Recent torque reversal of 4U 1907+09

We present timing and spectral analysis of RXTE-PCA (Proportional Counter Array) observations of the accretion powered pulsar 4U 1907+09 between 2007 June and 2008 August. 4U 1907+09 had been in a spin-down episode with a spin-down rate of −3.54 × 10−14 Hz s−1 before 1999. From RXTE observations after 2001 March, the source showed a ∼60 per cent decrease in spin-down magnitude, and INTEGRAL observations after 2003 March showed that source started to spin-up. We found that the source recently entered into a new spin-down episode with a spin-down rate of −3.59 × 10−14 Hz s−1. This spin-down rate is pretty close to the previous long-term spin-down rate of the source measured before 1999. From the spectral analysis, we showed that hydrogen column density varies with the orbital phase.