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4U 1626-67 Torque Reversal Simultaneous with Swift/BAT Flux Increase

ATEL # 2099; Ascension Camero-Arranz (NASA/FECYT), Mark H. Finger (USRA), Colleen Wilson (NASA/MSFC)
on 24 Jun 2009; 17:17 UT
Password Certification: Dr. Mark H. Finger (

Subjects: X-ray, Gamma Ray, Binaries, Neutron Stars, Pulsars

The recent torque reversal in the accretion-powered pulsar 4U 1626-67 (ATel #2095), which occurred after 18 years of steady spin-down, was centered near MJD 54500 (2008 Feb 4) and lasted about 150 days. This was simultaneous with an increase of flux reported by Krimm et al. (ATel #1426). We observed the spin-up first in the Fermi/GBM data (see our web page). Using Swift/BAT observations from 2004 up to the present, we have resolved the frequency history of this source through the torque reversal (Camero-Arranz et al. 2009, astro-ph 0906.4224). The mean spin-down rate between MJD 53310 and MJD 54410 was -4.82(7)E-13 Hz/s. The mean spin-up rate between MJD 54690 and MJD 55004 was 4.06(2)E-13 Hz/s.

GBM Pulsar Project

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