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GCN Circular 36842

Subject
EP240708a: NOT optical observations
Date
2024-07-10T14:38:50Z (9 days ago)
From
Dong Xu at NAOC/CAS <dxu@nao.cas.cn>
Via
Web form
S.Q. Jiang, X. Liu, Z.P. Zhu, S.Y. Fu, J. An, L.B. He, D. Xu (NAOC), J.P.U. Fynbo (DAWN/NBI), B.N. Hauptmann (NOT) report on behalf of a large collaboration:

We observed the field of EP240708a detected by EP/WXT (Chen et al., GCN 36838) using the 2.56-m Nordic Optical Telescope (NOT) equipped with the ALFOSC camera, and obtained 5 x 300 s frames in the Sloan r-band at a median time of 4.20 hr fter the EP trigger.

No credible uncatalogued optical transient is detected in our stacked image within the EP/FXT 10 arcsec error circle (Hu et al., GCN 36840) as well as in its neighboring region, down to a limiting magnitude of r ~ 24.1 mag, calibrated with nearby PanSTARRS stars and not corrected for the Galactic extinction.

We note that there is a marginal detection of an uncatalogued source in the NOT image at coordinates

R.A.(J2000) = 23:03:50.556
Dec.(J2000) = -22:50:47.99

with an uncertainty of ~0.5 arcsec. It has r ~ 24.0 +/- 0.3 mag and is away from the center of the FXT error circle by ~ 21.7 arcsec, and not present in the archival Pan-STARRS or Legacy Survey. Given the low S/N, this source could be due to background fluctuation.
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