The Discovery of the Optical and Near‐IR Afterglows of the FirstSwiftGamma‐Ray Bursts

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Abstract
We present optical and near-infrared searches for afterglow emission from the first four Swift bursts with accurate positions from the X-Ray Telescope (XRT). Using telescopes at Las Campanas, Keck, and Palomar observatories, we rapidly identified and followed up afterglows for three of the four bursts and subsequently identified the redshift of GRB 050126 (z = 1.290). In three cases the burst positions were also observed with the Very Large Array, but no radio afterglow emission was detected. The optical/near-IR afterglows are fainter than about 70% of all afterglows detected to date, with GRB 050126 being the faintest, and were identified thanks to accurate and rapid positions from the XRT and rapid response with 1 m telescopes. This suggests that the fraction of dust-obscured bursts is small, 20% when combined with afterglows localized by the HETE-2 Soft X-ray Camera. The X-ray fluxes are typical of the known population, with the exception of GRB 050126, which has the faintest X-ray afterglow to date (normalized to Δt = 10 hr) and was detected thanks to a response time of only 130 s after the burst. Finally, we find that all three optical/near-IR afterglows are located 2'' away from the nominal XRT positions, suggesting that the XRT is capable of delivering highly accurate positions, which will revolutionize afterglow studies.
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