E. Smith (GSFC/L3), J. Swank(GSFC), C. Markwardt(GSFC/UMD), Y.
Rephaeli(UCSD/TAU), D. Gruber(Eureka), M. Persic(Obs.Ast.Trieste),
and R. Rothschild (UCSD)
The Proportional Counter Array (PCA) on the Rossi X-Ray Timing
Explorer (RXTE) detected the precursor and the main flares of SGR
1806-20 on 2004-12-27 (Borkowski et al., GCN #2920). The times of the
flares were 21:28:03.5 and 21:30:26.6 UTC, respectively, which agree
with the arrival times reported by the Swift-BAT Team (Palmer et al.,
GCN #2925). Two of the All Sky Monitor detectors were turned off by
the high rates. HEXTE detected only the initial 1 s spike of the main
The SGR was 31 degrees off the boresight of the 1.1 degree shielded
copper collimators of the PCA and the lead collimators of HEXTE. As
seen by the PCA, the precursor lasted approximately 1.2 s. After an
initial pulse of the main flare, the flux was pulsed at a period of
7.579 +/- 0.002 s (non-barycentered). The PCA observed 3 peaks in the
pulses, as did the BAT, during an interval of approximately 360 s.
Three PCA detectors were on and recorded peak count rates of 17-25
kct/s (0.125 s bins). However, the detectors were probably saturated
during the initial peak of the main flare.