Fermi LAT Detection of Continued GeV Activity of the PSR B1259-63 Be-pulsar Binary System with Another Rapid Flare

ATel #10972; T. J. Johnson (GMU, resident at NRL), K. S. Wood (Praxis Inc., resident at NRL), P. S. Ray (NRL), M. T. Kerr (NRL), C. C. Cheung (NRL), on behalf of the Fermi Large Area Telescope Collaboration
on 14 Nov 2017; 23:35 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 flare in >100 MeV gamma rays from PSR B1259-63 over the time interval 2017-11-13 07:12:26 UTC to 2017-11-14 07:36:40 UTC with a significance of approximately 9 sigma. Our likelihood analysis yields a preliminary photon flux (from 100 MeV to 300 GeV) of (2.5 +/- 0.4) x 10^-6 ph/cm^2/s, and a power-law photon index of 2.7 +/- 0.2, quoted uncertainties throughout are statistical only.

In the four days leading up to this most-recent flare, only the previous day yields a significant detection of approximately 3 sigma with a flux of (0.8 +/- 0.3) x 10^-6 ph/cm^2/s. The 95% confidence-level flux upper limits for the three days prior to that detection are 0.7, 0.6, and 1.0 x 10^-6 ph/cm^2/s, respectively.

Similar to the recent flare reported in ATels #10924 and #10925, dividing the time interval into 6-hour bins reveals that the emission was concentrated in just one out the four 6-hour intervals, from 2017-11-13 13:12:26 to 19:12:26 UTC. The peak flux in this 6-hour bin is (6.9 +/- 1.2) x 10^-6 ph/cm^2/s, assuming the same photon index. The other three intervals had 95% confidence-level upper limits of 2.1, 1.6, and 2.1 x 10^-6 ph/cm^2/s. At a distance of 2.3 kpc, the peak 6-hour flare corresponds to a gamma-ray luminosity of (1.8 +/- 0.3) x 10^36 erg/s, about twice the spin-down power of the pulsar (8.3 x 10^35 erg/s). This implies that the emission can not be solely powered by the rotation of the pulsar and/or significant beaming is required.

The PSR B1259-63 system consists of a pulsar in a 3.4 year orbit with a Be star. The most-recent periastron passage was 2017-09-22, which is 52 days prior to the flare reported in this ATel. The behavior of this system continues to be very different from the two previous periastron passages observed by Fermi (see ATel #10918), in which emission started to rise 30 days after periastron, and peaked 36 and 38 days after periastron, with consistent daily detections until almost 70 days after periastron.

GeV gamma-ray emission prior to periastron from PSR B1259-63 was reported in ATel #10775, and a smaller GeV flare shortly after periastron was reported in ATel #10818.

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.