GCN Circular 39583
Subject
EP250304a: TRT optical counterpart detection
Date
2025-03-04T08:17:49Z (5 days ago)
From
Dong Xu at NAOC/CAS <dxu@nao.cas.cn>
Via
Web form
X. Liu, J. An, N.C. Sun (NAOC), S. Tinyanont, R. Anutarawiramkul, P. Butpan (NARIT), S.Q. Jiang, S.Y. Fu, Z.P. Zhu, D. Xu, Z. Fan, W.X. Li, Y.N. Wang (NAOC) report on behalf of a large collaboration:
We observed the field of EP250304a (Chen et al, GCN 39580), using the 0.7-m telescope of the Thai Robotic Telescope network (TRT), located at Cerro Tololo Inter-American Observatory, Chile. Observations started at 02:18:49 UTC on 2025-03-04, i.e., ~1.12 hr after the EP/WXT trigger. A series of B-/V-/R-/I- band frames were obtained.
An uncatalogued and varying optical source is detected within the EP/FXT error circle (Chen et al, GCN 39580) at coordinates
R.A. (J2000) = 13:53:34.68
Dec. (J2000) = -42:48:16.71
with an uncertainty of ~ 1 arcsec.
Preliminary photometry shows that the source has B = 20.5 +/- 0.1 mag at 1.39 hr post-trigger, and R = 20.8 +/- 0.1 mag at 2.4 hr post-trigger, calibrated with SkyMapper DR2 catalog converted using Lupton (2005) equations and not corrected for Galactic extinction.
We thus think this source is the optical counterpart of EP250304a.