# The host of the SN-less GRB 060505 in high resolution

### Abstract

The spiral host galaxy of the Swift GRB 060505 at z = 0.089 was the site of a puzzling long duration burst without an accompanying supernova. Studies of the burst environment by Thöne et al. suggested that this Gamma-ray Burst (GRB) came from the collapse of a massive star and that the GRB site was a region with properties different from the rest of the galaxy. We reobserved the galaxy in high spatial resolution using the VIMOS integral- field unit at the VLT with a spaxel size of 0.67 arcsec. Furthermore, we use long-slit high-resolution data from HIRES/Keck at two different slit positions covering the GRB site, the centre of the galaxy and an H II region next to the GRB region. We compare the properties of different H II regions in the galaxy with the GRB site and study the global and local kinematic properties of this galaxy. The resolved data show that the GRB site has the lowest metallicity in the galaxy with ̃1/3 Z$_☉$, but its specific star formation rate (SSFR) of 7.4 M$_☉$ yr$^-1$/L/L* and age (determined by the Hα EW) are similar to other H II regions in the host. The galaxy shows a gradient in metallicity and SSFR from the bulge to the outskirts as it is common for spiral galaxies. This gives further support to the theory that GRBs prefer regions of higher star formation and lower metallicity, which, in S-type galaxies, are more easily found in the spiral arms than in the centre. Kinematic measurements of the galaxy do not show evidence for large perturbations but a minor merger in the past cannot be excluded. This study confirms the collapsar origin of GRB 060505 but reveals that the properties of the H II region surrounding the GRB were not unique to that galaxy. Spatially resolved observations are key to know the implications and interpretations of unresolved GRB hosts observations at higher redshifts.

Publication
Monthly Notices of the Royal Astronomical Society