PSR B1259-63/LS 2883 is a classical gamma-ray binary detected from radio to TeV energies near periastron. Using over 17 years of Fermi-LAT observations, we report the first significant detection (8σ in likelihood analysis) of the system in the 10-100 GeV energy range, over orbital phases from -400 to +100 days relative to periastron. The observed spectrum is well described by a power law with photon index Γ=1.9±0.1 and shows a flux level consistent with that measured at TeV energies by H.E.S.S. The smooth connection between the Fermi-LAT and TeV spectra suggests that the detected multi-GeV emission traces the rising tail of the inverse-Compton component extending into the TeV regime. The presence of detectable emission hundreds of days before periastron indicates high-energy activity over a larger orbital phase range than previously established, enabling new constraints on particle-acceleration and radiative processes in the system.
@article{arxiv.2509.10037,
title = {Multi-GeV Fermi-LAT Detection of PSR B1259-63},
author = {D. Malyshev and M. Chernyakova and A. Finn Gallagher and A. Kuzin and N. Matchett and A. Santangelo and Iu. Shebalkova and B. van Soelen},
journal= {arXiv preprint arXiv:2509.10037},
year = {2025}
}