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RXTE Discovery of Pulsations from SGR 0418+5729

ATel #2076; Ersin Gogus (Sabanci Univ.), Peter Woods (Dynetics) & Chryssa Kouveliotou (MSFC/NSSTC) report on behalf of a larger collaboration
on 10 Jun 2009; 16:29 UT
Credential Certification: Peter Woods (Peter.Woods@dynetics.com)

Subjects: X-ray, Neutron Star, Soft Gamma-ray Repeater, Transient, Pulsar

Referred to by ATel #: 2096, 2121, 2127, 2151, 2244

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 strong, coherent pulsations from the new SGR in the 2-10 keV PCA 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.