Physical parameters of GRB 970508 and GRB 971214 from their afterglow synchrotron emission

We have calculated synchrotron spectra of relativistic blast waves, and find predicted characteristic frequencies that are more than an order of magnitude different from previous calculations. For the case of an adiabatically expanding blast wave, which is applicable to observed gamma-ray burst (GRB) afterglows at late times, we give expressions to infer the physical properties of the afterglow from the measured spectral features. We show that enough data exist for GRB970508 to compute unambiguously the ambient density, n=0.03/cm**3, and the blast wave energy per unit solid angle, E=3E52 erg/4pi sr. We also compute the energy density in electrons and magnetic field. We find that they are 12% and 9%, respectively, of the nucleon energy density and thus confirm for the first time that both are close to but below equipartition. For GRB971214, we discuss the break found in its spectrum by Ramaprakash et al. (1998). It can be interpreted either as the peak frequency or as the cooling frequency; both interpretations have some problems, but on balance the break is more likely to be the cooling frequency. Even when we assume this, our ignorance of the self-absorption frequency and presence or absence of beaming make it impossible to constrain the physical parameters of GRB971214 very well.Comment: very strongly revised analysis of GRB971214 and discussion, submitted to ApJ, 11 pages LaTeX, 4 figures, uses emulateapj.sty (included

Tau physics with polarized beams

We present the first results on tau physics using polarized beams. These include measurements of the \tau Michel parameters \xi and \xi\delta and the \tau neutrino helicity h_\nu. The measurements were performed using the SLD detector at the Stanford Linear Collider (SLC). (Invited talk at the 1995 International Europhysics Conference on High Energy Physics, Brussels, Belgium, July 27 - August 2, 1995.