The HI absorption distance of HESS J1943+213 favours its extragalactic nature

TL;DR

This study measures the distance to HESS J1943+213's radio counterpart using HI absorption, providing strong evidence that it is an extragalactic source, supporting its classification as a BL Lac object.

Contribution

The paper presents the first reliable distance measurement to HESS J1943+213, confirming its extragalactic nature through HI absorption analysis.

Findings

Distance to HESS J1943+213 is at least 16 kpc.

The extragalactic origin is strongly supported by the distance measurement.

Results favor the BL Lacertae object classification.

Abstract

The H.E.S.S. collaboration (Abramowski et al. 2011) dicovered a new TeV point-like source HESS J1943+213 in the Galactic plane and suggested three possible low-energy-band counterparts: a $\gamma$-ray binary, a pulsar wind nebula (PWN), or a BL Lacertae object. We measure the distance to the radio counterpart G57.76-1.29 of HESS J1943+213. We analyze Very Large Array observations to obtain a reliable HI absorption spectrum.The resulting distance limit is $\ge$ 16 kpc. This distance strongly supports that HESS J1943+213 is an extragalactic source, consistent with the preferred counterpart of the HESS collaboration.