Fermi-LAT detection of emission above 100 MeV associated with the PSR B1259-63/LS 2883 binary system approximately 30 days after periastron

ATel #16747; G. Marti-Devesa (Univ. and INFN Trieste), T. Burnett (UW), K. Wood (TSC, resident at NRL), C. C. Cheung (NRL), Z. Wadiasingh (UMD and NASA/GSFC), on behalf of the Fermi-LAT Collaboration
on 31 Jul 2024; 21:17 UT
Credential Certification: Guillem Marti-Devesa (guillem.marti-devesa@ts.infn.it)

Tweet

The Large Area Telescope (LAT), one of the two instruments on the Fermi Gamma-ray Space Telescope, has observed enhanced emission, on a one-day time scale, associated with the PSR B1259-63/LS 2883 binary system, approximately 30 days after periastron. This follows 51 days after the pre-periastron rapid flare reported previously (ATel #16656).

Analyzing the LAT data in the region around PSR B1259-63 over the time interval 2024-07-24 05:11:11 to 2024-07-31 05:11:11 UTC, we derived the photon flux above 100 MeV in one-day bins for PSR B1259-63. We assume a photon index of 2.8 based on previous periastron passages, and freed it for daily bins with significant flux detection. We find no gamma-ray signal from 2024-07-24, 25, 26, 27, and 28, with 95% confidence level upper limits on the flux ranging from 0.2 to 1.6 x 10^-6 ph/cm^2/s. From 2024-07-29 to 31, we find significant detections (>5 sigma) with flux values of (1.5+/- 0.4) x 10^-6 ph/cm^2/s and (2.0 +/- 0.4) x 10^-6 ph/cm^2/s, with photon index values of 2.9 +/- 0.6 and 2.5 +/- 0.2, respectively. An independent analysis with photon weights confirms the detection at ~7 sigma after 2024-07-30 00:00:00 UTC.

The Fermi-LAT has observed enhanced emission following the four previous periastron passages of PSR B1259-63. The delay between periastron and onset of emission is similar to those found in 2010 and 2014, while much shorter than the 60 days post-periastron flare in 2021 (ATel #14540).

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.