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Fermi/GBM Observations of XTE J1946+274

ATel #2677; Ascension Camero-Arranz, Mark H. Finger, Colleen Wilson-Hodge and Peter Jenke on behalf of the GBM pulsar and Earth Occultation projects
on 16 Jun 2010; 00:11 UT
Credential Certification: Dr. Mark H. Finger (Mark.Finger@msfc.nasa.gov)

Subjects: X-ray, Gamma Ray, Binary, Transient, Pulsar

Referred to by ATel #: 2692, 3048

We report on recent observations with Fermi/GBM of the transient Be/X-ray binary system XTE J1946+274 (GRO J1944+26) which is currently in outburst. Swift/BAT reported renewed activity (15-50 keV) starting on 2010 June 04 (ATel #2663). XTE J1946+274 was detected in pulsation by GBM in the June 5.0-7.0 data with a rms flux of 8+/-2 mCrab in the 12-25 keV band, increasing to 20+/-2 mCrab by June 11.0-13.0. Prior to these observations the most recent pulsed detection of the source in July 2001 (Wilson et al, 2003, ApJ 584:996). Earth Occultation measurements have shown 12-25 keV fluxes above 130 mcrab since June 8, reaching a flux of 220+/-40 mcrab on June 14.

The pulse frequency, corrected with the orbital parameters of Wilson et al. (2003), increased at a rate of 2.05(15)X10E-11 Hz/s during June 11.0-15.0, reaching 63.4155(2) mHz on June 14.0. Some of this apparent spin-up may be due to an error in the current periastron epoch, due to the uncertainty in the orbital period.

GBM Pulsar and Earth Occultation Projects