Gravitational-Wave Bursts from Soft Gamma-Ray Repeaters: Can They Be Detected?

Abstract

We suggest a scenario for simultaneous emission of gravitational-wave (GW) and $\ensuremath{\gamma}$-ray bursts from soft gamma-ray repeaters. We argue that both of the radiations can be generated by super-Eddington accreting neutron stars in x-ray binaries. We estimate the rise time scale, $\ensuremath{\Delta}{t}_{c}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}0.21\mathrm{ms}$, the accretion rate needed to trigger the $\ensuremath{\gamma}$-ray emission, ${\stackrel{\ifmmode \dot{}\else \.{}\fi{}}{M}}_{\ensuremath{\lambda}}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}4.5\ifmmode\times\else\texttimes\fi{}1{0}^{28}\mathrm{g}/\mathrm{s}$, its associated effective temperature, ${T}_{\mathrm{eff}}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}740\mathrm{keV}$, and the time scale for repeating a burst of $\ensuremath{\gamma}$ rays, $\ensuremath{\Delta}{\ensuremath{\tau}}_{R}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}11.3\mathrm{yr}$. We find the associated GW amplitude and frequency to be ${h}_{c}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}2.7\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}23}/(\mathrm{Hz}{)}^{1/2}$ and ${f}_{\mathrm{GW}}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}966\mathrm{Hz}$, for a source distance $\ensuremath{\sim}55\mathrm{kpc}$. Detectability of the pulses by the forthcoming GW antennas is discussed and found likely.