The unidentified PeV source LHAASO J2108+5157: A microquasar remnant?
Abstract
Context. LHAASO~J2108+5157 is one of the most intriguing Galactic ultra-high-energy γ-ray sources. It is detected up to hundreds of TeV but lacks a clear counterpart at lower frequencies. Fermi-LAT observations have revealed a compact GeV source spatially coincident with the PeV emission, while VERITAS and LST-1 impose stringent upper limits in the intermediate TeV band, producing a pronounced spectral suppression between the GeV and TeV domains. Aims. We investigate a time-dependent hadronic scenario in which a past episode of microquasar jet activity injected relativistic protons that are now observed in a relic phase. Methods. Energy-dependent diffusion naturally segregates the particle population: Lower-energy protons remain confined near dense molecular gas and account for the GeV emission, whereas higher-energy particles reach more distant material, producing the hard TeV--PeV component. Results. For representative interstellar conditions, the model is simultaneously consistent with the broadband spectral energy distribution, the spatial compact--extended dichotomy, and the lack of detectable radio or X-ray counterparts. Conclusions. The observed bimodal γ-ray phenomenology thus emerges as a transport effect of a single injected proton population, supporting the interpretation of LHAASO~J2108+5157 as a fossil microquasar remnant observed at an intermediate evolutionary stage and highlighting relic jet systems as a viable class of Galactic PeVatrons.
Related
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- An ALMA view of the Jet-Arc CO clouds toward the TeV γ-ray source HESS J1023-575 and Westerlund 2; Evidence for the footprints of microquasar jets, the very powerful cosmic-ray accelerator in the Galactic disk
- Propagation Diagnostics of Supernova Remnant Environments around Young Repeating Fast Radio Bursts. I. Hydrodynamic Evolution of the Source-local Dispersion Measure
- Propagation Diagnostics of Supernova Remnant Environments around Young Repeating Fast Radio Bursts. I. Hydrodynamic Evolution of the Source-local Dispersion Measure
- Radio Galaxies as UHECR Sources in Light of Recent Microquasar Results
BibTeX
@misc{martı2026unidentified,
title = {{The unidentified PeV source LHAASO J2108+5157: A microquasar remnant?}},
author = {Josep Mart\'ı and Pedro L. Luque-Escamilla and Leandro Abaroa and Gustavo E. Romero and Valent\'ı Bosch-Ramon and Josep M. Paredes and Cintia S. Peri},
howpublished = {arXiv},
year = {2026},
month = sep,
doi = {10.48550/arxiv.2609.18353},
eprint = {2609.18353},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2609.18353},
note = {CC BY 4.0},
}
RIS
TY - UNPB
TI - The unidentified PeV source LHAASO J2108+5157: A microquasar remnant?
AU - Josep Mart\'ı
AU - Pedro L. Luque-Escamilla
AU - Leandro Abaroa
AU - Gustavo E. Romero
AU - Valent\'ı Bosch-Ramon
AU - Josep M. Paredes
AU - Cintia S. Peri
PY - 2026
DA - 2026/09/16
PB - arXiv
DO - 10.48550/arxiv.2609.18353
UR - https://arxiv.org/abs/2609.18353
AB - Context. LHAASO~J2108+5157 is one of the most intriguing Galactic ultra-high-energy γ-ray sources. It is detected up to hundreds of TeV but lacks a clear counterpart at lower frequencies. Fermi-LAT observations have revealed a compact GeV source spatially coincident with the PeV emission, while VERITAS and LST-1 impose stringent upper limits in the intermediate TeV band, producing a pronounced spectral suppression between the GeV and TeV domains. Aims. We investigate a time-dependent hadronic scenario in which a past episode of microquasar jet activity injected relativistic protons that are now observed in a relic phase. Methods. Energy-dependent diffusion naturally segregates the particle population: Lower-energy protons remain confined near dense molecular gas and account for the GeV emission, whereas higher-energy particles reach more distant material, producing the hard TeV--PeV component. Results. For representative interstellar conditions, the model is simultaneously consistent with the broadband spectral energy distribution, the spatial compact--extended dichotomy, and the lack of detectable radio or X-ray counterparts. Conclusions. The observed bimodal γ-ray phenomenology thus emerges as a transport effect of a single injected proton population, supporting the interpretation of LHAASO~J2108+5157 as a fossil microquasar remnant observed at an intermediate evolutionary stage and highlighting relic jet systems as a viable class of Galactic PeVatrons.
ER -