Abstract
Context: We present high resolution VLT UVES and low resolution FORS optical spectroscopy of supernova 2006aj and its host galaxy, associated with the nearby (z = 0.03342) gamma-ray burst GRB 060218. This host galaxy is a unique case, as it is one of the few nearby GRB host galaxies known, and it is only the second time high resolution spectra have been taken of a nearby GRB host galaxy (after GRB 980425). Aims: The resolution, wavelength range and S/N of the UVES spectrum combined with low resolution FORS spectra allow a detailed analysis of the circumburst and host galaxy environments. Methods: We analyse the emission and absorption lines in the spectrum, combining the high resolution UVES spectrum with low resolution FORS spectra and find the metallicity and chemical abundances in the host. We probe the geometry of the host by studying the emission line profiles. Results: Our spectral analysis shows that the star forming region in the host is metal poor with 12 + log(O/H) = 7.54+0.17-0.10 (~0.07 Zo), placing it among the most metal deficient subset of emission-line galaxies. It is also the lowest metallicity found so far for a GRB host from an emission-line analysis. Given the stellar mass of the galaxy of ~107 Mo and the SFRHalpha = 0.065 ± 0.005 Mo yr-1, the high specific star formation rate indicates an age for the galaxy of less than ~200 Myr. The brightest emission lines are clearly asymmetric and are well fit by two Gaussian components separated by Eœ 22 km s-1. We detect two discrete Na I and Ca II absorption components at the same redshifts as the emission components. We tentatively interpret the two components as arising from two different starforming regions in the host, but high resolution imaging is necessary to confirm this. Based on observations obtained at the ESO VLT under ESO programme 076.A-0737(A).
Highlights
Long-duration gamma-ray bursts (GRBs) are widely accepted to be related to core-collapse supernovae: clear supernova signatures are seen in the afterglow spectra of low redshift GRBs (e.g. Stanek et al 2003; Hjorth et al 2003; Pian et al 2006)
We present high resolution VLT Ultraviolet and Visual Echelle Spectrograph (UVES) and low resolution FORS optical spectroscopy of supernova 2006aj and its host galaxy, associated with the nearby (z = 0.03342) gamma-ray burst GRB 060218
In this paper we study the host of GRB 060218 through a high resolution VLT Ultraviolet and Visual Echelle Spectrograph (UVES; Dekker et al 2000) spectrum, taken around the peak magnitude of the supernova
Summary
Long-duration gamma-ray bursts (GRBs) are widely accepted to be related to core-collapse supernovae: clear supernova signatures are seen in the afterglow spectra of low redshift GRBs (e.g. Stanek et al 2003; Hjorth et al 2003; Pian et al 2006). In this paper we study the host of GRB 060218 through a high resolution VLT Ultraviolet and Visual Echelle Spectrograph (UVES; Dekker et al 2000) spectrum, taken around the peak magnitude of the supernova. This spectrum shows a variety of well resolved emission lines, associated with ionized gas in the starforming regions in the host. Modjaz et al (2006) report a metallicity of 0.15 Z , Mirabal et al (2006) derive 0.46 Z , while Sollerman et al (2006) mention that the abundance is below Solar, but that the exact value is unconstrained from the strong emission lines.
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
