Leptonic and Hadronic Models of High-energy Nebula Around V4641 Sgr

TL;DR

This paper develops and compares leptonic, hadronic, and combined models to explain the gamma-ray and X-ray emission from the high-energy nebula around V4641 Sgr, providing insights into its composition and morphology.

Contribution

It presents self-consistent leptonic, hadronic, and leptohadronic models that fit the nebula's spectrum and morphology, and offers predictions to distinguish these scenarios.

Findings

Leptonic models are energetically favorable but require specific morphology assumptions.

Hadronic models better explain gamma-ray morphology but need large proton energy and can't reproduce X-ray emission.

Combined models can fit both spectral and morphological data, with predictions for future observations.

Abstract

A prominent, 200-pc-scale high-energy nebula surrounding the microquasar V4641~Sgr is the brightest known gamma-ray source in the Southern sky at $E > 100\,\mathrm{TeV}$. In this paper, we develop self-consistent leptonic, hadronic, and leptohadronic models that reproduce both the observed spectrum and morphology of the source. Purely leptonic models are energetically more favorable yet they require rather specific morphological assumptions. The gamma-ray morphology of the source can be better explained within a hadronic scenario based on the identification of cold gas structures spatially correlated with the observed gamma-ray emission. However, a purely hadronic model for the source emission requires a substantial energy reservoir in protons and fails to reproduce the extended X-ray emission recently detected by XRISM. We show that emission including a combination of leptonic and hadronic components can reproduce both the spectral and morphological properties of the source. We provide predictions for the X-ray and neutrino spectra of~the~nebula that can discriminate the hadronic and leptonic contributions to the overall source signal.