TITLE:   GCN CIRCULAR
NUMBER:  39969
SUBJECT: GRB20250327B: 45th Parallel Observatory upper limit 
DATE:    25/03/31 12:21:20 GMT
FROM:    Vincenzo Della Vecchia <v.dellavecchia@uai.it>

Vincenzo della Vecchia (45th Parallel Observatory, Italy)

Member of:
AAVSO - American Association of Variable Star Observers
UAI - Unione Astrofili Italiani - Gamma Ray Burst Section

In a large collaboration with:
M.G. Dainotti (National Astronomical Observatory of Japan),
Y. Niino (Tokyo University, Institute of Astronomy),
K. Kalinowski (Aarhus University, Department of Physics and Astronomy),
report:

We imaged the field of GRB 250327B detected by SVOM (burst-id sb25032706, GCN Circular 39888) and Swift XRT (GCN circ. 39895) with the 0.25-m f/5.6 Ritchey-Chrétien telescope of the 45th Parallel Observatory (IAU code D43).

The observation started 22.33 hours after the GRB trigger, with acceptable sky transparency and seeing.
A series of 10 sec observations has been added for a total integration time of approximately 30 minutes.

Start T0+   End T0+     CR lim
22.33 hour  22.83 hour  19.5

CR as unfiltered with R zero point.

No optical counterpart has been detected at the position expected for the GRB.

Limit magnitudes are estimated with the Pan-STARSS DR1 catalogue and are not corrected for galactic dust extinction.
I am grateful to Ulisse Quadri (Bassano Bresciano Astronomical Observatory) for his support.

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