Rykoff, ESYost, SAKrimm, HAAharonian, FAkerlof, CWAlatalo, KAshley, MCB2025-01-272025-01-2720050004-637X1538-4357https://doi.org/10.1086/497370https://hdl.handle.net/20.500.12428/22752The ROTSE-IIIa telescope at Siding Spring Observatory, Australia, detected prompt optical emission from Swift GRB 050401. We present observations of the early optical afterglow, first detected by the ROTSE-IIIa telescope 33 s after the start of gamma-ray emission, contemporaneous with the brightest peak of this emission. This GRB was neither exceptionally long nor bright. This is the first prompt optical detection of a GRB of typical duration and luminosity. We find that the early afterglow decay does not deviate significantly from the power-law decay observable at later times and is uncorrelated with the prompt gamma-ray emission. We compare this detection with the other two GRBs with prompt observations, GRB 990123 and GRB 041219a. All three bursts exhibit quite different behavior at early times.eninfo:eu-repo/semantics/openAccessgamma rays : burstsArticle6312L121L12410.1086/497370Q1WOS:0002323657000062-s2.0-27744505849Q1