Fermi LAT Detection of a GeV Gamma-Ray Flare from the Be-Pulsar Binary System PSR B1259-63 with Rapid Variability

ATel #10925; T. J. Johnson (GMU, resident at NRL), K. S. Wood (Praxis Inc., resident at NRL), P. S. Ray (NRL), E. C. Ferrara (UMD/NASA GSFC), M. T. Kerr (NRL), C. C. Cheung (NRL), on behalf of the Fermi Large Area Telescope Collaboration
on 3 Nov 2017; 21:52 UT
Credential Certification: Tyrel Johnson (tyrel.j.johnson@gmail.com)

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Using data from the Large Area Telescope (LAT), one of the two instruments on board the Fermi Gamma-ray Space Telescope, we have detected a >100 MeV flare from PSR B1259-63 over the time interval 2017-11-02 01:47:25 UTC to 2017-11-03 06:29:13 UTC with a significance of approximately 10 sigma, a preliminary photon flux (from 100 MeV to 300 GeV) of (3.1 +/- 0.4) x 10^-6 ph/cm^2/s, and a power-law photon index of 2.6 +/- 0.1, quoted uncertainties are statistical only. This follows a less intense flare shortly after periastron (ATel #10818) and prior to periastron (ATel #10775). During the six days prior no significant emission was detected, with flux upper limits of 0.9, 1.1, 0.5, 0.6, 1.0, and 0.7 x 10^-6 ph/cm^2/s.

We further split the time interval with significant emission into four 6-hour bins and one 4.7-hour bin and performed likelihood fits in each time bin. We detect a peak flux of (7.6 +/- 1.5) x 10^-6 ph/cm^2/s in the 2017-11-02 13:47:24.0 to 19:47:24.0 UTC time bin. Significant emission was not detected in the final two time bins, with upper limits of 2.7 and 1.2 x 10^-6 ph/cm^2/s, indicating rapid variability. These time-resolved results are in agreement with the aperture photometry reported in ATel #10924.

PSR B1259-63 is in a 3.4 yr binary orbit with a Be star. The most recent periastron passage occurred on 2017-09-22, 41 days before the flare reported in this ATel. As noted in ATel #10918, after the two prior periastron passages observed by Fermi, in 2010 and 2014, intense >100 MeV flares were detected starting 30 days after periastron, peaking 36 and 38 days after periastron, respectively, and lasting until 70 days after periastron.

Because Fermi operates in an all-sky scanning mode, regular gamma-ray monitoring of this source will continue. In consideration of the expected ongoing activity of this source we strongly encourage multi-wavelength observations. For this source the Fermi LAT contacts are Tyrel Johnson (tyrel.johnson.ctr@nrl.navy.mil) and Kent Wood (kent.wood.ctr@nrl.navy.mil).

The Fermi LAT is a pair conversion telescope designed to cover the energy band from 20 MeV to greater than 300 GeV. It is the product of an international collaboration between NASA and DOE in the U.S. and many scientific institutions across France, Italy, Japan and Sweden.