GRB 251013C
GCN Circular 42301
Subject
GRB 251013C: Kilonova-Catcher optical afterglow detection
Date
2025-10-15T20:35:57Z (a day ago)
From
Damien Turpin at CEA-Saclay <dturpin-astro@hotmail.com>
Via
Web form
S. Leonini, M. Freeberg, R. Hellot (KNC), D. Turpin (CEA-Saclay/Irfu), C. Andrade(UMN), S. Antier (OCA/IJCLab), M. Coughlin (UMN), S. Karpov (FZU), P. Hello (IJCLAB), M. Pillas (IAP) on behalf of the GRANDMA/Kilonova-Catcher collaboration:
We observed the field of GRB 251013C detected by Fermi/GBM (Fermi GBM team, GCN 42221), SVOM/ECLAIRs and GRM (Rakotondrainibe et al., GCN 42223) and AstroSat CZTI (Arya et al., GCN 42246) with the GRANDMA citizen science project Kilonova-catcher (KNC). Our observations were performed with the TEC180FL, iT32 and iT72 telescopes operated by M. Freeberg, the automated and remoted 0.53m Ritchey-Chretien telescope at Montarrenti Observatory (Siena, Italy, IAU code C88) operated by S. Leonini and a CDK17 telescope located at AITP San Pedro Chile Observatory operated by R. Hellot. Our observations started at TGRB+3.0hr and were taken with Clear, sdss gri and Rc Ic filters.
In our stacked frames, subtracted from the PanSTARRS DR2 template image, we detect the optical counterpart firstly reported by SVOM/VT (Palmerio et al., GCN 42223) and later confirmed by many other teams.
We report part of our follow-up results in the table below:
+---------------+----------+------------+----------------+------------------+
| Tmid-TGRB (hr)| Exp (s) | Filter | Magnitude | Instrument |
+===============+==========+============+================+==================+
| 3.18 | 30 x 30s | Rc (Vega) | 16.29 +/- 0.04 | Montarrenti Obs. |
| 6.47 | 5 x 300s | Rc (Vega) | 17.63 +/- 0.02 | iT72 |
| 8.26 | 6 x 300s | r (AB) | 18.24 +/- 0.05 | CDK17 AITP |
+---------------+----------+------------+----------------+------------------+
All the data have been reduced by a single data processing pipeline, STDPipe (Karpov et al., 2022). Images obtained with the sloan filters were calibrated using the PanSTARRS DR1 catalog. Images obtained with the Johnson-cousins filters were calibrated using the GAIA DR3 synphot catalog.
We use the SkyPortal application (skyportal.io) to monitor our observational campaign (Coughlin et al. 2023).
GRANDMA is a worldwide telescope network (grandma.ijclab.in2p3.fr) devoted to the observation of transients in the context of multi-messenger astrophysics (Antier et al. 2020 MNRAS 497, 5518). Kilonova-Catcher (KNC) is the citizen science program of GRANDMA (http://kilonovacatcher.in2p3.fr/).
GCN Circular 42298
Subject
GRB 251013C: Swift/UVOT Detection
Date
2025-10-15T19:54:12Z (a day ago)
From
Mike Siegel at PSU/Swift MOC <mhs18@psu.edu>
Via
Web form
M. H. Siegel (PSU) reports on behalf of the Swift/UVOT team:
The Swift/UVOT began settled observations of the field of GRB 251013C 0.4 ks after the Fermi/SVOM trigger (GCN Circ. 42221, Rakotondrainibe et al., GCN Circ. 42222). A bright source consistent with the XRT position (Evans et al., GCN Circ. 42232) and optical counterpart (Palmerio et al., GCN Circ. 42223, Perez-Garcia et al., GCN Circ. 42225; Konno et al., GCN Circ. 42226; Masi et al., GCN Circ. 42228; Moskvitin, GCN Circ. 42230; Gompertz et al., GCN Circ. 42231; Garnavich, GCN Circ. 42240; Watson et al., GCN Circ. 42241) is detected in the UVOT exposures.
The preliminary UVOT position is:
RA (J2000) = 23:03:20.55 = 345.83562 (deg.)
Dec (J2000) = -00:12:36.9 = -0.21024 (deg.)
with an estimated uncertainty of 0.42 arc sec. (radius, 90% confidence).
Preliminary detections and 3-sigma upper limits using the UVOT photometric system
(Breeveld et al. 2011, AIP Conf. Proc. 1358, 373) for the early exposures are:
Filter T_start(s) T_stop(s) Exp(s) Mag
u 480 5581 1785 15.22+/-0.03
white 129831 141519 2753 21.66+/-0.20
The magnitudes in the table are not corrected for the Galactic extinction
due to the reddening of E(B-V) = 0.045 in the direction of the burst
(Schlegel et al. 1998).
GCN Circular 42295
Subject
GRB 251013C, GCN Circular 42267, errata corrige
Date
2025-10-15T17:50:14Z (a day ago)
From
I. Peretto at MarSEC (Marana Space Explorer Center) <ricerca@marsec.org>
Via
Web form
Ivo Peretto (MarSEC, Marana Space Explorer Center, Marana Di Crespadoro, VI, Italy)
Member of:
UAI/SSV - Unione Astrofili Italiani/Sezione Stelle Variabili, GRB section.
AAVSO (American Association Variable Stars Observers).
We report our photometry analysis:
HJD Rc Mag Err
-------------------------------------
2460962.4676701734 17.581 0.09
Reference:
https://www.marsec.org/
The message may be cited.
GCN Circular 42294
Subject
GRB 251013C: detection of a radio counterpart at 15.5GHz
Date
2025-10-15T16:27:02Z (a day ago)
From
Lauren Rhodes at McGill <lauren.rhodes@mcgill.ca>
Via
Web form
Lauren Rhodes (McGill/TSI), Andrew Hughes (Oxford), Rob Fender (Oxford), Dave Green (Cambridge), Dave Titterington (Cambridge) report:
We observed the field of the afterglow candidate GRB 251013C (GCN 42221) with the Arcminute Microkelvin Imager Large-Array (AMI-LA) at 15.5 GHz beginning at UT 19:27:08.0 on 14-Oct-2025 for a total of 4 hours. The flux standard 3c286 was used to calibrate the bandpass response and flux scale of the AMI-LA and J2320+0513 was used as an interleaved complex gain calibrator.
We detected a point source with a peak flux density of 0.34 +/- 0.08 mJy/beam with a position of
RA = 23h03m20.5+/- 0.2s
Dec = -00d12'26+/- 9"
Further observations are planned.
We thank the staff at the Mullard Radio Astronomy Observatory for carrying out these observations and operating the AMI-LA.
GCN Circular 42292
Subject
GRB 251013C: SVOM/ECLAIRs refined analysis
Date
2025-10-15T15:52:54Z (a day ago)
From
SVOM_group <svomgroup@bao.ac.cn>
Via
Web form
H. Yang, M. Brunet, O. Godet (IRAP), B. Hubert (CEA), F. Piron (LUPM), N. A. Rakotondrainibe, C. Adami (LAM)
Using the event-by-event data downloaded through the X-band ground station, we report further analysis of ECLAIRs observations of GRB 251013C (SVOM burst-id sb2525101311, GCN 42222) detected at T0 = 2025-10-13T17:39:42, which was also detected by SVOM/GRM and Fermi/GBM (GCN 42221).
The burst that triggered ECLAIRs consists of a single peak, with a typical fast-rising and exponential-decay profile, starting at T0-0.4 s and lasting about 30 s in the 4-120 keV energy band.
The time-averaged spectrum from the peak (T0-0.4 s to T0+30 s) in the 4-120 keV energy range is well fitted by a power-law model with a photon index of 1.59 +/-0.03. With this model, the total 4-120 keV fluence is (1.95 + 0.02/-0.03)e-06 erg/cm^2 .
All the quoted errors are at the 68% confidence level.
The Space-based multi-band astronomical Variable Objects Monitor (SVOM) is a China-France joint mission led by the Chinese National Space Administration (CNSA), French Space Agency (CNES), and the Chinese Academy of Sciences (CAS), which is dedicated to observing gamma-ray bursts and other transient phenomena in the energetic universe. ECLAIRs was developed jointly by CNES, CEA-IRFU, CNRS-IRAP, CNRS-APC.
The SVOM/ECLAIRs point of contact for this burst is: Hui Yang (IRAP) (hui.yang@irap.omp.eu).
GCN Circular 42283
Subject
GRB 251013C: MAO/AZT-22 optical observations
Date
2025-10-15T09:38:38Z (a day ago)
From
Yodgor Rajabov at UBAI <rajabov@astrin.uz>
Via
Web form
B.Abidkhanov, Y. Rajabov, O. Burkhonov, S. Ehgamberdiev, Y. Tillayev (UBAI), A. Shaymanov (Maidanak Observatory/UBAI) report on behalf of UBAI team.
We observed the field of the GRB 251013C (Rakotondrainibe et al., GCN Circ. 42222) with the 1.5-m at Maidanak Observatory telescope AZT-22 equipped with the 4kx4k CCD SNUCAM camera (Im et al., 2010).
The OT (Palmerio et al., GCN Circ. 42223; Perez-Garcia et al., GCN Circ. 42225; Konno et al., GCN Circ. 42226; Martin-Carrillo et al., GCN Circ. 42227; Masi et al., GCN Circ. 42228; Palmerio et al., GCN Circ. 42229; Moskvitin et al., GCN Circ. 42230; Gompertz et al., GCN Circ. 42231; Lipunov et al., GCN Circ. 42235; Garnavich et al., GCN Circ. 42240; Watson et al., GCN Circ. 42241; Lopez-Camara et al., GCN Circ. 42242; Zhang et al., GCN Circ. 42248; Brosio et al., GCN Circ. 42251; Reguitti et al., GCN Circ. 42253; Quintana-Ansaldo et al., Circ. GCN 42254; Maksut et al., GCN Circ. 42256; Ghosh et al., GCN Circ. 42261; Quadri et al., GCN Circ. 42262; Adami et al. GCN Circ. 42266; Peretto et al., GCN Circ. 42267; Ruocco et al., GCN Circ. 42269; Calapai, GCN Circ. 42275; Adami et al. GCN Circ. 42276; and Globus et all GCN 42279 ) is clearly detected in the individual and stacked frames.
Preliminary photometry is as follows:
Date UTstart Exptime t-T0 Filter OT Err. UL Site/Telescope
(nxs) (mid, days)
2025-10-14 17:34:48 6x300 0.99659 R 20.96 0.04 23.10 MAO/AZT-22
All the data have been reduced by a single data processing pipeline, STDPipe (Karpov et al., 2022). Images obtained in Johnson Cousins filters were calibrated using the PanSTARRS DR1 catalog. The data has not corrected for the Galactic extinction.
Maidanak astronomical observatory (MAO) is an observational facility of the Ulugh Beg Astronomical Institute (UBAI), Uzbekistan Academy of Sciences (http://maidanak.uz/).
GCN Circular 42281
Subject
GRB 251013C: Swift ToO observations
Date
2025-10-15T05:41:19Z (2 days ago)
Edited On
2025-10-15T20:09:16Z (a day ago)
From
Phil Evans at U of Leicester <pae9@star.le.ac.uk>
Edited By
Vidushi Sharma at NASA GSFC/UMBC <vidushi.sharma@nasa.gov> on behalf of P.A. Evans at U. Leicester <pae9@leicester.ac.uk>
Via
email
P. A. Evans (U. Leicester) reports on behalf of the Swift team:
EDIT: This circular was submitted as the result of a system error regarding the follow up ToO observation for this GRB.
The correct URL for GRB 251013C products is https://www.swift.ac.uk/xrt_products/01404126
This circular is, nonetheless, an official product of the Swift-XRT team.
GCN Circular 42279
Subject
GRB 251013C: SVOM/COLIBRÍ (FM-GFT) further multi-band optical observations
Date
2025-10-15T04:56:43Z (2 days ago)
Edited On
2025-10-15T20:09:45Z (a day ago)
From
globus@astro.unam.mx
Edited By
Vidushi Sharma at NASA GSFC/UMBC <vidushi.sharma@nasa.gov> on behalf of globus@astro.unam.mx
Via
Web form
Noémie Globus (UNAM), Jean-Grégoire Ducoin (CPPM), Alan M. Watson (UNAM), Camila Angulo (UNAM), Ny Avo Rakotondrainibe (LAM), Stéphane Basa (UAR Pytheas), William H. Lee (UNAM), Jean-Luc Atteia (IRAP), Dalya Akl (NYUAD), Sarah Antier (OCA), Rosa L. Becerra (U Roma), Nathaniel R. Butler (ASU), Damien Dornic (CPPM), Francis Fortin (IRAP), Leonardo García-García (UNAM), Ramandeep Gill (UNAM), Kin Ocelotl López (UNAM), Diego López-Cámara (UNAM), Francesco Magnani (CPPM), Enrique Moreno Méndez (UNAM), Margarita Pereyra (UNAM), Fredd Sánchez Álvarez (UNAM), Benjamin Schneider (LAM), and Antonio de Ugarte Postigo (LAM) report:
We imaged the field of the SVOM GRB 251013C (Rakotondrainibe et al., GCN Circ. 42222) using the DDRAGO two-channel, wide-field imager on the SVOM/COLIBRÍ (FM-GFT) telescope from 2025-10-15 02:56 to 04:18 UTC (33.27 to 34.64 hours after the trigger), obtaining 32 minutes of exposure in the g filter, 32 minutes in the r filter, and 64 minutes in the z filter.
The images were analyzed with STDWeb/STDPipe (Karpov 2025). The photometry was calibrated using nearby stars from the PanSTARRS DR1 catalog, is in the AB system, and is not corrected for Galactic extinction.
We detected the optical counterpart (Palmerio et al., GCN Circ. 42223; Perez-Garcia et al., GCN Circ. 42225; Konno et al., GCN Circ. 42226; Martin-Carrillo et al., GCN Circ. 42227; Masi et al., GCN Circ. 42228; Palmerio et al., GCN Circ. 42229; Moskvitin et al., GCN Circ. 42230; Gompertz et al., GCN Circ. 42231; Lipunov et al., GCN Circ. 42235; Garnavich et al., GCN Circ. 42240; 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; Reguitti et al., GCN Circ. 42253; Quintana-Ansaldo et al., Circ. GCN 42254; Maksut et al., GCN Circ. 42256; Ghosh et al., GCN Circ. 42261; Quadri et al., GCN Circ. 42262; Adami et al. GCN Circ. 42266; Peretto et al., GCN Circ. 42267; Ruocco et al., GCN Circ. 42269; Calapai, GCN Circ. 42275; and Adami et al. GCN Circ. 42276) with preliminary magnitudes of:
g = 21.59 +/- 0.04
r = 21.29 +/- 0.04
z = 20.93 +/- 0.07
We measure a g-r color of 0.30 +/- 0.06, which is consistent with the color of 0.31 +/- 0.01 at about 2 hours after the trigger reported by Palmerio et al. (GCN Circ. 42229), but significantly different to the color of -0.18 +/- 0.12 at about 28 hours after the trigger reported by Adami et al. (GCN Circ. 42276).
Further observations and analysis are ongoing.
We thank the staff of the Observatorio Astronómico Nacional on the Sierra de San Pedro Mártir and the COLIBRÍ and DDRAGO engineering teams.
COLIBRÍ is an astronomical observatory developed and operated jointly by France (AMU, CNES and CNRS) and Mexico (UNAM and SECIHTI). It is located at the Observatorio Astronómico Nacional on the Sierra de San Pedro Mártir, Baja California, Mexico.
GCN Circular 42276
Subject
GRB 251013C: OHP/T193 further optical observations and possible color evolution
Date
2025-10-15T00:11:23Z (2 days ago)
From
Christophe Adami at LAM <christophe.adami@lam.fr>
Via
Web form
C. Adami (LAM/Pytheas/AMU), B. Schneider (LAM), E. Le Floc'h (CEA/Irfu), N.A. Rakotondrainibe (LAM), V. Buat (LAM/Pytheas/AMU), S. Basa (Pytheas/OHP/LAM), M. Dennefeld (IAP) report on behalf of the MISTRAL GRB collaboration:
We carried out further observations of the GRB 251013C optical and NIR afterglow (Palmerio et al., GCN 42223 ; Perez-Garcia et al., GCN 42225 ; Konno et al., GCN 42226 ; Martin-Carrillo et al., GCN 42227 ; Masi et al., GCN 42228 ; Palmerio et al., GCN 42229 ; Moskvitin et al., GCN 42230 ; Gompertz et al., GCN 42231 ; Lipunov et al., GCN 42235 ; Garnavich, GCN42240; Watson et al., GCN 42241 ; Lopez-Camara et al., GCN 42242 ; Zhang et al., GCN 42248; Brosio et al., GCN 42251; Reguitti et al., GCN 42253 ; Quintana-Ansaldo et al., GCN 42254; Maksut et al., GCN 42256; Ghosh et al., GCN 42261 ; Quadri et al., GCN 42262 ; Adami et al. GCN 42266 ; Peretto et al., GCN 42267 ; Ruocco et al., GCN 42269 ; Calapai, GCN 42275) using the T193cm telescope at Observatoire de Haute-Provence (France) equipped with the MISTRAL spectro-imager. We obtained 3 exposures of 10min followed by 1 exposure of 5min in the r-band, corresponding to T-T0 = 27.89 hr (mid-time). In addition, we obtained 2 exposures of 10min followed by 1 exposure of 15min in the g-band, corresponding to T-T0 = 28.71 hr (mid-time).
The afterglow is well detected in the two bands and we measured the following preliminary magnitudes:
g’ = 21.11 +/- 0.10 mag (AB)
r’ = 21.29 +/- 0.07 mag (AB)
This may suggest a color evolution compared to e.g. previous g-r values reported by Palmerio et al. (GCN 42229): 0.31 +/- 0.01 at T-T0 ~ 2.05 hr. In comparison, our preliminary values seem to indicate g’-r’ = -0.18 +/- 0.12 at T-T0 ~ 28.3 hr.
The photometric calibration was performed using nearby stars from the PanSTARRS catalog and the magnitudes are not corrected for Galactic extinction. We used the STDWeb/STDPipe tools (Karpov 2025).
We acknowledge the excellent support from the Observatoire de Haute-Provence and in particular Jean Balcaen and the SOPHIE observers J.B. Salomon and J.L. Halbwachs
GCN Circular 42275
Subject
GRB 251013C: Calapai Observatory, Massa S. Giorgio (Messina), optical observation
Date
2025-10-14T23:48:43Z (2 days ago)
From
Giovanni Calapai at Calapai Astronomical Observatory, Massa S. Giorgio, Messina, Italy <giovannicalapai@tiscali.it>
Via
Web form
Giovanni Calapai at Calapai Astronomical Observatory, Massa S. Giorgio, (Messina) Italy
Member of: GRB/UAI Gamma Ray Burst Section of Unione Astrofili Italiani.
Report:
We observed the field of GRB 251013C detected by SVOM (Rakotondrainibe et al., GCN 42222) with the 11 inches Schmidt-Cassegrain (Celestron 11) telescope F/D=6,3.
The observations were started at 2025-10-13 19:01:08 UT (approximately 1.36 hours after burst) stacking 40 sets of unfiltered CCD image. The observations were carried out with clear skies and good visibility conditions.
The OT was detected at the following position:
RA (J2000.0) 23h 03m 20.56s
Decl. (J2000.0) -00° 12' 37.00"
We report our photometry analysis:
HJD Exposure CR Mag Err
-------------------------------------------
2460962.295312 8x60s 15.56 0.01
2460962.301088 8x60s 15.75 0.01
2460962.306863 8x60s 15.97 0.01
2460962.312627 8x60s 16.09 0.01
2460962.318414 8x60s 16.16 0.01
2460962.324190 8x60s 16.20 0.01
2460962.329954 8x60s 16.27 0.01
2460962.335718 8x60s 16.41 0.01
2460962.341481 8x60s 16.53 0.01
2460962.347245 8x60s 16.61 0.01
2460962.353009 8x60s 16.68 0.01
2460962.358773 8x60s 16.69 0.01
2460962.364537 8x60s 16.72 0.01
2460962.370301 8x60s 16.80 0.01
2460962.376065 8x60s 16.80 0.01
2460962.381840 8x60s 16.90 0.01
2460962.387627 8x60s 16.91 0.01
2460962.393403 8x60s 17.02 0.01
2460962.399178 8x60s 17.02 0.01
2460962.404954 8x60s 17.17 0.01
2460962.410729 8x60s 17.17 0.02
2460962.416505 8x60s 17.22 0.02
2460962.422280 8x60s 17.23 0.02
2460962.428067 8x60s 17.31 0.02
2460962.433843 8x60s 17.35 0.02
2460962.439618 8x60s 17.38 0.02
2460962.445382 8x60s 17.44 0.02
2460962.451157 8x60s 17.43 0.02
2460962.456933 8x60s 17.58 0.03
2460962.462697 8x60s 17.56 0.03
2460962.468461 8x60s 17.70 0.03
2460962.474224 8x60s 17.62 0.03
2460962.479618 8x60s 17.72 0.03
2460962.485903 8x60s 17.75 0.03
2460962.491678 8x60s 17.86 0.04
2460962.497454 8x60s 18.02 0.05
2460962.503241 8x60s 18.03 0.05
2460962.509016 8x60s 17.97 0.05
2460962.514792 8x60s 17.99 0.05
2460962.521667 11x60s 18.06 0.05
Magnitude was calibrated with the nearby PanSTARRS stars converted using Lupton (2005) equations.
No correction for galactic dust extinction was applied.
Our observations are consistent with other already reported Perez-Garcia et al. (GCN circ. 42225), Konno et al. (GCN circ. 42226), 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), Maksut et al. (GCN circ. 42256), Quadri et al.(GCN 42262), Adami et al.(GCN 42266), Peretto et al.(GCN 42267), Ruocco et al. (GCN 42269).
The message may be cited.
GCN Circular 42269
Subject
GRB 251013C: Osservatorio Astronomico "Nastro Verde" optical observations: detection of an bright optical counterpart
Date
2025-10-14T20:51:20Z (2 days ago)
From
Nello Ruocco at Osservatorio Nastro Verde - Sorrento (Naples) - Italy - MPC Code C82 <osservatorionastroverde@gmail.com>
Via
Web form
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.
GCN Circular 42267
Subject
GRB 251013C: MarSEC, optical afterglow photometry
Date
2025-10-14T19:43:03Z (2 days ago)
From
I. Peretto at MarSEC (Marana Space Explorer Center) <ricerca@marsec.org>
Via
Web form
Ivo Peretto (MarSEC, Marana Space Explorer Center, Marana Di Crespadoro, VI, Italy)
Member of:
UAI/SSV - Unione Astrofili Italiani/Sezione Stelle Variabili, GRB section.
AAVSO (American Association Variable Stars Observers).
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) and Stefano Lora, Giovanni Furlato and Giuseppe Peretto (MarSEC, Marana Space Explorer Center, Marana di Crespadoro, VI, Italy)
report:
We imaged the field of GRB 251013C detected by SVOM (Rakotondrainibe et al., GCN 42222), with the robotic telescope of (IAU station 565) with the telescope 14” RC Officine Stellari of MarSEC (Marana Space Explorer Center) with CCD Moravian G2-1600-MKII.
The observations with a series of 90 sec exposures, 2025-10-13T23:13:26.703'UT of midpoint of exposure, with a Ritchey-Chretien telescope D=360 mm f/8. The afterglow was clearly detected at the following position:
RA(J2000) = 23h 03m 20,7s
Dec(J2000) = -00d 13' 37"
We report our photometry analysis:
HJD Rc Mag Err
-------------------------------------
2460962.4676701734 16.813 0.08
Weather conditions were good, sqm medium 20,85
We co-added 14 exposures of 90 sec. each.
Magnitudes were estimated with the pan-STARRS cat and are derived using Lupton (2005) equations and are not corrected for galactic dust extinction.
Reference:
https://www.marsec.org/
The message may be cited.
GCN Circular 42266
Subject
GRB 251013C: OHP/T193 optical afterglow photometry and spectroscopy
Date
2025-10-14T19:29:02Z (2 days ago)
From
Christophe Adami at LAM <christophe.adami@lam.fr>
Via
Web form
C. Adami (LAM/Pytheas/AMU), B. Schneider (LAM), E. Le Floc'h (CEA/Irfu), A. de Ugarte Postigo (LAM), S. Basa (Pytheas/OHP/LAM), F. Schüssler (CEA/Irfu), N.A. Rakotondrainibe (LAM), report on behalf of a larger collaboration:
We observed the field of GRB 251013C detected by FERMI (Fermi GBM Team, GCN Circ. 42221) and SVOM/ECLAIRs (Rakotondrainibe et al., GCN Circ. 42222) using the T193cm telescope at Observatoire de Haute-Provence (France) equipped with the MISTRAL spectro-imager. We obtained one exposure of 3min in the r-band starting at 19:28:38 UT on 2025-10-13.
The optical counterpart previously reported by different groups is well detected. Consistent with previously reported photometric measurements, the preliminary magnitude derived for that source is:
r’ = 15.92 +/- 0.04 mag (AB)
We also obtained a 10min spectrum roughly covering the 4800-8200A range, starting at 19:19:40 UT 2025-10-13. We detect a strong continuum but no prominent lines in our range, consistently with the redshift measured by Martin-Carrillo (GCN 42227).
The photometric calibration was performed using nearby stars from the PanSTARRS catalog and the magnitudes are not corrected for Galactic extinction. We used the STDWeb/STDPipe tools (Karpov 2025).
We acknowledge the excellent support from the Observatoire de Haute-Provence and in particular Jean Balcaen and the SOPHIE observers J.B. Salomon and J.L. Halbwachs
GCN Circular 42262
Subject
GRB 251013C: Bassano Bresciano Observatory optical observations
Date
2025-10-14T16:09:54Z (2 days ago)
From
Ulisse Quadri at Bassano Bresciano Observatory <osservatoriobassano@gmail.com>
Via
Web form
U.Quadri, L.Strabla and P.Madurini (Bassano Bresciano Astronomical Observatory)
Members of:
GRB/UAI - Gamma ray Burst section of Unione Astrofili Italiani.
AAVSO - American Association of Variable Star Observers.
GAC - Gruppo Astrofili Cremonesi.
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 251013C detected by SVOM (Rakotondrainibe et al., GCN 42222), with the robotic telescope of (IAU station 565) Bassano Bresciano Observatory, Italy .
The observations started 1h 47m after the trigger with our Newton telescope D=440 mm F/D=4.5.
We co-added series of 10 exposures of 30 sec each.
We clearly detect a bright afterglow 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)) at the following position (+/- 3 arcsec):
RA (J2000.0) = 23 03 20.5
DEC(J2000.0) = -00 12 37
We report our photometry analysis:
HJD CR Mag Err
-----------------------------
2460962.318647 15.63 0.01
2460962.318647 15.63 0.01
2460962.322293 15.67 0.01
2460962.325915 15.73 0.01
2460962.329549 15.72 0.01
2460962.333183 15.77 0.01
2460962.336817 15.84 0.01
2460962.340463 15.92 0.01
2460962.344097 15.98 0.01
2460962.347730 16.05 0.01
2460962.351307 16.12 0.01
2460962.355022 16.18 0.01
2460962.358656 16.24 0.01
2460962.362302 16.24 0.02
2460962.365947 16.24 0.02
2460962.369581 16.29 0.02
2460962.373227 16.31 0.01
2460962.376873 16.35 0.02
2460962.380507 16.37 0.02
2460962.384141 16.37 0.02
2460962.387775 16.43 0.02
2460962.391397 16.47 0.02
2460962.395032 16.54 0.02
2460962.398665 16.55 0.02
2460962.402299 16.56 0.02
2460962.405933 16.61 0.02
2460962.409568 16.64 0.02
2460962.413190 16.64 0.02
2460962.416824 16.68 0.02
2460962.420458 16.71 0.02
2460962.424092 16.78 0.02
2460962.427715 16.83 0.02
2460962.431349 16.83 0.03
2460962.434982 16.84 0.03
2460962.438617 16.98 0.03
2460962.442251 17.06 0.04
2460962.445885 17.03 0.05
2460962.449519 17.02 0.04
2460962.453153 17.09 0.04
2460962.456787 17.02 0.04
-----------------------------
CR magnitude is unfiltered with R zero point.
Magnitudes were estimated with the pan-STARRS cat and are derived using Lupton (2005) equations.
Not corrected for galactic dust extinction.
Reference:
http://www.osservatoriobassano.altervista.org
The message may be cited.
GCN Circular 42261
Subject
GRB 251013C: Early and late-time optical counterpart detection by LCO
Date
2025-10-14T15:45:51Z (2 days ago)
From
ankur ghosh at CAPP, University of Johannesburg <ghosh.ankur1994@gmail.com>
Via
Web form
Ankur Ghosh, Soebur Razzaque (CAPP, University of Johannesburg), Rahul Gupta (NASA GSFC), Alexander Moskvitin, Yulia Sotnikova (SAO RAS), Naveen Dukiya (ARIES) on behalf of a larger collaboration.
We observed the field of the GRB 251013C triggered by Fermi (Fermi GBM team, GCN circ. 42221), and SVOM (Rakotondrainibe et al., GCN circ. 42222) in V and r filters of the 1-meter Sinistro telescope at the Las Cumbres Observatory Global Telescope (LCOGT) node located at South African Astronomical Observatory (SAAO). The 1-m Sinistro telescope is equipped with a 4K x 4K CCD (FOV: 26 x 26 arcmin, scale: 0.39 arcsec/pixel).
Observations began on October 13, 2025, starting from 2.88 hours after the GRB trigger. Further observations are still ongoing.
We clearly detect the optical transient (OT) 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)).
------------------------------------------------------------------------------------------------------
|Date| |JDstart| |t-T0 (hours)| |Exp (sec)| |Filter| |Magnitude|
------------------------------------------------------------------------------------------------------
2025-10-13 2460962.35625 2.88 1 x 300 V V = 16.61 +/- 0.01
2025-10-14 2460963.01397 18.67 1 x 600 V V = 20.73 +/- 0.05
------------------------------------------------------------------------------------------------------
The field was calibrated against nearby APASS stars, with magnitudes converted using Lupton (2005) equations, and has not been corrected for Galactic extinction.
GCN Circular 42259
Subject
GRB 251013C: Fermi GBM Observation
Date
2025-10-14T15:35:36Z (2 days ago)
From
Jacob Smith at Fermi-GBM Team <jrs0118@uah.edu>
Via
Web form
Jacob Smith (UAH), E. Palafox (INAOE), and C. Meegan (UAH) report on behalf of
the Fermi Gamma-ray Burst Monitor Team:
"At 17:39:41.94 UT on 13 October 2025, the Fermi Gamma-ray Burst Monitor (GBM)
triggered and located GRB 251013C (trigger 782069986/251013736),
which was also detected by SVOM (N. A. Rakotondrainibe et al. 2025, GCN 42222) and Swift XRT (P.A. Evans et al. 2025, GCN 42232).
The Fermi GBM on-ground location is consistent with the Swift BAT position.
NOT measured a spectroscopic redshift z = 0.572 (A. Martin-Carrillo et al. 2025, GCN 42227).
The angle from the Fermi LAT boresight is 60 degrees.
The GBM light curve consists of a single emission episode with a duration (T90)
of about 12 s (50-300 keV). The time-averaged spectrum
from T0-0.1 to T0+4.0 s is best fit by
a simple power law function with index -1.50 +/- 0.02.
A Comptonized function fits equally well with Epeak = 7291.00 +/- 4840.00 and alpha = -1.46 +/- 0.03.
The event fluence (10-1000 keV) in this time interval is
(2.4 +/- 0.1)E-06 erg/cm^2. The 1-sec peak photon flux measured
starting from T0+0.32 s in the 10-1000 keV band is 5 +/- 0.2 ph/s/cm^2.
The spectral analysis results presented above are preliminary;
final results will be published in the GBM GRB Catalog:
https://heasarc.gsfc.nasa.gov/W3Browse/fermi/fermigbrst.html
For Fermi GBM data and info, please visit the official Fermi GBM Support Page:
https://fermi.gsfc.nasa.gov/ssc/data/access/gbm/"
GCN Circular 42256
Subject
GRB 251013C NUTTelA-TAO / BSTI Early Measurements
Date
2025-10-14T13:45:06Z (2 days ago)
From
Zhanat Maksut at Nazarbayev University <zhanat.maksut@nu.edu.kz>
Via
Web form
Z. Maksut (NU), B. Grossan (UCB, NU), T. Komesh (NU), D. Berdikhan (NU), M. Krugov (FAI) and E. Abdikamalov (NU) report on behalf of the Energetic Cosmos Laboratory:
The Nazarbayev University Transient Telescope at Assy-Turgen Astrophysical Observatory (NUTTelA-TAO) pointed at GRB 251013C on receipt of an automated GCN SVOM/ECLAIRs position alert, with the Burst Simultaneous Three-Channel Imager (BSTI; Grossan, Kumar & Smoot 2019, JHEA, 32, 14).
We started observations at UT 2025 October 13, 17:41:17, 95 s after the ECLAIRs trigger (N. A. Rakotondrainibe, et. al., GCN 42222). Observations were made in conditions that started good and deteriorated to cloudy over the night. A new and changing source consistent with the XRT position (P.A. Evans et al., GCN 42232) was detected. Note that these observations provide essentially full-time coverage until conditions deteriorated, about 3 hours of coverage. The source was off our field in g' and r' band cameras, but on the sensor with adequate margin in our Sloan i' camera. We report the following preliminary, uncorrected, selected photometric values for the optical transient:
tc-t0(s) texp i'(mag) err(mag)
-------- ------ ------- --------
96 3.0 13.67 0.1
123 3.0 14.20 0.1
141 3.0 14.27 0.1
185 30.0 14.69 0.06
245 30.0 14.96 0.06
305 30.0 15.16 0.06
425 30.0 15.06 0.06
635 30.0 15.14 0.06
tc-t0 = trigger time minus image center time. Calibration was done with 5 bright Pan-STARRS catalog stars on our images (see Komesh, T. et al. 2023, MNRAS 520, 6104).
We find a rapid fading to a plateau starting at ~300 s.
We caution the reader that these are preliminary results, without color or other corrections, and will likely change. Please also note that times are approximate. Systematic errors are estimated from previous measurements. We welcome requests for additional data.
----------------------------------
NU = Nazarbayev University, Astana, Kazakhstan
UCB = University of California, Berkeley, USA
FAI = Fesenkov Astrophysical Institute, Kazakhstan
This research has been funded by the Science Committee of the Ministry of Science and Higher Education of the Republic of Kazakhstan (Grant No. AP26103591). The NUTTelA-TAO Team acknowledges the support of the staff of the Assy-Turgen Astrophysical Observatory, Almaty, Kazakhstan, and the Fesenkov Astrophysical Institute, Almaty, Kazkhstan.
GCN Circular 42254
Subject
GRB 251013C: ULL-ASTRO-MASTER detection of the optical afterglow with the LCO 40-cm telescope at Sutherland Observatory
Date
2025-10-14T12:02:29Z (2 days ago)
From
Ismael Perez-Fournon at Instituto de Astrofisica de Canarias <ipf@iac.es>
Via
Web form
M. Quintana-Ansaldo, J. Basurto Merino, P.G. Berdayes, A. Caballero-Almagro, A. Cerón, M. Contreras, F. Díaz-Segado, T. Ferrer-Laviña, B. Gandolfi, V. Ghiraldo, J. Hernández Fung, L. Juliá-Maroto, E. Lekaroz-Urriza, M. Manzano García, E. Mejía-Martínez, J. Prieto Polo, M. Pulido-Torres, , A. Schenone-Zanuzzi, A. Selezneva, T. Tundidor Rodríguez, E. Urquijo-Rodríguez (all ULL), M. Abdul-Masih (IAC and ULL), and I. Pérez-Fournon (IAC and ULL).
Following the detection of GRB 251013C by Fermi (Fermi GBM team, GCN circ. 42221),
and SVOM (Rakotondrainibe et al., GCN circ. 42222), we observed the field with the Las Cumbres Observatory (LCO) 40-cm telescope (a Planewave Delta Rho 350 telescope equipped with a CMOS QHY600 camera) located at the LCO node at Sutherland Observatory (South Africa). The observation, a single exposure of 300 sec in the SDSS r filter, started on 2025-10-13 at 18:27:18 UT, about 47 minutes after the Fermi and SVOM trigger.
The optical counterpart detected by SVOM/VT (Palmerio et al., GCN circ. 42223) is
clearly detected in our image with a magnitude of r = 14.84 +/- 0.02 (AB), calibrated against PanSTARRS-1 DR2 and not corrected for galactic extinction.
This result confirms the rebrightening reported by Konno et al. (GCN circ. 42226).
Other optical and near-IR detections have been reported by 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), and Brosio et al. (GCN circ. 42251).
A redshift of z = 0.572 has been measured by Martin-Carrillo et al. (GCN circ. 42227). GRB 251013C has also been detected by Swift-XRT (Evans et al., GCN circ. 42232), AstroSat (Arya et al., GCN circ. 42246), Einstein Probe (Wang et al., GCN circ. 42247), and ALMA Laskar et al. (GCN circ. 42243).
Based on observations made with the Las Cumbres Observatory’s education network telescopes that were upgraded through generous support from the Gordon and Betty Moore Foundation (program IAC2025B-010). These observations are part of a course in Astrophysical Techniques of the Master in Astrophysics of the Astrophysics Department of the University of La Laguna in collaboration with the Instituto de Astrofísica de Canarias (La Laguna, Tenerife, Canary Islands, Spain).
GCN Circular 42253
Subject
GRB 251013C: Asiago optical observations
Date
2025-10-14T11:40:21Z (2 days ago)
From
Andrea Reguitti at INAF - Osservatorio Astronomico di Padova <andreareguitti@gmail.com>
Via
Web form
A. Reguitti (INAF/OAPd) reports on behalf of a larger collaboration:
I observed the field of GRB 251013C (Fermi GBM Team, GCN 42221; Rakotondrainibe et al., GCN 42222) using the 67/92 Schmidt Telescope located at the Asiago observatory (Italy). Observations were carried out using Sloan r and i filters.
The optical counterpart (Palmerio et al., GCN 42223; Perez-Garcia et al., GCN 42225; Konno et al., GCN 42226; Martin-Carrillo et al., GCN 42227; Masi, GCN 42228; Palmerio et al., GCN 42229; Moskvitin et al., GCN 42230; Gompertz et al., GCN 42231; Garnavich, GCN 42240; Watson et al., GCN 42241; López-Cámara et al., GCN 42242; Brosio et al., GCN 42251) is clearly detected in our frames. At mean epoch 2025 Oct 13.85 UT (2.75 hr after the GRB), I measure AB magnitudes r = 16.51 +- 0.05 and i = 16.27 +- 0.04 (calibrated against magnitudes from the Pan-STARRS catalog).
GCN Circular 42251
Subject
GRB 251013C: ABObservatory optical observations
Date
2025-10-14T10:53:56Z (2 days ago)
Edited On
2025-10-14T14:24:18Z (2 days ago)
From
A. Brosio at ABObservatory Rosarno <antonino.brosio@gmail.com>
Edited By
Vidushi Sharma at NASA GSFC/UMBC <vidushi.sharma@nasa.gov> on behalf of A. Brosio at ABObservatory Rosarno <antonino.brosio@gmail.com>
Via
Web form
A. Brosio (ABObservatory Rosarno), M. A. Tripodi (ABObservatory Rosarno), S. Savaglio (University of Calabria), G. Bracco, P. Cianfarra, L. Sangaletti, S. Tosi & S. Zappatore (University of Genoa), S. Benatti & M. G. Guarcello (INAF Palermo), L.Cabona, M. Rainer, F. M. Zerbi, M. Basilicata (INAF Brera), D. Ricci (INAF Padova), A. Di Dato (INAF Capodimonte), S. Masiero & A. Nastasi (GAL Hassin), D. Liguori (Osservatorio "G. Galilei" Cariati), L. Betti (Osservatorio Polifunzionale del Chianti), R. Nesci (Associazione Astronomica Antares APS di Foligno), for the NOCTIS team report
We observed the field of GRB 251013C, which was detected by Fermi GBM team (GCN 42221) with the 30-cm automated telescope at ABObservatory (Rosarno, Italy) in V filter.
The observations began on 2025 october 13 at 20:56:53 UT, approximately 2.38 hours after the trigger. The observation consisted of 50 exposures of 120 seconds each,with good sky conditions.
The mid-exposure time was 22:12:46 UT, and the final exposure ended at 23:32:52 UT.
From photometry, we detect the optical counterpart in our images at the following coordinates:
R.A (J2000.0) = 23 03 19.712
Dec. (J2000.0) = -00 12 53.17
The measured magnitude at JD 2460962.37284 is:
16.86 +/- 0.06 in V band with SNR 14.98 (AB, calibrated with the GAIA DR3 on SIMBAD).
We also obtained a decay curve which, during the period we monitored the object, showed a decline down to magnitude +17.848 +/-0.275 at 23:27:57 UT
GCN Circular 42248
Subject
GRB 251013C: J band observations by SYSU 80cm infrared telescope
Date
2025-10-14T07:17:23Z (2 days ago)
From
zhanghr33@mail2.sysu.edu.cn
Via
Web form
Hao-Ran Zhang, Chen Chun, Duo-Le Cao, Zhong-Nan Dong, Wei-Sen Huang, Jin-Ji Li, Jia-Qi Lin, Pu Lin, Yan Yu, Hao-Nan Yang, P H Thomas Tam, Rong-Feng Shen, Bin Ma (Sun Yat-sen University) report on behalf of the SYSU 80cm infrared telescope team:
We observed the field of GRB 251013C detected by SVOM (N. A. Rakotondrainibe et al., GCN 42222) and Fermi (Fermi GBM Team, GCN 42221), using the Sun Yat-sen University 80cm infrared telescope with 20 s exposures in J band. The calculated position is R.A. = 345.8301 deg, Dec = -0.2207deg J2000, from SVOM observation. Our observations began at 2025-10-13 18:03:42 UTC, 0.41 hours after the SVOM trigger.
We clearly detect an infrared counterpart at the position of the optical afterglow (J. T. Palmerio et al., GCN 42223; I. Perez-Garcia et al., GCN 42225; R. Konno et al., GCN 42226; L. A. Martin-Carrillo et al., GCN 42227; Gianluca Masi, GCN 42228; J. T. Palmerio et al., GCN 42229; A. S. Moskvitin et al., GCN 42230; B. P. Gompertz et al., GCN 42231; V.Lipunov et al., GCN 42235; P. Garnavich, GCN 42240; Alan M. Watson et al., GCN 42241; Diego López-Cámara et al., GCN 42242). The earliest detection is confirmed at 2025-10-13 18:03:42UTC (T – T0 = 0.41 h) with J mag: 13.49+/-0.14 (Vega system). Preliminary photometry shows a rise of ~0.4mag at 18:26:00UTC (T – T0 = 0.78 h), followed by a rapid decay. The photometric calibration was performed using nearby stars from the 2MASS catalog. The photometric accuracy is limited due to the cloudy weather.
The SYSU 80cm infrared telescope is operated and managed by the Department of Astronomy, Sun Yat-sen University.
GCN Circular 42247
Subject
GRB 251013C: EP-FXT counterpart detection
Date
2025-10-14T05:55:24Z (3 days ago)
From
EP Team at NAOC/CAS <ep_ta@bao.ac.cn>
Via
Web form
B.T. Wang (YNAO, CAS), H. Zhou (PMO, CAS), Z.M. Wang (BNU), P.Y. Han (HUST), R.X. Hu (WHU), D.Z. Du (ZJU), and C.C. Jin (NAO, CAS) on behalf of the Einstein Probe (EP) team:
EP-FXT performed a follow-up observation of the SVOM/ECLAIRs-detected burst GRB 251013C (SVOM/sb25101311, Rakotondrainibe et al., GCN #42222, also detected by Fermi/GBM GCN #42221) at 2025-10-13T19:39:21 (UTC), about 2.0 hours after the SVOM/ECLAIRs trigger, with an exposure time of 1690 s. One uncatalogued source is detected within the ECLAIRs error circle, and the source is spatially consistent with the counterpart reported in optical and X-ray bands (Palmerio et al. GCN #42223, Perez-Garcia et al., GCN #42225, Konno et al., GCN #42226, Masi et al., GCN #42228, Palmerio et al., GCN #42229, Moskvitin et al., GCN #42230, Gompertz et al., GCN #42231, Evans et al., GCN #42232, Garnavich et al., GCN #42240, Watson et al., GCN #42241, López-Cámara et al., GCN #42242) with redshift at 0.572 (Martin-Carrillo et al., GCN #42227). Preliminary analysis on this source are automatically conducted, and details are listed as follows.
Source 1: EPF_J230320.5-001237
RA (J2000): 345.8356
Dec (J2000): -0.2103
Flux: 3.75 x 10^-10 erg/s/cm2 (observed, 0.5-10 keV)
Flux_err: 7.89 x 10^-12 erg/s/cm2 (1 sigma)
The position uncertainty of the source is about 10 arcsec in radius (90% C.L. statistical and systematic).
Launched on January 9, 2024, EP is a space X-ray observatory to monitor the soft X-ray sky with X-ray follow-up capability (Yuan et al. 2022, Handbook of X-ray and Gamma-ray Astrophysics).
GCN Circular 42246
Subject
GRB 251013C: AstroSat CZTI detection
Date
2025-10-14T05:53:26Z (3 days ago)
From
Anuraag Arya at IIT Bombay <aryaanuraag910@gmail.com>
Via
Web form
A. Arya (IITB), U. Pathak (IITB), A. Goyal (IITB), Harsha K. H. (IUCAA), M. Tembhurnikar (IUCAA), S. Salunke (IUCAA), G. Waratkar (Caltech/IITB), A. Vibhute (IUCAA), V. Bhalerao (IITB), D. Bhattacharya (Ashoka University/IUCAA), A. R. Rao (IUCAA/TIFR), and S. Vadawale (PRL) report on behalf of the AstroSat CZTI collaboration:
Analysis of AstroSat CZTI data with the CIFT framework (Sharma et al., 2021, JApA, 42, 73) showed the detection of a long GRB 251013C which was also detected by Fermi GBM (Fermi GBM Team, GCN Circ. 42221), and SVOM/ECLAIRs (Rakotondrainibe et. al., GCN Circ. 42222).
The source was clearly detected in the CZT detectors in the 20-200 keV energy range. The light curve peaks at 2025-10-13 17:39:42.75 UTC. The measured peak count rate associated with the burst is 87 (+43, -15) counts/s above the background in the combined data of three quadrants (out of four), with a total of 337 (+89, -97) counts. The local mean background count rate was 202 (+3, -3) counts/s. Using cumulative rates, we measure a T90 of 7.3 (+0.7, -1.1) s. We caution that there is a 0.3 s dead time in the CZTI data just after the burst, hence the actual T90 may be slightly longer.
The source was also clearly detected in the CsI anticoincidence (Veto) detector in the 100-500 keV energy range. The light curve peaks at 2025-10-13 17:39:42.33 UTC. The measured peak count rate associated with the burst is 281 (+68, -36) counts/s above the background in the combined data of all quadrants, with a total of 1351 (+229, -274) counts. The local mean background count rate was 1171 (+6, -9) counts/s. We measure a T90 of 6.7 (+0.8, -1.8) s from the cumulative Veto light curve.
CZTI is built by a TIFR-led consortium of institutes across India, including VSSC, URSC, IUCAA, SAC, and PRL. The Indian Space Research Organisation funded, managed, and facilitated the project.
CZTI GRB detections are reported regularly on the payload site at:
http://astrosat.iucaa.in/czti/?q=grb
GCN Circular 42243
Subject
GRB 251013C: ALMA detection
Date
2025-10-14T03:51:49Z (3 days ago)
From
Tanmoy Laskar at U of Utah <tanmoylaskar@gmail.com>
Via
Web form
T. Laskar (University of Utah), C. Christy, N. Franz, K. D. Alexander (University of Arizona), E. Berger (Harvard University), R. Chornock (UC Berkeley), H. J. van Eerten (University of Bath), G. Farley (U. Utah), W. Fong (Northwestern University), R. Gill (UNAM), J. Granot (Open University), R. Margutti (UC Berkeley), and P. Schady (University of Bath) report:
“We observed GRB 251013C (Fermi GBM team, GCN 42221; Rakotondrainibe et al., GCN 42222) with the Atacama Large Millimeter/Submillimeter Array (ALMA) at 97.5 GHz beginning on 2025 October 13 at 23:07 UT (5.5 hours after the burst).
Preliminary analysis reveals a mm source with flux density of ~ 0.3 mJy at position:
RA (J2000) = 23:03:20.56
Dec (J2000) = -00:12:37.21
with an uncertainty of 0.02" in each coordinate. This is consistent with the X-ray position (Rakotondrainibe et al., GCN 42222; Evans et al., GCN 42232) and optical position (Palmerio et al., GCN 42223; Masi et al., GCN 42228). Further observations are planned.
We thank the NAASC staff, P2G, AoD, JAO staff, and the entire ALMA team for their help with these observations."
GCN Circular 42242
Subject
GRB 251013C: SVOM/COLIBRÍ (FM-GFT) detection of the optical counterpart
Date
2025-10-14T03:33:15Z (3 days ago)
From
Diego López-Cámara at Instituto de Ciencias Nucleares, UNAM <diego@correo.nucleares.unam.mx>
Via
Web form
Diego López-Cámara (UNAM), Francesco Magnani (CPPM), Alan M. Watson (UNAM), Camila Angulo (UNAM), Ny Avo Rakotondrainibe (LAM), Stéphane Basa (UAR Pytheas), William H. Lee (UNAM), Jean-Luc Atteia (IRAP), Dalya Akl (NYUAD), Sarah Antier (OCA), Rosa L. Becerra (U Roma), Nathaniel R. Butler (ASU) , Damien Dornic (CPPM), Jean-Grégoire Ducoin (CPPM), Francis Fortin (IRAP), Leonardo García-García (UNAM), Ramandeep Gill (UNAM), Noémie Globus (UNAM), Kin Ocelotl López (UNAM), Enrique Moreno Méndez (UNAM), Margarita Pereyra (UNAM), Fredd Sánchez Álvarez (UNAM), Benjamin Schneider (LAM), and Antonio de Ugarte Postigo (LAM) report:
We imaged the field of the SVOM GRB 251013C (Rakotondrainibe et al., GCN Circ. 42222) using the DDRAGO wide-field imager on the SVOM/COLIBRÍ (FM-GFT) telescope. We obtained a 60 seconds exposure in the r filter starting at 2025-10-14 02:18 (8.65 hours after the trigger).
The image was analyzed with STDWeb/STDPipe (Karpov 2025). The photometry was calibrated using nearby stars from the PanSTARRS catalog, is in the AB system, and is not corrected for Galactic extinction.
We detected the optical counterpart, (Palmerio et al., GCN Circ. 42223; Perez-Garcia et al., GCN Circ. 42225; Konno et al., GCN Circ. 42226; Martin-Carrillo et al., GCN Circ. 42227; Masi et al., GCN Circ. 42228; Palmerio et al., GCN Circ. 42229; Moskvitin et al., GCN Circ. 42230; Gompertz et al., GCN Circ. 42231; Lipunov et al., GCN Circ. 42235; and Garnavich et al., GCN Circ. 42240; Watson et al. GCN Circ. 42241) with a preliminary magnitude of:
r = 18.50 +/- 0.03
Compared to the observation reported by Garnevich (GCN Circ. 42240), our observation suggests an abrupt fading between 6.4 and 8.7 hours.
Further observations and analysis are ongoing.
We thank the staff of the Observatorio Astronómico Nacional on the Sierra de San Pedro Mártir and the COLIBRÍ and DDRAGO engineering teams.
COLIBRÍ is an astronomical observatory developed and operated jointly by France (AMU, CNES and CNRS) and Mexico (UNAM and SECIHTI). It is located at the Observatorio Astronómico Nacional on the Sierra de San Pedro Mártir, Baja California, Mexico.
GCN Circular 42241
Subject
GRB 251013C: DDOTI detection of the optical afterglow
Date
2025-10-14T03:26:13Z (3 days ago)
From
Alan Watson at UNAM <alan@astro.unam.mx>
Via
Web form
Alan M. Watson (UNAM), Camila Angulo Valdez (UNAM), Rosa L. Becerra (U Roma), Nat Butler (ASU), Simone Dichiara (Penn State University), Tsvetelina Dimitrova (ASU), Alexander Kutyrev (GSFC/UMD), William H. Lee (UNAM), Océlotl López (UNAM), Margarita Pereyra (UNAM) and Eleonora Troja (U Roma) report:
We observed the field of GRB 251013C detected by Fermi/GBM (Fermi GBM Team, GCN Circ. 42221) and SVOM/ECLAIRS (Rakotondrainibe et al., GCN Circ. 42222) with the DDOTI wide-field imager at the Observatorio Astronómico Nacional on Sierra San Pedro Mártir (http://ddoti.astroscu.unam.mx) from 2025-10-14 02:41 to 03:08 (8.80 to 9.45 hours after the trigger) and obtained a total of 23 minutes of exposure in the w filter.
We detect the optical afterglow (Palmerio et al., GCN Circ. 42223; Perez-Garcia et al., GCN Circ. 42225; Konno et al., GCN Circ. 42226; Martin-Carrillo et al., GCN Circ. 42227; Masi et al., GCN Circ. 42228; Palmerio et al., GCN Circ. 42229; Moskvitin et al., GCN Circ. 42230; Gompertz et al., GCN Circ. 42231; Lipunov et al., GCN Circ. 42235; and Garnavich et al., GCN Circ. 42240) with a preliminary magnitude of
w = 18.95 +/- 0.04
Our photometry is calibrated against the USNO-B1 and Pan-STARRS PS1 DR2 catalogues and is not corrected for Galactic extinction.
Observations are continuing.
We thank the staff of the Observatorio Astronómico Nacional at the Sierra de San Pedro Mártir for their excellent support.
GCN Circular 42235
Subject
Fermi GRB 251013C: Global MASTER-Net observations report
Date
2025-10-13T23:46:00Z (3 days ago)
From
Vladimir Lipunov at Moscow State U/Krylov Obs <lipunov@xray.sai.msu.ru>
Via
email
V.Lipunov, E.Gorbovskoy, A.Kuznetsov, K.Zhirkov, I.Panchenko, N.Tiurina, P.Balanutsa, V.Topolev, D.Vlasenko,
G.Antipov, A.Sankovich, Yu.Tselik, Ya.Kechin, V.Senik, A.Chasovnikov, K.Labsina, I. Gorbunov (Lomonosov MSU),
O.Gress, N.Budnev (ISU),
C.Francile, F. Podesta, R.Podesta, E. Gonzalez (Observatorio Astronomico Felix Aguilar (OAFA),
A. Tlatov, D. Dormidontov (Kislovodsk Solar Station of the Pulkovo Observatory),
A.Sosnovskij (CrAO),
A. Gabovich, V.Yurkov (Blagoveschensk Educational StateUniversity),
D.Buckley (SAAO),
R.Rebolo (The Instituto de Astrofisica de Canarias),
L.Carrasco, J.R.Valdes, V.Chavushyan, V.M.Patino Alvarez, J.Martinez,
A.R.Corella, L.H.Rodriguez (INAOE, Guillermo Haro Astrophysics Observatory)
MASTER-SAAO robotic telescope (Global MASTER-Net: http://observ.pereplet.ru, Lipunov et al., 2010, Advances in Astronomy, vol. 2010, 30L) located in South Africa (South African Astronomical Observatory) started inspect of the Fermi GRB 251013C ( Fermi GBM team, GCN 42221) errorbox 10000 sec after notice time and 10034 sec after trigger time at 2025-10-13 20:26:56 UT, with upper limit up to 20.4 mag. The observations began at zenith distance = 32 deg. The sun altitude is -41.1 deg.
The galactic latitude b = -59 deg., longitude l = 72 deg.
Real time updated cover map and OT discovered available here:
https://master.sai.msu.ru/site/master2/observ.php?id=3013941
We obtain a following upper limits.
Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment
_________|_____________________|_____________________|____________________________________|_____|_______|_______|________
10064 | 2025-10-13 20:26:56 | MASTER-SAAO | (23h 02m 39.24s , -00d 30m 39.4s) | C | 60 | 18.6 |
10158 | 2025-10-13 20:28:29 | MASTER-SAAO | (23h 02m 46.41s , -00d 31m 36.1s) | C | 60 | 18.7 |
10251 | 2025-10-13 20:30:02 | MASTER-SAAO | (23h 02m 40.37s , -00d 32m 32.6s) | C | 60 | 18.9 |
10345 | 2025-10-13 20:31:37 | MASTER-SAAO | (23h 02m 47.55s , -00d 32m 05.9s) | C | 60 | 18.8 |
10441 | 2025-10-13 20:33:12 | MASTER-SAAO | (23h 02m 45.46s , -00d 30m 49.0s) | C | 60 | 18.7 |
10539 | 2025-10-13 20:34:50 | MASTER-SAAO | (23h 02m 46.25s , -00d 32m 02.3s) | C | 60 | 18.6 |
10664 | 2025-10-13 20:36:25 | MASTER-SAAO | (23h 02m 49.67s , -00d 30m 22.6s) | C | 120 | 18.9 |
10817 | 2025-10-13 20:38:58 | MASTER-SAAO | (23h 02m 45.08s , -00d 31m 17.6s) | C | 120 | 18.8 |
10980 | 2025-10-13 20:41:42 | MASTER-SAAO | (23h 02m 47.31s , -00d 30m 13.8s) | C | 120 | 19.0 |
11135 | 2025-10-13 20:44:17 | MASTER-SAAO | (23h 02m 52.66s , -00d 31m 09.8s) | C | 120 | 19.0 |
11292 | 2025-10-13 20:46:54 | MASTER-SAAO | (23h 02m 47.94s , -00d 32m 05.5s) | C | 120 | 19.2 |
11446 | 2025-10-13 20:49:27 | MASTER-SAAO | (23h 02m 55.30s , -00d 32m 00.3s) | C | 120 | 19.2 |
11630 | 2025-10-13 20:52:01 | MASTER-SAAO | (23h 02m 53.52s , -00d 30m 03.7s) | C | 180 | 19.2 |
11847 | 2025-10-13 20:55:39 | MASTER-SAAO | (23h 02m 54.71s , -00d 31m 32.8s) | C | 180 | 19.2 |
12064 | 2025-10-13 20:59:15 | MASTER-SAAO | (23h 02m 58.96s , -00d 29m 55.7s) | C | 180 | 19.4 |
12247 | 2025-10-13 21:02:48 | MASTER-SAAO | (23h 02m 53.36s , -00d 30m 39.0s) | C | 120 | 19.4 |
12399 | 2025-10-13 21:05:21 | MASTER-SAAO | (23h 02m 55.07s , -00d 29m 35.0s) | C | 120 | 19.4 |
12519 | 2025-10-13 21:05:21 | MASTER-SAAO | (23h 02m 55.07s , -00d 29m 35.0s) | C | 360 | 20.1 | Coadd
12554 | 2025-10-13 21:07:55 | MASTER-SAAO | (23h 03m 01.04s , -00d 30m 30.6s) | C | 120 | 19.4 |
12722 | 2025-10-13 21:10:43 | MASTER-SAAO | (23h 02m 55.49s , -00d 31m 25.3s) | C | 120 | 19.7 |
12875 | 2025-10-13 21:13:16 | MASTER-SAAO | (23h 03m 01.00s , -00d 31m 12.9s) | C | 120 | 19.4 |
12995 | 2025-10-13 21:13:16 | MASTER-SAAO | (23h 03m 01.00s , -00d 31m 12.9s) | C | 360 | 20.4 | Coadd
13030 | 2025-10-13 21:15:51 | MASTER-SAAO | (23h 02m 59.29s , -00d 29m 35.6s) | C | 120 | 19.7 |
13194 | 2025-10-13 21:18:36 | MASTER-SAAO | (23h 02m 59.68s , -00d 30m 53.7s) | C | 120 | 19.6 |
13347 | 2025-10-13 21:21:09 | MASTER-SAAO | (23h 03m 02.87s , -00d 29m 15.8s) | C | 120 | 19.9 |
13502 | 2025-10-13 21:23:44 | MASTER-SAAO | (23h 02m 57.06s , -00d 30m 00.8s) | C | 120 | 19.8 |
16491 | 2025-10-13 22:14:02 | MASTER-SAAO | (23h 07m 20.08s , -06d 42m 29.2s) | C | 60 | 18.9 |
Filter C is a clear (unfiltred) band.
The observation and reduction will continue.
The message may be cited.
GCN Circular 42232
Subject
GRB 251013C: Swift-XRT counterpart detection
Date
2025-10-13T22:23:39Z (3 days ago)
From
Phil Evans at U of Leicester <pae9@star.le.ac.uk>
Via
email
P.A. Evans (U. Leicester), J.A. Kennea (PSU), E. Ambrosi (INAF-IASFPA) , A.P.
Beardmore (U. Leicester), M.G. Bernardini (INAF-OAB), R. Brivio (INAF-OAB), D.N.
Burrows (PSU), S. Campana (INAF-OAB), M. Capalbi (INAF-OAR), A. D'Ai (INAF-IASFPA),
P. D'Avanzo (INAF-OAB), V. D'Elia (SSDC & INAF-OAR), S. Dichiara (PSU), M. Ferro
(INAF-OAB), A. Melandri (INAF-OAR), J.P. Osborne (U. Leicester), K.L. Page (U.
Leicester), M. Perri (SSDC & INAF-OAR), C. Salvaggio (INAF-OAB), T. Sbarrato
(INAF-OAB), B. Sbarufatti (INAF-OAB), M.A. Williams (PSU) report on behalf of the
Swift-XRT team:
Swift-XRT has performed follow-up observations of the SVOM/ECLAIRs-detected source
GRB 251013C (Rakotondrainibe et al., GCN 42222), collecting 1.8 ks of Photon
Counting (PC) mode data between T0+344 s and T0+5.5 ks after the trigger. A bright,
fading counterpart has been found, coincident with the VT optical, fading source
reported by Palmerio et al. (GCN 42223), which has a redshift of 0.572
(Martin-Carrillo et al., GCN 42227). Thus, we can conclude that this is the XRT
counterpart of GRB 251013C. The details of this source are:
Source 1 (SWIFT J230320.5-001235):
==================================
RA (J2000.0): 345.8358 = 23 03 20.59
Dec (J2000.0): -0.2100 = -00 12 36.0
Error: 3.5 (arcsec, radius, 90% confidence).
Detect flag: GOOD
Distance: 3.6 arcmin from the SVOM/ECLAIRs position.
Mean rate: 2.356 +/- 0.081 ct s^-1
Mean flux: (8.71 +/- 0.30)e-11 erg cm^-2 s^-1
Peak rate: 10.2 +/- 1.9 ct s^-1
Peak flux: (3.76 +/- 0.69)e-10 erg cm^-2 s^-1
ECF: 3.70e-11 erg cm^-2 ct^-1
assuming NH=6.48e+20 cm^-2, gamma=1.78
determined from a spectral fit.
XMM UL: 6.3e-13 erg cm^-2 s^-1, (0.3-10 keV)
so the source is 5.4-sigma above this 3-sigma upper limit.
All fluxes are 0.3-10 keV, observed. For all flux conversions and comparisons with
catalogues and upper limits from other missions, we assumed a power-law spectrum
with NH=3x10^20 cm^-2 and photon index (Gamma)=1.7 unless otherwise stated.
The results of the XRT-team automatic analysis of the XRT observations, including a
position-specific upper limit calculator, are available at
https://www.swift.ac.uk/SVOM/SVOM_FIELD00041.
This circular is an official product of the Swift-XRT team.
GCN Circular 42231
Subject
GRB 251013C: GOTO optical afterglow detection
Date
2025-10-13T22:14:00Z (3 days ago)
From
Ben Gompertz at U of Birmingham <b.gompertz@bham.ac.uk>
Via
email
B. P. Gompertz, B. Godson, D. O'Neill, R. Starling, K. Ackley, M. J. Dyer, J. Lyman, K. Ulaczyk, D. Steeghs, D. K. Galloway, V. Dhillon, G. Ramsay, P. O'Brien, K. Noysena, R. Kotak, R. P. Breton, L. K. Nuttall, and J. Casares report on behalf of the GOTO collaboration:
We report on optical observations with the Gravitational-wave Optical Transient Observer (GOTO; Steeghs et al. 2022, Dyer et al. 2024) in response to GRB 251013C (Fermi GBM Team, GCN 42221; Rakotondrainibe et al, GCN 42222). Targeted observations were taken at 2025-10-13 21:40:06 UT (4.1h post trigger). The observations consisted of 4x45s exposures in the GOTO L-band (400-700 nm). Images were processed immediately after acquisition using the GOTO pipeline. Difference imaging was performed using deeper template observations.
We detect the optical counterpart (Palmerio et al., GCN 42223; Perez-Garcia et al., GCN 42225; Konno et al., GCN 42226; Martin-Carrillo et al., GCN 42227; Masi, GCN 42228; Palmerio et al., GCN 42229; Moskvitin et al., GCN 42230) with an AB magnitude of L = 17.11 ± 0.02 mag.
Magnitudes were calibrated using ATLAS-REFCAT2 (Tonry et al. 2018) and are not corrected for Galactic extinction.
GOTO (https://goto-observatory.org) is a network of telescopes that is principally funded by the STFC and operated at the Roque de los Muchachos Observatory on La Palma, Spain, and Siding Spring Observatory in NSW, Australia, on behalf of a consortium including the University of Warwick, Monash University, Armagh Observatory & Planetarium, the University of Leicester, the University of Sheffield, the National Astronomical Research Institute of Thailand (NARIT), the University of Turku, the University of Portsmouth, the University of Manchester and the Instituto de Astrofisica de Canarias (IAC).
GCN Circular 42230
Subject
GRB 251013C: SAO RAS optical observations
Date
2025-10-13T21:31:40Z (3 days ago)
From
Alexander Moskvitin at SAO RAS <mosk@sao.ru>
Via
Web form
A. S. Moskvitin, O. I. Spiridonova, V. V. Vlasyuk (SAO RAS),
N. Pankov (HSE, IKI), A. Pozanenko (IKI), A. Ghosh, S. Razzaque
(CAPP, University of Johannesburg), Tao An and Yuanqi Liu
(Shanghai Astronomical Observatory) report on behalf of GRB follow-up
collaboration and IKI-GRB-FuN.
We observed the field of the GRB 251013C (The Fermi GBM team,
GCN 42221; Rakotondrainibe et al., GCN 42222) with the 1-m SAO RAS
telescope Zeiss-1000 equipped with the CCD-photometer.
The observations started on 2025.10.13T19:47:54 UT
(t_mid - T0 = 2.1369 hours).
The OT (Palmerio et al., GCN 42223; Perez-Garcia et al., GCN 42225;
Konno et al., GCN 42226; Martin-Carrillo et al., GCN 42227; Masi,
GCN 42228; Palmerio et al, GCN 42229) is clearly detected
in the individual images with the following brightness.
Date UT start t-T0 Exp. Filter OT Err.
(mid, d) (s)
2025.10.13 19:47:54 0.03631 300 Rc 15.84 +/- 0.01
2025.10.13 20:04:02 0.04033 100 Rc 16.05 +/- 0.01
2025.10.13 20:15:34 0.04353 100 Rc 16.21 +/- 0.01
Preliminary photometry is based on the nearby SDSS objects
(magnitudes converted with Lupton 2005 equations)
and has not corrected for the Galactic extinction.
The observations with the 1-m telescope in BVRI filters
and also with the 0.5-m telescope AS-500/2 are ongoing.
GCN Circular 42229
Subject
GRB 251013C: LCO optical afterglow detection
Date
2025-10-13T21:13:53Z (3 days ago)
From
SVOM_group <svomgroup@bao.ac.cn>
Via
Web form
J. T. Palmerio, D. Turpin, A. Saccardi, B. Cordier (CEA/Irfu), L. P. Xin (NAOC), C. Wu (NAOC), report on behalf of the SVOM mission team:
We observed the field of GRB 251013C (SVOM/ECLAIRs and GRM, Rakotondrainibe et al. GCN 42223; Fermi/GBM, Fermi GBM team, GCN 42221) with the LCO 1m telescope at South African Astronomical Observatory equipped with the Sinistro instrument. Our observation started at 2025-10-13T19:27:33.084 about 1.8 hours after the SVOM/ECLAIRs T0 time.
We obtained 3 series of 3x200 s exposures in the SDSS gri filters. The bright optical counterpart detected by SVOM/VT (Palmerio et al. GCN 42223), BOOTES-6 (Perez-Garcia et al., GCN 42225), LAST (Konno et al., GCN 42226), NOT (Martin-Carrillo et al., GCN 42227 and the Visual Telescope Project (Masi et al., GCN 42228) is clearly detected in our first images subtracted to the Pan-STARRS DR2 catalog image. We measure the following magnitude:
g = 16.30 +/- 0.01 (AB), at Tmid-T0 = 2.1 hours
r = 15.99 +/- 0.01 (AB), at Tmid-T0 = 2.0 hours
i = 15.70 +/- 0.01 (AB), at Tmid-T0 =1.8 hours
Further observations are planned and spectroscopic observations are encouraged.
This project is funded by the SVOM collaboration.
GCN Circular 42228
Subject
GRB 251013C: Optical Observations via Virtual Telescope Project, Italy
Date
2025-10-13T21:07:58Z (3 days ago)
From
Gianluca Masi at Virtual Telescope Project <gianluca@bellatrixobservatory.org>
Via
Web form
Gianluca Masi, Virtual Telescope Project (Italy), reports:
We attempted to observe the optical counterpart of GRB 251013C (Rakotondrainibe et al., GCN 42222) with the 14” robotic unit available at the Virtual Telescope Project facility in Manciano, Italy, equipped with a KAF-3200E based CCD camera, its QE peaking (90%) in the red part of the spectrum.
We collected three, 120-second unfiltered exposures, then we averaged them. The central time of the resulting stack was 13 Oct., 20:54:57 UTC, that is about 3.25 hours after the burst.
We detected a bright object at the following position (J2000.0):
R.A.: 23 03 20.56
Decl.: -00 13 37.1
mean residuals < 1” on both axes
R= 15.9 (assuming R-mags from Gaia DR2 for the reference stars).
This position is consistent with Palmerio et al. (GCN 42223)and Perez-Garcia et al., GCN 42225.
GCN Circular 42227
Subject
GRB 251013C: NOT spectroscopic redshift z = 0.572
Date
2025-10-13T21:02:05Z (3 days ago)
From
Antonio Martin-Carrillo at UCD,Space Science Group <antonio.martin-carrillo@ucd.ie>
Via
Web form
A. Martin-Carrillo (UCD), L. Izzo (INAF/OACN and DARK/NBI), D. B. Malesani (DAWN/NBI and Radboud), G. Corcoran (UCD), B. Schneider (LAM), A. de Ugarte Postigo (LAM), A. Saccardi (CEA/Irfu), B. P. Gompertz (Birmingham), K. Valeckas (NOT and NBI) report on behalf of a larger collaboration:
We observed the optical afterglow (Palmerio et al., GCN 42223; Perez-Garcia et al., GCN 42225; Konno et al., GCN 42226) of GRB 251013C (Rakotondrainibe et al., GCN 42222; Fermi GBM team, GCN 42221) with the Nordic Optical Telescope (NOT) equipped with the ALFOSC camera. A spectrum using grism #4 was secured starting on 2025-10-13 at 19:46:24 UT (2.11 hr after the GRB), under good conditions. The exposure time was 2x1200 s and the covered wavelength range is 3500-9600 AA.
In a preliminary reduction of the spectra, we clearly detect a continuum over the whole covered wavelength range. From the detection of multiple absorption features, including Fe II 2600, the Mg II doublet, weak Mg I, and the Ca II doublet, we infer a redshift of z = 0.572.
Photometry of the afterglow was carried out in the ugriz filters. In a 30-s r-band image, we measure r = 16.52 +/- 0.02 AB (at a time of 2.88 hr after the GRB), calibrated against the Pan-STARRS catalog, and not corrected for Galactic extinction.
GCN Circular 42226
Subject
GRB 251013C: LAST detection of optical counterpart
Date
2025-10-13T20:58:35Z (3 days ago)
From
Ruslan Konno at Weizmann Institute of Science <ruslankonno@gmail.com>
Via
Web form
R. Konno (WIS), S. Garrappa (WIS), E. A. Zimmerman (WIS), A. Horowicz (WIS), E. O. Ofek (WIS), S. Ben-Ami (WIS), D. Polishook (WIS), O. Yaron (WIS), S. Fainer (WIS), A. Krassilchtchikov (WIS), Y. M. Shani (WIS), E. Segre (WIS), A. Gal-Yam (WIS), and S. Spitzer (WIS) report on behalf of the LAST Collaboration.
We report observations of GRB 251013C, detected by SVOM (Rakotondrainibe et al., GCN 42222) and Fermi (Fermi GBM Team, GCN 42221). Observations were conducted with the Large Array Survey Telescope (LAST; Ofek et al. 2023, PASP 135, 5001; Ben-Ami et al. 2023, PASP 135, 5002).
We observed the field of GRB 251013C using four parallel telescopes (each with a 7.4 deg^2 FoV) in clear band (similar to the Gaia Bp band) over several epochs. Each coadd consists of 20x20 s exposures, yielding a limiting magnitude of about 20.5 AB mag.
We clearly detect the optical counterpart reported by Palmerio et al. (GCN 42223) and Perez-Garcia et al. (GCN 42225). The earliest detection (20x20 s coadd) is confirmed at 2025-10-13 18:10:27 UTC (T − T0 = 0.51 h) with AB mag 16.14 +/- 0.02. Preliminary automated photometry shows a rise to 15.20 +/- 0.01 mag at 18:32:15 UTC (T − T0 = 0.87 h), followed by a power-law decay. The source remains detectable.
We encourage continued multi-wavelength follow-up of this bright optical counterpart.
LAST is a survey telescope array of the Weizmann Astrophysical Observatory (https://www.weizmann.ac.il/wao/).
GCN Circular 42225
Subject
GRB 251013C: BOOTES-6 early optical detection
Date
2025-10-13T19:07:16Z (3 days ago)
From
I. Perez-Garcia at Institute of Astrophysics of Andalusia <ipg@iaa.es>
Via
Web form
I. Perez-Garcia, S.-Y. Wu, E. Fernandez-Garcia, M.D. Caballero-Garcia, R. Sanchez-Ramirez, S. Guziy and A. J. Castro-Tirado (IAA-CSIC, Granada), P. J. Meintjes and H. J. van Heerden (UFS, South Africa), A. Martin-Carrillo and L. Hanlon (UCD, Ireland), M. Gritsevich (Univ. of Helsinki) and C. J. Perez del Pulgar (UMA, Malaga), on behalf of a larger collaboration, report:
Following the detection of GRB 251013C by SVOM (Rakotondrainibe et al., GCN 42222), the BOOTES-6/DPRT 0.6m robotic telescope at Boyden Observatory in Maselspoort (South Africa) responded to this high-energy event starting on Oct 13, 17:42:32 UT (i.e., 170 sec after detection). Series of images in clear filter were gathered and we detect an optical source consistent with the one reported by Palmerio et al. (GCN 42223). Using GaiaDR3 Gmag as reference we report our photometry analysis:
| UT mid exposure | mag | error | filter | exposure time (sec) |
| ------------------- | ----- | ----- | ------ | ------------------- |
| 2025-10-13 17:43:02 | 14.42 | 0.02 | clear | 60 |
| 2025-10-13 17:44:31 | 14.82 | 0.02 | clear | 60 |
| 2025-10-13 17:50:23 | 14.79 | 0.03 | clear | 60 |
| 2025-10-13 17:51:52 | 15.03 | 0.02 | clear | 60 |
| 2025-10-13 17:57:44 | 15.77 | 0.03 | clear | 60 |
| 2025-10-13 17:59:13 | 15.79 | 0.03 | clear | 60 |
| 2025-10-13 18:05:04 | 16.07 | 0.03 | clear | 60 |
Further analysis of the additional images is ongoing.
We thank the staff at Boyden Observatory for their excellent support.
GCN Circular 42223
Subject
GRB 251013C: SVOM/VT optical observation
Date
2025-10-13T18:18:36Z (3 days ago)
From
SVOM_group <svomgroup@bao.ac.cn>
Via
Web form
J. T. Palmerio (CEA/Irfu), Ny Avo Rakotondrainibe, C. Adami (LAM), H. L. Li, L. P. Xin, Y. L. Qiu, C. Wu (NAOC) report on behalf of the SVOM/VT team:
After the trigger by SVOM/ECLAIRs at 2025-10-13T17:39:42 UTC (T0), SVOM performed an automatic slew on the burst location (Rakotondrainibe et al., GCN 42222). SVOM/VT began observing the field at 2025-10-13T17:44:04, 261.08 seconds after T0, in the VT_B (400nm-650nm) and VT_R (650nm-1000nm) channels simultaneously.
From a preliminary analysis of the 1-bit subimage and source list downloaded via VHF network, at least one credible candidate is identified, the details of which are presented below.
VT_ID 117:
This bright candidate was flagged as a catalogued source but significantly brighter than its catalogued magnitude.
The position of this candidate is R.A., Dec. 345.8356, -0.2103 degrees, corresponding to:
R.A. (J2000) = 23h03m20.6s
Dec. (J2000) = -0d12m37.1s
with an uncertainty of 0.5 arcsec.
This location is within the R90 uncertainty region of the SVOM/MXT onboard localization.
The source was detected in both VT_R and VT_B. The candidate's magnitudes are:
| date-obs (UTC) | mid-time | exposure | band | mag(AB) |
| -------------------- | ----------- | --------- | ----- | ------------- |
| 2025-10-13T17:44:04 | 6.85 min | 6*50 sec | VT_B | 15.38 ± 0.01 |
| 2025-10-13T17:44:04 | 6.85 min | 6*50 sec | VT_R | 14.76 ± 0.01 |
Magnitudes were not corrected for dust extinction.
The VT color of the counterpart suggests it is not very high redshift or highly extinguished.
The Space-based multi-band astronomical Variable Objects Monitor (SVOM) is a China-France joint mission led by the Chinese National Space Administration (CNSA), French Space Agency (CNES), and the Chinese Academy of Sciences (CAS), which is dedicated to observing gamma-ray bursts and other transient phenomena in the energetic universe.
SVOM/VT was jointly developed by Xi'an Institute of Optics and Precision Mechanics (XIOPM), CAS and National astronomical observatories (NAOC), CAS.
GCN Circular 42222
Subject
GRB 251013C: SVOM detection of a burst
Date
2025-10-13T18:17:34Z (3 days ago)
From
SVOM_group <svomgroup@bao.ac.cn>
Via
Web form
N. A. Rakotondrainibe, C. Adami (LAM), D. Turpin, D. Götz (CEA/Irfu), H. Yang (IRAP)
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 (Fermi GBM team GCN 42221).
The following trigger information was received on the ground with low latency by the SVOM VHF Alert Network.
The burst was detected both by the Count-Rate Trigger (CRT) and the Image Trigger (IMT), which produced a sequence of 16 alerts. CRT provided the alert with the best signal-to-noise-ratio in the image (SNR) of 35.62 in the [8-120] keV energy band over a time window of 10.24 seconds starting at 2025-10-13T17:39:42. The SVOM/ECLAIRs light curve showed a single peak structure of a T90 duration of 17.1 (+6.9/-1.5) s.
The localization of the best alert is R.A., Dec. 345.8809, -0.1698 degrees (J2000) with a 90% confidence level (C.L.) radius of 2.94 arcmin (including systematic error of 2 arcmin added in quadrature).
This burst also triggered SVOM/GRM at 2025-10-13T17:39:43 on a timescale of 18 seconds with an SNR of 11.
SVOM slewed to the burst.
SVOM/MXT began observing the field at 2025-10-13T17:43:05 UTC, 203 seconds after T0. Using onboard processed data we found an uncatalogued X-ray source located at R.A., Dec. 345.8301, -0.2207 degrees:
R.A. (J2000) = 23h03m19s
Dec. (J2000) = -0d13m14s
with a 90% C.L. radius of 69 arcseconds.
This location is 4.31 arcminutes from the ECLAIRs onboard position. This position may be improved as more data is received.
VT began observing the field after the slew. The analysis of the data will be published in a future circular.
The Space-based multi-band astronomical Variable Objects Monitor (SVOM) is a China-France joint mission led by the Chinese National Space Administration (CNSA), French Space Agency (CNES), and the Chinese Academy of Sciences (CAS), which is dedicated to observing gamma-ray bursts and other transient phenomena in the energetic universe. SVOM/ECLAIRs was developed jointly by CNES, CEA-IRFU, CNRS-IRAP, CNRS-APC. SVOM/GRM was developed by the Institute of High Energy Physics (IHEP) of CAS. SVOM/MXT was developed jointly by CNES, CEA-IRFU, CNRS-IJCLab, University of Leicester, MPE.
The Burst Advocate (BA) on shift for this alert is Ny Avo Rakotondrainibe: ny-avo.rakotondrainibe@lam.fr
Please contact the BA by email if you require additional information.
GCN Circular 42221
Subject
GRB 251013C: Fermi GBM Final Real-time Localization
Date
2025-10-13T17:50:11Z (3 days ago)
From
Fermi GBM Team at MSFC/Fermi-GBM <do_not_reply@GIOC.nsstc.nasa.gov>
Via
email
The Fermi GBM team reports the detection of a likely LONG GRB
At 17:39:41 UT on 13 Oct 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 251013C (trigger 782069986.941944 / 251013736).
The on-ground calculated location, using the Fermi GBM trigger data, is RA = 348.9, Dec = -6.3 (J2000 degrees, equivalent to J2000 23h 15m, -6d 17'), with a statistical uncertainty of 5.0 degrees.
The angle from the Fermi LAT boresight is 65.0 degrees.
The skymap can be found here:
https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn251013736/quicklook/glg_skymap_all_bn251013736.png
The HEALPix FITS file, including the estimated localization systematic, can be found here:
https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn251013736/quicklook/glg_healpix_all_bn251013736.fit
The GBM light curve can be found here:
https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn251013736/quicklook/glg_lc_medres34_bn251013736.gif