We present optical , near-infrared , and X-ray observations of the optical afterglow ( OA ) of the X-ray rich , long-duration gamma-ray burst GRB 011211 .
Hubble Space Telescope ( HST ) data obtained 14 , 26 , 32 , and 59 days after the burst , show the host galaxy to have a morphology that is fairly typical of blue galaxies at high redshift .
We measure its magnitude to be R = 24.95 \pm 0.11 .
We detect a break in the OA R -band light curve which is naturally accounted for by a collimated outflow geometry .
By fitting a broken power-law to the data we find a best fit with a break 1.56 \pm 0.02 days after the burst , a pre-break slope of \alpha _ { 1 } = -0.95 \pm 0.02 , and a post-break slope of \alpha _ { 2 } = -2.11 \pm 0.07 .
The UV-optical spectral energy distribution ( SED ) around 14 hours after the burst is best fit with a power-law with index \beta = -0.56 \pm 0.19 reddened by an SMC-like extinction law with a modest A _ { V } = 0.08 \pm 0.08 mag .
By comparison , from the XMM-Newton X-ray data at around the same time , we find a decay index of \alpha _ { \mathrm { X } } = -1.62 \pm 0.36 and a spectral index of \beta _ { \mathrm { X } } = -1.21 ^ { +0.10 } _ { -0.15 } .
Interpolating between the UV-optical and X-ray implies that the cooling frequency is located close to \sim 10 ^ { 16 } Hz in the observer frame at the time of the observations .
We argue , using the various temporal and spectral indices above , that the most likely afterglow model is that of a jet expanding into an external environment that has a constant mean density rather than a wind-fed density structure .
We estimate the electron energy index for this burst to be p \sim 2.3 .