27 research outputs found
Measuring eccentricity in binary black hole inspirals with gravitational waves
When binary black holes form in the field, it is expected that their orbits
typically circularize before coalescence. In galactic nuclei and globular
clusters, binary black holes can form dynamically. Recent results suggest that
of mergers in globular clusters result from three-body
interactions. These three-body interactions are expected to induce significant
orbital eccentricity when they enter the Advanced LIGO band at a
gravitational-wave frequency of 10 Hz. Measurements of binary black hole
eccentricity therefore provide a means for determining whether or not dynamic
formation is the primary channel for producing binary black hole mergers. We
present a framework for performing Bayesian parameter estimation on
gravitational-wave observations of black hole inspirals. Using this framework,
and employing the non-spinning, inspiral-only EccentricFD waveform approximant,
we determine the minimum detectable eccentricity for an event with masses and
distance similar to GW150914. At design sensitivity, we find that the current
generation of advanced observatories will be sensitive to orbital
eccentricities of at a gravitational-wave frequency of 10 Hz,
demonstrating that existing detectors can use eccentricity to distinguish
between circular field binaries and globular cluster triples. We compare this
result to eccentricity distributions predicted to result from three black hole
binary formation channels, showing that measurements of eccentricity could be
used to infer the population properties of binary black holes.Comment: 12 pages, 7 figures, 2 table
Detection of a glitch in the pulsar J1709-4429
We report the detection of a glitch event in the pulsar J17094429 (also
known as B170644) during regular monitoring observations with the Molonglo
Observatory Synthesis Telescope (UTMOST). The glitch was found during timing
operations, in which we regularly observe over 400 pulsars with up to daily
cadence, while commensally searching for Rotating Radio Transients, pulsars,
and FRBs. With a fractional size of ,
the glitch reported here is by far the smallest known for this pulsar,
attesting to the efficacy of glitch searches with high cadence using UTMOST.Comment: 3 pages, 1 figur
The UTMOST pulsar timing programme II:Timing noise across the pulsar population
While pulsars possess exceptional rotational stability, large scale timing
studies have revealed at least two distinct types of irregularities in their
rotation: red timing noise and glitches. Using modern Bayesian techniques, we
investigated the timing noise properties of 300 bright southern-sky radio
pulsars that have been observed over 1.0-4.8 years by the upgraded Molonglo
Observatory Synthesis Telescope (MOST). We reanalysed the spin and spin-down
changes associated with nine previously reported pulsar glitches, report the
discovery of three new glitches and four unusual glitch-like events in the
rotational evolution of PSR J18250935. We develop a refined Bayesian
framework for determining how red noise strength scales with pulsar spin
frequency () and spin-down frequency (), which we apply to a
sample of 280 non-recycled pulsars. With this new method and a simple power-law
scaling relation, we show that red noise strength scales across the
non-recycled pulsar population as , where and . This method can be
easily adapted to utilise more complex, astrophysically motivated red noise
models. Lastly, we highlight our timing of the double neutron star PSR
J07373039, and the rediscovery of a bright radio pulsar originally found
during the first Molonglo pulsar surveys with an incorrectly catalogued
position.Comment: Accepted by MNRAS. 28 pages, 8 figures, 8 table
The gravitational-wave background null hypothesis: Characterizing noise in millisecond pulsar arrival times with the Parkes Pulsar Timing Array
The noise in millisecond pulsar (MSP) timing data can include contributions
from observing instruments, the interstellar medium, the solar wind, solar
system ephemeris errors, and the pulsars themselves. The noise environment must
be accurately characterized in order to form the null hypothesis from which
signal models can be compared, including the signature induced by
nanohertz-frequency gravitational waves (GWs). Here we describe the noise
models developed for each of the MSPs in the Parkes Pulsar Timing Array (PPTA)
third data release, which have been used as the basis of a search for the
isotropic stochastic GW background. We model pulsar spin noise, dispersion
measure variations, scattering variations, events in the pulsar magnetospheres,
solar wind variability, and instrumental effects. We also search for new timing
model parameters and detected Shapiro delays in PSR~J06143329 and
PSR~J19025105. The noise and timing models are validated by testing the
normalized and whitened timing residuals for Gaussianity and residual
correlations with time. We demonstrate that the choice of noise models
significantly affects the inferred properties of a common-spectrum process.
Using our detailed models, the recovered common-spectrum noise in the PPTA is
consistent with a power law with a spectral index of , the value
predicted for a stochastic GW background from a population of supermassive
black hole binaries driven solely by GW emission.Comment: 18 pages, 10 figures. Accepted for publication in ApJ