[vsnet-grb-info 8444] GRB 090927: Faulkes Telescope South Detection of the Optical Afterglow

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  9960
SUBJECT: GRB 090927: Faulkes Telescope South Detection of the Optical  Afterglow
DATE:    09/09/28 16:42:32 GMT
FROM:    Zach Cano at ARI/John Moores Liverpool  <zec at astro.livjm.ac.uk>

Z. Cano, A. Melandri, C. Mundell, D. Bersier, R.J. Smith, I. A. Steele, S.
Kobayashi, C.J. Mottram (Liverpool JMU), A. Gomboc (U. Ljubljana) report,
on behalf of the Liverpool GRB group:

The Faulkes Telescope South (Australia) observed the field of GRB
090927 (Swift trigger=370846, Grupe et al., GCN 9945) on 2009 September 27
and 28.

The afterglow candidate reported by Gronwell & Grupe (GCN 9946) is clearly
visible and fading at position:

RA(J2000):   22 55 53.42
Dec(J2000): -70 58 49.54

with the following magnitudes calibrated wrt USNO-B1 objects in the field:

I = 19.4 +/- 0.1  @ 3.66 hrs
I = 21.3 +/- 0.2  @ 27.23 hrs

R = 19.9 +/- 0.1 @ 4.21 hrs

Observations are on-going, but we derive preliminary decay rates using the
above FTS measurements and the R-band magnitude reported by Levan et al.
(GCN 9958) to be: alpha_I=0.9+/-0.2, alpha_R=1.2+/-0.2.