**Noise Mitigation Methods in the Era of Open Public Alerts**

# Parallel Session: GRAVITATIONAL WAVES - GROUND BASED EXPERIMENTS (L)

## Location: Park 3.01

#### L1 - Monday 14:00-15:40 (Jess McIver)

**14:00-14:34**

**Patrick Godwin (Physics, Pennsylvania State University)**

Advanced LIGO and Virgo’s third observing run opens a new era of sending out automated open public alerts

from gravitational-wave candidates. In addition, improvements in the global detector network sensitivity

has increased the rate at which gravitational-wave detections are made, necessitating the use of automated noise

mitigation methods and rapid follow-up. In this talk, I will discuss the current state in low-latency

noise mitigation methods and event validation, recent work in gravitational wave detector characterization,

as well as future prospects as the detector network sensitivity increases in future observing runs.

**Compact Binary Merger Candidates from a Broad Multi-Detector Search of the Public Advanced LIGO and Virgo data**

**14:34-14:56**

**Alexander Nitz (MPI for Gravitational Physics – AEI Hannover)**

We report the latest results in searches for gravitational waves from compact binary mergers from the complete set of public Advanced LIGO and Virgo data spanning 2015-2017. Our search employs new multi-detector analysis methods we developed to look for a wide range of binary neutron star, neutron star – black hole, and binary black hole mergers. The analysis finds candidates missed by initial LIGO searches. We’ll discuss the population of sub-threshold compact binary coalescences and compare our results to those reported earlier this year by the IAS.

**Search for eccentric binary black hole mergers during the first and second observing run of LIGO and Virgo**

**14:56-15:18**

**Shubhanshu Tiwari (Physics , University of Zurich)**

In this talk we will present the results of the Advanced LIGO and Advanced Virgo search for binary black hole mergers that inspiral in eccentric orbits during the first and second observing runs (O1 and O2). The search uses minimal assumptions on the morphology of the transient gravitational waveform and was employed for first gravitational waves transient catalogue GWTC-1. We show that the search is sensitive to binary mergers with a detection range that is weakly dependent on eccentricity for all bound systems. Our search did not identify any new binary merger candidates. We interpret these results in light of eccentric binary formation models.

**Identification and downranking of non-stationarity in LIGO data**

**15:18-15:40**

**Simone Mozzon (Institute of Cosmology and Gravitation, University of Portsmouth)**

Data from the Laser Interferometer Gravitational-wave Observatory (LIGO) can be highly non-stationary, which means the broadband detector noise can change on the order of tens of seconds. Transient searches of gravitational waves, such as those from colliding black holes, estimate this noise in order to construct a signal-to-noise ratio timeseries of the data,

and thereby identify candidate gravitational-wave events. During times of non-stationarity we see a higher rate of false events being reported. To accurately separate signal from noise, it is imperative to take in to account the changing detector state into gravitational-wave searches. This talk will present a new approach to identify non-stationarity in LIGO data from the

second observing run. We will also discuss a method for downranking candidate gravitational-wave events found by the PyCBC pipeline during times of non-stationarity, thereby increasing our confidence of any putative signals found.

#### L2 - Monday 16:10-17:50 (Jess McIver)

**Directional limits on persistent gravitational waves using data from Advanced LIGO’s first two observing runs**

**16:10-16:35**

**Patrick Meyers (Physics, University of Melbourne)**

One of the next frontiers of gravitational-wave (GW) astrophysics is a measurement of persistent gravitational wave signals. Persistent GWs can come from quasi-periodic sources like pulsars and from a stochastic GW background. In this talk, I will discuss methods and results from the recent searches for an anisotropic stochastic gravitational-wave background that used data from Advanced LIGO’s first two observation runs. We set limits on broadband GW energy density and flux from both point and extended sources on the sky. We also set limits on narrowband GWs from three astrophysically interesting directions—Scorpius X-1, the Galactic center, and SN 1987a. I will also briefly discuss prospects for detection in coming observing runs.

** LIGO-Virgo Searches for Gravitational Waves from Scorpius X-1**

**16:35-17:00**

**John Whelan (School of Mathematical Sciences, Rochester Institute of Techbology)**

The low-mass X-ray binary Scorpius X-1 is a promising source of continuous gravitational waves. Its high X-ray luminosity indicates a large rate of accretion, which may power GW emission. A variety of methods have been developed and applied to search for a GW signal, which presents challenges because of the unknown signal frequency and residual uncertainties in orbital parameters. I will summarize the search results from Advanced LIGO and Advanced Virgo’s first two Observing Runs (O1 and O2), and describe prospects for searches in the O3 run.

**Search for sub-threshold lensed images of gravitational wave observations**

**17:00-17:25**

**Connor McIsaac (Institute of Cosmology and Gravitation, University of Portsmouth)**

Gravitational lensing occurs when a large distribution of mass exists between a source and observer, acting as a lens and magnifying the amplitude of a signal emitted from the source. Gravitational waves can be lensed in this manner, similar to electromagnetic signals. In the case of strong lensing this can produce multiple images of the same gravitational-wave signal, each arriving at different times and with different magnification factors. The possibility that observed gravitational wave events are images of a single event has previously been explored in the literature. However, the possibility remains that additional images of these events remain in the background, unrecovered by previous searches. We carry out a targeted search specifically looking for sub-threshold lensed images of existing observations, using a reduced set of waveform filters. We present the results of this search and discuss the astrophysical implications of our new results.

**Probing the angular distribution of binary black-hole mergers with ground based gravitational-wave detectors.**

**17:25-17:50**

**Sharan Banagiri (School of Physics and Astronomy, University of Minnesota)**

The Advanced LIGO and Advanced Virgo detectors have detected ten binary-black hole (BBH) mergers in the first two observing runs, with many new candidate events in the ongoing third observing run. In addition to these events there exists a background of a much larger number of mergers which are not individually detectable. This background has generally been a target for cross-correlation based stochastic searches by LIGO and Virgo. The statistics of this ensemble of mergers encode much information of astrophysical and cosmological interest. A new method developed by Smith and Thrane using BBH parameter estimation promises to be much more sensitive to this background and its properties than cross-correlation methods. In this talk I will describe how this technique can be used to study the angular distribution of the binary black hole merger distribution in the sky. I will also describe a statistical formalism to combine the information from the binary black hole spatial distribution with electromagnetic tracers like galaxy counts, to study the structure of the universe at the scales simultaneously accessible to both probes.