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A rapid increase of the spin frequency of GX301-2 during an unusual apastron X-ray flare observed by Fermi/GBM

ATEL # 2712; Mark H. Finger (USRA), Ascension Camero-Arranz (FECYT), Colleen Wilson-Hodge (NASA/MSFC) and Peter Jenke (ORAU) on behalf of the Fermi/GBM Pulsar and Occultation Project teams
on 1 Jul 2010; 16:00 UT
Password Certification: Dr. Mark H. Finger (

Subjects: X-ray, Gamma Ray, Binaries, Pulsars, Transients

Recent Fermi/GBM observations of the high mass X-ray binary system GX301-2 show an unusually bright flare near the apastron (2010 June 29.85) of its ~41.5 day binary orbit. Earth Occultation flux measurements from June 25.0 - 26.0 were 277+/-112 mCrab (8-12 keV), 426+/-40 mCrab (12-25 keV) and 177+/-64 mCrab (25-50 keV). By June 29.0-30.0 the fluxes increased to 503+/-81 mCrab (8-12 keV), 932+/-35 mCrab (12-25 keV) and 447+/-53 mCrab (25-50 keV).

Rapid spin-up, beginning on June 25, was also observed. Pulse timing measurements from the interval of June 25.3-30.0 show a spin-up rate of nu_dot=2.6+/-0.5X10E-12 Hz/s, giving a spin-up time scale of ~18 yr. On June 28 the spin frequency was 1.45954(3) mHz (P=685.147(14) s). Both spin-up and spin frequency assume the orbital parameters from Doroshenko et al. 2010 (A&A 515, A10).

This episode of rapid spin-up is similar to two episodes of rapid spin-up seen with BATSE (Koh et al. 1997, ApJ 479, 933), with spin-up rates of 4.5X10E-12 Hz/s and 3.0X10E-12 Hz/s; and an episode previously seen with GBM from 2009 Jan 4 - 24, with a spin-up rate of 3.2X10E-12 Hz/s.

Fermi/GBM Pulsar and Occultation Projects

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