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 Tenma 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 ~ 1.2, with variable low-energy cut-off. The derived column density increased by $$\sim\,2\times {10}^{22}\,\text{cm}^{-2}$$ 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.