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Ilya Mandel

Publications and source records attributed to Ilya Mandel.

At least 127 records · Page 7Linked to original sources
arXiv2019

Explosions Driven by the Coalescence of a Compact Object with the Core of a Massive-Star Companion Inside a Common Envelope: Circumstellar Properties, Light Curves, and Population Statistics

We model explosions driven by the coalescence of a black hole or neutron star with the core of its massive-star companion. Upon entering a common envelope phase, a compact object may spiral all the way to the core. The concurrent release of energy is likely to be deposited into the surrounding common envelope, powering a merger-driven explosion. We use hydrodynamic models of binary coalescence to model the common envelope density distribution at the time of coalescence. We find toroidal profiles of material, concentrated in the binary's equatorial plane and extending to many times the massive star's original radius. We use the spherically-averaged properties of this circumstellar material (CSM) to estimate the emergent light curves that result from the interaction between the blast wave and the CSM. We find that typical merger-driven explosions are brightened by up to three magnitudes by CSM interaction. From population synthesis models we discover that the brightest merger-driven explosions, $M_V \sim -18$ to $-19$, are those involving black holes because they have the most massive and extended CSM. Black hole coalescence events are also common; they represent about 50% of all merger-driven explosions and approximately 0.3% of the core-collapse rate. Merger-driven explosions offer a window into the highly-uncertain physics of common envelope interactions in binary systems by probing the properties of systems that merge rather than eject their envelopes.

astro-ph.HE↗
arXiv2019

Astrophysical science metrics for next-generation gravitational-wave detectors

The second generation of gravitational-wave detectors are being built and tuned all over the world. The detection of signals from binary black holes is beginning to fulfill the promise of gravitational-wave astronomy. In this work, we examine several possible configurations for third-generation laser interferometers in existing km-scale facilities. We propose a set of astrophysically motivated metrics to evaluate detector performance. We measure the impact of detector design choices against these metrics, providing a quantitative cost-benefit analyses of the resulting scientific payoffs.

astro-ph.HE↗
arXiv2019

Massive Stellar Mergers as Precursors of Hydrogen-rich Pulsational Pair Instability Supernovae

Interactions between massive stars in binaries are thought to be responsible for much of the observed diversity of supernovae. As surveys probe rarer populations of events, we should expect to see supernovae arising from increasingly uncommon progenitor channels. Here we examine a scenario in which massive stars merge after they have both formed a hydrogen-exhausted core. We suggest this could produce stars which explode as pair-instability supernovae (PISNe) with significantly more hydrogen, at a given metallicity, than in single-star models with the same pre-explosion oxygen-rich core mass. We investigate the subset of those stellar mergers which later produce pulsational PISNe, and estimate that the rate of such post-merger, hydrogen-rich pulsational PISNe could approach a few in a thousand of all core-collapse supernovae. The nature and predicted rate of such hydrogen-rich pulsational PISNe are reminiscent of the very unusual supernova iPTF14hls. For plausible assumptions, PISNe from similar mergers might dominate the rate of PISNe in the local Universe.

astro-ph.HE↗
arXiv2019

Extracting distribution parameters from multiple uncertain observations with selection biases

We derive a Bayesian framework for incorporating selection effects into population analyses. We allow for both measurement uncertainty in individual measurements and, crucially, for selection biases on the population of measurements, and show how to extract the parameters of the underlying distribution based on a set of observations sampled from this distribution. We illustrate the performance of this framework with an example from gravitational-wave astrophysics, demonstrating that the mass ratio distribution of merging compact-object binaries can be extracted from Malmquist-biased observations with substantial measurement uncertainty.

physics.data-an↗
arXiv2018

saprEMo: a simplified algorithm for predicting detections of electromagnetic transients in surveys

The multi-wavelength detection of GW170817 has inaugurated multi-messenger astronomy. The next step consists in interpreting observations coming from population of gravitational wave sources. We introduce saprEMo, a tool aimed at predicting the number of electromagnetic signals characterised by a specific light curve and spectrum, expected in a particular sky survey. By looking at past surveys, saprEMo allows us to constrain models of electromagnetic emission or event rates. Applying saprEMo to proposed astronomical missions/observing campaigns provides a perspective on their scientific impact and tests the effect of adopting different observational strategies. For our first case study, we adopt a model of spindown-powered X-ray emission predicted for a binary neutron star merger producing a long-lived neutron star. We apply saprEMo on data collected by XMM-Newton and Chandra and during $10^4$ s of observations with the mission concept THESEUS. We demonstrate that our emission model and binary neutron star merger rate imply the presence of some signals in the XMM-Newton catalogs. We also show that the new class of X-ray transients found by Bauer et al. in the Chandra Deep Field-South is marginally consistent with the expected rate. Finally, by studying the mission concept THESEUS, we demonstrate the substantial impact of a much larger field of view in searches of X-ray transients.

astro-ph.IM↗
arXiv2018

On the formation history of Galactic double neutron stars

Double neutron stars (DNSs) have been observed as Galactic radio pulsars, and the recent discovery of gravitational waves from the DNS merger GW170817 adds to the known DNS population. We perform rapid population synthesis of massive binary stars and discuss model predictions, including formation rates, mass distributions, and delay time distributions. We vary assumptions and parameters of physical processes such as mass transfer stability criteria, supernova kick distributions, remnant mass distributions and common-envelope energetics. We compute the likelihood of observing the orbital period-eccentricity distribution of the Galactic DNS population under each of our population synthesis models, allowing us to quantitatively compare the models. We find that mass transfer from a stripped post-helium-burning secondary (case BB) onto a neutron star is most likely dynamically stable. We also find that a natal kick distribution composed of both low (Maxwellian $σ=30\rm~km~s^{-1}$) and high ($σ=265\rm~km~s^{-1}$) components is preferred over a single high-kick component. We find that the observed DNS mass distribution can place strong constraints on model assumptions.

astro-ph.SR↗
arXiv2018

Late-time Evolution of Afterglows from Off-Axis Neutron-Star Mergers

Gravitational-wave detected neutron star mergers provide an opportunity to investigate short gamma-ray burst (GRB) jet afterglows without the GRB trigger. Here we show that the post-peak afterglow decline can distinguish between an initially ultra-relativistic jet viewed off-axis and a mildly relativistic wide-angle outflow. Post-peak the afterglow flux will decline as $F_ν\propto t^{-α}$. The steepest decline for a jet afterglow is $α>3p/4$ or $> (3p+1)/4$, for an observation frequency below and above the cooling frequency, respectively, where $p$ is the power-law index of the electron energy distribution. The steepest decline for a mildly relativistic outflow, with initial Lorentz factor $Γ_0\lesssim 2$, is $α\lesssim(15p-19)/10$ or $α\lesssim(15p-18)/10$, in the respective spectral regimes. If the afterglow from GW170817 fades with a maximum index $α> 1.5$ then we are observing the core of an initially ultra-relativistic jet viewed off the central axis, while a decline with $α\lesssim 1.4$ after $\sim 5$--10 peak times indicates that a wide-angled and initially $Γ_0\lesssim 2$ outflow is responsible. At twice the peak time, the two outflow models fall on opposite sides of $α\approx 1$. So far, two post-peak X-ray data points at 160 and 260 days suggest a decline consistent with an off-axis jet afterglow. Follow-up observations over the next 1--2 years will test this model.

astro-ph.HE↗
arXiv2018

Comment on "An excess of massive stars in the local 30 Doradus starburst"

Schneider et al. (Science, 2018) used an ad hoc statistical method in their calculation of the stellar initial mass function. Adopting an improved approach, we reanalyse their data and determine a power law exponent of $2.05_{-0.14}^{+0.13}$. Alternative assumptions regarding data set completeness and the star formation history model can shift the inferred exponent to $2.11_{-0.19}^{+0.17}$ and $2.15_{-0.13}^{+0.13}$, respectively.

astro-ph.SR↗
arXiv2018

Accuracy of inference on the physics of binary evolution from gravitational-wave observations

The properties of the population of merging binary black holes encode some of the uncertain physics of the evolution of massive stars in binaries. The binary black hole merger rate and chirp mass distribution are being measured by ground-based gravitational-wave detectors. We consider isolated binary evolution and explore how accurately the physical model can be constrained with such observations by applying the Fisher information matrix to the merging black hole population simulated with the rapid binary population synthesis code COMPAS. We investigate variations in four COMPAS parameters: common envelope efficiency, kick velocity dispersion, and mass loss rates during the luminous blue variable and Wolf--Rayet stellar evolutionary phases. We find that 1000 observations would constrain these model parameters to a fractional accuracy of a few percent. Given the empirically determined binary black hole merger rate, we can expect gravitational-wave observations alone to place strong constraints on the physics of stellar and binary evolution within a few years.

astro-ph.HE↗
arXiv2018

The orbit of GW170817 was inclined by less than 28 degrees to the line of sight

We combine the gravitational-wave measurement of the effective distance to the binary neutron star merger GW170817, the redshift of its host galaxy NGC 4993, and the latest Hubble constant measurement from the Dark Energy Survey to constrain the inclination between the orbital angular momentum of the binary and the line of sight to $18 \pm 8$ degrees (less than 28 degrees at 90% confidence). This provides a complementary constraint on models of potential afterglow observations.

astro-ph.HE↗
arXiv2017

The astrophysical science case for a decihertz gravitational-wave detector

We discuss the astrophysical science case for a decihertz gravitational-wave mission. We focus on unique opportunities for scientific discovery in this frequency range, including probes of type IA supernova progenitors, mergers in the presence of third bodies, intermediate mass black holes, seeds of massive black holes, improved sky localization, and tracking the population of merging compact binaries.

astro-ph.HE↗
arXiv2017

The Distance to NGC 4993: The Host Galaxy of the Gravitational-wave Event GW170817

The historic detection of gravitational waves from a binary neutron star merger (GW170817) and its electromagnetic counterpart led to the first accurate (sub-arcsecond) localization of a gravitational-wave event. The transient was found to be $\sim$10" from the nucleus of the S0 galaxy NGC 4993. We report here the luminosity distance to this galaxy using two independent methods. (1) Based on our MUSE/VLT measurement of the heliocentric redshift ($z_{\rm helio}=0.009783\pm0.000023$) we infer the systemic recession velocity of the NGC 4993 group of galaxies in the cosmic microwave background (CMB) frame to be $v_{\rm CMB}=3231 \pm 53$ km s$^{-1}$. Using constrained cosmological simulations we estimate the line-of-sight peculiar velocity to be $v_{\rm pec}=307 \pm 230$ km s$^{-1}$, resulting in a cosmic velocity of $v_{\rm cosmic}=2924 \pm 236$ km s$^{-1}$ ($z_{\rm cosmic}=0.00980\pm 0.00079$) and a distance of $D_z=40.4\pm 3.4$ Mpc assuming a local Hubble constant of $H_0=73.24\pm 1.74$ km s$^{-1}$ Mpc$^{-1}$. (2) Using Hubble Space Telescope measurements of the effective radius (15.5" $\pm$ 1.5") and contained intensity and MUSE/VLT measurements of the velocity dispersion, we place NGC 4993 on the Fundamental Plane (FP) of E and S0 galaxies. Comparing to a frame of 10 clusters containing 226 galaxies, this yields a distance estimate of $D_{\rm FP}=44.0\pm 7.5$ Mpc. The combined redshift and FP distance is $D_{\rm NGC 4993}= 41.0\pm 3.1$ Mpc. This 'electromagnetic' distance estimate is consistent with the independent measurement of the distance to GW170817 as obtained from the gravitational-wave signal ($D_{\rm GW}= 43.8^{+2.9}_{-6.9}$ Mpc) and confirms that GW170817 occurred in NGC 4993.

astro-ph.GA↗
arXiv2017

Hierarchical analysis of gravitational-wave measurements of binary black hole spin-orbit misalignments

Binary black holes may form both through isolated binary evolution and through dynamical interactions in dense stellar environments. The formation channel leaves an imprint on the alignment between the black hole spins and the orbital angular momentum. Gravitational waves from these systems directly encode information about the spin--orbit misalignment angles, allowing them to be (weakly) constrained. Identifying sub-populations of spinning binary black holes will inform us about compact binary formation and evolution. We simulate a mixed population of binary black holes with spin--orbit misalignments modelled under a range of assumptions. We then develop a hierarchical analysis and apply it to mock gravitational-wave observations of these populations. Assuming a population with dimensionless spin magnitudes of $χ= 0.7$, we show that tens of observations will make it possible to distinguish the presence of subpopulations of coalescing binary black holes based on their spin orientations. With $100$ observations it will be possible to infer the relative fraction of coalescing binary black holes with isotropic spin directions (corresponding to dynamical formation in our models) with a fractional uncertainty of $\sim 40\%$. Meanwhile, only $\sim 5$ observations are sufficient to distinguish between extreme models---all binary black holes either having exactly aligned spins or isotropic spin directions.

astro-ph.HE↗
arXiv2017

Distinguishing Spin-Aligned and Isotropic Black Hole Populations With Gravitational Waves

The first direct detections of gravitational waves from merging binary black holes open a unique window into the binary black hole formation environment. One promising environmental signature is the angular distribution of the black hole spins; systems formed through dynamical interactions among already-compact objects are expected to have isotropic spin orientations whereas binaries formed from pairs of stars born together are more likely to have spins preferentially aligned with the binary orbital angular momentum. We consider existing gravitational wave measurements of the binary effective spin, the best-measured combination of spin parameters, in the four likely binary black hole detections GW150914, LVT151012, GW151226, and GW170104. If binary black hole spin magnitudes extend to high values we show that the data exhibit a $2.4σ$ ($0.015$ odds ratio) preference for an isotropic angular distribution over an aligned one. By considering the effect of 10 additional detections, we show that such an augmented data set would enable in most cases a preference stronger than $5σ$ ($2.9 \times 10^{-7}$ odds ratio). The existing preference for either an isotropic spin distribution or low spin magnitudes for the observed systems will be confirmed (or overturned) confidently in the near future.

astro-ph.HE↗
arXiv2017

Accelerating gravitational wave parameter estimation with multi-band template interpolation

Parameter estimation on gravitational wave signals from compact binary coalescence (CBC) requires the evaluation of computationally intensive waveform models, typically the bottleneck in the analysis. This cost will increase further as low frequency sensitivity in later second and third generation detectors motivates the use of longer waveforms. We describe a method for accelerating parameter estimation by exploiting the chirping behaviour of the signals to sample the waveform sparsely for portions where the full frequency resolution is not required. We demonstrate that the method can reproduce the original results with a waveform mismatch of $\leq 5\times 10^{-7}$, but with a waveform generation cost up to $\sim 50$ times lower for computationally costly frequency-domain waveforms starting from below 8 Hz.

gr-qc↗
arXiv2017

Ultra-luminous X-ray sources and neutron-star-black-hole mergers from very massive close binaries at low metallicity

Gravitational waves from the binary black hole (BH) merger GW150914 may enlighten our understanding of ultra-luminous X-ray sources (ULXs), as BHs>30Msun can reach luminosities>4x10^39 erg s^-1 without exceeding their Eddington limit. It is then important to study variations of evolutionary channels for merging BHs, which might instead form accreting BHs and become ULXs. It was recently shown that massive binaries with mass ratios close to unity and tight orbits can undergo efficient rotational mixing and evolve chemically homogeneously, resulting in a compact BH binary. We study similar systems by computing ~120000 detailed binary models with the MESA code covering a wide range of initial parameters. For initial mass ratios M2/M1~0.1-0.4, primaries >40Msun can evolve chemically homogeneously, remaining compact and forming a BH without undergoing Roche-lobe overflow. The secondary then expands and transfers mass to the BH, initiating a ULX phase. We predict that ~1 out of 10^4 massive stars evolves this way, and that in the local universe 0.13 ULXs per Msun yr^-1 of star-formation rate are observable, with a strong preference for low-metallicities. At metallicities log Z>-3, BH masses in ULXs are limited to 60Msun due to the occurrence of pair-instability supernovae which leave no remnant, resulting in an X-ray luminosity cut-off. At lower metallicities, very massive stars can avoid exploding as pair-instability supernovae and instead form BHs with masses above 130Msun, producing a gap in the ULX luminosity distribution. After the ULX phase, neutron-star-BH binaries that merge in less than a Hubble time are produced with a formation rate <0.2 Gpc^-3 yr^-1. We expect that upcoming X-ray observatories will test these predictions, which together with additional gravitational wave detections will provide strict constraints on the origin of the most massive BHs that can be produced by stars.

astro-ph.HE↗
arXiv2017

Exploring the Parameter Space of Compact Binary Population Synthesis

As we enter the era of gravitational wave astronomy, we are beginning to collect observations which will enable us to explore aspects of astrophysics of massive stellar binaries which were previously beyond reach. In this paper we describe COMPAS (Compact Object Mergers: Population Astrophysics and Statistics), a new platform to allow us to deepen our understanding of isolated binary evolution and the formation of gravitational-wave sources. We describe the computational challenges associated with their exploration, and present preliminary results on overcoming them using Gaussian process regression as a simulation emulation technique.

astro-ph.HE↗