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Fermi LAT Detection of Early Post-Periastron Increased GeV Gamma-Ray Emission From The Be-Pulsar Binary System PSR B1259-63

ATel #10818; T. J. Johnson (GMU, resident at NRL), K. S. Wood (Praxis Inc., resident at NRL), P. S. Ray (NRL), M. T. Kerr (NRL) on behalf of the Fermi Large Area Telescope Collaboration
on 5 Oct 2017; 03:52 UT
Credential Certification: Tyrel Johnson (tyrel.j.johnson@gmail.com)

Subjects: Gamma Ray, >GeV, Binary, Pulsar

Referred to by ATel #: 10918, 10924, 10925, 10972

Using data from the Large Area Telescope (LAT), one of the two instruments on board the Fermi Gamma-ray Space Telescope, we have detected >100 MeV flux enhancement from PSR B1259-63, in a 3.4 yr binary orbit with a Be star, on three consecutive days (2017-10-01 06:24:04 UTC through 2017-10-04 06:37:41 UTC), with approximate significances of 4.7, 3.0, and 3.8 sigma and photon fluxes (from 100 MeV to 300 GeV) of (13.6 +/- 3.4), (8.4 +/- 3.3), and (10.0 +/- 3.0) x 10^-7 ph/cm^2/s, respectively. Fitting this entire time period together, we detect emission from PSR B1259-63 with a significance of 6.8 sigma, power-law photon index of (2.8 +/- 0.2), and a photon flux of (10.5 +/- 1.9) x 10^-7 ph/cm^2/s. All uncertainties are statistical only.

The most recent periastron passage of the PSR B1259-63 system occurred on 2017-09-22, 9 days before our first daily detection. During the 2010 periastron passage, daily emission was detected 15 and 18 days after periastron at the level of 10 x 10^-7 ph/cm^2/s and 8 x 10^-7 ph/cm^2/s, respectively, followed by an interval of no detectable emission before the onset of a bright flare 30 days after periastron. During the 2014 periastron passage, emission was not detected on a daily basis until 24 days after periastron with a flux of 8 x 10^-7 ph/cm^2/s, followed by no detectable emission before the onset of a bright flare 30 days after periastron. This emission, both brighter and earlier than these previous "precursors", may signal a substantial departure from this pattern.

Pre-periastron GeV emission during the 2017 periastron passage has been reported (ATel #10775).

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.