Probing the radio to X-ray connection of the Vela X PWN with Fermi LAT and H.E.S.S

TL;DR

This study investigates the complex multi-wavelength emission of the Vela X pulsar wind nebula, analyzing how different energy regions connect and predicting gamma-ray structures observable by Fermi LAT based on magnetic field estimates.

Contribution

It provides a detailed multi-wavelength analysis of Vela X, proposing a consistent lepton spectrum model and predicting gamma-ray structures detectable by Fermi LAT.

Findings

Two distinct lepton spectra describe radio and X-ray/VHE gamma-ray emissions.

A magnetic field strength of 5 μG explains the spectral break and predicts X-ray flux.

Fermi LAT could resolve high-energy gamma-ray structures if the field strength is uniform.

Abstract

Morphologically it appears as if the Vela X PWN consists of two emission regions: whereas X-ray (1 keV) and very high energy (VHE) H.E.S.S. gamma-ray observations appear to define a cocoon type shape south of the pulsar, radio observations reveal an extended area of size 2 deg by 3 deg (including the cocoon area), also south of the Vela pulsar. Since no wide field of view (FoV) observations of the synchrotron emission between radio and X-rays are available, we do not know how the lepton (e+/-) spectra of these two components connect and how the morphology changes with energy. Currently we find that two distinct lepton spectra describe the respective radio and X-ray/VHE gamma-ray spectra, with a field strength of 5 muG self-consistently describing a radiation spectral break (or energy maximum) in the multi-TeV domain as observed by H.E.S.S. (if interpreted as IC radiation), while predicting the total hard X-ray flux above 20 keV (measured by the wide FoV INTEGRAL instrument) within a factor of two. If this same field strength is also representative of the radio structure (including filaments), the implied IC component corresponding to the highest radio frequencies should reveal a relatively bright high energy gamma-ray structure and Fermi LAT should be able to resolve it. A higher field strength in the filaments would however imply fewer leptons in Vela X and hence a fainter Fermi LAT signal.