e-MERLIN observations of the puzzling TeV source HESS J1943+213

TL;DR

This study uses e-MERLIN radio observations to investigate the structure of the TeV source HESS J1943+213, revealing a compact core and missing flux likely due to larger-scale or foreground structures.

Contribution

First high-resolution e-MERLIN observations of HESS J1943+213, clarifying its structure and flux distribution compared to previous EVN and WSRT data.

Findings

Detected only a point source with e-MERLIN, indicating a compact core.

Missing flux suggests larger-scale or foreground structures.

Source may be a BL Lac object with extended or foreground components.

Abstract

HESS J1943+213 is a TeV source close to the Galactic plane proposed to be a BL Lac object. Our high resolution EVN observation failed to recover two thirds of the source flux density detected simultaneously by the WSRT. Our recent e-MERLIN observations in L and C bands show only a point source with flux density comparable to the EVN detection. Thus the structure responsible for the missing flux density has to be larger than 2". It may be related to the presumed extragalactic source (thus would have a kpc-scale size), or to the Galactic foreground material close to the line of sight to the source.