A Leptonic Interpretation of the Ultra-high-energy Gamma-Ray Emission from V4641 Sgr

Abstract Recently, the microquasar V4641 Sgr and its surrounding have been detected at TeV–PeV gamma-ray band. Interestingly, the spectrum follows a power-law function continuing up to 0.8 PeV as reported by LHAASO, and the morphology of the emission appears to be a puzzling elongated structure. In this work, we propose that the elongated ultra-high-energy (UHE) emission from V4641 Sgr could originate from the inverse Compton radiation of electrons with a very hard spectrum, which may result from shear acceleration mechanism in the jets driven by V4641 Sgr. We also calculate the corresponding X-ray synchrotron emission from the same electron population, predicting the potential range of nonthermal X-ray flux of the source. The recent observation by XRISM toward the central part of the UHE source could pose a constraint on the model’s parameters. In the future, a full coverage of the source by sensitive X-ray instruments and high-resolution TeV–PeV gamma-ray instruments may provide a critical test of the model.