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Title: The afterglow and the host galaxy of GRB 011211
Authors: Jakobsson, P.
Hjorth, J.
Fynbo, J. P. U.
Pedersen, K.
Michelsen, R.
Jensen, B. L.
Pedersen, H.
Jakobsson, P.
Levan, A.
Fynbo, J. P. U.
Thomsen, B.
Weidinger, M.
Gorosabel, J.
Gorosabel, J.
Burud, I.
Levan, A.
Fruchter, A.
Rhoads, J.
Kouveliotou, C.
Tanvir, N.
Grav, T.
Hansen, M. W.
Andersen, M. I.
Bhargavi, S. G.
Cowsik, R.
Pandey, S. B.
First Published: Sep-2003
Publisher: EDP Sciences for European Southern Observatory (ESO)
Citation: Astronomy & Astrophysics, 2003, 408 (3), pp. 941-947
Abstract: 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 $\alpha_{{\rm X}} = -1.62 \pm 0.36$ and a spectral index of $\beta_{\rm X} = -1.21^{+0.10}_{-0.15}$. Interpolating between the UV-optical and X-ray implies that the cooling frequency is located close to ~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 $p \sim2.3$.
DOI Link: 10.1051/0004-6361:20031044
ISSN: 0004-6361
Version: Publisher Version
Status: Peer-reviewed
Type: Journal Article
Rights: Copyright © 2003 ESO. Reproduced with permission from Astronomy & Astrophysics, © ESO.
Appears in Collections:Published Articles, Dept. of Physics and Astronomy

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