GCN Circular 42333

Subject
GRB 251013C: Leavitt Observatory optical photometry
Event
GRB 251013C
Date
2025-10-17T20:56:44Z (15 hours ago)
From
leavittob@gmail.com
Via
Web form
E. Pavoni, L. Moretti (Leavitt Observatory, Italy)

Members of:
GRB/UAI - Gamma Ray Burst Section of Unione Astrofili Italiani

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 performed a follow-up observation of the field of GRB 251013C (Fermi GBM team, GCN 42221Loading...
 
 ; Rakotondrainibe et al., GCN 42222Loading...
 
 ) using our 250mm f/8 Ritchey-Chrétien telescope (Leavitt Observatory, Manciano, Italy).

Observations began on 2025-10-13 at 19:09:11 UT (≈ 1.5 hours after the trigger) and ended at 22:19:55 UT. A series of images in Rc and Ic filter (Johnson-Cousins system) was obtained under good weather conditions.

We clearly detected a bright afterglow positionally consistent with the source reported in previous circulars. The OT coordinates are:

RA (J2000) =  23:03:20.55
Dec(J2000) = -00:12:35.12
(±2 arcsec on both axes)

Photometry was performed using nearby stars from the Pan-STARRS catalog (magnitudes converted using Lupton (2005) equations) and analysed with AstroImageJ (2017AJ....153...77C). The following magnitudes were measured (not corrected for Galactic extinction):

HJD at mid-exposure		Filter		Mag.   	Mag. err.
2460962.30386029		Rc		15.38	0.01
2460962.30725948		Rc		15.51	0.01
2460962.30996796		Rc		15.67	0.01
2460962.31258558		Rc		15.73	0.02
2460962.31556121		Rc		15.74	0.02
2460962.31806558		Rc		15.76	0.02
2460962.32017580		Rc		15.86	0.02
2460962.32228375		Rc		15.84	0.02
2460962.32439216		Rc		15.84	0.02
2460962.32650057		Rc		15.89	0.02
2460962.32860895		Rc		15.90	0.02
2460962.33071795		Rc		15.92	0.02
2460962.33282552		Rc		15.97	0.02
2460962.33493454		Rc		15.96	0.02
2460962.33704239		Rc		16.04	0.02
2460962.33915074		Rc		16.12	0.02
2460962.34126105		Rc		16.12	0.02
2460962.34337272		Rc		16.19	0.02
2460962.34548188		Rc		16.27	0.02
2460962.34759218		Rc		16.29	0.02
2460962.35500912		Rc		16.33	0.02
2460962.35926398		Rc		16.34	0.02
2460962.36351931		Rc		16.37	0.02
2460962.36777694		Rc		16.41	0.02
2460962.37203488		Rc		16.56	0.03
2460962.37629036		Rc		16.46	0.03
2460962.38920934		Rc		16.64	0.03
2460962.39346447		Rc		16.54	0.03
2460962.39772065		Rc		16.69	0.03
2460962.40623373		Rc		16.80	0.04
2460962.41049247		Rc		16.75	0.03
2460962.41474858		Rc		16.93	0.04
2460962.41900117		Rc		16.82	0.04
2460962.42325452		Rc		16.72	0.04
2460962.42750818		Rc		17.11	0.05

2460962.35287059		Ic		15.94	0.03
2460962.35712512		Ic		15.95	0.03
2460962.36138024		Ic		15.92	0.03
2460962.36563799		Ic		15.86	0.03
2460962.36989563		Ic		16.05	0.04
2460962.37415044		Ic		16.25	0.04
2460962.38706915		Ic		16.14	0.04
2460962.39132719		Ic		16.19	0.04
2460962.39558282		Ic		16.33	0.05
2460962.39983877		Ic		16.23	0.05
2460962.40409469		Ic		16.37	0.05
2460962.40835283		Ic		16.40	0.05
2460962.41261135		Ic		16.43	0.06
2460962.41686396		Ic		16.24	0.05
2460962.42111700		Ic		16.42	0.06
2460962.42537095		Ic		16.49	0.06
2460962.42997457		Ic		16.68	0.07
2460962.43422909		Ic		16.63	0.07


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Reference:
https://leavittobservatory.altervista.org