Abstract
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.
Highlights
Long-duration gamma-ray bursts (GRBs) give rise to a synchrotron afterglow, detectable at optical wavelengths if sufficiently rapid and deep follow-up observations are made
We present the case for GRB 100205A being a largely overlooked high-redshift event
By combining optical and near-infrared Gemini afterglow imaging 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
Summary
Long-duration gamma-ray bursts (GRBs) give rise to a synchrotron afterglow, detectable at optical wavelengths if sufficiently rapid and deep follow-up observations are made. When the Xray to optical spectral slope, βOX, is below the recognised threshold of 0.5, the event is classified as ‘dark’ (Jakobsson et al 2004). This is typically evaluated at 11 hours postburst to avoid contamination from early-time effects including X-ray flares and plateaus. The X-ray afterglow was rapidly identified, and ground based observations were taken in the first hour after the burst None of these early optical observations revealed a candidate optical afterglow (see Malesani et al 2010; Cobb et al 2010; Tanvir et al 2010; Cucchiara et al 2010; Nicuesa et al 2010; Urata et al 2010; Perley et al 2010), marking GRB 100205A as a dark burst (Malesani et al 2010), and motivating further follow-up
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