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Fermi LAT Detection of a Rapid GeV Flare from the Gamma-ray Binary System PSR B1259-63

ATel #10924; Robin H. D. Corbet (UMBC/NASA GSFC/MICA)
on 3 Nov 2017; 20:51 UT
Credential Certification: Robin Corbet (corbet@umbc.edu)

Subjects: Gamma Ray, >GeV, Binary, Neutron Star, Pulsar

Referred to by ATel #: 10925, 10972, 10995, 11028

The gamma-ray binary system PSR B1259-63 is presently approximately 40 days after the periastron passage of its 3.4 year orbit. However, unlike the previous two periastron passages observed with the Fermi LAT, a bright post-periastron gamma-ray flare had not yet been seen (e.g. ATel #10818, #10918).

From aperture photometry of the Fermi LAT observations of this source (100 MeV - 300 GeV) with a 1 degree radius and 10 day time bins, an apparent brightening is now observed. Using time bins with length of the Fermi sky survey period (11,430 seconds) shows that the source brightened near MJD 58059.5 (2017-11-02.5) reaching a count rate within the aperture of approximately 8 x 10^-6 ph/cm^2/s. However, the source then returned to its previous brightness level near MJD 58059.8 (2017-11-02.8). Such a brief bright flare appears to be unprecedented for this source, and also for other gamma-ray binaries.

Observations at other wavelengths are encouraged, particularly of short timescale variations in the source.