We present the earliest ultraviolet (UV) spectrum of a gamma-ray burst (GRB) as observed with the Swift Ultra-Violet/Optical Telescope (UVOT). The GRB 081203A spectrum was observed for 50 s with the UV-grism starting 251 s after the Swift-Burst-Alert-Telescope (BAT) trigger. During this time, the GRB was ≈13.4 mag (u filter) and was still rising to its peak optical brightness. In the UV-grism spectrum, we find a damped Lyα line, Lyβ and the Lyman continuum break at a redshift z = 2.05 ± 0.01. A model At to the Lyman absorption implies a gas column density of log NHI = 22.0 ± 0.1 cm-2, which is typical of GRB host galaxies with damped Lyα absorbers. This observation of GRB 081203A demonstrates that for brighter GRBs (υ ≈ 14 mag) with moderate redshift (0.5 < z < 3.5) the UVOT is able to provide redshifts, and probe for damped Lyα absorbers within 4-6 min from the time of the Swift-BAT trigger.
|Original language||English (US)|
|Journal||Monthly Notices of the Royal Astronomical Society: Letters|
|State||Published - May 2009|
All Science Journal Classification (ASJC) codes
- Astronomy and Astrophysics
- Space and Planetary Science