Interaction of a Cosmological Gamma-ray Burst with a Dense Molecular Cloud and the Formation of Jets.

The interaction of a powerful cosmological gamma-ray burst (GRB) with a dense molecular cloud is modeled. Two-dimensional gas-dynamical flows were computed for various configurations of the cloud. In the spherically symmetrical case, the gas velocity does not exceed ∼ 2 × 10³&radicE/1.6 × 1053;km/s. If the GRB precursor has an anisotropic wind, a conical cavity can form in the nearby region of themolecular cloud. The propagation of the gamma-ray pulse in this cavity leads to the formation of a rapidly moving hot clump of matter, with the gas velocity reaching 1.8 ×104 km/s for gammaray energy of E = 1.6×1053 erg. In all the computations, the velocity of the moving material ismuch lower than the velocity of light, the volume of gas affected by the motion is small, and the influence of the gas motions on the light curve of the optical afterglow is insignificant. [ABSTRACT FROM AUTHOR]