General Relativistic Collapse of Neutron Stars to Strange Stars: A Mechanism for Gamma Ray Bursts

It is known that Neutron Stars may be converted into more compact Strange Stars (SS) on capture/formation of a ``seed'' of strange matter. It is also known that the binding energy of the nascent hot SS is likely to be radiated as $\nu -\bar\nu$s so that an electromagnetic pair fireball (FB) may be created by neutrino annihilation. And already this process has been considered as a probable source of Gamma Ray Bursts (GRB) by several authors, the most notable of which is due to Cheng & Dai (PRL, 77, 1210, 1996). They mentioned that this process may generate a FB luminosity (outside the neutrinosphere) of 10**(49) erg. But we point out here that a SS is a relativistic object with surface gravitation z=0.5. Accordingly, we present here a Relativistic Model of this process, and show that, for a massive SS with M=2 solar mass, one may explain a GRB energy of ~ 10**(53) erg., which is 4 orders higher than previous non-relativistic estimate. Further since the baryonic mass of the thin crust of a strange star is negligible, this FB will generate an extremely relativistic blast wave. Thus this process may be one of the viable routes for the genesis of hitherto unexplained cosmic Gamma Ray Bursts. While some of the GRBs might be beamed, many of them do not show any long term spectral break in their afterglows and are likely to be quasi-spherical. A particular example is GRB 971214 for which estimated GRB energy is 3. 10**(53) erg. Our model may be useful for understanding the genesis of such powerful and unexplained bursts.