GRB 050223: a dark GRB in a dusty starburst galaxy

PELLIZZA, L. J.; DUC, P.-A.; LE FLOC'H, E.; MIRABEL, I. F.; ANTONELLI, L. A.; CAMPANA, S.; CHINCARINI, G.; CIMATTI, A.; COVINO, S.; DELLA VALLE, M.; FIORE, F.; FUGAZZA, D.; GIOMMI, P.; GOLDONI, P.; ISRAEL, G. L.; MOLINARI, E.; MORETTI, A.; PIRO, L.; SARACCO, P.; STELLA, L.; TAGLIAFERRI, G.; VIETRI, M.

ASTRONOMY AND ASTROPHYSICS

EDP Sciences

Lugar: Les Ulis, Francia; Año: 2006 vol. 459 p. 5 - 8

0004-6361

Aims: We aim at detecting and determining the properties of the host galaxy of the dark GRB 050223. Methods: We use VLT optical/NIR images coupled to Swift X-ray positioning, and optical spectra of the host galaxy to measure its properties. Results: We find a single galaxy within the Swift error box of GRB 050223. It is located at z = 0.584 and its luminosity is L ∼ 0.4 L*. Emission lines in the galaxy spectrum imply an intrinsic SFR > 7 M_sun yr-1, and a large extinction AV > 2 mag within it. We also detect absorption lines, which reveal an underlying stellar population with an age between 40 Myr and 1.5 Gyr. Conclusions: The identification of a host galaxy with atypical properties using only the X-ray transient suggests that a bias may be present in the former sample of host galaxies. Dust obscuration together with intrinsic faintness are the most probable causes for the darkness of this burst.