Orbital Modulation of Gamma-Rays Beyond 100 TeV from LS 5039
Abstract
Gamma-ray binaries are systems composed of a compact object orbiting a massive companion star. The interaction between these two objects can drive relativistic outflows, either jets or winds, in which particles can be accelerated to energies reaching hundreds of tera-electronvolts (TeV). It is however still debated where and under which physical conditions particles are accelerated in these objects and ultimately whether protons can be accelerated up to PeV energies. Among the well-known gamma-ray binaries, LS 5039 is a high-mass X-ray binary (HMXB) with an orbital period of 3.9 days that has been observed up to TeV energies by the High Energy Stereoscopic System (H.E.S.S.). In this work, we present new observations of LS 5039 obtained with the High Altitude Water Cherenkov (HAWC) observatory. Our data reveal that the gamma-ray spectrum of LS 5039 extends up to 200 TeV with no apparent spectral cut-off. Furthermore, we confirm, with a confidence level of 4.7{\sigma}, that the emission between 2 TeV and 118 TeV is modulated by the orbital motion of the system, which indicates that these photons are likely produced within or near the binary orbit where they can undergo absorption by the stellar photons. In a leptonic scenario, the highest energy photons detected by HAWC can be emitted by ~200 TeV electrons inverse Compton scattering stellar photons, which would require an extremely efficient acceleration mechanism operating within LS 5039. Alternatively, a hadronic scenario could explain the data through proton-proton or proton-{\gamma} collisions of protons accelerated to peta-electronvolt (PeV) energies.
Keywords
Cite
@article{arxiv.2503.20947,
title = {Orbital Modulation of Gamma-Rays Beyond 100 TeV from LS 5039},
author = {R. Alfaro and M. Araya and J. C. Arteaga-Velázquez and D. Avila Rojas and H. A. Ayala Solares and R. Babu and P. Bangale and E. Belmont-Moreno and A. Bernal and K. S. Caballero-Mora and T. Capistrán and A. Carramiñana and S. Casanova and U. Cotti and J. Cotzomi and S. Coutiño de León and D. Depaoli and P. Desiati and N. Di Lalla and R. Diaz Hernandez and B. L. Dingus and M. A. DuVernois and K. Engel and T. Ergin and C. Espinoza and K. L. Fan and K. Fang and J. A. García-González and H. Goksu and A. Gonzalez Muñoz and J. A. González and M. M. González and J. A. Goodman and S. Groetsch and J. P. Harding and S. Hernández-Cadena and I. Herzog and D. Huang and F. Hueyotl-Zahuantitla and P. Hüntemeyer and S. Kaufmann and D. Kieda and A. Lara and J. Lee and H. León Vargas and J. T. Linnemann and A. L. Longinotti and G. Luis-Raya and K. Malone and O. Martinez and J. Martínez-Castro and J. A. Matthews and P. Miranda-Romagnoli and J. A. Morales-Soto and E. Moreno and M. Mostafá and M. Najafi and L. Nellen and M. U. Nisa and N. Omodei and E. Ponce and Y. Pérez and Araujo and E. G. Pérez-Pérez and C. D. Rho and A. Rodriguez Parra and D. Rosa-González and M. Roth and H. Salazar and D. Salazar-Gallegos and A. Sandoval and M. Schneider and G. Schwefer and J. Serna-Franco and A. J. Smith and Y. Son and R. W. Springer and O. Tibolla and K. Tollefson and I. Torres and R. Torres-Escobedo and R. Turner and E. Varela and X. Wang and Z. Wang and I. J. Watson and H. Wu and S. Yu and S. Yun-Cárcamo and H. Zhou and C. de León},
journal= {arXiv preprint arXiv:2503.20947},
year = {2025}
}