Gamma-Ray Bursts at Low Redshift

Abstract

Long duration gamma-ray bursts (GRB) are at cosmological distance, they appear to be located near star forming regions, and are likely associated with some type of supernovae. They are also likely to be strongly beamed, which lowers their energetics by several orders of magnitude, and increases their rate by the same factor. Therefore, it is likely that one out of 100 - 1000 core collapse supernovae generates ultra-relativistic jets, which beam gamma-rays and all other early emission into two narrow cones. After a year, or so, the jets are decelerated and become non-relativistic, and their emission becomes more or less isotropic. At least two GRB: 970508 (z = 0.835) and 980703 (z = 0.966) show strong radio emission from late, and therefore non-relativistic afterglows. Such events should be readily detectable at low redshift, say z = 0.03. A search for strong radio emitters among recent nearby supernovae should be done $ \sim 1 $ year after the explosion. If some of these explosions generated GRB and their gamma-ray beam missed us, the bipolar structure of the radio remnant should be resolvable with VLBA.