[vsnet-grb-info 2702] GRB060108: photometric redshift determination

[GCN Circulars]

TITLE:   GCN GRB OBSERVATION REPORT
NUMBER:  4539
SUBJECT: GRB060108: photometric redshift determination
DATE:    06/01/18 01:05:00 GMT
FROM:    Cristiano Guidorzi at ARI,Liverpool JMU  <crg at astro.livjm.ac.uk>

A. Melandri (Liverpool), A. Grazian (Rome), C. Guidorzi (Liverpool),
A. Monfardini (Liverpool), C.G. Mundell (Liverpool), A. Gomboc
(Liverpool) report:

"Following the identification of the afterglow of GRB060108 (Butler &
Bloom GCN 4500, Monfardini et al. 4502, D'Avanzo et al. 4501) we have
combined contemporaneous optical and NIR photometry, derived from
BRi' Faulkes North Telescope and UKIRT imaging (Levan et al. GCN 4503),
with the VLT J-band upper limit (D'Avanzo et al. GCN 4501) extrapolated
to the same time period assuming three powerlaw decay index values:
alpha = 0.5, 1.0, 2.0 ( F(t)~t^(-alpha) ).

Adopting a chi-square minimisation of the observed spectral energy
distribution, we have derived upper limits and best fitting redshifts
for the three power law indices. We assumed a power-law energy spectrum:
F(nu)~nu^(-beta).

Conservatively, we derive z<2.7 with z_best = 2.03 and
1.14 < beta < 1.22.

This confirms that GRB060108 is not an ultra-high z burst."