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The short gamma-ray burst (GRB) 170817A was the first GRB associated with agravitational-wave event. Due to the exceptionally low luminosity of the prompt$\gamma$-ray and the afterglow emission, the origin of both radiationcomponents is highly debated. The most discussed models for the burst and theafterglow include a regular GRB jet seen off-axis and the emission from thecocoon encompassing a "choked" jet. Here, we report low radio-frequencyobservations at 610 and 1390~MHz obtained with the Giant Metrewave RadioTelescope (GMRT). Our observations span a range of $\sim7$ to $\sim152$ daysafter the burst. The afterglow started to emerge at these low frequencies about60~days after the burst. The $1390$~MHz light curve barely evolved between 60and 150 days, but its evolution is also marginally consistent with a$F_\nu\propto t^{0.8}$ rise seen in higher frequencies. We model the radio dataand archival X-ray, optical and high-frequency radio data with models oftop-hat and Gaussian structured GRB jets. We performed a Markov Chain MonteCarlo analysis of the structured-jet parameter space. Though highly degenerate,useful bounds on the posterior probability distributions can be obtained. Ourbounds of the viewing angle are consistent with that inferred from thegravitational wave signal. We estimate the energy budget in prompt emission tobe an order of magnitude lower than that in the afterglow blast-wave.

Low frequency view of GW 170817/GRB 170817A with the Giant Meterwave Radio Telescope