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Strategies for selection of small γ-ray showers using the Imaging Atmospheric Cherenkov Technique |
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| Authors: | P Moriarty C Masterson DJ Fegan JH Buckley M Catanese J Quinn PT Reynolds F Krennrich |
| Institution: | a Department of Physical Sciences, Regional Technical College, Galway, Ireland b Physics Department, University College, Dublin 4, Ireland c Whipple Observatory, Harvard-Smithsonian CfA, P.O. Box 97, Amado, AZ 85645-0097, USA d Department of Physics and Astronomy, Iowa State University, Ames, IA 50011-3160, USA e School of Science, Regional Technical College, Tallaght, Dublin 24, Ireland |
| Abstract: | Methods of selecting small candidate γ-ray events obtained using the Imaging Atmospheric Cherenkov Technique are presented. Three approaches are described: a variant of the standard ‘Supercuts’ analysis technique, a parameter weights approach, and a neural network approach. A cut on the parameter combination Length/Size is developed and shown to be effective at rejecting background due to muons. The techniques are applied to observations of Markarian 421 taken during 1995 and 1996 with the Whipple 10 m reflector. The efficiency and stability of the three approaches are compared, and the Supercuts variant is shown to be the most robust. A signal is detected in the energy range 170 GeV to 300 GeV at a significance level of 6.5 σ, in 7 hours of observation (the standard analysis gives 15.2 σ for E > 300 GeV). This represents the first significant detection of a source at an energy threshold below 200 GeV using the Whipple 10 m system. |
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