A. Cucchiara, J. X. Prochaska, D. A. Perley, S. B. Cenko, J. Werk, Y. Cao, J. S. Bloom, B. E. Cobb
We present early optical photometry and spectroscopy of the afterglow and host galaxy of the bright short-duration gamma-ray burst \grb. Using our target-of-opportunity program on the Gemini South telescope, our prompt optical spectra reveal a strong trace from the afterglow superimposed on continuum and emission lines from the $z = 0.3568 \pm 0.0005$ host galaxy. The combination of a relatively bright optical afterglow ($r^{\prime} = 21.52$ at $\Delta t = 8.4$\,hr), together with an observed offset of 0\farcs9 from the host nucleus (4.8 kpc projected distance at $z = 0.3568$), allow us to extract a relatively clean spectrum dominated by afterglow light -- the first \textit{bona fide} short-duration GRB for which this has been possible. Furthermore, the spatially resolved spectrum allows us to constrain the properties of the explosion site directly, and compare these with the host galaxy nucleus, as well as other short-duration GRB host galaxies. We find that while the host is a relatively luminous ($L \approx 0.8 L^{*}_{B}$), star-forming (SFR $\gtrsim 1.3$\,M${_\odot}$\,yr$^{-1}$) galaxy with almost solar metallicity, the spectrum of the afterglow exhibits neither emission nor absorption features. The explosion site therefore appears to lack evidence of recent star formation, consistent with the relatively long delay time distribution expected in a compact binary merger scenario. The star formation rate (both in an absolute sense and normalized to the luminosity) and metallicity of the host are both consistent with the known sample of short-duration GRB hosts.
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http://arxiv.org/abs/1306.2028
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