Speaker
Description
We present a comprehensive multiwavelength afterglow analysis of the nearby LL GRBs GRB~171205A ($z=0.0368$), associated with SN~2017iuk, to constrain its underlying jet structure. Using the standard synchrotron external forward shock framework and Markov Chain Monte Carlo (MCMC) methods, we perform a comparative study of two distinct jet geometries---the canonical top-hat jet and the smoothly structured Gaussian jet---against extensive radio observations spanning $0.25$--$97.5$~GHz and $4.79$--$937.17$~days post-burst. Both models provide reasonable fits to the broadband afterglow data, but the top-hat jet model is statistically preferred with $\chi^2_\nu = 101.99$ compared to $\chi^2_\nu = 114.50$ for the Gaussian model. Information criteria strongly favour the top-hat geometry, indicating that a structured jet with a sharp outer edge better describes the observed emission. The inferred parameters for the top-hat model yield a jet viewing angle $\theta_{\mathrm{obs}} \sim 33.85^\circ$, while the Gaussian model gives $\theta_{\mathrm{obs}} \sim 38.17^\circ$. Both models consistently indicate a low-density circumburst environment ($n_0 \sim 10^{-2.23}$ to $10^{-0.55}~\mathrm{cm}^{-3}$), characteristic of a wind-like medium expected from a massive Wolf-Rayet progenitor. The high reduced chi-squared values ($\chi^2_\nu \sim 100$--$115$) suggest that the simplified synchrotron model may not fully capture all physical complexities, potentially requiring additional processes such as energy injection, inverse Compton scattering, or more sophisticated emission mechanisms. Our results demonstrate the critical importance of multiwavelength radio observations in constraining jet geometry and provide strong evidence for off-axis viewing in LL GRBs.