paper

Optical pulsations from the anomalous X-ray pulsar 1E 1048.1-5937

arXiv:0901.1559 · doi:10.1111/j.1745-3933.2009.00623.x

Abstract

We present high-speed optical photometry of the anomalous X-ray pulsar 1E 1048.1-5937 obtained with ULTRACAM on the 8.2-m Very Large Telescope in June 2007. We detect 1E 1048.1-5937 at a magnitude of i'=25.3+/-0.2, consistent with the values found by Wang et al. (2008) and hence confirming their conclusion that the source was approximately 1 mag brighter than in 2003-2006 due to an on-going X-ray flare that started in March 2007. The increased source brightness enabled us to detect optical pulsations with an identical period (6.458 s) to the X-ray pulsations. The rms pulsed fraction in our data is 21+/-7%, approximately the same as the 2-10 keV X-ray rms pulsed fraction. The optical and X-ray pulse profiles show similar morphologies and appear to be approximately in phase with each other, the latter lagging the former by only 0.06+/-0.02 cycles. The optical pulsations in 1E 1048.1-5937 are very similar in nature to those observed in 4U 0142+61. The implications of our observations for models of anomalous X-ray pulsars are discussed.

5 pages, 3 figures, accepted for publication in MNRAS Letters

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