GRB Explosion in a Galactic Supershell : GRB 971214

Among a number of gamma-ray bursts whose host galaxies are known, GRB971214 stands out for its high redshift(z=3.25) and the Lya emission line having a P-Cygni type profile. which is interpreted to be a direct consequence of the expanding supershell. From a simple Voigt-fitting analysis, we estimate the expansion velocity of the supershell and the neutral column density. The theory on the evolution of supernova remnants is used to propose that the supershell is at the adiabatic phase, with its radius $R=10E^{1/2}_{53}$pc, its age t=4.7\times 10^3 E^{1/2}_{53} yrs, and the density of the ambient medium $n_1=5.4E^{-1/2}_{53} cm^{-3}$, where $E_{53}=E/10^{53}$ ergs. I estimate the kinetic energy of the supershell to be $E_k=7.3\times 10^{52} E_{53}$ ergs. I provide an observational evidence that the gamma-ray burst can occur in a giant H II region whose environment is similar to that in star-forming galaxies.