Closing down the observation gap on millisecond to second timescale relativistic radio and X-ray transients

Over the past few decades, transient astronomy has boomed with discovery of different types of transient phenomena (e.g. Gamma-ray Bursts — GRBs, Fast Radio Burst — FRBs, compact binary coalescence in gravitational waves — CBCs). Most of these transient are highly relativistic events and key to understand them is to do multi-wavelength and multi-messenger observations. In this talk, I will present our efforts to build instrumentation to detect milliseconds to second timescale relativistic transient phenomena at radio and X-ray wavelengths. In particular, in the first part, I will talk about our novel efforts to detect radio transients at seconds timescale with the CHIME radio telescope. This parameter space is as-yet unexplored and could harbour interesting transients such as "slower" duration or extremely scattered FRBs, radio counterparts of GRBs or binary neutron star mergers, flaring stars, magnetized white dwarfs and radio emission from X-ray binaries. In the second part, I will present the proposed Daksha mission which aims to detect GRBs and electromagnetic counterparts of GW events. Once launched, Daksha will be the most sensitive X-ray/gamma-ray telescope. In particular, I will talk about prospects of measuring hard X-ray polarisation of GRBs using Daksha, which is a key to understand emission mechanisms and geometry of GRB jets. For this analysis, we have carried out detail simulations and have developed a pipeline to measure the polarisation. We estimate that Daksha will have Minimum Detectable Polarisation of 36% for a GRB with fluence 1e-4 erg/cm2. With this sensitivity, Daksha will be able to measure polarisation of at least five GRBs per year (Bala and Mate et. al. in prep).