A rapid change to double pulsing in Her X-1
Abstract
Her X-1 has been observed in the 13-180 keV energy range by the HEAO-1 A4 Low Energy Detectors during selected phases of the 35-day cycle. During one pointed observation in Sept 1978 the pulse profile was observed to change continuosly from its normal shape to an anomalous double-peaked form. Moreover, at this time the ``main-on'' state, normally of duration ten days, was seen to terminate after only seven days. Since a doubled pulse profile has earlier been reported by Trumper et al. /1/ to occur during a ``short-on'' state, we examined three such ``short-on'' episodes in the HEAO-1 data: the pulse doubling was confirmed in one of these; sensitivity was inadequate in the other two for any definite conclusion. Although this observation confirms the EXOSAT observation on which the free precession model was based, we have attempted without success to explain the Sept 1978 rapid change to double pulsing in terms of this model.
- Publication:
-
Advances in Space Research
- Pub Date:
- 1988
- DOI:
- 10.1016/0273-1177(88)90450-4
- Bibcode:
- 1988AdSpR...8b.503G