Stacking Gravitational Wave Signals from Soft Gamma Repeater Bursts

TL;DR

This paper introduces a stacking method to enhance gravitational wave detection from multiple soft gamma repeater bursts, improving sensitivity by combining signals assuming small timing differences.

Contribution

It presents a novel stacking strategy for GW signals from SGR bursts, increasing detection sensitivity by a factor proportional to the square root of the number of stacked events.

Findings

Sensitivity improves as N^{1/2} with number of bursts stacked

Monte Carlo simulations confirm the method's effectiveness

Estimated sensitivities for specific SGR events are provided

Abstract

Soft gamma repeaters (SGRs) have unique properties that make them intriguing targets for gravitational wave (GW) searches. They are nearby, their burst emission mechanism may involve neutron star crust fractures and excitation of quasi-normal modes, and they burst repeatedly and sometimes spectacularly. A recent LIGO search for transient GW from these sources placed upper limits on a set of almost 200 individual SGR bursts. These limits were within the theoretically predicted range of some models. We present a new search strategy which builds upon the method used there by "stacking" potential GW signals from multiple SGR bursts. We assume that variation in the time difference between burst electromagnetic emission and burst GW emission is small relative to the GW signal duration, and we time-align GW excess power time-frequency tilings containing individual burst triggers to their corresponding electromagnetic emissions. Using Monte Carlo simulations, we confirm that gains in GW energy sensitivity of N^{1/2} are possible, where N is the number of stacked SGR bursts. Estimated sensitivities for a mock search for gravitational waves from the 2006 March 29 storm from SGR 1900+14 are also presented, for two GW emission models, "fluence-weighted" and "flat" (unweighted).