4 research outputs found

    Prompt optical observations of GRB 080330 and GRB 080413A

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    We report on the results of rapid responses to GRB 080330 and GRB 080413A by the ROTSE-IIIb and ROTSE-IIIc telecopes. In both cases, optical follow-up started during the prompt emission phase and recorded optical flares peaking at similar times as the last hard X-ray pulses detected by the Swift BAT. For both events, the XRT observations started at the end of the prompt BAT detection and displayed an evolution in time opposite to the optical lightcurve. These very early observations provide us an opportunity to probe the onset of afterglow for these two events

    Taking a broad view of prompt emission

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    We discuss the diversity of prompt Gamma-Ray Burst (GRB) spectra from high to low energies, comparing optical observations to simultaneous garnma-ray emission. These events show a wide variety of relations between gamma-ray and optical spectral and temporal properties. Using optical detections and limits from ROTSE as well as the literature, we constrain the broad-band spectral shape during GRB events. With no single result for low-energy emission behavior, GRB models will need to account for diverse outcomes

    GRB 081008: FROM BURST TO AFTERGLOW AND THE TRANSITION PHASE IN BETWEEN

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    We present a multi-wavelength study of GRB 081008, at redshift 1.967, by Swift, ROTSE-III, and Gamma-Ray Burst Optical/NearInfrared Detector. Compared to other Swift GRBs, GRB 081008 has a typical gamma-ray isotropic equivalent energy output (similar to 10(53) erg) during the prompt phase, and displayed two temporally separated clusters of pulses. The early X-ray emission seen by the Swift X-Ray Telescope was dominated by the softening tail of the prompt emission, producing multiple flares during and after the Swift Burst Alert Telescope detections. Optical observations that started shortly after the first active phase of gamma-ray emission showed two consecutive peaks. We interpret the first optical peak as the onset of the afterglow associated with the early burst activities. A second optical peak, coincident with the later gamma-ray pulses, imposes a small modification to the otherwise smooth light curve and thus suggests a minimal contribution from a probable internal component. We suggest the early optical variability may be from continuous energy injection into the forward shock front by later shells producing the second epoch of burst activities. These early observations thus provide a potential probe for the transition from the prompt phase to the afterglow phase. The later light curve of GRB 081008 displays a smooth steepening in all optical bands and X-ray. The temporal break is consistent with being achromatic at the observed wavelengths. Our broad energy coverage shortly after the break constrains a spectral break within optical. However, the evolution of the break frequency is not observed. We discuss the plausible interpretations of this behavior
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