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Fermi LAT Detection of an Intense GeV Gamma-ray Flare From the Be-Pulsar Binary PSR B1259-63 at 70 Days After Periastron

ATel #11028; 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 Collabora
on 1 Dec 2017; 21:31 UT
Credential Certification: Tyrel Johnson (tyrel.j.johnson@gmail.com)

Subjects: Gamma Ray, >GeV, Binary, Pulsar

We have detected an intense flare in >100 MeV gamma rays from the Be-pulsar binary system PSR B1259-63, using data from the Large Area Telescope (LAT), one of the two instruments on board the Fermi Gamma-ray Space Telescope. Fitting LAT data from 2017-12-01 05:04:30 to 13:22:43 UTC, the flare was detected at ~8 sigma significance with a preliminary integrated flux of (9.8 +/- 1.5) x 10^-6 ph/cm^2/s and a photon index of 2.6 +/- 0.2; all quoted uncertainties are statistical only. In contrast, fitting the prior ~1.5 days of LAT data yielded only a low significance (~2 sigma) detection with a preliminary integrated flux of (0.6 +/- 0.3) x 10^-6 ph/cm^2/s, suggesting a 10-fold increase in flux on the timescale of a few hours.

PSR B1259-63 is in an eccentric orbit with a Be star, with an orbital period of 3.4 years. The most-recent periastron passage occurred on 2017-09-22, meaning the flare reported in this ATel is 70 days post periastron. Fermi was operational through the two previous periastron passages of this system (in 2010 and 2014), and no significant emission was detected this late after periastron for either event (see, for example, Caliandro et al. 2015, ApJ, 811, 68). The flux of this flare is also greater than reported in any previous ATel during this recent 2017 periastron passage (ATels #10775, #10818, #10924, #10925, #10972, and #10995).

Because Fermi operates in an all-sky scanning mode, regular gamma-ray monitoring of this source will continue. In consideration of the unusual activity of this source so late after periastron, we strongly encourage multi-wavelength observations to continue. 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.