Search for Gravitational Wave Bursts from Soft Gamma Repeaters

TL;DR

This paper reports on a LIGO search for gravitational waves from soft gamma repeaters, setting upper limits on GW emission, introducing a stacking method to improve sensitivity, and discussing detector calibration techniques.

Contribution

It is the first GW search sensitive to neutron star f-modes from SGRs, with new stacking methods and calibration procedures.

Findings

No GW signals detected from SGR bursts.

Upper limits on GW energy emission range from 3x10^45 to 9x10^52 erg.

Stacking can improve GW sensitivity proportional to the square root of the number of bursts.

Abstract

We present the results of a LIGO search for short-duration gravitational waves (GW) associated with soft gamma repeater (SGR) bursts. This is the first GW search sensitive to neutron star f-modes, usually considered the most efficient GW emitting modes. We find no evidence of GWs associated with any SGR burst in a sample consisting of the 2004 December 27 giant flare from SGR 1806-20 and 190 lesser events from SGR 1806-20 and SGR 1900+14 which occurred during the first year of LIGO's fifth science run. GW strain upper limits and model-dependent GW emission energy upper limits are estimated for individual bursts using a variety of simulated waveforms. We find upper limit estimates on the model-dependent isotropic GW emission energies (at a nominal distance of 10 kpc) between 3x10^45 and 9x10^52 erg depending on waveform type, detector antenna factors and noise characteristics at the time of the burst. These upper limits are within the theoretically predicted range of some SGR models. We also propose a new method which extends the initial SGR burst search, exploring the possibility that SGR sources emit similarly in GWs from burst to burst by "stacking" potential GW signals. We show 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 GWs from the 2006 March 29 storm from SGR 1900+14 are presented for two stacking scenarios: a "fluence-weighted" scenario and a "flat" (unweighted) scenario. Finally, we present a method for calibrating gravitational wave detectors via photon actuators. The photon calibrators' nominal 2-sigma confidence error bars are currently estimated to be ~3%. They have provided a valuable check on the official calibration, uncovering problems that may otherwise have gone unnoticed.