GammaTPC: A Next Generation Gamma Ray Instrument

We present GammaTPC, a new Compton telescope instrument concept focussed on the largely unexplored MeV energy range. GammaTPC holds the promises of providing large area and high sensitivity at moderate cost. It uses liquid argon time projection chamber (TPC) technology, building on substantial developments of such instruments for neutrino physics and dark matter searches. Core to GammaTPC is GAMPix, a new charge readout scheme that achieves fine grained, low noise readout at very low power. There are other interesting aspects to fielding a liquid noble TPC in low Earth orbit. We discuss the status of the GammaTPC development, and present our first estimates of its sensitivity.