TITLE:   GCN CIRCULAR
NUMBER:  21843
SUBJECT: GRB 170906C: optical observations
DATE:    17/09/07 09:58:45 GMT
FROM:    Luca Izzo at IAA-CSIC  <Luca.Izzo@ICRA.it>

L. Izzo, A. de Ugarte Postigo, D.A. Kann (IAA-CSIC/HETH) report on behalf of a larger collaboration:

We observed the field of GRB 170906C (Siegel et al., GCN 21826) with the T24 (Plane Wave CDK 0.61m) of the iTelescope.Net (http://www.itelescope.net) located at Auberry, CA. A set of 3 images of 300 s each were taken in the I filter, starting at 10:30:39 UT, ~ 2.9 hours after the GRB trigger.

We do not detect any source inside the XRT refined error region (Evans et al., GCN 21831) and estimate a 3-sigma upper limit of I > 19.0