Daksha: On Alert for High Energy Transients

The proposed Daksha mission comprises of a pair of broadband high-energy satellites designed to give the most sensitive continuous coverage of the high-energy transient sky. With a formidable combination of sensitivity and coverage, Daksha is well-poised to spearhead the high-energy studies in the global multi-messenger astrophysics effort. The workshorses for Daksha are Cadmium Zinc Telluride detectors that give Swift-BAT-like sensitivity over the entire sky, with a median effective area of 1300 cm2 in the 20-200 keV range, and highly uniform sky coverage. At lower energies, Silicon Drift Detectors extend the sensitivity to 1 keV, while NaI scintillators extend the high energy coverage to 1 MeV. The two antipodal satellites in a low-inclination low-earth orbit given an effective 84% time-averaged sky coverage, up from ~50% for single missions. On-board data processing will be used to detect and broadcast transients with a latency of < 1 minute. All photon data will be downloaded later for sophisticated ground analysis. The Daksha satellites will be able to detect the largest number of electromagnetic counterparts to high energy sources, detect high redshift GRBs, perform finely time-resolved spectroscopy of bright bursts, and will enable a wide range of science cases including X-ray binary outbursts, pulsar studies, magnetar flares, counterparts to Fast Radio Bursts, Earth-occultation imaging, solar sudies, terrestrial gamma-ray flashes. Daksha will also be the only mission to provide all-sky coverage in the soft-X-ray band, yielding the best soft spectra of prompt emission from transient sources. Scaling massively from the legacy of the Cadmium Zinc Telluride Imager on board AstroSat, Daksha will measure polarisation of dozens of GRBs every year. Daksha has been recommended as one of the leading space astronomy missions in India, and development of a proof of concept is at an advanced stage with seed funding from the Indian Space Research Organisation. I will talk about the mission, its science goals, current status, and opportunities for international collaborations in hardware and science.