GRB 050904: the oldest cosmic explosion ever observed in the Universe

Swiftdiscovered the high redshift (z=6.29) GRB 050904 with the BurstAlert Telescope and began observing with its narrow field instruments only 161 s after the burstonset. GRB 050904 was a long, multi‐peaked, bright GRB with a presence of flaring activity lasting up to 1–2 hours after the burstonset. The spectral energy distributionshows a clear softening trend along the burstevolution with a photon index decreasing from −1.2 up to −1.9. The observed variabilityis more dramatic than the typical Swift afterglow, the amplitude and rise/ fall timesof the flares are consistent with the behavior of nearby (z ⩽ 1) long GRBs and suggest the interpretation of the BAT and XRT data as a single continuous observation of long lasting prompt emission.