Candidate X-ray Counterparts of Ultra-High-Energy Emission of the Galactic Microquasar V4641 Sgr Revealed by Einstein Probe
Year: 2026
Type: preprint
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 $\sim20$-$40$ pc from V4641 Sgr, extending over several arcminutes. These structures exhibit X-ray fluxes of $\sim1$-$3\times10^{-13}$ erg s$^{-1}$ cm$^{-2}$ and photon indices of $Γ\sim2$-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.
Source: arXiv (Cornell University)
Authors: Chi, Yi-Heng, Xi, Shao-Qiang, Zhou, Ping, Feng, Hua, Liu, Ruo-Yu, Chen, Songzhan, Tsuji, Naomi, Tresoldi, Caterina, Ponti, Gabriele, Cao, Zhen, Chen, Yong, Jia, Shumei, Jin, Chi-Chuan, Li, Chengkui, Liu, Yuan, Lundy, Matthew, Mori, Kaya, Pan, Haiwu, Tao, Lian, Wang, Junfeng, Yuan, Weimin, Zhang, Juan, Zhao, Haisheng
Institutions: Chinese Academy of Sciences, Institute of High Energy Physics, Nanjing University, RIKEN, Institute for Cosmic Ray Research, RIKEN Center for Interdisciplinary Theoretical and Mathematical Sciences, The University of Tokyo, University of Insubria, Brera Astronomical Observatory, National Institute for Astrophysics, National Astronomical Observatories, University of Chinese Academy of Sciences, Columbia University, Xiamen University
Language: English
Subfield: Nuclear and High Energy Physics
Field: Physics and Astronomy
Domain: Physical Sciences
Open Access status: green
Funders: Science and Industry Endowment Fund, Australian Government, European Space Agency, Commonwealth Scientific and Industrial Research Organisation, National Research Foundation, National Natural Science Foundation of China, Chinese Academy of Sciences, Government of Western Australia, Fundamental Research Funds for the Central Universities, Northwest Fisheries Science Center
Awards: G4790422525, G7322757637, G7859926257
OpenAlex ID: W7220390398