WIDGET: System performance and grb prompt optical observations

Abstract

The WIDeField telescope for Gamma-ray burst Early Timing (WIDGET) is used for a fully automated, ultrawide- field survey aimed at detecting the prompt optical emission associated with Gamma-ray Bursts (GRBs). WIDGET surveys the HETE-2 and Swift/BAT pointing directions, covering a total field of view of 62° × 62° every 10 secounds using a unfiltered system. This monitoring survey allows the exploration of optical emission before the γ-ray trigger. The unfiltered magnitude is well converted to the SDSS r' system at a 0.1 mag level. Since 2004, WIDGET has made a total of ten simultaneous and one pre-trigger GRB observations. The efficiency of synchronized observations with HETE-2 is four-times better than that of Swift. There has been no bright optical emission similar to that from GRB 080319B. A statistical analysis implies that GRB 080319B is a rare event. This paper summarizes the design and operation of the WIDGET system and the simultaneous GRB observations obtained with this instrument. © 2011. Astronomical Society of Japan.