Raptor Observations of the Early Optical Afterglow from Grb 050319

The RAPid Telescopes for Optical Response (RAPTOR) system at Los Alamos National Laboratory observed GRB 050319 starting 25.4 seconds after γ-ray emission triggered the Burst Alert Telescope (BAT) on-board the Swift satellite. Our well sampled light curve of the early optical afterglow is composed of 32 points (derived from 70 exposures) that measure the flux decay during the first hour after the GRB. The GRB 050319 light curve measured by RAPTOR can be described as a relatively gradual flux decline (power-law index α = −0.37) with a transition, at about ∼ 400 s after the GRB, to a faster flux decay (α = −0.91). The addition of other available measurements to the RAPTOR light curve suggests that another emission component emerged after ∼ 10 4 s. We hypothesize that the early afterglow emission is powered by extended energy injection or delayed reverse shock emission followed by the emergence of forward shock emission. Recent years have brought interesting developments in the domain of observations of the early optical emission from Gamma-Ray Bursts (GRBs). Several groups now have the routine capability to respond to GRB triggers in real time using rapidly slewing robotic instruments (e.g. Despite much effort in this area, so far only a handful of GRBs have been detected within the first minutes after the onset of the γ-ray 2005a,b). Even fewer events have good S/N and coverage. The discovery of the near infra-red transient from GRB 041219a (Blake & Bloom 2004; Blake et al. 2005) and its parallel detection in the optical band (Wren et al. 2004) expanded the list of known GRB properties. The RAPTOR (Rapid Telescopes for Optical Response ; Vestrand et al. 2002) optical light curve of GRB 041219a (Vestrand et al. 2005) overlaps with the γ-ray emission by an unprecedented ∼ 6.4 minutes. Vestrand et al. (2005) discovered a qualitatively new component of the early optical emission from GRBs, and presented evidence for internal shocks (Meszaros & Rees 1999) as the emission mechanism. The presence of the new component was established on purely empirical basis by its distinct close correlation with strongly time-varying γ-ray flux. The updated taxonomy for GRB-related optical transient (OT) emission proposed by Vestrand et al. (2005) comprises: (1) Prompt optical emission contempora-neous with and consistent with a constant flux ratio to γ-rays (the ratio is ∼ 1.2 × 10 −5 in GRB 041219a (Vestrand et al. 2005)); (2) Early afterglow emission …