Joint Astrophysics Colloquium

Observation of Very High Energy Gamma-ray Sources Below 100 GeV from Ground: The Detection of the Crab Pulsar at 25 GeV

Nepomuk Otte

UC Santa Cruz

The sky in gamma rays above 25 GeV is a map of some of the most violent places in our Galaxy and universe. The first glimpse of this region of the electromagnetic spectrum was obtained in 1989. Now, 20 years later, we know about 100 sources of very high-energy gamma rays. Identified objects are active galactic nuclei, microquasars, supernova remnants, pulsars, and pulsar wind nebulae, all of which are putative sources of cosmic rays. The origin of cosmic rays is a long standing, almost a century old, mystery. Very high-energy gamma rays not only deepen our understanding of the processes that accelerate cosmic rays. They are also used to address fundamental topics such as dark matter, cosmology and quantum gravity. I will review the imaging Cherenkov technique that is currently the most sensitive method to detect gamma rays between 100 GeV and 10 TeV. I also present selected highlights of observations from the past four years. Among them is the recent detection of the Crab pulsar. The first pulsar that was detected in gamma-rays above 25 GeV.