Discovery of a New Torque Reversal of the Accreting X-ray Pulsar 4U 1626-67 by Fermi/GBM
arXiv:0912.3809
Abstract
Recent X-ray observations by Fermi/GBM discovered a new torque reversal of 4U 1626-67 after 18 years of steady spinning down. Using Swift/BAT observations we were able to center this new torque reversal on Feb 4 2008, lasting approximately 150 days. From 2004 up to the end of 2007, the spin-down rate averaged at a mean rate of ~dnu/dt=-4.8e-13 Hz s-1 until the torque reversal reported here. Since then it has been following a steady spin-up at a mean rate of ~dnu/dt= 4e-13 Hz s-1. The properties of this torque reversal, as well as the lack of correlation between the X-ray flux and the torque applied to the neutron star before this transition, challenges our understanding of the physical mechanisms operating in this system.
arXiv comment2009 Fermi Symposium, eConf Proceedings C091122