The X-ray properties of 3A1907+09

A series of EXOSAT observations of the high-mass X-ray binary 3A1907+09 in 1984 early June show a spin-down of the neutron star since the discovery of X-ray pulsations in 1983 September by the Tenma Satellite. The mildly eccentric orbit derived from Tenma data is confirmed and orbital parameters are refined. The pulse-averaged spectra were consistent with a hard power-law, photon index approx. 1.2, with variable low-energy cut-off. The derived column density increased by approx. 2 X 1022 cm-2 over a period of time spanning the primary flare of the 8.37-day X-ray modulation cycle, with marginal evidence for a decrease during the secondary flare. The low-energy cut-off showed no pulse-phase dependency, unlike the spectral slope which showed marked softening during the deep pulse minimum. (author)