TITLE: GCN CIRCULAR NUMBER: 6508 SUBJECT: GRB 070610: OPTIMA-Burst detection of continued strong flaring activity DATE: 07/06/12 01:47:18 GMT FROM: Alexander Stefanescu at MPE A. Stefanescu (1), A. Slowikowska (2)(3), G. Kanbach (1), S. Duscha (1), F. Schrey (1), H. Steinle (1), Z. Ioannou (4) of the OPTIMA-Burst Team report the following: (1)=MPE, Garching, (2)=FORTH, Heraklion (3)=NCAC, Torun (4)=Univ. of Crete "OPTIMA-Burst at the 1.3m Skinakas Observatory, of the University of Crete, Greece continued observations of the source reported on earlier in GCN 6492 (Stefanescu et al.), GCN 6501 (de Ugarte Postigo et al.) and GCN 6505 (Kann et al.) Observations started at 20:40 UT, 0.991 days after the burst. Taking the same reference star as Kann et al. (GCN 6505), we detect the source with the following magnitudes in our CCD frames: UT_mid T_GRB [d] t_exp I mag 20:42:38 0.99319 300 19.2 20:57:26 1.00347 1200 17.0 21:25:37 1.02304 300 20.7 21:31:19 1.02700 300 21.2 After this time, observations with the high-time-resolving main instrument of OPTIMA-Burst commenced. The following describes a quick-look analysis of 83min of data, binned to a time-resolution of 10s. During it's low brightness periods, the source was not detected above the noise in our photon counting detectors. However, we detected bright flares with pronounced substructure around the following times: UT T_GRB [d] duration (approx) peak brightness (preliminary!) 22:09 1.052 3.0 min 18.0 mag 22:20 1.060 7.5 min 17.4 mag 22:40 1.074 5.9 min 17.6 mag In addition to these we detected 5 smaller flares at the 2.5 to 3 sigma level, each lasting for about 1 minute and having a peak brightness of about 19.7 mag. Further observations and further analysis is in progress. Since it seems strong variability is still in progress, we strongly recommend further observations." This message may be cited.