Conversion of Neutron Stars to Strange Stars as a Possible Origin of γ-Ray Bursts

We propose that some neutron stars in low-mass x-ray binaries can accrete sufficient mass to undergo a phase transition to become strange stars. The energy released per conversion event satisfies the requirements of cosmological $\gamma$-ray bursts, and the Lorentz factor of the resultant expanding fireball may exceed $5\times {10}^3$ because the strange star has very low baryon contamination. The model burst rate is consistent with observations.