Searches for Prompt Low-Frequency Radio Counterparts to Gravitational Wave Event S250206dm with the OVRO-LWA Time Machine

TL;DR

This paper reports a sensitive search for prompt low-frequency radio emission from a neutron star merger using the OVRO-LWA, setting upper limits that challenge some theoretical models of coherent emission.

Contribution

First large-area, millisecond-timescale search for prompt low-frequency radio counterparts to GW mergers with OVRO-LWA, establishing a framework for future population constraints.

Findings

No radio counterpart detected above 150 Jy ms threshold.

Placed a 95% confidence upper limit on source luminosity at 4 x 10^41 erg s^-1.

Constraints challenge certain models of coherent emission from neutron star mergers.

Abstract

We report on a search for prompt, low-frequency radio emission from the gravitational-wave (GW) merger S250206dm using the Owens Valley Radio Observatory Long Wavelength Array (OVRO-LWA). Early alerts favored a neutron-star-containing merger, making this a compelling target. Motivated by theoretical predictions of coherent radio bursts from mergers involving a neutron star, we utilized the OVRO-LWA Time Machine system to analyze voltage data recorded around the time of the event. The Time Machine is a two-stage voltage buffer and processing pipeline that continuously buffers raw data from all antennas across the array's nearly full-hemisphere instantaneous field of view, enabling retrospective beamforming, dedispersion, and fast-transient candidate identification. For this event, we analyzed a 30-minute interval beginning 3.5 minutes after the merger, which included two minutes of pre-alert data recovered by the ring buffer. We searched the 50% localization probability region with millisecond time resolution in the 69-86 MHz frequency band. No radio counterpart was detected above a 7-sigma fluence detection threshold of ~150 Jy ms. Using Bayesian analysis, we place a 95% confidence upper limit on the source luminosity of L95 = 4 x 10^41 erg s^-1. These constraints start to probe the bright end of the coherent-emission parameter space predicted by jet-ISM shock processes, magnetar and blitzar-like mechanisms, and recent simulation-based scenarios for neutron-star-containing mergers. This study presents the first sensitive, large-area, millisecond-timescale search for prompt low-frequency radio emission from a GW merger with the OVRO-LWA, establishing a framework in which about ten additional events will yield stringent population-level constraints.