On the spin down episodes of Vel X-1.
Molteni, D.; Robba, N. R.; Rapisarda, M.; Re, S.
Italy
Abstract
The ESA COS-B satellite observed the X-ray source Vela X-1 in July/August 1976 and in October/November 1979 in the energy range 2-12 keV. Different pulse periods, 282.819 and 282.782 s, were determined for the two observations respectively. These values confirm the presence of spin up and spin down processes in this source.