Session H09: Gravitational Wave Searches: Transient Sources

A Method for Comparison of GstLAL Performance in Gaussian Data and LIGO Detectors Data

We propose a method to quantitatively compare the performance of GW search "methods" in real detector data against simulated colored-Gaussian data. We use this method to compare the results of the GstLAL pipeline applied to real LIGO and Virgo data.

The method consists of comparing results from the behaviours of a given template bank on the two data-sets.

We find that, between the detectors, V1 shows the greatest divergence from Gaussianity (Non-Gaussianity Measure of 11.5), followed by H1 (Non-Gaussianity Measure of 10.4), and finally L1 (Non-Gaussianity Measure of 8.4). Within the detectors, we find that the triggers associated with BNS templates present the highest divergence from gaussianity, but due to the number of triggers, the ones associated to higher mass templates present the biggest contribution to the non-gaussianity measure of the detectors, with all detectors having most of its non-gaussianity coming from NSBH triggers.   

Increasing GstLAL search sensitivity through iDQ binning scheme

iDQ is a data quality pipeline that can detect transient noise in gravitational wave data by using each interferometer's auxiliary data. During the LVK's third observational run the GstLAL pipeline used iDQ to downrank single detector candidates when noise was non-Gaussian, therefore improving single detector sensitivity. We propose to incorporate iDQ information at the background collection stage. This will be helpful in mitigating GstLAL's unnecessary penalization of stretches of data that happen to be coincident with a less noisy background. I will be discussing our methods and improvements to GstLAL's sensitivity.   

The improvement of GstLAL's ranking statistics toward the fourth observing run

Given the upgraded sensitivity of the ground-based gravitational-wave (GW) detectors, the upcoming fourth observing run (O4) by the LIGO Scientific, Virgo, KAGRA Collaboration is expected to have more GW detections from compact binary systems than ever. During this exciting era of the GW astronomy, the improvement of GW detection pipelines plays a crucial role in further increasing GW detection rate. In this talk, we present the ongoing development for the GstLAL low-latency pipeline prepared for O4, focusing on the improvement for computing a likelihood ratio, with which to rank event's significance. Specifically, the major improvement is contributed by the removal of signal contamination, the new grouping scheme of a template bank, and the new signal model in SNR-chisq parameter space. As a result, we show the increase in the pipeline's search sensitivity by 10-20% in a simulated injection search.   

A global p-astro for gravitational-waves: consistently combining information from multiple search pipelines

Recent LVK analyses have used p-astro to characterize the significance of gravitational-wave candidates. Unlike false alarm rates which only capture the statistics of the instrumental noise triggers, p-astro incorporates the rate at which triggers are generated by both real signals and instrumental noise in estimating the probability that a candidate is real. The LVK Collaboration employs multiple search pipelines, each of which independently calculates p-astro values. However, the comparison of these numbers across pipelines is complicated by the fact that they are tuned in different ways and make different population assumptions. Multiple p-astro values also make the interpretation of marginal candidates more ambiguous. We develop a statistical formalism to calculate a joint p-astro for a gravitational-wave candidate, consistently accounting for triggers from all pipelines. We demonstrate the properties of this method using a toy model and by application to the publicly available list of gravitational-wave candidates from the O3a run.   

Search for Eccentric Binary Black Hole Mergers with Gravitational Waves

Since the first gravitational wave detection in 2015, LIGO, Virgo, and KAGRA have detected a total of 90 signals from binary black hole and neutron star mergers. Despite the large number of observations, the astrophysical origin of these binary black hole systems still remains undetermined. Binary black holes primarily originate from two types of environments: when two stars evolve together in isolation, undergo supernovae and form a binary black hole system that coalesces within the age of the Universe, and when two black holes become bound due to strong gravitational interactions in dense environments like globular clusters and young star clusters. Several hints can be found in the properties of the two black holes that help us determine which of these two environments the binary formed and merged in. One distinguishing feature between gravitational waves originating from these two environments is the orbital eccentricity of the binary since this leaves a unique imprint on the morphology of the signal. In my presentation, I will talk about why the detection of gravitational wave signals from eccentric binary black holes is challenging, how LIGO-Virgo-KAGRA (LVK) mitigates these challenges, and our sensitivity to such sources. I will also briefly discuss the dependence of LVK's search sensitivity on the source properties of the binary black hole system.   

A hierarchical approach to multi-messenger gravitational wave searches

We introduce a streamlined, externally triggered gravitational wave (GW) search for multi-messenger compact binary coalescence events. Telescopes with large or sub-threshold catalogs are good candidates for multi-messenger searches with LIGO-Virgo-KAGRA GW data but can come with thousands of events per year to follow up. PyGRB, the state-of-the-art CBC multi-messenger search algorithm, is sensitive but computationally expensive, processing only ~100 events per year at 2 or more weeks of wall time each. This makes it unsuited for large multi-messenger follow up efforts. We introduce a hierarchical search algorithm, PyNu, to process these large catalogs to pass potential coincident events to PyGRB for follow-up. Our algorithm is based in PyCBC, a Python-based GW search package used by the LVK to identify events in GWTC-3. In our hierarchical approach, we use a trigger's time of arrival and sky location to identify potential signals in LVK data, cutting down large catalogs to only "interesting" potential coincidences. Events that are sufficiently interesting are then passed to PyGRB for acceptance or rejection. In this talk we present PyNu's method, demonstrate its sub-1-hour runtime and potential to identify events using GW170817, and discuss its future applications.   

GRB, FRB and Magnetar Triggered Searches for Gravitational Waves in Advanced LIGO, Advanced Virgo and KAGRA's Third and Fourth Observing Runs

This talk will present a summary of the results of and plans for searches for gravitational waves associated with gamma-ray bursts, fast radio bursts, and magnetars in the third observing and fourth observing runs of Advanced LIGO and Advanced Virgo and KAGRA. The third observing run concluded on Mar 27, 2020, and the fourth observing run will be starting close to the time of the April APS meeting, 2023. This talk will cover the current status of the efforts to conduct both targeted template-based and unmodeled searches for gravitational waves in Advanced LIGO, Advanced Virgo and KAGRA data. This will include both the high-latency, deep analyses, and efforts that are being made to bring a lightweight, rapid-followup analysis into production. The impact of the discovery of a kilonova associated with GRB 211211A on upcoming search plans will also be highlighted.   

RAVEN: LIGO-Virgo-KAGRA gravitational wave focused multi-messenger pipeline

Assigning statistical significance to gravitational-wave triggers with external triggers such as electromagnetic waves (or neutrinos) is important for the astronomical community. We can compute the joint false alarm rate of these joint candidates, including sky localization information, within seconds and alert astronomers within a minute. Such analysis has to be performed simultaneously after the detection, since signals from astrophysical transients fade quickly, enabling follow-up studies that provide a deeper insight into the source objects and the physical processes within them. One such scenario would be the coincident detection of GW170817 and GRB170817A. In this talk, we will present the design and the testing of a low-latency framework adopted by the LVK collaboration, Rapid, on-source VOEvent Coincident Monitor (RAVEN). In addition, we will present the new features added to the O4 observing runs, such as using multi-ordered skymaps, filtering burst searches, sub-threshold searches, and the results from the mock data challenge (MDC) in preparation for testing for O4 readiness.