TITLE: GCN CIRCULAR NUMBER: 40076 SUBJECT: EP250404a: Osservatorio Astronomico "Nastro Verde" optical observations: detection of an optical counterpart DATE: 25/04/05 10:05:39 GMT FROM: Nello Ruocco at Osservatorio Nastro Verde - Sorrento (Naples) - Italy - MPC Code C82 osservatorionastroverde@gmail.com
Nello Ruocco at Osservatorio Nastro Verde - Sorrento (Naples) - Italy in a large collaboration with: M.G. Dainotti (National Astronomical Observatory of Japan), Y. Niino (Tokyo University, Institute of Astronomy) and K. Kalinowski (Aarhus University, Department of Physics and Astronomy) report:
Following the detection of an X-ray transient by the Wide-field X-ray Telescope (WXT) on board the Einstein Probe (EP) mission triggered EP-WXT (ID: 01709133918) (GCN Circular 40051 J. W. Hu (NAO, CAS), Q. C. Liu (THU), B. B. Zhang (BNU), Y. L. Hua (PMO, CAS), Y. Liu (NAO, CAS) on behalf of the Einstein Probe (EP) team), I pointed at the coordinates RA(J2000)= 08:20:14.59 : Dec(J2000)= +35:31:42.3 and started observations with telescope of Nastro Verde Observatory - Sorrento (Naples), Italy. Member of: AAVSO - American Association of Variable Star Observers. GRB/UAI Gamma Ray Burst Section of Unione Astrofili Italiani.
Clear sky but moon presence at about 20 degrees from the target. The observations started at 20:36 UT of 2025/04/04, after about 6 hours after the GRB trigger, with clear sky, with principal telescope SC 0.35 f/10 with focal reduced + CCD Sbig ST10 XME I took 22 unfiltered images of 120 sec . Start End Rlim 20:36:23 UT 21:22:15 UT 20.5
All images, calibrated with masterdark and masterflat have been measured with Thycho Tracker software We have detected a faint source at the enhanced position reported by the Wide-field X-ray Telescope (WXT) on board the Einstein Probe (EP) mission AT following position
RA (J2000.0) 08 20 15.95 Dec (J2000.0) +35 31 48.3
with the following photometry and astrometry:
EP250404a 08 20 15.95 +35 31 48.3 19.0 C82
Magnitudes were estimated with the ATLAS cat. and are not corrected for galactic dust extinction.
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