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ATel #3408; Ascension Camero-Arranz (USRA), Mark H. Finger (USRA), Peter Jenke (NPP/MSFC), and Valerie Connaughton (UAH), on behalf of the GBM Pulsar team
on 6 Jun 2011; 22:54 UT
Credential Certification: Ascension Camero-Arranz (Ascension.Camero@uv.es)

Subjects: X-ray, Request for Observations, Binary, Neutron Star, Pulsar

Referred to by ATel #: 3430, 10608

We report on the detection of a weak outburst of the transient accreting X-ray pulsar 4U 0115+63 by GBM. X-ray pulsation from the source was detected from May 20 to May 27. The highest r.m.s. pulsed flux of 17 +-1 mCrab, in the 8-25 keV band, was observed on May 22-23. A pulse frequency of 276.6885(2) mHz was measured in the interval May 22.0-24.0. The frequency in May 20.0-22.0 was consistent with this value, but following May 24.0 the frequency decreased at the rate of df/dt =-5.6(2)E-12 Hz/s. These measurements are orbitally corrected using ephemeris from Bildsten et al (1997). The pulse profile consists of a rapid rise to peak followed by a slower fall to minimum, as has been previously seen at low flux levels for this source (Raichur & Paul, 2010, MNRAS, 406, 2663). This source was last active in March 2008 (ATel #1426).

4U 0115+63 has an orbital period of 24.3 days, and another outburst may possibly occur in mid June. Observations with other instruments are therefore encouraged.

GBM Pulsar project