1112.0786 (Stefan Klepser)
Stefan Klepser
Astrophysical sources of TeV gamma rays are usually established by Cherenkov
telescope observations. These counting type instruments have a field of view of
few degrees in diameter and record large numbers of particle air showers via
their Cherenkov radiation in the atmosphere. The showers are either induced by
gamma rays or diffuse cosmic ray background. The commonly used test statistic
to evaluate a possible gamma-ray excess is Li and Ma (1983), Eq. 17, which can
be applied to independent on- and off-source observations, or scenarios that
can be approximated as such. This formula however is unsuitable if the data are
taken in so-called "wobble" mode (pointing to several offset positions around
the source), if at the same time the acceptance shape is irregular or even
depends on the pointing direction. To provide a robust test statistic in such
cases, this paper explores a possible generalization of the likelihood ratio
concept on which the formula of Li and Ma is based. In doing so, we fully
exploit the multi-pointing nature of the data and the typically known
instrument point spread function to derive a new, seminumerical test statistic.
Due to its flexibility and robustness against systematic uncertainties, it is
not only useful for detection purposes, but also for skymapping and source
shape fitting. We present simplified Monte Carlo simulations to verify the
results, and discuss several applications and further generalizations of the
concept.
View original:
http://arxiv.org/abs/1112.0786
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