| Abstract: | The nine-year H.E.S.S. Galactic Plane Survey (HGPS) yielded the most uniform
observation scan of the inner Milky Way in the TeV gamma-ray band to date. The
sky maps and source catalogue of the HGPS allow for a systematic study of the
population of TeV pulsar wind nebulae found throughout the last decade. To
investigate the nature and evolution of pulsar wind nebulae, for the first time
we also present several upper limits for regions around pulsars without a
detected TeV wind nebula. Our data exhibit a correlation of TeV surface
brightness with pulsar spin-down power $dot{E}$. This seems to be caused both
by an increase of extension with decreasing $dot{E}$, and hence with time,
compatible with a power law $R_mathrm{PWN}(dot{E}) sim dot{E}^{-0.65 pm
0.20}$, and by a mild decrease of TeV gamma-ray luminosity with decreasing
$dot{E}$, compatible with $L_{1-10,mathrm{TeV}} sim dot{E}^{0.59 pm
0.21}$. We also find that the offsets of pulsars with respect to the wind
nebula centres with ages around 10 kyr are frequently larger than can be
plausibly explained by pulsar proper motion and could be due to an asymmetric
environment. In the present data, it seems that a large pulsar offset is
correlated with a high apparent TeV efficiency
$L_{1-10,mathrm{TeV}}/dot{E}$. In addition to 14 HGPS sources considered as
firmly identified pulsar wind nebulae and 5 additional pulsar wind nebulae
taken from literature, we find 10 HGPS sources that form likely TeV pulsar wind
nebula candidates. Using a model that subsumes the present common understanding
of the very high-energy radiative evolution of pulsar wind nebulae, we find
that the trends and variations of the TeV observables and limits can be
reproduced to a good level, drawing a consistent picture of present-day TeV
data and theory. |
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