TITLE: GCN CIRCULAR NUMBER: 42269 SUBJECT: GRB 251013C: Osservatorio Astronomico "Nastro Verde" optical observations: detection of an bright optical counterpart DATE: 25/10/14 20:51:20 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 circular GCN 42222, in which N. A. Rakotondrainibe, C. Adami (LAM), D. Turpin, D. Götz (CEA/Irfu), H. Yang (IRAP), in which at 2025-10-13T17:39:42 UTC (T0), SVOM/ECLAIRs triggered and located the gamma-ray burst GRB 251013C (SVOM burst-id sb25101311) also detected by Fermi/GBM, I pointed at the coordinates RA(J2000)=23h 03m 22s: Dec(J2000)=-00d 12' 37" and started my 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.
The observations started at 20:04:39 UT of 2025/10/13, after about 3.30 hours after the GRB trigger, with clear sky, with principal telescope SC 0.35 f/10 with focal reduced + CCD Sbig ST10 XME, using the V and Rc photometric filters. I took 20 unfiltered images of 60 sec in each filter. The images were added in groups of five to obtain a higher S/N Start End 20:04:39 UT 20:56:46 UT
All images, calibrated with masterdark and masterflat have been measured with Maxim DL software I have detected a bright source at the enhanced position reported by GCNs (Konno et al. (GCN circ. 42226), Perez-Garcia et al. (GCN circ. 42225), Martin-Carrillo et al. (GCN circ. 42227), Masi (GCN circ. 42228), Palmerio et al. (GCN circ. 42229), Moskvitin et al. (GCN circ. 42230), Gompertz et al. (GCN circ. 42231), Watson et al. (GCN circ. 42241), López-Cámara et al. (GCN circ. 42242), Zhang et al. (GCN circ. 42248), Brosio et al. (GCN circ. 42251), Quintana-Ansaldo et al. (GCN circ. 42254), and Maksut et al. (GCN circ. 42256), U. Quadri et al.(GCN 42262), C. Adami et al.(GCN 42266), I. Peretto et al.(GCN 42267) at following position
RA (J2000.0) 23 03 20.55 Dec (J2000.0) -00 12 37.0
with the following photometry:
(JD) Mag Err Filter 2460962.3649074 17.259 0.101 V 2460962.3561574 16.903 0.065 V 2460962.3473842 16.697 0.041 V 2460962.3374884 16.576 0.044 V 2460962.3639930 16.5 0.044 Rc 2460962.3552430 16.43 0.039 Rc 2460962.3464815 16.281 0.027 Rc 2460962.3365625 16.114 0.023 Rc
Magnitudes were estimated with the pan-STARRS cat and are derived using Lupton (2005) equations.
Not corrected for galactic dust extinction..
The message may be cited.
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