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- · arXiv e-print (arXiv:1012.4009)
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| Title: |
| The Optical Afterglow and z=0.92 Early-type Host Galaxy of the Short GRB 100117A |
| Authors: |
| Fong, Wen-fai; Berger, Edo; Chornock, Ryan; Tanvir, Nial R.; Levan, Andrew J.; Graham, John F.; Fruchter, Andrew S.;Cucchiara, Antonino; Fox, Derek B. |
| Publication: |
| eprint arXiv:1012.4009 |
| Publication Date: |
| 12/2010 |
| Origin: |
| ARXIV |
| Keywords: |
| Astrophysics - High Energy Astrophysical Phenomena |
| Comment: |
| Submitted to ApJ; emulateapj style; 15 pages, 1 table, 9 figures |
| Bibliographic Code: |
| 2010arXiv1012.4009F |
Abstract
We present the discovery of the optical afterglow and early-type host galaxy of the short-duration GRB 100117A. The faint afterglow is detected 8.3 hr after the burst with r_AB = 25.46 +/- 0.20 mag. Follow-up optical and near-IR observations uncover a coincident compact red galaxy, identified as an early-type galaxy at a photometric redshift of z~0.6-0.9 (2-sigma) with a mass of 3x10^10 M_Sun, an age of ~1 Gyr, and a luminosity of L_B~0.5L_star. Spectroscopic observations of the host reveal a notable break corresponding to the Balmer 4000-Angstrom break at z~0.9, and stellar population spectral evolution template fits indicate z~0.915, which we adopt as the redshift of the host, with stellar population ages of ~1-3 Gyr. From a possible weak detection of [OII]-3727 emission at z=0.915 we infer an upper bound on the star formation rate of ~0.1 M_Sun per yr, leading to a specific star formation rate of <0.004 per Gyr. Thus, GRB 100117A is only the second short burst to date with a secure early-type host (the other being GRB 050724 at z=0.257) and it has one of the highest short GRB redshifts. The offset between the host center and the burst position, 470 +/- 310 pc, is the smallest to date. Combined with the old stellar population age, this indicates that the burst likely originated from a progenitor with no significant kick velocity. However, from the brightness of the optical afterglow we infer a relatively low density of n~3x10^-4 cm^-3 when epsilon_e and epsilon_B = 0.1. The combination of an optically faint afterglow and host suggest that previous such events may have been missed, thereby potentially biasing the known short GRB host population against z>1 early-type hosts.
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