VLBI search for the radio counterpart of HESS J1943+213

TL;DR

This study used high-resolution radio observations to determine that HESS J1943+213 is likely a pulsar wind nebula within our galaxy, rather than an extragalactic BL Lac object, based on its radio and X-ray properties.

Contribution

The paper provides the first high-resolution radio imaging of HESS J1943+213, revealing features that support a galactic PWN origin over an extragalactic BL Lacertae object.

Findings

Radio counterpart is compact with low brightness temperature.

The source's properties suggest a pulsar wind nebula rather than a BL Lac object.

Located within a large H I structure, indicating a possible physical association.

Abstract

HESS J1943+213, a TeV point source close to the Galactic plane recently discovered by the H.E.S.S. collaboration, was proposed to be an extreme BL Lacertae object, though a pulsar wind nebula (PWN) nature could not be completely discarded. To investigate its nature, we performed high-resolution radio observations with the European Very Long Baseline Interferometry Network (EVN) and reanalyzed archival continuum and H {\sc i} data. The EVN observations revealed a compact radio counterpart of the TeV source. The low brightness temperature and the resolved nature of the radio source are indications against the beamed BL Lacertae hypothesis. The radio/X-ray source appears immersed in a $\sim$ 1\arcmin elliptical feature suggesting a possible galactic origin (PWN nature) for the HESS source. We found that HESS\,J1943+213 is located in the interior of a $\sim1\degr$ diameter H {\sc i} feature, and explored the possibility of they being physically related.