Candidate X-ray Counterparts of Ultra-High-Energy Emission of the Galactic Microquasar V4641 Sgr Revealed by Einstein Probe
Abstract
Microquasars have emerged as promising PeVatron candidates capable of accelerating particles to PeV energies, with recent observations revealing ultra-high-energy (UHE) γ-ray emission from extended structures associated with these systems. Multi-wavelength studies of such extended structures are crucial for understanding the acceleration, transport, and radiation processes of UHE cosmic rays (CRs), yet observational evidence remains limited. Here, we report the discovery of diffuse X-ray structures spatially coincident with the TeV γ-ray emission regions to the north and south of the microquasar V4641 Sgr, using the Follow-up X-ray Telescope (FXT) onboard the Einstein Probe. We identify X-ray structures located ∼20-$40$ pc from V4641 Sgr, extending over several arcminutes. These structures exhibit X-ray fluxes of ∼1-3×10−13 erg s−1 cm−2 and photon indices of Γ∼2-3 in 0.5-8 keV per individual knot. Under the one-zone leptonic interpretation, the weak X-ray emission implies a magnetic field of order $1-2 μ$G. Stronger fields remain possible if only part of the TeV-PeV emission is produced by inverse Compton scattering, with the remaining emission arising from hadronic interactions. The EP-FXT observations support the presence of relativistic electrons on tens-of-parsec scales, while the origin of the UHE γ-ray emission remains open.
Related
- AT2019aalc: An obscured tidal disruption event candidate in an active galactic nucleus revealed by its first flare?
- AT2019aalc: An obscured tidal disruption event candidate in an active galactic nucleus revealed by its first flare?
- 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
- High-resolution CO ( J = 1–0) and ( J = 3–2) Observations of Molecular Counterparts to the Double Helix Nebula in the Galactic Center
- Milky Way Near Twins (MWNeTs). I. A Hierarchical Framework for Identifying Candidate Evolutionary Counterparts of the Milky Way
BibTeX
@misc{chi2026candidate,
title = {{Candidate X-ray Counterparts of Ultra-High-Energy Emission of the Galactic Microquasar V4641 Sgr Revealed by Einstein Probe}},
author = {Yi-Heng Chi and Shao-Qiang Xi and Ping Zhou and Hua Feng and Ruo-Yu Liu and Songzhan Chen and Naomi Tsuji and Caterina Tresoldi and Gabriele Ponti and Zhen Cao and Yong Chen and Shumei Jia and Chi-Chuan Jin and Chengkui Li and Yuan Liu and Matthew Lundy and Kaya Mori and Haiwu Pan and Lian Tao and Junfeng Wang and Weimin Yuan and Juan Zhang and Haisheng Zhao},
howpublished = {arXiv},
year = {2026},
month = oct,
doi = {10.48550/arxiv.2610.02962},
eprint = {2610.02962},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2610.02962},
}
RIS
TY - UNPB
TI - Candidate X-ray Counterparts of Ultra-High-Energy Emission of the Galactic Microquasar V4641 Sgr Revealed by Einstein Probe
AU - Yi-Heng Chi
AU - Shao-Qiang Xi
AU - Ping Zhou
AU - Hua Feng
AU - Ruo-Yu Liu
AU - Songzhan Chen
AU - Naomi Tsuji
AU - Caterina Tresoldi
AU - Gabriele Ponti
AU - Zhen Cao
AU - Yong Chen
AU - Shumei Jia
AU - Chi-Chuan Jin
AU - Chengkui Li
AU - Yuan Liu
AU - Matthew Lundy
AU - Kaya Mori
AU - Haiwu Pan
AU - Lian Tao
AU - Junfeng Wang
AU - Weimin Yuan
AU - Juan Zhang
AU - Haisheng Zhao
PY - 2026
DA - 2026/10/02
PB - arXiv
DO - 10.48550/arxiv.2610.02962
UR - https://arxiv.org/abs/2610.02962
AB - Microquasars have emerged as promising PeVatron candidates capable of accelerating particles to PeV energies, with recent observations revealing ultra-high-energy (UHE) γ-ray emission from extended structures associated with these systems. Multi-wavelength studies of such extended structures are crucial for understanding the acceleration, transport, and radiation processes of UHE cosmic rays (CRs), yet observational evidence remains limited. Here, we report the discovery of diffuse X-ray structures spatially coincident with the TeV γ-ray emission regions to the north and south of the microquasar V4641 Sgr, using the Follow-up X-ray Telescope (FXT) onboard the Einstein Probe. We identify X-ray structures located ∼20-$40$ pc from V4641 Sgr, extending over several arcminutes. These structures exhibit X-ray fluxes of ∼1-3×10^−13 erg s^−1 cm^−2 and photon indices of Γ∼2-3 in 0.5-8 keV per individual knot. Under the one-zone leptonic interpretation, the weak X-ray emission implies a magnetic field of order $1-2 μ$G. Stronger fields remain possible if only part of the TeV-PeV emission is produced by inverse Compton scattering, with the remaining emission arising from hadronic interactions. The EP-FXT observations support the presence of relativistic electrons on tens-of-parsec scales, while the origin of the UHE γ-ray emission remains open.
ER -