Observation of an Outburst from the X-Ray Pulsator 0115+63

The Ariel 6 X-ray instruments observed 0115+63 during 1980 December 16–30, when the mean flux was ~ 150 millicrab. Analysis of the ~ 3.6s pulsations given a refined orbital period of 24.3155 ± 0.0002 days and a periastron angle of 47°.15 ±0 °.13, setting a limit on the rate of advance of periastron since 1978 of 0.11 yr−1. During the observation the pulse period was decreasing faster than during the 1978 outburst, but in the 3 year interval there had been a spin down.