TY - JOUR
T1 - Probing gamma-ray burst environments with time variability
T2 - ULTRASPEC fast imaging of GRB 080210
AU - De Cia...[et al.], A.
AU - Jakobsson, P.
AU - Vreeswijk, Paul Marijn
AU - Fynbo, Johan Peter Uldall
AU - Leloudas, Georgios
AU - Malesani, Daniele
AU - Zafar, Tayyaba
PY - 2011/4/1
Y1 - 2011/4/1
N2 - We present high time resolution (1.09s) photometry of GRB080210 obtained with ULTRASPEC mounted on the ESO/3.6-m telescope, starting 68.22 min after the burst and lasting for 26.45 min. The light curve is smooth on both short (down to 2.18s) and long time scales, confirmed by a featureless power spectrum. On top of the fireball power-law decay, bumps and wiggles at different time scales can, in principle, be produced by density fluctuations in the circumburst medium, by substructures in the jet or by refreshed shocks. Comparing our constraints with variability limits derived from kinematic arguments, we exclude under-density fluctuations producing flux dips larger than 1per cent with time scales Δt > 9.2 min (2per cent on Δt > 2.3 min for many fluctuating regions). In addition, we study the VLT/FORS2 afterglow spectrum, the optical-to-X-ray spectral energy distribution (SED) and the time decay. The SED is best fitted with a broken power law with slopes βopt= 0.71 ± 0.01 and βX= 1.59 ± 0.07, in disagreement with the fireball model, suggesting a non-standard afterglow for GRB080210. We find AV= 0.18 ± 0.03mag optical extinction due to SMC-like dust and an excess X-ray absorption of log(NH/cm-2) = 21.58+0.18-0.26 assuming solar abundances. The spectral analysis reveals a damped Lyα absorber (logcm-2) = 21.90 ± 0.10) with a low metallicity ([X/H]=-1.21 ± 0.16), likely associated with the interstellar medium of the GRB host galaxy (z= 2.641).
AB - We present high time resolution (1.09s) photometry of GRB080210 obtained with ULTRASPEC mounted on the ESO/3.6-m telescope, starting 68.22 min after the burst and lasting for 26.45 min. The light curve is smooth on both short (down to 2.18s) and long time scales, confirmed by a featureless power spectrum. On top of the fireball power-law decay, bumps and wiggles at different time scales can, in principle, be produced by density fluctuations in the circumburst medium, by substructures in the jet or by refreshed shocks. Comparing our constraints with variability limits derived from kinematic arguments, we exclude under-density fluctuations producing flux dips larger than 1per cent with time scales Δt > 9.2 min (2per cent on Δt > 2.3 min for many fluctuating regions). In addition, we study the VLT/FORS2 afterglow spectrum, the optical-to-X-ray spectral energy distribution (SED) and the time decay. The SED is best fitted with a broken power law with slopes βopt= 0.71 ± 0.01 and βX= 1.59 ± 0.07, in disagreement with the fireball model, suggesting a non-standard afterglow for GRB080210. We find AV= 0.18 ± 0.03mag optical extinction due to SMC-like dust and an excess X-ray absorption of log(NH/cm-2) = 21.58+0.18-0.26 assuming solar abundances. The spectral analysis reveals a damped Lyα absorber (logcm-2) = 21.90 ± 0.10) with a low metallicity ([X/H]=-1.21 ± 0.16), likely associated with the interstellar medium of the GRB host galaxy (z= 2.641).
U2 - 10.1111/j.1365-2966.2010.18046.x
DO - 10.1111/j.1365-2966.2010.18046.x
M3 - Journal article
SN - 0035-8711
VL - 412
SP - 2229
EP - 2240
JO - Royal Astronomical Society. Monthly Notices
JF - Royal Astronomical Society. Monthly Notices
IS - 4
ER -