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The properties of GRB 120923A at a spectroscopic redshift of z=7.8 | | N. R. Tanvir
; T. Laskar
; A. J. Levan
; D. A. Perley
; J. Zabl
; J. P. U. Fynbo
; J. Rhoads
; S. B. Cenko
; J. Greiner
; K. Wiersema
; J. Hjorth
; A. Cucchiara
; E. Berger
; M. N. Bremer
; Z. Cano
; B. E. Cobb
; S. Covino
; V. D'Elia
; W. Fong
; A. S. Fruchter
; P. Goldoni
; F. Hammer
; K. E. Heintz
; P. Jakobsson
; D. A. Kann
; L. Kaper
; S. Klose
; F. Knust
; T. Kruehler
; D. Malesani
; K. Misra
; A. Nicuesa Guelbenzu
; G. Pugliese
; R. Sanchez-Ramirez
; S. Schulze
; E. R. Stanway
; A. de Ugarte Postigo
; D. Watson
; R. A. M. J. Wijers
; D. Xu
; | | Date: |
27 Mar 2017 | | 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>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 VLT/X-shooter spectroscopy. At
this redshift the peak 15-150 keV luminosity of the burst was 3.2x10^52 erg/s,
and in fact the burst was close to the Swift/BAT detection threshold. The X-ray
and near-infrared afterglow were also faint, and in this sense it was a rather
typical long-duration GRB in terms of rest-frame luminosity. 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 with density, n~4x10^-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 ~5 degrees. The beaming corrected gamma-ray energy is then
E_gamma~2x10^50 erg, while the beaming-corrected kinetic energy is lower,
E_K~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. | | Source: | arXiv, 1703.9052 | | Services: | Forum | Review | PDF | Favorites | |
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