Soft gamma repeaters and anomalous x-ray pulsars are thought to be magnetars, neutron stars with strong magnetic fields of order ∼1013 -1015gauss. These objects emit intermittent bursts of hard x-rays and soft gamma rays. Quasiperiodic oscillations in the x-ray tails of giant flares imply the existence of neutron star oscillation modes which could emit gravitational waves powered by the magnetars magnetic energy reservoir. We describe a method to search for transient gravitational-wave signals associated with magnetar bursts with durations of 10 s to 1000 s of seconds. The sensitivity of this method is estimated by adding simulated waveforms to data from the sixth science run of Laser Interferometer Gravitational-wave Observatory (LIGO). We find a search sensitivity in terms of the root sum square strain amplitude of hrss = 1.3 × 10-21 Hz-1/2 for a half sine-Gaussian waveform with a central frequency f0 = 150 Hz and a characteristic time τ = 400 s. This corresponds to a gravitational wave energy of EGW = 4.3 × 1046 erg, the same order of magnitude as the 2004 giant flare which had an estimated electromagnetic energy of EEM = ∼1.7 × 1046(d/8.7 kpc)2 erg, where d is the distance to SGR 1806-20. We present an extrapolation of these results to Advanced LIGO, estimating a sensitivity to a gravitational wave energy of EGW = 3.2 × 1043 erg for a magnetar at a distance of 1.6 kpc. These results suggest this search method can probe significantly below the energy budgets for magnetar burst emission mechanisms such as crust cracking and hydrodynamic deformation.
Bibliographical noteFunding Information:
LIGO is funded by the U.S. National Science Foundation. This work was supported by NSF PHY-1607336. JC is supported through NSF PHY 1505824 and PHY 1505524. MC is supported by National Science Foundation Graduate Research Fellowship Program, under NSF grant number DGE 1144152. ET is supported through ARC FT150100281 and CE170100004.
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- data analysis
- gravitational waves