GRB Spectral Hardness and Afterglow Properties
  A possible relationship between the presence of a radio afterglow and gamma-ray burst spectral hardness is discussed. The correlation is marginally significant; the spectral hardness of the bursts with radio afterglows apparently results from a combination of the break energy Ebreak and the high-energy spectral index beta. If valid, this relationship would indicate that the afterglow does carry information pertaining to the GRB central engine. 
Jon Hakkila (1), Timothy Giblin (2), Robert D. Preece (2) ((1)   Minnesota State University, Mankato, (2) University of Alab...