Formation of a Gravitationally Bound Object after Binary Neutron Star Merging and GRB 970228

Abstract

The stages that follow the merging of two neutron stars are discussed. It is shown that if a rapidly rotating gravitationally bound object is formed after the merging (a spinar or a massive neutron star), then the characteristic time of its evolution is determined by a fundamental value t_{spin} = 3 k (m_p e^2 \hbar^{1/2}) / (m_e^3 c^{5/2} G^{1/2}) \approx 7e+5 s k, where the dimensionless value k depends on the exact equation of state of nuclear matter. The hypothesis is discussed as to whether the residual optical emission of the gamma-ray burst GRB 970228 is pulsar-like and its evolution driven by magnetodipole energy losses. It is shown that binary neutron star mergings can be accompanied by two gravitational wave burst separated either by the time interval t_{spin} or neutron star cooling time (~10 s), depending on the masses of neutron stars.