Identifying the host galaxy of the short GRB 100628A
Astronomy and Astrophysics
We report on the results of a comprehensive observing campaign to reveal the host galaxy of the short GRB 100628A. This burst was followed by a faint X-ray afterglow but no optical counterpart was discovered. However, inside the X-ray error circle a potential host galaxy at a redshift of z = 0.102 was soon reported in the literature. If this system is the host, then GRB 100628A was the cosmologically most nearby unambiguous short burst with a measured redshift so far. We used the multi-colour imager GROND at the ESO/La Silla MPG 2.2 m telescope, ESO/VLT spectroscopy, and deep Australia Telescope Compact Array (ATCA) radio-continuum observations together with publicly available Gemini imaging data to study the putative host and the galaxies in the field of GRB 100628A. We confirm that inside the X-ray error circle the most probable host-galaxy candidate is the morphologically disturbed, interacting galaxy system at z = 0.102. The interacting galaxies are connected by a several kpc long tidal stream, which our VLT/FORS2 spectroscopy reveals strong emission lines of [O ii], [O iii], Hα and Hβ, characteristic for the class of extreme emission-line galaxies and indicative of ongoing star formation. The latter leaves open the possibility that the GRB progenitor was a member of a young stellar population. However, we indentify a second host-galaxy candidate slightly outside the X-ray error circle. It is a radio-bright, luminous elliptical galaxy at a redshift z = 0.311. With a K-band luminosity of 2 × 1011L this galaxy resembles the probable giant elliptical host of the first well-localized short burst, GRB 050509B. If this is the host, then the progenitor of GRB 100628A was a member of an old stellar population.
Nicuesa Guelbenzu, A., Klose, S., Palazzi, E., Greiner, J., Michałowski, M., Kann, D., Hunt, L., Malesani, D., Rossi, A., Savaglio, S., Schulze, S., Xu, D., Afonso, P., Elliott, J., Ferrero, P., Filgas, R., Hartmann, D., Krühler, T., Knust, F., Masetti, N., Olivares E., F., Rau, A., Schady, P., Schmidl, S., Tanga, M., Updike, A., & Varela, K. (2015). Identifying the host galaxy of the short GRB 100628A. Astronomy and Astrophysics, 583 https://doi.org/10.1051/0004-6361/201425160