GCN Circular 2938

P. B. Cameron (Caltech) and S. R. Kulkarni (Caltech) report:

"We have carried out a more thorough calibration of the three VLA
epochs of the fading radio source toward SGR 1806-20 (GCN#s 2928,
2929, 2930, 2933, 2934, 2935). Combining this with the data from a
fourth epoch observation made with the Australia Compact Array (GCN#
2937) we do a joint fit of the form: F_nu \propto t^\alpha nu^\beta.

The best fit values are alpha= -1.62+/-0.06 and beta=-0.75+/-0.03.

There is evidence of deviations from this simple power-law behavior.
Fitting the decay rate alpha at each frequency we find a systematic
steepening. The value of alpha is -1.0 at 1.4 GHz, -1.5 at 4.9 GHz,
and -2.2 at 8.5 GHz. This behavior is reminiscent of the broadband
afterglow of GRB 991216 (Frail et al. ApJ, 538, 129). A plot of the
light curves is at: http://www.aoc.nrao.edu/~dfrail/sgr1806lc.eps.


The National Radio Astronomy Observatory is operated by Associated
Universities, Inc., under cooperative agreement with the National
Science Foundation. The Australia Telescope is funded by the
Commonwealth of Australia for operation as a National Facility managed
by CSIRO."