Three large gas-filled X-ray detectors on AstroSat, built by TIFR, with a combined collecting area of 8,000 cm². They time rapid changes in X-ray sources.
LAXPC counts X-ray photons and records the energy and arrival time of each. Black holes and neutron stars in binary systems flicker in X-rays within fractions of a second, and LAXPC's large area catches enough photons to follow those changes.
Each of the three identical units is a box of gas. When an X-ray enters, it knocks electrons loose, and the electric pulse they make reveals the X-ray's energy. Together the three have about 8,000 cm² of collecting area. When launched they were the largest-area counters of this type in space. The Tata Institute of Fundamental Research (TIFR) built them.
LAXPC was switched on in October 2015, soon after AstroSat's launch. With the soft X-ray telescope, it found that the black hole in one X-ray binary spins close to the maximum possible rate.