GCN Circular 9502
Ersin Gogus (Sabanci Univ.), Chryssa Kouveliotou (NASA/NSSTC), Peter M. Woods (Dynetics) report on behalf of a larger collaboration: Following the Fermi GBM/Konus/Swift detection of bursts from the new Soft Gamma Repeater SGR 0418+5729 (van der Horst et al. 2009, GCN #9499) we triggered our SGR ToO Program with RXTE. A 6.8 ks RXTE observation started on 2009 June 10, 03:42:56 UT. We detect a strong, coherent pulsations from the new SGR (2-10 keV) in the PCA GoodXenon mode data at 0.110152(2) Hz, corresponding to a spin period of 9.0783(1) sec. The pulse morphology is complex showing two asymmetric maxima per cycle. We note that there is no previously known X-ray source in the RXTE field of view with such periodicity. The detected coherent pulsations likely indicate the spin period of the newly discovered, burst-active SGR. We thank the project scientist Jean Swank, and the RXTE planner, Divya Pereira for the prompt scheduling of the RXTE observations.