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

By V. S. Dhillon, T. R. Marsh, S. P. Littlefair, C. M. Copperwheat, P. Kerry, R. Dib, M. Durant, Victoria Michelle Kaspi, R. P. Mignani and Andrew Shearer


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 2007 June. We detect 1E 1048.1-5937 at a magnitude of i' = 25.3 +/- 0.2, consistent with the values found by Wang et al. and hence confirming their conclusion that the source was approximately 1 mag brighter than in 2003-06 due to an on-going X-ray flare that started in 2007 March. The increased source brightness enabled us to detect optical pulsations with an identical period (6.458 s) to the X-ray pulsations. The root-mean-square (rms) pulsed fraction in our data is 21 +/- 7 per cent, 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

Topics: QB
Publisher: Wiley
Year: 2009
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