K. E. Gabanyi, G. Dubner, E. Giacani, Z. Paragi, Y. Pidopryhora, S. Frey
Recently, the H.E.S.S. Collaboration discovered a very high energy gamma-ray
point source close to the Galactic plane. They offered three possible
explanations for the nature of the source: a gamma-ray binary, a pulsar wind
nebula, or a BL Lac object. They concluded that the observations favoured an
extreme BL Lac object interpretation. We investigated the nature of the radio
source reported as the counterpart of the very high energy gamma-ray source. We
performed high-resolution radio interferometric observations with the European
Very Long Baseline Interferometry Network at a frequency of 1.6 GHz on 2011 May
18. We also reanalysed archival 1.4-GHz radio continuum and HI spectral line
data taken with the Very Large Array. The accurate position of the radio
source, as observed with EVN, is ~ 4" off from the one obtained in the NRAO VLA
Sky Survey. The new position is in excellent agreement with that of the
proposed X-ray counterpart of the TeV source. From HI absorption data, a
distance of about 11.5 +/- 1.5 kpc can be inferred for this source. The
large-scale HI data unveiled the presence of a shell-like feature with the
radio/X-ray/TeV point source in its interior. We interpret this shell as the
last vestige of a very old supernova that exploded in a tenuous environment
created by the stellar wind of its massive stellar precursor. The estimated
brightness temperature of the radio point source counterpart of HESS J1943+213
is well below the value expected from the Doppler-boosted radio emission of a
BL Lacertae object. This fact and the discovery of traces of a distant
supernova explosion around the location of the TeV source lead us to conclude
that the most likely origin of the high-energy emission is a remote pulsar wind
nebula. If this scenario is true, then the HI shell around HESS J1943+213 may
represent a population of hitherto missing Galactic SNRs.
View original:
http://arxiv.org/abs/1110.5039
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