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Astron. Astrophys. 336, 545-552 (1998)

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Detection of pulsed X-ray emission from the binary millisecond pulsar PSR J0218+4232

L. Kuiper 1, W. Hermsen 1, F. Verbunt 2 and T. Belloni 3

1 SRON-Utrecht, Sorbonnelaan 2, 3584 CA Utrecht, The Netherlands
2 Astronomical Institute, Utrecht University, P.O. Box 80000, 3508 TA Utrecht, The Netherlands
3 Astronomical Institute Anton Pannekoek and Center for High-Energy Astrophysics, Kruislaan 403, 1098 SJ Amsterdam, The Netherlands

Received 23 January 1998 / Accepted 18 April 1998


We report the detection of pulsed X-ray emission from the binary millisecond pulsar PSR J0218+4232 in a 100 ks ROSAT HRI observation. The lightcurve deviates from a flat distribution at a [FORMULA] level, showing a sharp main pulse with a duty cycle of [FORMULA], compatible with smearing due to the scatter in the ROSAT clock calibration. The intrinsic width can be smaller than [FORMULA]. There is an indication for a second peak at a phase separation of [FORMULA]. The pulsed fraction is [FORMULA]. No indication for a modulation at the orbital period of the binary system is found. This is the fourth millisecond pulsar showing modulation in X-rays at the radio-pulsar period. The sharp pulses, very similar to those of PSR B1821-24 and the Crab pulsar, point to a magnetospheric origin of the pulsed X-ray emission. The observed and derived parameters of PSR J0218+4232 and PSR B1821-24 are very consistent with the exception of the small pulsed fraction of PSR J0218+4232. The large unpulsed component in X-rays and that reported earlier in the radio domain can be explained by emission from a compact nebula with diameter [FORMULA].

Key words: pulsars: individual: PSR J0218+4232; PSR B1821-24 – stars: neutron – X-rays: stars

Send offprint requests to: e-mail: L.Kuiper[FORMULA]sron.ruu.nl

© European Southern Observatory (ESO) 1998

Online publication: July 20, 1998