Modeling Relativistic Jets and Their Synchrotron Signatures from Astrophysical Transients

Astrophysical transients, such as neutron star mergers and core-collapse supernovae, are some of the most energetic explosions in the universe. The outflows from these events are often relativistic and highly structured, primarily in the form of jets. These jets produce observable signatures through non-thermal radiation, overwhelmingly dominated by synchrotron emission, as they interact with the surrounding medium or their internal structure. As a theoretical and computational astrophysicist, my research focuses on the ”back-and-forth chase” between theoretical models and observational data, aiming to reconstruct the full story of these cosmic explosions. I will present my work on Firefly, a novel code I developed to transform the outputs of relativistic hydrodynamical simulations into observable signatures. Firefly can generate realistic light curves, spectra, and apparent motion for both on-axis and off-axis observers, covering the entire electromagnetic spectrum from radio to GeV. This capability is crucial, as analytical calculations for off-axis observations are extremely complex and require numerical efforts. I will discuss how Firefly has been successfully used to model the afterglow of GRB170817A (Dastidar & Duffell 2024), and some insights into counter-jet re-brightening. Additionally, the first off-axis jetted supernova discovery is on the horizon. I will highlight our collaborative work with observers using the Einstein Probe (Srinivasaragavan et al. 2025), ZTF (Schroeder et al. 2025) and future observations planned with NRAO and EVN for the same. Finally, I will outline the capabilities of synchrotron radiation to model other transients, such as core collapse supernovae and tidal disruption events, and the role Firefly can play in this context.