TITLE:   GCN CIRCULAR
NUMBER:  46189
SUBJECT: GRB 261108A: FRAM-Auger optical limits
DATE:    26/11/08 02:47:03 GMT
FROM:    Martin Jelinek at Astro.Inst-AVCR,Ondrejov <martin.jelinek@asu.cas.cz>

Martin Jelinek, Jan Strobl and Filip Novotny
(ASU CAS Ondrejov, CZ),

Martin Masek, Sergey Karpov, Petr Janecek, Jakub Jurysek,
Jan Ebr, Ronan Cunniffe, Petr Travnicek and Michael Prouza
(Institute of Physics, Prague, CZ)

report:

The 30cm robotic telescope FRAM-Auger at the Pierre Auger
Observatory (Cerro Los Leones, Malargue, Argentina) reacted
robotically to the SVOM/ECLAIRs alert of GRB 261108A (SVOM
GRB 261108.05, cf. Lipunov et al., GCN 46188; Fermi GBM also
triggered at the same time, trigger 815793204), obtaining a
series of 32 R-band images of 60 s each, starting at
01:29:44 UT, i.e. ~16 min after the trigger and ~2 min after
the alert was received, and continuing until ~55 min after
the trigger. The field was at an elevation of ~60 deg.

We do not detect any new source within the ECLAIRs error
circle, neither in single images nor in the combined frames,
when comparing to the catalogue. Neither does a subtraction
of the coadd of the second half of the series from the coadd
of the first half reveal any variable source. We obtain the
following limits:

T-T0[mid]  Images  Limit (Vega)
~16 min    1       R_C > 17.0
~26 min    16      R_C > 18.7
~45 min    16      R_C > 18.7

Single images reach R_C ~ 17.0 throughout the series. The
photometry is calibrated against the Atlas-REFCAT2 catalogue
(Tonry et al. 2018, ApJ, 867, 105) and is not corrected for
Galactic extinction.