[vsnet-grb-info 4766] GRB 070610: OPTIMA-Burst detection of continued strong flaring activity

[GCN Circulars]

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  <astefan at mpe.mpg.de>

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."

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