TITLE:   GCN CIRCULAR
NUMBER:  45702
SUBJECT: EP260920a: VLT/HAWK-I near-infrared counterpart confirmation
DATE:    26/09/23 12:09:55 GMT
FROM:    Emeric Le Floc'h at CEA-Saclay <emeric.lefloch@cea.fr>

J. An (NAOC), D. Xu (NAOC), G. Pugliese (API), D. B. Malesani (DAWN/NBI and Radboud), G. Corcoran (UCD), V. D’Elia (ASI/SSDC), M. Garnichey (LUX-Paris Obs.), L. Izzo (INAF/OAC), E. Le Floc’h (CEA/Irfu), A. Saccardi (CEA/Irfu), B. Schneider (LAM), N. R. Tanvir (U. Leicester), A. L. Thakur (INAF/IAPS), S. D. Vergani (LUX-Paris Obs.), report on behalf of the Stargate collaboration:

We obtained a second imaging observation of the field of EP260920a (Ni et al., GCN 45649) using the ESO/VLT UT4 (Yepun) equipped with the HAWK-I instrument. Data acquisition started on 2026-09-22 at 02:56:07 UT, i.e. 2.12 days after the trigger. A total of 20 x 60 s J-band frames were obtained.

The previously identified candidate afterglow (An et al., GCN 45679) is still detected and has faded compared to our earlier measurement. We measure the following magnitude, calibrated against 2MASS and not corrected for Galactic extinction:

J = 21.57 +/- 0.06 (Vega).

The fading (corresponding to a decay slope of 1.22 +/- 0.14) allows us to conclude that this object is the afterglow of EP260920a.

We acknowledge excellent support from the ESO staff in Paranal, in particular Carlos La Fuente, Francesca Lucertini, Fuyan Bian, and Robert De Rosa.