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Astron. Astrophys. 330, 189-194 (1998)

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X-ray observations of the slowest known Be/X-ray pulsars RX J0146.9 [FORMULA] 6121 and X Persei

F. Haberl 1, L. Angelini 2, 3, C. Motch 4 and N.E. White 2

1 Max-Planck-Institut für Extraterrestrische Physik, Giessenbachstrasse, D-85748 Garching, Germany
2 Laboratory for High Energy Astrophysics, NASA Goddard Space Flight Center, Greenbelt, MD 20771, USA
3 University Space Research Association
4 Universite Louis Pasteur, Observatoire Astronomique de Strasbourg, 11 rue de l'Universite, F-67000 Strasbourg, France

Received 28 July 1997 / Accepted 1 September 1997


We present ASCA and ROSAT observations of the Be/X-ray binary pulsars RX J0146.9 [FORMULA] 6121 and X Persei between 1994 and 1996. Measuring the neutron star spin period and X-ray luminosity of X Persei shows that the episode of low X-ray luminosity and monotonic spin-down since 1978 continued to at least August 1995. ASCA and ROSAT HRI observations of RX J0146.9 [FORMULA] 6121 detected the pulsar with the longest known neutron star spin period at low luminosities after the X-ray outburst seen by EXOSAT in August 1984. The large spin period decrease seen between 1984 and 1993 has nearly stopped at a period of 1407.3 s in February 1996. We discuss that the X-ray outburst behaviour of X Persei with respect to its Be star phase changes observed in the optical can be caused by an asymmetry in the matter distribution around the Be star.

Key words: stars: emission-line, Be – stars: individual: RX J0146.9+6121, X Persei – stars: neutron – X-rays: stars

Send offprint requests to: F. Haberl (fwh@mpe-garching.mpg.de)

© European Southern Observatory (ESO) 1998

Online publication: January 8, 1998