The first observation of optical pulsations from a soft gamma repeater:   SGR 0501+4516
  We present high-speed optical photometry of the soft gamma repeater SGR 0501+4516, obtained with ULTRACAM on two consecutive nights approximately 4 months after the source was discovered via its gamma-ray bursts. We detect SGR 0501+4516 at a magnitude of i' = 24.4+/-0.1. We present the first measurement of optical pulsations from an SGR, deriving a period of 5.7622+/-0.0003 s, in excellent agreement with the X-ray spin period of the neutron star. We compare the morphologies of the optical pulse profile with the X-ray and infrared pulse profiles; we find that the optical, infrared and harder X-rays share similar double-peaked morphologies, but the softer X-rays exhibit only a single-peaked morphology, indicative of a different origin. The optical pulsations appear to be in phase with the X-ray pulsations and exhibit a root-mean-square pulsed fraction of 52+/-7%, approximately a factor of two greater than in the X-rays. Our results find a natural explanation within the context of the magnetar model for SGRs. 
V. S. Dhillon, T. R. Marsh, S. P. Littlefair, C. M. Copperwheat, R. D.   G. Hickman, P. Kerry, A. J. Levan, N. Rea, C. D. J....
astro-ph.SR