A comprehensive study of pulse profile evolution in SGR 1806-20 and SGR 1900+14 with the Rossi X-Ray Timing Explorer Proportional Counter Array

Soft gamma repeaters undergo pulse pro le changes in connection with their burst activity. Here we present a comprehensive pulse profile history of SGR 1806-20 and SGR 1900+14 in three energy bands using Rossi X-Ray Timing Explorer/Proportional Counter Array observations performed between 1996 and 2001. Using the Fourier harmonic powers of pulse profiles, we quantify the pulse shape evolution. Moreover, we determined the firms pulsed count rates (PCRs) of each pro le. We show that the pulse profiles of SGR 1806-20 remain single pulsed, showing only modest changes for most of our observing span, while those of SGR 1900+14 change remarkably in all energy bands. Highly significant pulsations from SGR 1900+14 following the 1998 August 27 and 2001 April 18 bursts enabled us to study not only the decay of PCRs in different energy bands but also their correlations with each other.