are used to calibrate the galaxy-based mass proxies, and to test their performance. Richness, luminosity, galaxy overdensity, rms radius and dynamical mass proxies are all explored. These different mass indicators all have their merits, and we argue that using them in combination can provide protection against being misled by the effects of dynamical disturbance or variations in star formation efficiency. Using them in this way leads us to infer the presence of significant non-statistical scatter in the X-ray based mass estimates we employ. We apply a similar analysis to a set of mock groups derived from applying a semi-analytic galaxy formation code to the Millennium dark matter simulation. The relations between halo mass and the mass proxies differ significantly in some cases from those seen in the observational groups, and we discuss possible reasons for this.
The stability of antioxidants in an apple polyphenol–milk model system was examined. The model system consisted of skim milk fortified with pH-neutralised apple polyphenols (AP, 0–200mg per 100ml ...milk), with or without ascorbic acid (100mg per 100ml milk). Physical and chemical changes were evaluated after thermal treatment (120°C, 5min) and oxidative storage (20°C and 38°C, up to 12 weeks). Antioxidant capacity was determined using both oxygen radical absorbance capacity (ORAC) assay and ferric reducing antioxidant power (FRAP) assay. Significant antioxidant capacity was detected in the presence of milk. Antioxidant capacity was retained during thermal treatment but decreased slowly during storage.
The concentration of ascorbic acid decreased rapidly, and was close to zero after 2-week storage at 38°C or 10-week storage at 20°C. The brownness of the polyphenol–milk system increased over storage duration of 0–12 weeks; this effect was retarded by the addition of ascorbic acid. This high polyphenol–milk has demonstrated good physical stability.
Hollow-core photonic crystal fibres have excited interest as potential ultra-low loss telecommunications fibres because light propagates mainly in air instead of solid glass. We propose that the ...ultimate limit to the attenuation of such fibres is determined by surface roughness due to frozenin capillary waves. This is confirmed by measurements of the surface roughness in a HC-PCF, the angular distribution of the power scattered out of the core, and the wavelength dependence of the minimum loss of fibres drawn to different scales.
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