The host of GRB 060206: kinematics of a distant galaxy

Abstract

Context. GRB afterglow spectra are sensitive probes of interstellar matter along the line-of-sight in their host galaxies, as well as in intervening galaxies. The rapid fading of GRBs makes it very difficult to obtain spectra of sufficient resolution and S/N to allow for these kinds of studies. Aims. We investigate the state and properties of the interstellar medium in the host of GRB 060206 at z = 4.048 with a detailed study of groundstate and finestructure absorption lines in an early afterglow spectrum. This allows us to derive conclusions on the nature and origin of the absorbing structures and their connection to the host galaxy and/or the GRB. Methods. We used early (starting 1.6 h after the burst) WHT/ISIS optical spectroscopy of the afterglow of the gamma-ray burst GRB 060206 detecting a range of metal absorption lines and their finestructure transitions. Additional information is provided by the afterglow lightcurve. The resolution and wavelength range of the spectra and the bright afterglow have facilitated a detailed study and fitting of the absorption line systems in order to derive column densities. We also used deep imaging to detect the host galaxy and probe the nature of an intervening system at z = 1.48 seen in absorption in the afterglow spectra. Results. We detect four discrete velocity systems in the resonant metal absorption lines, best explained by shells within and/or around the host created by starburst winds. The finestructure lines have no less than three components with strengths decreasing from the redmost components. We therefore suggest that the finestructure lines are best explained as being produced by UV pumping from which follows that the redmost component is the one closest to the burst where N v was detected as well. The host is detected in deep HST imaging with F814W AB = 27.48 ± 0.19 mag and a 3σ upper limit of H = 20.6 mag (Vega) is achieved. A candidate counterpart for the intervening absorption system is detected as well, which is quite exceptional for an absorber in the sightline towards a GRB afterglow. The intervening system shows no temporal evolution as claimed by Hao et al. (2007, ApJ, 659, 99), which we prove from our WHT spectra taken before and Subaru spectra taken during those observations.

Spectroscopy of the short-hard GRB 130603B

“…Optical spectroscopy with OSIRIS, at the Gran Telescopio Canarias (GTC), starting 7 h after the GRB onset, revealed both absorption and emission features at a common redshift of 0.3565 ± 0.0002 (Thöne et al 2013). Three more spectra were obtained in the hours that followed with FORS2 and X-shooter ) at the Very Large Telescope and ACAM at the William Herschel Telescope (WHT).…”

Molecular hydrogen in the damped Lyman αsystem towards GRB 120815A atz= 2.36

“…T 90 is the time during which 90% of the GRB's γ-ray photons are emitted. Fynbo et al 2006;Thöne et al 2008) GRB-DLA. Given the very high column densities of gas regularly detected in GRB afterglow spectra (e.g., Jensen et al 2001;Hjorth et al 2003a;Vreeswijk et al 2004;Jakobsson et al 2006) and their direct link to star-formation (e.g., Galama et al 1998;Hjorth et al 2003b), this low detection rate of H 2 was initially quite surprising.…”

Physical conditions in high-redshift GRB-DLA absorbers observed with VLT/UVES: implications for molecular hydrogen searches

“…Unlike intervening QSO absorbers and damped Lyman-α (DLA) systems (N(H 0 ) ≥ 10 20.3 atoms cm −2 ) observed in QSO spectra, strong absorption lines involving fine-structure and other metastable levels of ions such as O 0 , Si + , and Fe + are ubiquitous in GRB-DLAs (Vreeswijk et al 2004;Chen et al 2005;Berger et al 2006;Penprase et al 2006;Prochaska et al 2006Prochaska et al , 2007aD'Elia et al 2007;Vreeswijk et al 2007;Thöne et al 2008). These levels could be populated by collisions with electrons if the particle density per unit volume is high enough, by indirect excitation by IR photons, or by the UV flux from the GRB afterglow.…”