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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