29 research outputs found
Importance of Tides for Periastron Precession in Eccentric Neutron Star - White Dwarf Binaries
Although not nearly as numerous as binaries with two white dwarfs, eccentric
neutron star-white dwarf (NS-WD) binaries are important gravitational-wave (GW)
sources for the next generation of space-based detectors sensitive to low
frequency waves. Here we investigate periastron precession in these sources as
a result of general relativistic, tidal, and rotational effects; such
precession is expected to be detectable for at least some of the detected
binaries of this type. Currently, two eccentric NS-WD binaries are known in the
galactic field, PSR J1141-6545 and PSR B2303+46, both of which have orbits too
wide to be relevant in their current state to GW observations. However,
population synthesis studies predict the existence of a significant Galactic
population of such systems. Though small in most of these systems, we find that
tidally induced periastron precession becomes important when tides contribute
to more than 3% of the total precession rate. For these systems, accounting for
tides when analyzing periastron precession rate measurements can improve
estimates of the WD component mass inferred and, in some cases, will prevent us
from misclassifying the object. However, such systems are rare due to rapid
orbital decay. To aid the inclusion of tidal effects when using periastron
precession as a mass measurement tool, we derive a function that relates the WD
radius and periastron precession constant to the WD mass.Comment: Published in The Astrophysical Journa
Machine-directed gravitational-wave counterpart discovery
Joint observations in electromagnetic and gravitational waves shed light on
the physics of objects and surrounding environments with extreme gravity that
are otherwise unreachable via siloed observations in each messenger. However,
such detections remain challenging due to the rapid and faint nature of
counterparts. Protocols for discovery and inference still rely on human experts
manually inspecting survey alert streams and intuiting optimal usage of limited
follow-up resources. Strategizing an optimal follow-up program requires
adaptive sequential decision-making given evolving light curve data that (i)
maximizes a global objective despite incomplete information and (ii) is robust
to stochasticity introduced by detectors/observing conditions. Reinforcement
learning (RL) approaches allow agents to implicitly learn the physics/detector
dynamics and the behavior policy that maximize a designated objective through
experience.
To demonstrate the utility of such an approach for the kilonova follow-up
problem, we train a toy RL agent for the goal of maximizing follow-up
photometry for the true kilonova among several contaminant transient light
curves. In a simulated environment where the agent learns online, it achieves
3x higher accuracy compared to a random strategy. However, it is surpassed by
human agents by up to a factor of 2. This is likely because our hypothesis
function (Q that is linear in state-action features) is an insufficient
representation of the optimal behavior policy. More complex agents could
perform at par or surpass human experts. Agents like these could pave the way
for machine-directed software infrastructure to efficiently respond to next
generation detectors, for conducting science inference and optimally planning
expensive follow-up observations, scalably and with demonstrable performance
guarantees.Comment: Submitted to the Astrophysical Journal; Comments welcome
The Mass Distribution of Stellar-Mass Black Holes
We perform a Bayesian analysis of the mass distribution of stellar-mass black
holes using the observed masses of 15 low-mass X-ray binary systems undergoing
Roche lobe overflow and five high-mass, wind-fed X-ray binary systems. Using
Markov Chain Monte Carlo calculations, we model the mass distribution both
parametrically---as a power law, exponential, gaussian, combination of two
gaussians, or log-normal distribution---and non-parametrically---as histograms
with varying numbers of bins. We provide confidence bounds on the shape of the
mass distribution in the context of each model and compare the models with each
other by calculating their relative Bayesian evidence as supported by the
measurements, taking into account the number of degrees of freedom of each
model. The mass distribution of the low-mass systems is best fit by a
power-law, while the distribution of the combined sample is best fit by the
exponential model. We examine the existence of a "gap" between the most massive
neutron stars and the least massive black holes by considering the value, M_1%,
of the 1% quantile from each black hole mass distribution as the lower bound of
black hole masses. The best model (the power law) fitted to the low-mass
systems has a distribution of lower-bounds with M_1% > 4.3 Msun with 90%
confidence, while the best model (the exponential) fitted to all 20 systems has
M_1% > 4.5 Msun with 90% confidence. We conclude that our sample of black hole
masses provides strong evidence of a gap between the maximum neutron star mass
and the lower bound on black hole masses. Our results on the low-mass sample
are in qualitative agreement with those of Ozel, et al (2010).Comment: 56 pages, 22 figures, 9 tables, as accepted by Ap
Inferencing Progenitor and Explosion Properties of Evolving Core-collapse Supernovae from Zwicky Transient Facility Light Curves
We analyze a sample of 45 Type II supernovae from the Zwicky Transient
Facility (ZTF) public survey using a grid of hydrodynamical models in order to
assess whether theoretically-driven forecasts can intelligently guide follow up
observations supporting all-sky survey alert streams. We estimate several
progenitor properties and explosion physics parameters including
zero-age-main-sequence (ZAMS) mass, mass-loss rate, kinetic energy, 56Ni mass
synthesized, host extinction, and the time of explosion. Using complete light
curves we obtain confident characterizations for 34 events in our sample, with
the inferences of the remaining 11 events limited either by poorly constraining
data or the boundaries of our model grid. We also simulate real-time
characterization of alert stream data by comparing our model grid to various
stages of incomplete light curves (t less than 25 days, t less than 50 days,
all data), and find that some parameters are more reliable indicators of true
values at early epochs than others. Specifically, ZAMS mass, time of explosion,
steepness parameter beta, and host extinction are reasonably constrained with
incomplete light curve data, whereas mass-loss rate, kinetic energy and 56Ni
mass estimates generally require complete light curves spanning greater than
100 days. We conclude that real-time modeling of transients, supported by
multi-band synthetic light curves tailored to survey passbands, can be used as
a powerful tool to identify critical epochs of follow up observations. Our
findings are relevant to identify, prioritize, and coordinate efficient follow
up of transients discovered by Vera C. Rubin Observatory.Comment: 27 pages, 14 figures, Accepted to The Astrophysical Journa
Updated observing scenarios and multi-messenger implications for the International Gravitational-wave Network's O4 and O5
Advanced LIGO and Virgo's third observing run brought another binary neutron
star merger (BNS) and the first neutron-star black-hole (NSBH) mergers. While
no confirmed kilonovae (KNe) was identified in conjunction with any of these
events, continued improvements of analyses surrounding GW170817 allow us to
project constraints on the Hubble Constant (), the Galactic enrichment
from -process nucleosynthesis, and ultra-dense matter possible from
forthcoming events. Here, we describe the expected constraints based on the
latest expected event rates from the international gravitational-wave network
(IGWN) and analyses of GW170817. We show the expected detection rate of
gravitational waves and their counterparts, as well as how sensitive potential
constraints are to the observed numbers of counterparts. We intend this
analysis as support for the community when creating scientifically-driven
electromagnetic follow-up proposals. During the next observing run O4, we
predict an annual detection rate of electromagnetic counterparts from BNS of
() for the Zwicky Transient
Facility (Rubin Observatory)