English (United Kingdom)

https://curated-unify.zendy.io/wp-json/zendy-region/v1/featured_content/oa?rat=en

https://curated-unify.zendy.io/wp-json/zendy-region/v1/highlighted_journal/

Global: Zendy Plus annual

Presents the access of premium content as premium feature

Premium Content

Presents the keyphrase highlighting as premium feature

Keyphrase Highlighting

Presents the summarisation as premium feature

Summarisation

Insights

Presents the pdf analysis as premium feature

PDF Analysis

Presents the zaia usage as premium feature

ZAIA

Global: Zendy Tools annual

Global: Zendy Free Plan

Global: Zendy Tools monthly

Global: Zendy Plus monthly

We report on the 1.6 GHz (18 cm) VLBI observations of the unresolved, steadyTeV source HESS J1943+213 located in the Galactic plane, performed with theEuropean VLBI Network (EVN) in 2014. Our new observations with a nearly fullEVN array provide the deepest image of HESS J1943+213 at the highest resolutionever achieved, enabling us to resolve the long-standing issues of the sourceidentification. The milliarcsecond-scale structure of HESS J1943+213 has aclear asymmetric morphology, consisting of a compact core and a diffusejet-like tail. This is broadly consistent with the previous e-EVN observationsof the source performed in 2011, and re-analyzed in this work. The corecomponent is characterized by the brightness temperature of $\gtrsim1.8 \times10^9$ K, which is typical for low-luminosity blazars in general. Overall, radioproperties of HESS J1943+213 are consistent with the source classification asan "extreme high-frequency-peaked BL Lac object". Remarkably, we note thatsince HESS J1943+213 does not reveal any optical or infrared signatures of theAGN activity, it would never be recognized and identified as a BL Lac object,if not its location close to the Galactic plane where the High EnergyStereoscopic System has surveyed, and the follow-up dedicated X-ray and radiostudies triggered by the source detection in the TeV range. Our results suggesttherefore a presence of an unrecognized, possibly very numerous population ofparticularly extreme HBLs, and simultaneously demonstrate that thelow-frequency VLBI observations with high-angular resolution are indispensablefor a proper identification of such objects.

EVN Observations of HESS J1943+213: Evidence for an Extreme TeV BL Lac Object