Fermi LAT Detection of Emission from the PSR B1259-63/LS 2883 Binary Just After Periastron

ATel #14399; T. J. Johnson (GMU, resident at NRL), K. S. Wood (TSC, resident at NRL), C. C. Cheung (NRL), and M. Kerr (NRL) , on behalf of the Fermi Large Area Telescope Collaboration
on 18 Feb 2021; 05:14 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 detect significant emission consistent with the position of the PSR B1259-63/LS 2883 system following its periastron on 2021-02-09.87, MJD 59254.87 (using the timing solution of Shannon et al. 2014, MNRAS, 437, 3255).

Analyzing LAT data in the region of PSR B1259-63 over the time interval 2021-02-07 06:12:21 UTC to 2021-02-17 05:32:31 UTC, two days before periastron to eight days after, we detect emission above 100 MeV from a point source at the position of PSR B1259-63 with a significance of approximately 5 sigma. Our likelihood analysis yields a preliminary photon flux (from 100 MeV to 300 GeV) of (2.6 +/- 1.1) x 10^-7 ph/cm^2/s and a power-law photon index of 2.4 +/- 0.2. All quoted uncertainties are statistical only.

Analyzing this data set on a daily basis yields low-significance detections (2-3 sigma) on only three days, approximately 2021-02-10, 2021-02-13, and 2021-02-16. Using a fixed photon index of 2.4, our likelihood analysis yields flux levels on these days of (2.4 +/- 1.5), (5.8 +/- 2.1), and (4.0 +/- 2.8) x 10^-7 ph/cm^2/s, respectively.

These results suggests that the system may display similar behavior to that observed during the 2017 periastron passage (Johnson et al. 2018, ApJ, 863, 27), which was followed by dramatically increased gamma-ray flux levels of a few x 10^-6 ph/cm^2/s in a three-day period approximately 10 days after periastron. The only other periastron passages observed by the LAT, in 2010 and 2014, did not display significant GeV emission so soon after periastron.

Because Fermi normally 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.