GCN Circular 44545

Subject

GRB 260511A: UTGO H50 optical afterglow observation

Event

GRB 260511A

Date

2026-05-11T12:13:03Z (18 days ago)

Edited On

2026-05-20T13:06:20Z (9 days ago)

From

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

Edited By

Judith Racusin at NASA/GSFC <judith.racusin@nasa.gov> on behalf of 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 stacked 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.

All the data have been reduced by our UTGO pipeline (Plunkett et al. 2025), image subtraction was performed using STDpipe (Karpov 2025). 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.