Abstract:
Future ground-based and space-borne interferometric gravitational-wave detectors may capture between tens and thousands of binary coalescence events per year. There is a significant and growing body of work on the estimation of astrophysically relevant parameters, such as masses and spins, from the gravitational-wave signature of a single event. This paper introduces a robust Bayesian framework for combining the parameter estimates for multiple events into a parameter distribution of the underlying event population. The framework can be readily deployed as a rapid post-processing tool.

Abstract:
We compute the probability distribution for the spin of a black hole following a series of minor mergers with isotropically distributed, non-spinning, inspiraling compact objects. By solving the Fokker-Planck equation governing this stochastic process, we obtain accurate analytical fits for the evolution of the mean and standard deviation of the spin distribution in several parameter regimes. We complement these analytical fits with numerical Monte-Carlo simulations in situations when the Fokker-Planck analysis is not applicable. We find that a ~150 solar-mass intermediate-mass black hole that gained half of its mass through minor mergers with neutron stars will have dimensionless spin parameter chi=a/M~0.2 \pm 0.08. We estimate the effect of the spin of the central black hole on the detection range for intermediate-mass-ratio inspiral (IMRI) detections by Advanced LIGO and extreme-mass-ratio inspiral(EMRI) detections by LISA. We find that for realistic black hole spins, the inclination-averaged Advanced-LIGO IMRI detection range may be increased by up to 10% relative to the range for IMRIs into non-spinning intermediate-mass black holes. For LISA, we find that the detection range for EMRIs into 10^5 solar-mass massive black holes (MBHs) is not significantly affected by MBH spin, the range for EMRIs into 10^6 solar-mass MBHs is affected at the ~ 10% level, and EMRIs into maximally spinning 10^7 solar-mass MBHs are detectable to a distance ~25 times greater than EMRIs into non-spinning black holes. The resulting bias in favor of detecting EMRIs into rapidly spinning MBHs will play a role when extracting the MBH spin distribution from EMRI statistics.

Abstract:
The most promising way to compute the gravitational waves emitted by binary black holes (BBHs) in their last dozen orbits, where post-Newtonian techniques fail, is a quasistationary approximation introduced by Detweiler and being pursued by Price and others. In this approximation the outgoing gravitational waves at infinity and downgoing gravitational waves at the holes' horizons are replaced by standing waves so as to guarantee that the spacetime has a helical Killing vector field. Because the horizon generators will not, in general, be tidally locked to the holes' orbital motion, the standing waves will destroy the horizons, converting the black holes into naked singularities that resemble black holes down to near the horizon radius. This paper uses a spherically symmetric, scalar-field model problem to explore in detail the following BBH issues: (i) The destruction of a horizon by the standing waves. (ii) The accuracy with which the resulting naked singularity resembles a black hole. (iii) The conversion of the standing-wave spacetime (with a destroyed horizon) into a spacetime with downgoing waves by the addition of a ``radiation-reaction field''. (iv) The accuracy with which the resulting downgoing waves agree with the downgoing waves of a true black-hole spacetime (with horizon). The model problem used to study these issues consists of a Schwarzschild black hole endowed with spherical standing waves of a scalar field. It is found that the spacetime metric of the singular, standing-wave spacetime, and its radiation-reaction-field-constructed downgoing waves are quite close to those for a Schwarzschild black hole with downgoing waves -- sufficiently close to make the BBH quasistationary approximation look promising for non-tidally-locked black holes.

Abstract:
The birth kicks of black holes, arising from asymmetric mass ejection or neutrino emission during core-collapse supernovae, are of great interest for both observationally constraining supernova models and population-synthesis studies of binary evolution. Recently, several efforts were undertaken to estimate black hole birth kicks from observations of black-hole low-mass X-ray binaries. We follow up on this work, specifically focussing on the highest estimated black-hole kick velocities. We find that existing observations do not require black hole birth kicks in excess of approximately 100 km/s, although higher kicks are not ruled out.

Abstract:
A star on a nearly radial trajectory approaching a massive black hole (MBH) gets tidally disrupted if it comes sufficiently close to the MBH. Here we explore what happens to binary stars whose centers of mass approach the MBH on nearly radial orbits. The interaction with the MBH often leads to both stars being disrupted in sequence. We argue that such events could produce light curves that are substantially different from those of the single disruptions, with possible features such as two local maxima. Tidal forces from the MBH can also lead the binary components to collide; these merger products can form highly magnetized stars, whose subsequent tidal disruption may enable prompt jet formation.

Abstract:
We develop a systematic approach to calculating the electrostatic force between point charges in an arbitrary geometry with arbitrary boundary conditions. When the boundary is present, the simple expression for the force acting on a charge as ``the charge times the field it is placed in'' becomes ill-defined. However, this rule can be salvaged if the field in question is redefined to include all the terms that do not diverge at the charge position, in particular, those due to the charge itself. The proof requires handling the self-action energy divergence for point charges, which is accomplished by means of a geometrical regularization.

Abstract:
The behavior of the magnetic potential near a point charge (fluxon) located at a curved regular boundary surface is shown to be essentially different from that of a volume point charge. In addition to the usual inverse distance singularity, two singular terms are generally present. The first of them, a logarithmic one, is axially symmetric with respect to the boundary normal at the charge location, and proportional to the sum of the two principal curvatures of the boundary surface at this point, that is, to the local mean curvature. The second term is asymmetric and proportional to the difference of the two principal curvatures in question; it is also bounded at the charge location. Both terms vanish, apparently, if the charge is at a planar point of the boundary, and only in this case. The field in the charge vicinity behaves accordingly, featuring generally two singular terms proportional to the inverse distance, in addition to the main inverse distance squared singularity. This result is significant, in particular, for studying the interaction of magnetic vortices in type II superconductors.

Abstract:
As the ground-based gravitational-wave telescopes LIGO, Virgo, and GEO 600 approach the era of first detections, we review the current knowledge of the coalescence rates and the mass and spin distributions of merging neutron-star and black-hole binaries. We emphasize the bi-directional connection between gravitational-wave astronomy and conventional astrophysics. Astrophysical input will make possible informed decisions about optimal detector configurations and search techniques. Meanwhile, rate upper limits, detected merger rates, and the distribution of masses and spins measured by gravitational-wave searches will constrain astrophysical parameters through comparisons with astrophysical models. Future developments necessary to the success of gravitational-wave astronomy are discussed.

Abstract:
Gravitational waves emitted during intermediate-mass-ratio inspirals (IMRIs) of intermediate-mass black holes (IMBHs) into supermassive black holes could represent a very interesting source for LISA. Similarly, IMRIs of stellar-mass compact objects into IMBHs could be detectable by Advanced LIGO. At present, however, it is not clear what waveforms could be used for IMRI detection, since the post-Newtonian approximation breaks down as an IMRI approaches the innermost stable circular orbit, and perturbative solutions are only known to the lowest order in the mass ratio. We discuss the expected mismatches between approximate and true waveforms, and the choice of the best available waveform as a function of the mass ratio and the total mass of the system. We also comment on the significance of the spin of the smaller body and the need for its inclusion in the waveforms.

Abstract:
Modern problems in astronomical Bayesian inference require efficient methods for sampling from complex, high-dimensional, often multi-modal probability distributions. Most popular methods, such as Markov chain Monte Carlo sampling, perform poorly on strongly multi-modal 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 lower autocorrelation time for the sampler (and therefore more efficient sampling). In particular, we present a simple, easily-implemented algorithm for dynamically adapting the temperature configuration of a sampler while sampling in order to maximise its efficiency. This algorithm dynamically adjusts the temperature spacing to achieve a uniform rate of exchanges between neighbouring temperatures. We compare the algorithm to conventional geometric temperature configurations on a number of test distributions, and report 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 test distributions a sampler using the dynamical adaptations to achieve uniform acceptance ratios between neighbouring chains outperforms one that does not.