TITLE:   GCN CIRCULAR
NUMBER:  37207
SUBJECT: GRB 240819A: TRT optical upper limits on the Swift/XRT and EP/FXT sources
DATE:    24/08/20 13:13:35 GMT
FROM:    Dong Xu at NAOC/CAS <dxu@nao.cas.cn>

S.Q. Jiang, J. An (NAOC), S. Tinyanont, R. Anutarawiramkul, P. Butpan (NARIT), X. Liu, S.Y. Fu, Z.P. Zhu, S.Y. Gao, D. Xu, Z. Fan, W.X. Li, N.C. Sun, Y.N. Wang (NAOC) report on behalf of a large collaboration:

We observed the field of GRB 240819A detected by SVOM/Eclairs using the 0.7-m telescope of the Thai Robotic Telescope network (TRT), located at Fresno, California, US. Observations started at 09:41:45.015 UTC on 2024-08-19, i.e., 7.107 hr after the T0 of this GRB, and 16 x 240 s  frames were obtained in R-band aiming to cover the whole SVOM/Eclairs error circle.

No new optical source is detected within the X-ray error circles provided by Swift/XRT (Evans et al., GCN37203) and EP/FXT (Li et al., GCN 37206), down to the following 3-sigma optical upper limits:

Source | R.A. | Dec. | Upper Limit (mag)
--------------------------------------------------------
XRT Source1          | 311.0531 | 49.6821 | R>19.0
XRT Source2*         | 310.9468 | 49.5141 | N/A
EP J204334.6+493448  | 310.8943 | 49.5800 | R>19.8
EP J204347.6+493054* | 310.9483 | 49.5149 | N/A
EP J204244.0+494023  | 310.6835 | 49.6730 | R>19.8

calibrated with PanSTARRS stars in the field and not corrected for Galactic extinction. The two sources marked with * are very likely an identical one detected by both Swift/XRT and EP/FXT, but not covered by TRT.