TITLE: GCN CIRCULAR NUMBER: 33380 SUBJECT: GRB 230228A: Miryang Arirang Astronomical Observatory (MAAO) 0.7-m telescope optical upper limit DATE: 23/02/28 13:33:13 GMT FROM: Gu Lim at Seoul National U lim9gu@gmail.com

Gu Lim (PNU), Donghyun Kim (PNU), Dohyeong Kim (PNU), Myungshin Im (SNU ARC/SNU), Gregory S.H. Paek (SNU ARC/SNU), Keun-Hong Park (MAAO), and Seonghun Lim (MAAO) on behalf of GECKO collaboration

We searched for the optical counterpart of a possible short burst GRB 230228A (Dichiara et al. GCN #33378) with the 0.7-m telescope at Miryang Arirang Astronomical Observatory (MAAO), located at Miryang, Republic of Korea. We observed the center of Swift-XRT localization (RA, Dec = 01:13:30.73, +44:28:58.4; Evans et al. GCN #33379) +4.09 hours after report, but could not find any possible transient within the field of view (28.2' x 28.2'). We performed flux calibration with the PS1 catalog and used the AB magnitude system. Each depth means 3 and 5 sigma upper limit for a point source detection. The magnitudes are not corrected for galactic extinction.

object exposures date-obs (UT) MJD band Depth(3σ) Depth(5 σ) FWHM(") ========================================================================================= GRB230228A 60sx8 2023-02-28T09:56:11 60003.414 V <18.77 <18.21 2.8

Gravitational wave Electromagnetic wave Counterpart Korean Observatory (GECKO) is a network of 10+ 0.5m to 1m class telescopes over the world.

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