Godet, O.O.GodetPage, K. L.K. L.PageOsborne, J. P.J. P.OsborneCapalbi, MilviaMilviaCapalbi2020-09-172020-09-172006-06-01https://hdl.handle.net/20.500.13025/446Astronomy and Astrophysics, Volume 452, Issue 3, June IV 2006, pp.819-825We present the Swift observations of the faint burst <ASTROBJ>GRB 050421</ASTROBJ>. The X-ray light-curve shows at least two flares the first flare peaking at ~110 s after the BAT trigger (T_0) and the second one peaking at ~154 s. The first flare presents a flux variation of delta F/F<SUB>peak</SUB> &tilde; 3.7 and a short timescale ratio delta t/t<SUB>peak</SUB> &tilde; 0.07. The second flare is smaller and presents a flux variation of delta F/F<SUB>peak</SUB> &tilde; 1.7 and a short timescale ratio delta t/t<SUB>peak</SUB> &tilde; 0.03. We argue that the mechanism producing these flares is probably late internal shocks. The X-ray light-curve is consistent with a rapid decline with a temporal index alpha&tilde; 3.1, which decays from ~10<SUP>-9</SUP> erg cm<SUP>-2</SUP> s<SUP>-1</SUP> at T_0+100 s to < 7 10<SUP>-13</SUP> erg cm<SUP>-2</SUP> s<SUP>-1</SUP> at T_0+900 s. A possible spectral softening is also observed with time, from beta &tilde; 0.1 to &tilde; 1.2. A good joint fit to the BAT and XRT spectra before T_0+171 s with beta<SUB>XRT-BAT</SUB>&tilde; 0.2 indicates that the early X-ray and Gamma-ray emissions are likely produced by the same mechanism. We argue that the X-ray spectral softening, if any, is due to a shift of the peak of the prompt emission spectrum down to lower energies, and that the rapid decline of the X-ray emission is probably the tail of the prompt emission. This suggests that the X-ray emission is completely dominated by high latitude radiation and the external shock, if any, is extremely faint and below the detection threshold. <ASTROBJ>GRB 050421</ASTROBJ> is likely the first ``naked burst'' detected by Swift.gamma ray bursts10.1051/0004-6361 20054435http://adsabs.harvard.edu/abs/2006A&A...452..819G2006A&A...452..819G