Rapid GeV gamma-ray flare from PSR B1259-63/LS 2883 21 days before its upcoming periastron passage
ATel #16656; T. Burnett (UW), K. Wood (TSC, resident at NRL), C. C. Cheung, M. Kerr (NRL), T. Johnson (GMU, resident at NRL), G. Marti-Devesa (University and INFN Trieste), P. Michelson (Stanford), on behalf of the Fermi-LAT Collaboration
on 15 Jun 2024; 15:11 UT
Credential Certification: Teddy Cheung (Teddy.Cheung@nrl.navy.mil)
Subjects: Gamma Ray, >GeV, Neutron Star
The Large Area Telescope (LAT), one of the two instruments on the Fermi Gamma-ray Space Telescope, has observed a transient gamma-ray source positionally consistent with the PSR B1259-63/LS 2883 binary system, 21 days before its upcoming periastron passage (2024 Jun 30).
Preliminary analysis indicates that the transient source has >5-sigma significance in the 6-hr interval (12:00-18:00 UT) of 2024 Jun 9, with a (E >100 MeV) flux of (3.2 +/- 0.9) x 10^-6 photons cm^-2 s^-1 and photon index of 2.3 +/- 0.2 (statistical uncertainties only). An independent analysis narrows this down to the 33-minute run centered at MJD 60470.665, 2024-06-09 15:57 UTC, with 7-sigma significance. A search for significant LAT flux following the flare and up to this time produces only upper limits, searching on timescales from single orbits to the full five days. In the preceding four periastron passages observed by the LAT there has been little or no pre-periastron detected flux. The orbital phase of this flare implies a significantly different viewing geometry from all previous flares detected by the LAT, since the neutron star velocity vector is in the hemisphere away from the direction to Earth.
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. PSR B1259-63 is included in the "LAT Monitored Sources" and consequently, a preliminary estimation of the daily gamma-ray flux observed by Fermi-LAT is publicly available (https://fermi.gsfc.nasa.gov/ssc/data/access/lat/msl_lc/source/PSR_B1259-63). For this source the Fermi LAT contacts are Kent Wood (kentswood@gmail.com) and Toby Burnett (tburnett@uw.edu).
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.
