Showing papers by "Matthew Pitkin published in 2022"

Nested sampling for physical scientists

Abstract: We review Skilling's nested sampling (NS) algorithm for Bayesian inference and more broadly multi-dimensional integration. After recapitulating the principles of NS, we survey developments in implementing efficient NS algorithms in practice in high-dimensions, including methods for sampling from the so-called constrained prior. We outline the ways in which NS may be applied and describe the application of NS in three scientific fields in which the algorithm has proved to be useful: cosmology, gravitational-wave astronomy, and materials science. We close by making recommendations for best practice when using NS and by summarizing potential limitations and optimizations of NS.

First joint observation by the underground gravitational-wave detector, KAGRA, with GEO600

Abstract: We report the results of the first joint observation of the KAGRA detector with GEO 600. GEO 600 and KAGRA performed a joint observing run from April 7 to 20, 2020. We present the results of the joint analysis of the GEO–KAGRA data for transient gravitational-wave signals, including the coalescence of neutron-star binaries and generic unmodeled transients. We also perform dedicated searches for binary coalescence signals and generic transients associated with gamma-ray burst events observed during the joint run. No gravitational-wave events were identified. We evaluate the minimum detectable amplitude for various types of transient signals and the spacetime volume for which the network is sensitive to binary neutron-star coalescences. We also place lower limits on the distances to the gamma-ray bursts analysed based on the non-detection of an associated gravitational-wave signal for several signal models, including binary coalescences. These analyses demonstrate the feasibility and utility of KAGRA as a member of the global gravitational-wave detector network.

Nested sampling for physical scientists

Abstract: We review Skilling's nested sampling (NS) algorithm for Bayesian inference and more broadly multi-dimensional integration. After recapitulating the principles of NS, we survey developments in implementing efficient NS algorithms in practice in high-dimensions, including methods for sampling from the so-called constrained prior. We outline the ways in which NS may be applied and describe the application of NS in three scientific fields in which the algorithm has proved to be useful: cosmology, gravitational-wave astronomy, and materials science. We close by making recommendations for best practice when using NS and by summarizing potential limitations and optimizations of NS.

All-sky search for continuous gravitational waves from isolated neutron stars using Advanced LIGO and Advanced Virgo O3 data

Abstract: We present results of an all-sky search for continuous gravitational waves which can be produced by spinning neutron stars with an asymmetry around their rotation axis, using data from the third observing run of the Advanced LIGO and Advanced Virgo detectors. Four different analysis methods are used to search in a gravitational-wave frequency band from 10 to 2048 Hz and a first frequency derivative from $-10^{-8}$ to $10^{-9}$ Hz/s. No statistically-significant periodic gravitational-wave signal is observed by any of the four searches. As a result, upper limits on the gravitational-wave strain amplitude $h_0$ are calculated. The best upper limits are obtained in the frequency range of 100 to 200 Hz and they are ${\sim}1.1\times10^{-25}$ at 95\% confidence-level. The minimum upper limit of $1.10\times10^{-25}$ is achieved at a frequency 111.5 Hz. We also place constraints on the rates and abundances of nearby planetary- and asteroid-mass primordial black holes that could give rise to continuous gravitational-wave signals.

Model-based Cross-correlation Search for Gravitational Waves from the Low-mass X-Ray Binary Scorpius X-1 in LIGO O3 Data

Abstract: We present the results of a model-based search for continuous gravitational waves from the low-mass X-ray binary Scorpius X-1 using LIGO detector data from the third observing run of Advanced LIGO and Advanced Virgo. This is a semicoherent search that uses details of the signal model to coherently combine data separated by less than a specified coherence time, which can be adjusted to balance sensitivity with computing cost. The search covered a range of gravitational-wave frequencies from 25 to 1600 Hz, as well as ranges in orbital speed, frequency, and phase determined from observational constraints. No significant detection candidates were found, and upper limits were set as a function of frequency. The most stringent limits, between 100 and 200 Hz, correspond to an amplitude h 0 of about 10−25 when marginalized isotropically over the unknown inclination angle of the neutron star’s rotation axis, or less than 4 × 10−26 assuming the optimal orientation. The sensitivity of this search is now probing amplitudes predicted by models of torque balance equilibrium. For the usual conservative model assuming accretion at the surface of the neutron star, our isotropically marginalized upper limits are close to the predicted amplitude from about 70 to 100 Hz; the limits assuming that the neutron star spin is aligned with the most likely orbital angular momentum are below the conservative torque balance predictions from 40 to 200 Hz. Assuming a broader range of accretion models, our direct limits on gravitational-wave amplitude delve into the relevant parameter space over a wide range of frequencies, to 500 Hz or more.

Search for subsolar-mass black hole binaries in the second part of Advanced LIGO’s and Advanced Virgo’s third observing run

Abstract: We describe a search for gravitational waves from compact binaries with at least one component with mass 0.2 M⊙–1.0 M⊙ and mass ratio q ≥ 0.1 in Advanced LIGO and Advanced Virgo data collected between 1 November 2019, 15:00 UTC and 27 March 2020, 17:00 UTC. No signals were detected. The most significant candidate has a false alarm rate of $0.2 \, \rm {yr}^{-1}$. We estimate the sensitivity of our search over the entirety of Advanced LIGO’s and Advanced Virgo’s third observing run, and present the most stringent limits to date on the merger rate of binary black holes with at least one subsolar-mass component. We use the upper limits to constrain two fiducial scenarios that could produce subsolar-mass black holes: primordial black holes (PBH) and a model of dissipative dark matter. The PBH model uses recent prescriptions for the merger rate of PBH binaries that include a rate suppression factor to effectively account for PBH early binary disruptions. If the PBHs are monochromatically distributed, we can exclude a dark matter fraction in PBHs fPBH ≳ 0.6 (at 90% confidence) in the probed subsolar-mass range. However, if we allow for broad PBH mass distributions we are unable to rule out fPBH = 1. For the dissipative model, where the dark matter has chemistry that allows a small fraction to cool and collapse into black holes, we find an upper bound fDBH < 10−5 on the fraction of atomic dark matter collapsed into black holes.

Search for gravitational waves from Scorpius X-1 with a hidden Markov model in O3 LIGO data

Abstract: Results are presented for a semi-coherent search for continuous gravitational waves from the low-mass X-ray binary Scorpius X-1, using a hidden Markov model (HMM) to allow for spin wandering. This search improves on previous HMM-based searches of Laser Interferometer Gravitational-wave Observatory (LIGO) data by including the orbital period in the search template grid, and by analyzing data from the latest (third) observing run (O3). In the frequency range searched, from 60 to 500 Hz, we find no evidence of gravitational radiation. This is the most sensitive search for Scorpius X-1 using a HMM to date. For the most sensitive sub-band, starting at $256.06$Hz, we report an upper limit on gravitational wave strain (at $95 \%$ confidence) of $h_{0}^{95\%}=6.16\times10^{-26}$, assuming the orbital inclination angle takes its electromagnetically restricted value $\iota=44^{\circ}$. The upper limits on gravitational wave strain reported here are on average a factor of $\sim 3$ lower than in the O2 HMM search. This is the first Scorpius X-1 HMM search with upper limits that reach below the indirect torque-balance limit for certain sub-bands, assuming $\iota=44^{\circ}$.

Search for continuous gravitational wave emission from the Milky Way center in O3 LIGO-Virgo data

Abstract: We present a directed search for continuous gravitational wave (CW) signals emitted by spinning neutron stars located in the inner parsecs of the Galactic Center (GC). Compelling evidence for the presence of a numerous population of neutron stars has been reported in the literature, turning this region into a very interesting place to look for CWs. In this search, data from the full O3 LIGO--Virgo run in the detector frequency band $[10,2000]\rm~Hz$ have been used. No significant detection was found and 95$\%$ confidence level upper limits on the signal strain amplitude were computed, over the full search band, with the deepest limit of about $7.6\times 10^{-26}$ at $\simeq 142\rm~Hz$. These results are significantly more constraining than those reported in previous searches. We use these limits to put constraints on the fiducial neutron star ellipticity and r-mode amplitude. These limits can be also translated into constraints in the black hole mass -- boson mass plane for a hypothetical population of boson clouds around spinning black holes located in the GC.

Search for gravitational-wave transients associated with magnetar bursts in Advanced LIGO and Advanced Virgo data from the third observing run

Abstract: Gravitational waves are expected to be produced from neutron star oscillations associated with magnetar giant flares and short bursts. We present the results of a search for short-duration (milliseconds to seconds) and long-duration ( ∼ 100 s) transient gravitational waves from 13 magnetar short bursts observed during Advanced LIGO, Advanced Virgo and KAGRA’s third observation run. These 13 bursts come from two magnetars, SGR 1935 + 2154 and Swift J1818.0 − 1607. We also include three other electromagnetic burst events detected by Fermi GBM which were identified as likely coming from one or more magnetars, but they have no association with a known magnetar. No magnetar giant flares were detected during the analysis period. We find no evidence of gravitational waves associated with any of these 16 bursts. We place upper bounds on the root-sum-square of the integrated gravitational-wave strain that reach 2 . 2 × 10 − 23 / √ Hz at 100 Hz for the short-duration search and 8 . 7 × 10 − 23 / √ Hz at 450 Hz for the long-duration search, given a detection efficiency of 50%. For a ringdown signal at 1590 Hz targeted by the short-duration search the limit is set to 1 . 8 × 10 − 22 / √ Hz. Using the estimated distance to each magnetar, we derive upper bounds on the emitted gravitational-wave energy of 3 . 2 × 10 43 erg ( 7 . 3 × 10 43 erg) for SGR 1935 + 2154 and 8 . 2 × 10 42 erg ( 2 . 8 × 10 43 erg) for Swift J1818.0 − 1607, for the short-duration (long-duration) search. Assuming isotropic emission of electromagnetic radiation of the burst fluences, we constrain the ratio of gravitational-wave energy to electromagnetic energy for bursts from SGR 1935 + 2154 with available fluence information. The lowest of these ratios is 3 Wen et al. 2019), making them detectable with Advanced LIGO (Aasi et al. 2015), Advanced Virgo (Acernese et al. 2015), and KAGRA (Akutsu et al. 2019; Akutsu et al. 2021) gravitational-wave observatories (Abbott et al. 2018). Detailed calculations of the rearrangement of the neutron star’s magnetic field using analytic calculations (Levin & van Hoven 2011) and numerical-relativity simulations (Ciolfi al. Zink & Rezzolla 2012; Tsokaros et al. 2021) yield more realistic estimates for the gravitational-wave energy emitted in the f -mode during these events. These models suggest gravitational waves associated with Galactic magnetar flares are not observable with the current

Search for Gravitational Waves Associated with Fast Radio Bursts Detected by CHIME/FRB During the LIGO--Virgo Observing Run O3a

Abstract: We search for gravitational-wave transients associated with fast radio bursts (FRBs) detected by the Canadian Hydrogen Intensity Mapping Experiment Fast Radio Burst Project (CHIME/FRB), during the first part of the third observing run of Advanced LIGO and Advanced Virgo (1 April 2019 15:00 UTC – 1 Oct 2019 15:00 UTC). Triggers from 22 FRBs were analyzed with a search that targets compact binary coalescences with at least one neutron star component. A targeted search for generic gravitational-wave transients was conducted on 40 FRBs. We find no significant evidence for a gravitational-wave association in either search. Given the large uncertainties in the distances of the FRBs inferred from the dispersion measures in our sample, however, this does not conclusively exclude any progenitor models that include emission of a gravitational wave of the types searched for from any of these FRB events. We report 90% confidence lower bounds on the distance to each FRB for a range of gravitational-wave progenitor models. By combining the inferred maximum distance information for each FRB with the sensitivity of the gravitational-wave searches, we set upper limits on the energy emitted through gravitational waves for a range of emission scenarios. We find values of order 10–10 erg for a range of different emission models with central gravitational wave frequencies in the range 70–3560 Hz. Finally, we also found no significant coincident detection of gravitational waves with the repeater, FRB 20200120E, which is the closest known extragalactic FRB.

CWInPy: A Python package for inference with continuous gravitational-wave signals from pulsars

Abstract: Continuous quasi-monochromatic gravitational-waves are expected to be emitted from nonaxisymmetric rapidly rotating neutron stars (see, e.g., Riles, 2022 for a review). There are thought to be on the order of 108 − 109 neutron stars within the Milky Way (Sartore et al., 2010). At the time of writing, around 3000 such stars, have been found through electromagnetic (primarily radio) observations of their highly regular pulsing profiles (Manchester et al., 2005). These are known as pulsars. A proportion of these pulsars with rotation frequencies ≳ 10Hz make enticing targets for the current and future generation of ground-based gravitational-wave observatories such as LIGO, Virgo and KAGRA (B. P. Abbott et al., 2019). The detection of gravitational-waves from such a source would reveal information on the size of any nonaxisymmetry, or more colloquially a “mountain”, on the star. This in turn provides valuable and novel information on neutron star matter and structure (see, e.g., Lasky, 2015).

lintegrate: A C/Python numerical integration library for working in log-space

Abstract: There are many situations in which the integral of a function must be evaluated numerically between given limits. For C codes, there is a range of numerical integration (sometimes called numerical quadrature) functions provided within the GNU Scientific Library (GSL) (Galassi et al., 2009). However, in situations where the integrand has an extremely large dynamic range these GSL functions can fail due to numerical instability. One way to get around numerical instability issues is to work with the natural logarithm of the function. The logarithm of the function cannot simply be integrated as this will not produce the logarithm of the integral of the original function. lintegrate provides a range of C integration functions, equivalent to functions in GSL, that allow the integration of a function when only working with the natural logarithm of the function is computationally practical. The result that is returned is the natural logarithm of the integral of the underlying function. lintegrate also provides a Python (vanRossum, 1995) module for accessing some of these functions in Python.