LOFAR observations of gravitational wave merger events: O3 results and O4 strategy

Abstract

The electromagnetic counterparts to gravitational wave (GW) merger events hold immense scientific value, but are difficult to detect due to the typically large localisation errors associated with GW events. The Low-Frequency Array (LOFAR) is an attractive GW follow-up instrument owing to its high sensitivity, large instantaneous field of view, and ability to automatically trigger on events to probe potential prompt emission within minutes. Here, we report on 144-MHz LOFAR radio observations of three GW merger events containing at least one neutron star that were detected during the third GW observing run. Specifically, we probe 9 and 16 per cent of the location probability density maps of S190426c and S200213t, respectively, and place limits at the location of an interesting optical transient (PS19hgw/AT2019wxt) found within the localisation map of S191213g. While these GW events are not particularly significant, we use multi-epoch LOFAR data to devise a sensitive wide-field GW follow-up strategy to be used in future GW observing runs. In particular, we improve on our previously published strategy by implementing direction dependent calibration and mosaicing, resulting in nearly an order of magnitude increase in sensitivity and more uniform coverage. We achieve a uniform $5\sigma$ sensitivity of $870$ $\mu$Jy across a single instantaneous LOFAR pointing's 21 deg${}^2$ core, and a median sensitivity of 1.1 mJy when including the full 89 deg${}^2$ hexagonal beam pattern. We also place the deepest transient surface density limits yet on of order month timescales for surveys between 60--340 MHz (0.017 deg${}^{-2}$ above $2.0$ mJy and 0.073 deg${}^{-2}$ above $1.5$ mJy).

Replaced with accepted version for publication in MNRAS

References in corpus (19)

• GW170817: Observation of Gravitational Waves from a Binary Neutron Star Inspiral
• Multi-messenger Observations of a Binary Neutron Star Merger
• An Ordinary Short Gamma-Ray Burst with Extraordinary Implications: Fermi-GBM Detection of GRB 170817A
• Swope Supernova Survey 2017a (SSS17a), the Optical Counterpart to a Gravitational Wave Source
• The LOFAR Two-metre Sky Survey - I. Survey Description and Preliminary Data Release
• A Radio Counterpart to a Neutron Star Merger
• The LOFAR Two-metre Sky Survey -- V. Second data release
• The LOFAR Two Meter Sky Survey: Deep Fields, I -- Direction-dependent calibration and imaging
• GWTC-2.1: Deep Extended Catalog of Compact Binary Coalescences Observed by LIGO and Virgo During the First Half of the Third Observing Run
• Mass ejection from neutron star mergers: different components and expected radio signals
• A search for long-timescale, low-frequency radio transients
• GW170817 4.5 years after merger: Dynamical ejecta afterglow constraints
• Constraining a neutron star merger origin for localized fast radio bursts
• LOFAR early-time search for coherent radio emission from GRB 180706A
• A Matched Filter Technique For Slow Radio Transient Detection And First Demonstration With The Murchison Widefield Array
• LOFAR Observations of Swift J1644+57 and Implications for Short-Duration Transients
• LOFAR 144-MHz follow-up observations of GW170817
• Searching for low radio-frequency gravitational wave counterparts in wide-field LOFAR data
• Limits on long-time-scale radio transients at 150 MHz using the TGSS ADR1 and LoTSS DR2 catalogues

Cited by in corpus (2)

• GWTC-3: Compact Binary Coalescences Observed by LIGO and Virgo During the Second Part of the Third Observing Run
• Early Warning From Eccentric Compact Binaries: Template Initialization And Sub-dominant Mode Effects