4U 1626-67 as Seen by Suzaku Before and After the 2008 Torque Reversal

Aims, The accretion-powered pulsar 4U 1626-67 experienced a new torque reversal at the beginning of 2008, after about 18 years of steadily spinning down. The main goal of the present work is to study this recent torque reversal that occurred in 2008 February. Methods. We present a spectral analysis of this source using two pointed observations pctformed by SuzakU in 2006 March and in 2010 September, Results, We confirm with Suzaku. the presence of a strong emission-Hne complex centered on 1 keV, with the stronge.!lt line being the bydrogen-like Ne Lya at 1,025(3) keY. We were able to resolve this complex with up to seven emission lines, A dnunR;tic increase of the intensity of the Ne Lya line after the 2008 torque rcven.al occurred, with me equivalent width of this line reaching almost the same value measured by ASCA in 1993 . We also report on the detection of a cyclotron line feature centered at -37k.cV. In spite of the fact that an increase of the X-ray luminosity (O.5-100keV) of a factor of -2.8 occwred between these two observations, no significant change in the energy of the cyclotron line feature was observed. However, the intensity of the -1 keY line complex increased by an overall factor of -8. Conclusions. Our results favor a scenario in which the neutron star in 4U 1626-67 accretes material 'from a geometrically thin disk during both the spin-up and spin-down phases. Key word •. accretion, accretion disks - binaries:close - pulsars: individual (4U 1626-67 ) - stars : neutron - X-rays: binaries