[AAVSO-HEN] RXTE Discovery of Pulsations from SGR 0418+5729

[grb at aavso.org]

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TITLE:   GCN CIRCULAR
NUMBER:  9502
SUBJECT: RXTE Discovery of Pulsations from SGR 0418+5729
DATE:    09/06/10 15:43:29 GMT
FROM:    Ersin Gogus at Sabanci U/Turkey  <ersing at sabanciuniv.edu>

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.