The case for a high-redshift origin of GRB 100205A
Cenko, S. B.; Lyman, J. D.; Berger, E.; Bloom, J. S.; Cucchiara, A.; Fruchter, A. S.; Perley, D. A.; Wheatley, P. J.; Wiersema, K.; Levan, A. J.; Chrimes, A. A.; Tanvir, N. R.; Hjorth, J.; Jakobsson, P.; Stanway, E. R.; Gompertz, B. P.; O'Brien, P.; Cobb, B. E.
United Kingdom, Netherlands, United States, US Virgin Islands, Denmark, Iceland
Abstract
The number of long gamma-ray bursts (GRBs) known to have occurred in the distant Universe (z > 5) is small (∼15); however, these events provide a powerful way of probing star formation at the onset of galaxy evolution. In this paper, we present the case for GRB 100205A being a largely overlooked high-redshift event. While initially noted as a high-z candidate, this event and its host galaxy have not been explored in detail. By combining optical and near-infrared Gemini afterglow imaging (at t < 1.3 d since burst) with deep late-time limits on host emission from the Hubble Space Telescope, we show that the most likely scenario is that GRB 100205A arose in the range 4 < z < 8. GRB 100205A is an example of a burst whose afterglow, even at ∼1 h post burst, could only be identified by 8-m class IR observations, and suggests that such observations of all optically dark bursts may be necessary to significantly enhance the number of high-redshift GRBs known.