Broadband Observations of the Naked‐Eye GRB 080319B

On behalf of a large international collaboration [1], we present the unprecedented broadband observations of GRB 080319B, whose prompt optical emission peaked at a visual magnitude of 5.3, making it briefly visible with the naked eye. GRB 080319B was discovered by Swift and captured in exquisite detail by ground based wide‐field telescopes, imaging the burst location from before the time of the explosion. The combination of these unique optical data with simultaneous γ‐ray observations provides powerful diagnostics of the detailed physics of this explosion within seconds of its formation. We show that the prompt optical and γ‐ray emissions from this event arise from different spectral components within the same physical region located at a large distance from the source, implying an extremely relativistic outflow. Our observations also provide good evidence for a bright reverse shock component. The chromatic behavior of the broadband afterglow is consistent with viewing the GRB down the very narrow inner core of a two‐component jet that is expanding into a wind‐like environment consistent with the massive star origin of long GRBs.