GCN Circular 44545

Subject

GRB 260511A: UTGO H50 optical afterglow observation

Event

GRB 260511A

Date

2026-05-11T12:13:03Z (3 days ago)

From

Harrison at University of Tasmania <hgharper9962@gmail.com>

Via

Web form

H. Harper (UTAS), K. Siellez (UTAS), B. Emptage (UTAS), K. Hill (UTAS), T. Plunkett (UTAS), A. Cole (UTAS), J.-P. Beaulieu (IAP/UTAS) report:

We observed the field of the SVOM/ECLAIRs and Fermi/GBM GRB 260511A (Godet et al., GCN 44532; Fermi GBM Team, GCN 44529) with the Harlingten 50cm (H50) at Greenhill Observatory, University of Tasmania (UTGO).

Our observation started on 2026-05-11 at 08:58:59UT, ~165 minutes after Fermi trigger Observations. We obtained 11 x 120s exposure in the SDSS r’ filter.

The optical counterpart (Jiang et al., GCN 44533; Akl et al. GCN 44534; Saccardi et al. GCN 44535; Zheng et al. GCN 44536; Wu et al., GCN 44538) is clearly detected in our images at RA = 13:11:35.9244 (J2000) (197.8996850 deg) and Dec = -33:48:15.887 (J2000) (-33.8044130 deg) with an uncertainty of ~0.4 arcsec.

Image subtraction was performed using STDpipe. We measured the following magnitude not corrected for Galactic extinction:

r = 20.68 +/- 0.12 AB (mid time ~176minutes after trigger)

Refined processing and more observations are still ongoing.