GRB 081203A: Swift UVOT captures the earliest ultraviolet spectrum of a gamma-ray burst
Abstract
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 fit to the Lyman absorption implies a gas column density of log NHI = 22.0 +/- 0.1cm-2, which is typical of GRB host galaxies with damped Lyα absorbers. This observation of GRB 081203A demonstrates that for brighter GRBs (v ~ 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.
- Publication:
-
Monthly Notices of the Royal Astronomical Society
- Pub Date:
- May 2009
- DOI:
- 10.1111/j.1745-3933.2009.00632.x
- arXiv:
- arXiv:0812.2943
- Bibcode:
- 2009MNRAS.395L..21K
- Keywords:
-
- instrumentation: spectrographs;
- gamma-rays: bursts;
- Astrophysics
- E-Print:
- 4 pages, 4 figures, accepted by MNRAS letters