SIMBAD references

We model the intermediate-time evolution of a ``jetted'' gamma-ray burst (GRB) as two blobs of matter colliding with the interstellar medium. We follow the hydrodynamic evolution of this system numerically and calculate the bremsstrahlung and synchrotron images of the remnant. We find that for a burst energy of 10⁵¹ ergs the remnant becomes spherical after ∼5000 yr, when it has collected ∼50 M_☉ of interstellar mass. This result is independent of the exact details of the GRB, such as the opening angle. After this time a gamma-ray burst remnant has an expanding sphere morphology. The similarity to a supernova remnant makes it difficult to distinguish between the two at this stage. The expected number of nonspherical gamma-ray burst remnants is ∼0.05 per galaxy for a beaming factor of 0.01 and a burst energy of 10⁵¹ ergs. Our results suggest that the double-shell object DEM L316 is not a GRB remnant.