High-speed, multicolour optical photometry of the anomalous x-ray pulsar 4u 0142+61 with ultracam
Dhillon, V. S. Marsh, T. R. Hulleman, F. van Kerkwijk, M. H. Shearer, A. Littlefair, S. P. Gavriil, F. P. Kaspi, V. M.
Dhillon, V. S.
Marsh, T. R.
Hulleman, F.
van Kerkwijk, M. H.
Shearer, A.
Littlefair, S. P.
Gavriil, F. P.
Kaspi, V. M.
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Publication Date
2005-10-21
Type
Article
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Citation
Dhillon, V. S. Marsh, T. R.; Hulleman, F.; van Kerkwijk, M. H.; Shearer, A.; Littlefair, S. P.; Gavriil, F. P.; Kaspi, V. M. (2005). High-speed, multicolour optical photometry of the anomalous x-ray pulsar 4u 0142+61 with ultracam. Monthly Notices of the Royal Astronomical Society 363 (2), 609-614
Abstract
We present high-speed, multicolour optical photometry of the anomalous X-ray pulsar 4U 0142+61, obtained with ULTRACAM on the 4.2-m William Herschel Telescope. We detect 4U 0142+61 at magnitudes of i' = 23.7 +/- 0.1, g' = 27.2 +/- 0.2 and u' > 25.8, consistent with the magnitudes found recently by Hulleman et al. and hence confirming their discovery of both a spectral break in the optical and a lack of long-term optical variability. We also confirm the earlier discovery of Kern & Martin that 4U 0142+61 shows optical pulsations with an identical period (similar to 8.7 s) to the X-ray pulsations. The rms pulsed fraction in our data is 29 +/- 8 per cent, 5-7 times greater than the 0.2-8 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 former lagging the latter by only 0.04 +/- 0.02 cycles. In conjunction with the constraints imposed by X-ray observations, the results presented here favour a magnetar interpretation for the anomalous X-ray pulsars.
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Publisher
Oxford University Press (OUP)
Publisher DOI
10.1111/j.1365-2966.2005.09465.x
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Attribution-NonCommercial-NoDerivs 3.0 Ireland