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Tanvir, NR, Laskar, T, Levan, AJ, Perley, DA, Zabl, J, Fynbo, JPU, Rhoads, J, Cenko, SB, Greiner, J, Wiersema, K, Hjorth, J, Cucchiara, A, Berger, E, Bremer, MN, Cano, Z, Cobb, BE, Covino, S, D'Elia, V, Fong, W, Fruchter, AS , Goldoni, P, Hammer, F, Heintz, KE, Jakobsson, P, Kann, DA, Kaper, L, Klose, S, Knust, F, Kruehler, T, Malesani, D, Misra, K, Guelbenzu, AN, Pugliese, G, Sanchez-Ramirez, R, Schulze, S, Stanway, ER, de Ugarte Postigo, A, Watson, D, Wijers, RAMJ and Xu, D (2018) The Properties of GRB 120923A at a Spectroscopic Redshift of z approximate to 7.8. Astrophysical Journal, 865 (2). ISSN 0004-637X
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The Properties of GRB 120923A at a Spectroscopic Redshift of z ≈ 7.8.pdf - Accepted Version Download (3MB) | Preview |
Abstract
Gamma-ray bursts (GRBs) are powerful probes of early stars and galaxies, during and potentially even before the era of reionization. Although the number of GRBs identified at z gsim 6 remains small, they provide a unique window on typical star-forming galaxies at that time, and thus are complementary to deep field observations. We report the identification of the optical drop-out afterglow of Swift GRB 120923A in near-infrared Gemini-North imaging, and derive a redshift of $z={7.84}_{-0.12}^{+0.06}$ from Very Large Telescope/X-shooter spectroscopy. At this redshift the peak 15–150 keV luminosity of the burst was 3.2 × 1052 erg s−1, and in this sense it was a rather typical long-duration GRB in terms of rest frame luminosity. This burst was close to the Swift/Burst Alert Telescope detection threshold, and the X-ray and near-infrared afterglow were also faint. We present ground- and space-based follow-up observations spanning from X-ray to radio, and find that a standard external shock model with a constant-density circumburst environment of density n ≈ 4 × 10−2 cm−3 gives a good fit to the data. The near-infrared light curve exhibits a sharp break at t ≈ 3.4 days in the observer frame which, if interpreted as being due to a jet, corresponds to an opening angle of ${\theta }_{\mathrm{jet}}\approx 5^\circ $. The beaming-corrected γ-ray energy is then ${E}_{\gamma }\approx 2\times {10}^{50}$ erg, while the beaming-corrected kinetic energy is lower, ${E}_{{\rm{K}}}\approx {10}^{49}$ erg, suggesting that GRB 120923A was a comparatively low kinetic energy event. We discuss the implications of this event for our understanding of the high-redshift population of GRBs and their identification.
| Item Type: | Article |
|---|---|
| Uncontrolled Keywords: | 0201 Astronomical And Space Sciences, 0305 Organic Chemistry, 0306 Physical Chemistry (Incl. Structural) |
| Subjects: | Q Science > QB Astronomy Q Science > QC Physics Q Science > QD Chemistry |
| Divisions: | Astrophysics Research Institute |
| Publisher: | American Astronomical Society; IOP Publishing |
| Related URLs: | |
| Date Deposited: | 17 Oct 2018 08:30 |
| Last Modified: | 04 Sep 2021 10:01 |
| DOI or ID number: | 10.3847/1538-4357/aadba9 |
| URI: | https://researchonline.ljmu.ac.uk/id/eprint/9492 |
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