Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: VERITAS and VLBA Observations of HESS J1943+213   HESS J1943+213 is a very high energy (VHE; 100 GeV) {\gamma}-ray source in
the direction of the Galactic plane. 38 hours of deep VERITAS observations
taken over two seasons detect the source with ~20 {\sigma} significance.
Monitoring observations of HESS J1943+213 show a remarkably stable flux and
spectrum in VHE {\gamma}-rays. Studies exploring the classification of HESS
J1943+213 are converging towards accepting the source as an extreme synchrotron
BL Lac object. Specifically, overall SED characteristics of the source, the
detection of a potential host galaxy in near-IR imaging, and VLBI observations
of the HESS J1943+213 radio counterpart showing extended jet-like emission at
milliarcsecond scale and core flux density variability establish the source as
a blazar. Recent Very Long Baseline Array (VLBA) observations of the source
(shown here for the first time) confirm the extended structure found in the 1.6
GHz band and detect the jet-like component in the 4.6 GHz and the 7.3 GHz
bands. The spectral indices of the core and the jet-like components derived
from the VLBA observations are in a range typical for blazars. HESS J1943+213
fits the extreme HBL description; however, with variability detected only at
milliarcseconds scales in radio, it appears to be an abnormally stable VHE
{\gamma}-ray blazar.

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The categories of this paper are: supr-con
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The categories of this paper are: ao-sci
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The categories of this paper are: dg-ga
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The categories of this paper are: atom-ph
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The categories of this paper are: chem-ph
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The categories of this paper are: q-alg
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The categories of this paper are: gr-qc
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The categories of this paper are: stat
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The categories of this paper are: comp-gas
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The categories of this paper are: eess
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The categories of this paper are: econ
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The categories of this paper are: patt-sol
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The categories of this paper are: chao-dyn
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The categories of this paper are: hep-th
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The categories of this paper are: math
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The categories of this paper are: bayes-an