TITLE: GCN CIRCULAR NUMBER: 8118 SUBJECT: Discovery of the Spin Period of the New Soft Gamma Repeater SGR 0501+4516 DATE: 08/08/22 21:39:33 GMT FROM: Chryssa Kouveliotou at MSFC E. Gogus (Sabanci University), P. Woods (Dynetics), and C. Kouveliotou (NASA/MSFC), report on behalf of a larger collaboration: We triggered our SGR ToO Program with RXTE following the Swift detection of a burst from the new Soft Gamma Repeater SGR 0501+4516 (Barthelmy et al. 2008, GCN # 8113). A 600 s RXTE observation started on 2008 August 22, 16:39:09 UT. During this pointing we detected one short SGR burst-like event in the PCA data (2-60 keV), confirming that the new source was in the field of view. We searched for a spin period for the new SGR in the 2.5-13.5 keV band PCA event mode data and detected a coherent signal (barycenter corrected) at 0.17334 Hz, corresponding to a spin period of 5.769 +- 0.004 s. A longer RXTE observation of SGR 0501+4516 is currently underway. We thank the RXTE planner, Divya Pereira, for prompt scheduling.