Development of an optical photon counting imager using a monolithic Geiger APD array

We have developed a photo-sensor for an optical photon counting imager for astronomy with high timing resolution. We customize a Multi Pixel Photon Counter as a monolithic Geiger avalanche photodiode array with a pixel size of 100 micro-meter. The prototype model consists of 4x4 pixels. Excellent timing response is achieved as fast as an order of nanosecond. We evaluate the basic performance of the sensor and confirm the gain linearity, uniformity and low dark count rates. We observe the Crab pulsar using this system with a 35-cm telescope, and successfully detected periodic pulses with a frequency consistent with that reported by radio observatory.