TITLE: GCN CIRCULAR NUMBER: 44686 SUBJECT: GRB 260511A: iTelescope T-75 optical detection DATE: 26/05/21 22:55:39 GMT FROM: Takanori Sakamoto at AGU <tsakamoto@phys.aoyama.ac.jp> H. Ban, T. Kato, K. Hotta, Y. Kawakubo, M. Serino, T. Sakamoto (AGU) We observed the field of GRB 260511A detected by the Fermi/GBM (Fermi GBM Team, GCN Circ. 44529), the SVOM/ECLAIRs (Godet et al., GCN Circ. 44532), the NuSTAR CsI anti-coincidence shields (Waratkar et al., GCN Circ. 44555), the Konus-Wind (Ridnaia et al., GCN Circ. 44585), the Glowbug (Woolf et al., GCN Circ. 44586), and the GRID (Li et al., GCN Circ. 44664) with the iTelescope.Net (http://www.itelescope.net) T75 (ASAN250) telescope located at Rio Hurtado Valley, Chile. We took 20 images of 60 sec exposures in the Red filter starting from May 11 at 06:37:27 (UT), about 24 minutes after the Fermi/GBM trigger and stopped at 07:07:42. The afterglow (Jiang et al., GCN Circ. 44533; Akl et al., GCN Circ. 44534; Saccardi et al., GCN Circ. 44535; Zheng et al., GCN Circ. 44536; Wu et al., GCN Circ. 44538; Harper et al., GCN Circ. 44545; Brivio et al., GCN Circ. 44562; Li et al., GCN Circ. 44575; Fu et al., GCN Circ. 44579; Zhu et al., GCN Circ. 44584) is detected in the stacked image of the first eight images (total exposure of 480 s) collected between 06:37:27 and 06:49:12. The afterglow magnitude is 19.3 +- 0.6 using the USNO-B1 catalog. No afterglow was detected in the following twelve images collected between 06:49:44 and 07:07:42. The 5-sigma upper limit of the stacked image of the last twelve images (total exposure of 720 s) is 18.3 mag. View this GCN Circular online at https://gcn.nasa.gov/circulars/44686. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...