A Leptonic Interpretation of the UHE Gamma-ray Emission from V4641 Sgr

TL;DR

This paper proposes a leptonic model involving shear acceleration in V4641 Sgr's jets to explain its elongated ultra-high-energy gamma-ray emission, predicting associated X-ray flux and suggesting future observational tests.

Contribution

It introduces a novel leptonic interpretation based on shear acceleration for the UHE gamma-ray emission from V4641 Sgr, linking gamma-ray and X-ray observations.

Findings

The gamma-ray emission can be explained by inverse Compton scattering of electrons with a hard spectrum.

Predicted X-ray flux provides a testable signature for the model.

Future observations could confirm the shear acceleration mechanism in V4641 Sgr.

Abstract

Recently, the microquasar V4641 Sgr and its surrounding is 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 a puzzling elongated structure. In this work, we propose that the elongated 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 non-thermal 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 parameters. In the future, a full coverage of the source by sensitive X-ray instrument and high-resolution TeV-PeV gamma-ray instrument may provide a critical test of the model.