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GRB 251002A

GCN Circular 42125

Subject
GRB 251002A: LAST optical observations
Date
2025-10-06T16:43:55Z (2 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) on behalf of the LAST Collaboration

We report observations of GRB 251002A (Saccardi et al. GCN 42060), detected by SVOM, with the Large Array Survey Telescope (LAST; Ofek et al. 2023 PASP 135, 5001; Ben-Ami et al. 2023 PASP 135, 5002).

We observe the field of GRB 251002A using 4 divergent telescopes, each with a FoV of 7.4 deg^2 and no filter (clear - similar to the GAIA Bp band) over several epochs. In each epoch, we coadd 20 images with each of 20s exposure. We clearly detect the optical counterpart reported by Palmerio et al. GCN 42061; Turpin et. al, GCN 42062; Jelinek et. al, GCN 42063; Juliá-Maroto et. al, GCN 42064; Moskvitin et. al, GCN 42065; Perez-Garcia et. al, GCN 42066; Saccardi et. al, GCN 42076; Mandarakas et. al, GCN 42077; Cao et. al, GCN 42078; Schneider et. al, GCN 42080; Pankov et. al, GCN 42081; Leonini et. al, GCN 42082; Odeh et. al, GCN 42087; Wortley et. al, GCN 42091; Shilling, GCN 42099; Calapai & Giorgio, GCN 42101; Pankov et. al, GCN 42110. 

The earliest detection with a 20x20s exposure image is confirmed at 2025-10-02 20:48:23 UTC (T-T0=0.55h) at an AB magnitude of 18.53 +/- 0.05.

LAST is a survey telescope array of the Weizmann Astrophysical Observatory (https://www.weizmann.ac.il/wao/).

GCN Circular 42110

Subject
GRB 251002A: Mondy/AZT-33IK optical observations
Date
2025-10-05T07:05:17Z (3 days ago)
From
Nicolai Pankov at HSE, IKI RAS <colinsergesen@gmail.com>
Via
Web form
N. Pankov (HSE, IKI), A. Pozanenko (IKI), E. Klunko (ISTP) report on behalf of IKI-GRB-FuN:

We performed optical observations of the field of GRB 251002A detected by SVOM (Saccardi et. al, GCN 42060) in the R-filter with the AZT-33IK 1.5m telescope of the Sayan Solar Observatory (Mondy). The observations began on 2025-10-03 17:00 UT, i.e. ~0.88 days since trigger and consisted of 30x120 s exposures. The optical source found by SVOM (Palmerio et. al, GCN 42061) at z = 2.178 (Saccardi et. al, GCN 42076) and also observed by (Turpin et. al, GCN 42062; Jelinek et. al, GCN 42063; Juliá-Maroto et. al, GCN 42064; Moskvitin et. al, GCN 42065; Perez-Garcia et. al, GCN 42066; Saccardi et. al, GCN 42076; Mandarakas et. al, GCN 42077; Cao et. al, GCN 42078; Schneider et. al, GCN 42080; Pankov et. al, GCN 42081; Leonini et. al, GCN 42082; Odeh et. al, GCN 42087; Wortley et. al, GCN 42091; Shilling, GCN 42099; Calapai & Giorgio, GCN 42101) is detected in the co-add image of 30x120 s. Preliminary photometry and observation details are presented below:

Date       UT start  t-T0       Exp.   Filter OT    Err. UL
                     (mid,days) (nxs)                    (3sigma)
2025-10-03 17:00:32  0.88586    30x120 R      20.96 0.12 22.0

The photometry was calibrated using reference stars from (Moskvitin et. al, GCN 42065) and not corrected for the Galactic extinction.

GCN Circular 42109

Subject
GRB 251002A: Insight-HXMT detection
Date
2025-10-05T06:33:10Z (3 days ago)
From
xueyuan zao <zaoxueyuan@gmail.com>
Via
Web form
Xue-Yuan Zao, Zheng-Hang Yu, Cheng-Kui Li, Shao-Lin Xiong, and Chao Zheng report on behalf of the Insight-HXMT team:

At 2025-10-02T20:14:52.800 (T0), Insight-HXMT/HE detected a long burst GRB 251002A, which is also detected by Fermi/GBM (Jacob Smith et al., GCN #42093) and SVOM/ECLAIRs (A. Saccardi et al., GCN #42060). 

The Insight-HXMT/HE light curve mainly consists of multiple pulses with a T90 of 13.8 +2.3/-3.1 s. The 1s peak rate, measured from T0+6.050 s, is 1080 cnts/sec. The total counts from this burst is 4528 counts. 
 
The HXMT/HE light curve can be found here: 
https://www.bursthub.cn//admin/static/hxmtgrb251002A.png 

All measurements above are made with the CsI detectors operating in the regular mode with the energy range of about 30-1000 keV (deposited energy). Only gamma-rays with energy greater than about 200 keV can penetrate the spacecraft and leave signals in the CsI detectors installed inside of the telescope.   

Insight-HXMT is the first Chinese space X-ray telescope, which was funded jointly by the China National Space Administration (CNSA) and the Chinese Academy of Sciences (CAS). More information about it could be found at: http://www.hxmt.org.

GCN Circular 42108

Subject
GRB 251002A: Insight-HXMT detection
Date
2025-10-05T05:30:19Z (3 days ago)
From
xueyuan zao <zaoxueyuan@gmail.com>
Via
Web form
Xue-Yuan Zao, Zheng-Hang Yu, Cheng-Kui Li, Shao-Lin Xiong, and Chao Zheng report on behalf of the Insight-HXMT team:

At 2025-10-02T20:14:52.800 (T0), Insight-HXMT/HE detected a long burst GRB 251002A, which is also detected by Fermi/GBM (Jacob Smith et al., GCN #42093) and SVOM/ECLAIRs (A. Saccardi et al., GCN #42060). 

The Insight-HXMT/HE light curve mainly consists of multiple pulses with a T90 of 13.8 +2.3/-3.1 s. The 1s peak rate, measured from T0+6.050 s, is 1080 cnts/sec. The total counts from this burst is 4528 counts.

The HXMT/HE light curve can be found here: 
https://www.bursthub.cn//admin/static/hxmtgrb251002A.png 

All measurements above are made with the CsI detectors operating in the regular mode with the energy range of about 30-1000 keV (deposited energy). Only gamma-rays with energy greater than about 200 keV can penetrate the spacecraft and leave signals in the CsI detectors installed inside of the telescope.

Insight-HXMT is the first Chinese space X-ray telescope, which was funded jointly by the China National Space Administration (CNSA) and the Chinese Academy of Sciences (CAS). More information about it could be found at: http://www.hxmt.org.

GCN Circular 42105

Subject
GRB 251002A: NIR observations with WINTER
Date
2025-10-04T04:03:05Z (5 days ago)
Edited On
2025-10-05T16:40:16Z (3 days ago)
From
Geoffrey Mo at Caltech / Carnegie Observatories <gmo@mit.edu>
Edited By
Vidushi Sharma at NASA GSFC/UMBC <vidushi.sharma@nasa.gov> on behalf of Geoffrey Mo at Caltech / Carnegie Observatories <gmo@mit.edu>
Via
Web form

Geoffrey Mo (Caltech/Carnegie), Tomas Ahumada (Caltech), Viraj Karambelkar (Columbia/CCA), Benjamin Schneider (LAM), Robert Stein (UMD), Danielle Frostig (CfA), Nathan Lourie (MIT), Robert Simcoe (MIT), and Mansi Kasliwal (Caltech) report:

We observed the field of GRB 251002A (Saccardi et al., GCN 42060

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; Sun et al., GCN 42075; Kenya et al., GCN 42084; Smith et al., GCN 42093) in the near-infrared J band with the Palomar 1-m telescope, equipped with the 1.2-square degree WINTER camera (Lourie et al. 2020, Frostig et al. 2024).

Observations began at 2025-10-03T03:49:03 UTC in the J band (~7.6 hours after the GRB trigger), consisting of 15 x 120 s exposures. The images were processed using the WINTER data reduction pipeline implemented with mirar (https://github.com/winter-telescope/mirar, https://doi.org/10.5281/zenodo.13352565

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).

We do not detect a source at the optical counterpart location (Palmerio et al., GCN 42061

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; Turpin et al., GCN 42062; Jelinek et al., GCN 42063; Juliá-Maroto et al., GCN 42064; Moskvitin et al., GCN 42065; Perez-Garcia et al., GCN 42066; Senik et al., GCN 42067; Saccardi et al., GCN 42076; Mandarakas et al., GCN 42077; Cao et al., GCN 42078; Schneider et al., GCN 42080; Pankov et al., GCN 42081; Leonini et al., GCN 42082; Odeh et al., GCN 42087; Wortley et al., GCN 42091; Shilling et al., GCN 42099; Calapai et al., GCN 42101). We obtain the following 5-sigma upper limit: J ~ 19.2 mag (AB).

WINTER (Wide-field INfrared Transient ExploreR) is a partnership between MIT and Caltech, housed at Palomar Observatory, and funded by NSF MRI, NSF AAG, the David and Lucile Packard Foundation, and the MIT Kavli Institute for Astrophysics and Space Research.

GCN Circular 42101

Subject
GRB 251002A: Calapai Observatory, Massa S. Giorgio (Messina), optical observation.
Date
2025-10-03T21:48:34Z (5 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 251002A detected by SVOM/ECLAIRs (Saccardi et al., GCN 42060) with the 11 inches Schmidt-Cassegrain (Celestron 11) telescope F/D=6,3. 
  
The observations were started at 2025-10-02 22:27:43 UT (approximately 2.21 hours after burst) stacking a sets of unfiltered CCD image. The observations were carried out with sky disturbed by passing clouds, and Moon (illumination: 78%, distance: 57°).

The OT was detected at the following position:

RA    (J2000.0)  00h 55m 37.91s   
Decl. (J2000.0) -05° 34' 01.42" 	 

Photometry was obtained using nearby PanSTARRS stars as follows: 

Observation    Mid-Time    T-T0 (hr)      Exposure        Filter      Mag.     Mag. err.
2025-10-02   23:08:13 UT    2.89           42x60s           CR       19.16     +/-0.08

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 Palmerio et al. (GCN 42061); Turpin et al. (GCN 42062); Jelinek et al. (GCN 42063); Juliá-Maroto et al. (GCN 42064); Moskvitin et al. (GCN 42065); Perez-Garcia et al. (GCN 42066); Saccardi et al. (GCN 42076); Mandarakas et al. (GCN 42077); Cao et al. (42078); Schneider et al. (GCN 42080); Pankov et al. (GCN 42081); Leonini et al. (GCN 42082); Odeh et al. (GCN 42087); Wortley et al. (GCN 42091); Shilling (GCN 42099).

The message may be cited.

GCN Circular 42099

Subject
GRB 251002A: Swift/UVOT detection
Date
2025-10-03T18:26:26Z (5 days ago)
From
s.shilling@lancaster.ac.uk
Via
Web form
S.P.R. Shilling (Lancaster U.) reports on behalf of the Swift/UVOT team:

The Swift/UVOT began settled observations of the field of GRB 251002A in the U band for a total of 1.5 ks, starting 3.6 ks after the SVOM/ECLAIRs trigger (Saccardi et al., GCN Circ. 42060).

A source is detected in the U band at a position that is consistent with other detections by other instruments in the optical (Palmerio et al., GCN 42061; Turpin et al., GCN 42062; Jelinek et al., GCN 42063; Julia-Maroto et al., GCN 42064; Moskvitin et al., GCN 42065; Perez-Garcia et al., GCN 42606; Senik et al., GCN 42067; Saccardi et al., GCN 42076; Mandarakas et al., GCN 42077; Cao et al., GCN 42078; Schneider et al., GCN 42080; Pankov et al., GCN 42081; Leonini et al., GCN 42082; Odeh et al., GCN 42087; Wortley et al., GCN 42091).

Preliminary detections using the UVOT photometric system (Breeveld et al. 2011, AIP Conf. Proc. 1358, 373) for the stacked U band images are:

Filter         T_start(s)   T_stop(s)      Exp(s)           Mag

U	             3628        9263        1476           19.02 +/- 0.08

The magnitude reported here is not corrected for Galactic extinction.

GCN Circular 42093

Subject
GRB 251002A: Fermi GBM Observation
Date
2025-10-03T14:21:41Z (5 days ago)
From
Jacob Smith at Fermi-GBM Team <jrs0118@uah.edu>
Via
Web form
Jacob Smith (UAH), O. Mukherjee (USRA) and C. Meegan (UAH) report on behalf of
the Fermi Gamma-ray Burst Monitor Team:

"At 20:14:51.01 UT on 02 October 2025, the Fermi Gamma-ray Burst Monitor (GBM)
triggered and located GRB 251002A (trigger 781128896/251002844).
which was also detected by SVOM/ECLAIRs (A. Saccardi et al. 2025, GCN 42060).
The Fermi GBM on-ground location is consistent with the SVOM/ECLAIRs position.
VLT/X-shooter detected a spectroscopic redshift of z = 2.178 (A. Saccardi et al. 2025, GCN 42076).

The angle from the Fermi LAT boresight is 53 degrees.

The GBM light curve multiple emission episodes with a duration (T90)
of about 26 s (50-300 keV). The time-averaged spectrum
from T0-6.9 to T0+14.6 s is best fit by
a power law function with an exponential high-energy cutoff.
The power law index is -0.88 +/- 0.07 and the cutoff energy,
parameterized as Epeak, is 180 +/- 10 keV.

The event fluence (10-1000 keV) in this time interval is
(4.6 +/- 0.2)E-06 erg/cm^2. The 1-sec peak photon flux measured
starting from T0+7.9 s in the 10-1000 keV band is 7.1 +/- 0.2 ph/s/cm^2.

A Band function fits the spectrum equally well
with Epeak= 140 +/- 20 keV, alpha = -0.7 +/- 0.1 and beta = -2.2 +/- 0.1.

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 42091

Subject
GRB 251002A: GOTO detection of optical counterpart
Date
2025-10-03T13:45:47Z (5 days ago)
From
MEW020@student.bham.ac.uk
Via
Web form
M. E. Wortley, B. P. Gompertz, D. O’Neill, G. Ramsay, R. Starling, M. Kennedy, B. Godson, J. Lyman, K. Ackley, M. J. Dyer, K. Ulaczyk, A. Kumar,, D. Steeghs, D. K. Galloway, V. Dhillon, 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 observations with the Gravitational-wave Optical Transient Observer (GOTO; Steeghs et al. 2022, Dyer et al. 2024) that serendipitously covered the field of GRB 251002A (Saccardi et al., GCN 42060) during survey operations.

We detect the optical counterpart (Palmerio et al., GCN 42061; Turpin et al., GCN 42062; Jelinek et al., GCN 42063; Julia-Maroto et al., GCN 42064; Moskvitin et al., GCN 42065; Perez-Garcia et al., GCN 42606; Senik et al., GCN 42067; Saccardi et al., GCN 42076; Mandarakas et al., GCN 42077; Cao et al., GCN 42078; Schneider et al., GCN 42080; Pankov et al., GCN 42081; Leonini et al., GCN 42082; Kennea et al., GCN 42084; Odeh et al., GCN 42087) in GOTO L-band (400-700 nm) imaging taken at 2025-10-03 01:03:06 UT (4.80h post-trigger) consisting of 4x45s exposures. The measured AB magnitude is L = 19.87 ± 0.31.

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 42087

Subject
GRB 251002A: AKO Early Optical Afterglow Detection
Date
2025-10-03T11:28:22Z (5 days ago)
From
Mohammad Odeh at Al Khatim Observatory M44 <mshodeh@gmail.com>
Via
email
Mohammad Odeh (Al-Khatim Observatory, AKO, operated by the International
Astronomical Center in Abu Dhabi, UAE), and Shaikha Alshamsi, and Nidhal
Guessoum (American University of Sharjah, UAE), report:

We observed the field of GRB 251002A detected by SVOM/ECLAIRs (Saccardi et
al., GCN 42060), using our 0.36m f/7.7 robotic telescope. The observation
session began on 02 October 2025 at 21:08 UT, with a midpoint at 21:44 UT,
approximately 1.49 hours after the trigger.

We obtained 20 exposures of 180 seconds each using the Ic filter. The
optical afterglow was detected at:
R.A. (J2000): 00:55:38.0
Dec. (J2000): -05:34:01.9

Our detection is consistent with the results of (Palmerio et al., GCN
42061), (Turpin et al., GCN 42062), (Jelinek et al., GCN 42063),
(Perez-Fournon et al., GCN 42064), (Moskvitin et al., GCN 42065),
(Perez-Garcia et al., GCN 42066), (Lipunov et al., GCN 42067), (Saccardi et
al., GCN 42076), (Mandrakas et al., GCN 42077), (Cao et al., GCN 42078),
(Schneider et al., GCN 42080), (Pankov et al., GCN 42081) and (Leonini et
al., GCN 42082).

The following observation was calculated using the Atlas catalogue as a
reference:
----------------------------------------------------------------------------
ObsTime (mid), Exposure (sec), Filter, Mag
----------------------------------------------------------------------------
2025-10-02T21:44:20Z, 20x180s (stacked), Ic, 18.57 +/- 0.27
----------------------------------------------------------------------------

The magnitude is not corrected for galactic extinction.

GCN Circular 42084

Subject
GRB 251002A: Swift-XRT afterglow detection
Date
2025-10-03T10:06:49Z (5 days ago)
From
Phil Evans at U of Leicester <pae9@star.le.ac.uk>
Via
email
J.A. Kennea (PSU), D.N. Burrows (PSU), A.P. Beardmore (U. Leicester),
J.P. Osborne (U. Leicester), P. D'Avanzo (INAF-OAB), M.G. Bernardini
(INAF-OAB), E. Ambrosi	(INAF-IASFPA), S. Lanava (PSU) and P.A. Evans
(U. Leicester) reports on behalf of the Swift-XRT team:

Swift-XRT has performed follow-up observations of GRB 251002A. We
searched for X-ray sources in  1.5 ks of Photon Counting (PC) mode
data. The total exposure at the position of the afterglow (see below)
is 1.5 ks, obtained between T0+3.6 ks and T0+9.2 ks.

Three uncatalogued X-ray sources are detected within the estimated
3-sigma SVOM/ECLAIRs error region (392 arcsec), of which one ("Source
1") is above the RASS 3-sigma upper limit at this position, and is
therefore likely the GRB afterglow. Using 1503 s of PC mode data and 2
UVOT images, we find an enhanced XRT position (using the XRT-UVOT
alignment and matching UVOT field sources to the USNO-B1 catalogue):
RA, Dec = 13.90813, -5.56678 which is equivalent to:

RA (J2000): 00h 55m 37.95s
Dec(J2000): -05d 34' 00.4"

with an uncertainty of 2.6 arcsec (radius, 90% confidence). This
position is consistent with the optical candidate (Palmerio et al. GCN
42061) and the EP-FXT X-ray candidate (Sun et al. GCN 24075).

The light curve can be modelled with a power-law decay with a decay
index of alpha=1.27 (+0.28, -0.25).

A spectrum formed from the PC mode data can be fitted with an absorbed
power-law with a photon spectral index of 1.62 (+0.20, -0.18). The
best-fitting absorption column is  8.3 (+6.5, -2.8) x 10^20 cm^-2,
consistent with the Galactic value of 5.5 x 10^20 cm^-2 (Willingale et
al. 2013). The counts to observed (unabsorbed) 0.3-10 keV flux
conversion factor deduced from this spectrum  is 4.2 x 10^-11 (4.7 x
10^-11) erg cm^-2 count^-1. 

A summary of the PC-mode spectrum is thus:
Total column:	     8.3 (+6.5, -2.8) x 10^20 cm^-2
Galactic foreground: 5.5 x 10^20 cm^-2
Excess significance: <1.6 sigma
Photon index:	     1.62 (+0.20, -0.18)

If the light curve continues to decay with a power-law decay index of
1.27, the count rate at T+24 hours will be 0.014 count s^-1,
corresponding to an observed (unabsorbed) 0.3-10 keV flux of 5.9 x
10^-13 (6.5 x 10^-13) erg cm^-2 s^-1.

The results of the XRT-team automatic analysis are available at
http://www.swift.ac.uk/xrt_products/03000125.
The results of the full analysis of the XRT observations are available
at https://www.swift.ac.uk/SVOM/SVOM_FIELD00039.

This circular is an official product of the Swift-XRT team.

GCN Circular 42082

Subject
GRB 251002A: Kilonova-Catcher optical afterglow detection
Date
2025-10-03T09:49:33Z (5 days ago)
From
Damien Turpin at CEA-Saclay <dturpin-astro@hotmail.com>
Via
Web form
S. Leonini, M. Freeberg (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 251002A detected by SVOM/ECLAIRs and GRM (Saccardi et al., GCN 42060) with the GRANDMA citizen science project Kilonova-catcher (KNC). Our observations were performed with the TEC160FL and iT72 telescopes operated by M. Freeberg and with the automated and remoted 0.53m Ritchey-Chretien telescope at Montarrenti Observatory (Siena, Italy, IAU code C88) operated by S. Leonini. Our observations started at TGRB+1.2hr. 

In our stacked frames, subtracted from the PanSTARRS DR2 template image, we detect the optical counterpart reported by SVOM/VT (Palmerio et al., GCN 42061), LCO-1m (Turpin et al., GCN 42062), FRAM-ORM (Jelinek et al., GCN 42063), LCO-40cm (Perez-Fournon et al., GCN 42064), SAO RAS (Moskvitin et al., GCN 42065), BOOTES-6 (Perez-Garcia et al., GCN 42066), MASTER (Lipunov et al., GCN 42067), VLT/Xshooter (Saccardi et al., GCN 42076), OHP/T193 (Mandrakas et al., GCN 42077), SYSU (Cao et al., GCN 42078), SVOM/COLIBRI (FM-GFT) (Schneider et al., GCN 42080) and AbAO (Pankov et al., GCN 42081).

We report part of our follow-up results in the table below:

+---------------+-----------+-----------+----------------------+-------------+
| Tmid-TGRB (hr)| Exp (s)   | Filter    | Magnitude            | Instrument  |
+===============+===========+===========+======================+=============+
| 2.28          | 60 x 40s  | Rc (Vega) | 19.08 +/- 0.22       | Montarrenti | 
| 5.10          | 18 x 180s | Rc (Vega) | 19.86 +/- 0.09       | iT72        | 
| 8.54          | 20 x 180s | r (AB)    | 20.42 (5 sigma U.L.) | TEC160FL    | 
+---------------+-----------+-----------+----------------------+-------------+

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 42081

Subject
GRB 251002A: AbAO optical observations
Date
2025-10-03T08:39:52Z (5 days ago)
From
Nicolai Pankov at HSE, IKI RAS <colinsergesen@gmail.com>
Via
Web form
N. Pankov (HSE, IKI), A. Pozanenko (IKI), R. Ya. Inasaridze (AbAO) report on behalf of IKI-GRB-FuN:

We performed optical observations of the field of GRB 251002A detected by SVOM (Saccardi et. al, GCN 42060) in the R-filter with the AS-32 0.7m telescope of the Abastumani Observatory (AbAO). The observations began on 2025-10-02 21:46 UT, i.e. ~0.09 days since trigger and consisted of 87x60 s exposures. The optical source found by SVOM (Palmerio et. al, GCN 42061) at z = 2.178 (Saccardi et. al, GCN 42076) and also observed by (Turpin et. al, GCN 42062; Jelinek et. al, GCN 42063; Juliá-Maroto et. al, GCN 42064; Moskvitin et. al, GCN 42065; Perez-Garcia et. al, GCN 42066; Saccardi et. al, GCN 42076; Mandarakas et. al, GCN 42077; Cao et. al, GCN 42078) is clearly visible in the co-add image of 87x60 s. Preliminary photometry and observation details are presented below:

Date       UT start  t-T0       Exp.  Filter OT    Err. UL
                     (mid,days) (s)                     (3sigma)
2025-10-02 21:46:03  0.09351    87*60 R      19.48 0.16 21.7

The photometry was calibrated using reference stars from (Moskvitin et. al, GCN 42065) and not corrected for the Galactic extinction.

GCN Circular 42080

Subject
GRB 251002A: SVOM/COLIBRÍ (FM-GFT) optical observations
Date
2025-10-03T08:37:03Z (5 days ago)
From
Benjamin Schneider at MIT <bschn@mit.edu>
Via
Web form
Benjamin Schneider (LAM), Enrique Moreno Méndez (UNAM), Camila Angulo (UNAM), Ny Avo Rakotondrainibe (LAM), Stéphane Basa (UAR Pytheas), William H. Lee (UNAM), Alan M. Watson (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), Diego López-Cámara (UNAM), Francesco Magnani (CPPM), Margarita Pereyra (UNAM), Fredd Sánchez Álvarez (UNAM), Antonio de Ugarte Postigo (LAM), Andrea Saccardi (CEA/Irfu), and Diego Gotz (CEA/Irfu):

We imaged the field of the SVOM GRB 251002A (Saccardi et al., GCN Circ. 42060) using the DDRAGO wide-field imager on the SVOM/COLIBRÍ (FM-GFT) telescope. We observed from 2025-10-03 03:33:53 to 05:48:35 UTC (from 7.32 to 9.56 hr after the trigger) and obtained 16 minutes of exposure in the g, r, i, z and y filters.

The data were reduced and coadded with the COLIBRÍ pipeline and 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 reported by Palmerio et al., GCN Circ. 42061, Turpin et al., GCN Circ. 42062; Jelinek et al., GCN Circ. 42063; Juliá-Maroto et al. GCN Circ. 42064; Moskvitin et al. GCN Circ. 42065; Perez-Garcia et al. GCN Circ. 42066; Senik et al., GCN Circ. 42067; Saccardi et al., GCN Circ. 42076; Mandarakas et al., GCN Circ. 42077; Cao et al, GCN 42078 at preliminary magnitudes of:

g = 20.96 +/- 0.09 (mid-time 8.41 hr)
r = 20.82 +/- 0.07 (mid-time 8.44 hr)
i = 20.64 +/- 0.07 (mid-time 8.46 hr)
z = 20.76 +/- 0.15 (mid-time 8.42 hr)
y = 20.30 +/- 0.22 (mid-time 7.84 hr)

Further observations and analysis are ongoing in g, r, i, z and y filters.

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 42078

Subject
GRB 251002A: J band observations by SYSU 80cm infrared telescope
Date
2025-10-03T07:45:53Z (5 days ago)
Edited On
2025-10-03T19:09:25Z (5 days ago)
From
caodle@mail2.sysu.edu.cn
Edited By
Vidushi Sharma at NASA GSFC/UMBC <vidushi.sharma@nasa.gov> on behalf of caodle@mail2.sysu.edu.cn
Via
Web form
Duo-Le Cao, Jia-Qi Lin, Chen Chun, Zhong-Nan Dong, Wei-Sen Huang, Jin-Ji Li, Pu Lin, Yan Yu, Hao-Nan Yang, Hao-Ran Zhang, 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 GRB251002A detected by SVOM/ECLAIRs (A. Saccardi et al., GCN 42060), using the Sun Yat-sen University 80cm infrared telescope with 20s exposures in J band. The calculated position is R.A. = 13.9082 deg, DEC = -5.5671 deg J2000, from SVOM/VT observation. Our observations began at 2025-10-2 20:55:00 UTC, 0.62 hours after the SVOM trigger. 

We detected an infrared counterpart at the position of the optical afterglow (J. T. Palmerio et al., GCN 42061; D. Turpin et al., GCN 42062; Martin Jelinek et al., GCN 42063; L. Juliá-Maroto et al., GCN 42064; A. S. Moskvitin et al., GCN 42065; I. Perez-Garcia et al., GCN 42066; V.Senik et al., GCN 42067; A. Saccardiet al., GCN 42076; N. Mandarakas et al., GCN 42077;) in the stacked images. The preliminary photometric magnitudes in J band are below:

Start Time (UTC)    |Band | Exp   | Mag (Vega)
------------------------|-------|---------|------------------
2025/10/2 20:55:00  | J   | 300s  | 17.03+/-0.24
2025/10/2 21:00:00  | J   | 300s  | 17.19+/-0.14
2025/10/2 21:05:00  | J   | 300s  | 17.64+/-0.20
2025/10/2 21:10:00  | J   | 300s  | 17.44+/-0.15
2025/10/2 21:15:00  | J   | 300s  | 17.74+/-0.19
2025/10/2 21:20:00  | J   | 900s  | 17.65+/-0.16
2025/10/2 21:35:00  | J   | 2100s  | 18.27+/-0.15

The photometric calibration was performed using nearby stars from the 2MASS catalog and the magnitudes are not corrected for Galactic extinction.

The SYSU 80cm infrared telescope is operated and managed by the Department of Astronomy, Sun Yat-sen University.

GCN Circular 42077

Subject
GRB 251002A: OHP/T193 MISTRAL optical afterglow detection
Date
2025-10-03T07:34:37Z (5 days ago)
From
Christophe Adami at LAM <christophe.adami@lam.fr>
Via
Web form
N. Mandarakas (LAM), C. Adami (LAM/Pytheas/AMU), N.A. Rakotondrainibe  (LAM), B. Schneider (LAM), E. Le Floc'h (CEA/Irfu), S.D. Vergani (LUX-Paris Obs.) report on behalf of a larger collaboration:

We observed the field of the SVOM/ECLARIs GRB 251002 (Saccardi et al., GCN 42060) using the T193cm telescope at Observatoire de Haute-Provence (France) equipped with the MISTRAL spectro-imager. We obtained three exposures of 240s (for a total of 12 min) in the r-band starting at 22:05:40 UT on 2025-10-02 (observations mid-time at T-To=2h20min), under modest weather conditions.
In the stacked images, we detect the optical counterpart reported and followed by Palmerio et al. (GCN 42061), Turpin et al. (GCN 42062), Jelinek et al. (GCN 42063), Julia-Maroto et al. (GCN 42064), Moskvitin et al. (GCN 42065), Perez-Garcia et al. (GCN 42066), Senik et al. (GCN 42067), Sun et al. (GCN 42075), and Saccardi et al. (GCN 42076)

The preliminary magnitude derived for that source is:

r’ = 19.39 +/- 0.07 mag (AB)

The detection limit (3 sigma) is r=21.10 +/- 0.15

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 Yoann Degot-Longhi.

GCN Circular 42076

Subject
GRB 251002A: VLT/X-shooter spectroscopic redshift z = 2.178
Date
2025-10-03T06:54:12Z (5 days ago)
Edited On
2025-10-03T19:10:56Z (5 days ago)
From
Andrea Saccardi at CEA/Irfu <andrea.saccardi@cea.fr>
Edited By
Vidushi Sharma at NASA GSFC/UMBC <vidushi.sharma@nasa.gov> on behalf of Andrea Saccardi at CEA/Irfu <andrea.saccardi@cea.fr>
Via
Web form
A. Saccardi (CEA/Irfu), N. Habeeb (U. Leicester), A. de Ugarte Postigo (LAM), B. Schneider (LAM), A. Martin-Carrillo (UCD), D. B. Malesani (DAWN/NBI and Radboud), S. D. Vergani (LUX-Paris Obs.), B. C. Rayson (Leicester), N. R. Tanvir (U. Leicester) report on behalf of the Stargate collaboration:

We observed the optical counterpart (Palmerio et al., GCN 42061; Turpin et al., GCN 42062; Jelinek et al., GCN 42063; Juliá-Maroto et al. GCN 42064; Moskvitin et al. GCN 42065; Perez-Garcia et al. GCN 42066) of the SVOM/ECLAIRs GRB 251002A (Saccardi et al., GCN 42060) using the ESO/VLT UT3 (Melipal) equipped with the X-shooter spectrograph.

From the 3x30 s acquisition image at 2025-10-03 04:55:20 UT (8.67 hr post-trigger), the optical afterglow is well detected with a magnitude of r = 20.74 +/- 0.12 (AB) calibrated against PanSTARRS nearby stars and not corrected for Galactic extinction.

Our spectra cover the wavelength range 3000-21000 AA and consist of 4 exposures of 600 s each. Observations started on 2025 October 3 at 05:04:11 UT (8.82 hr after the burst).

In a preliminary reduction of the spectra, we clearly detect a continuum over the entire wavelength range. From the detection of multiple absorption features, including Lya, S II, Si II, Si II*, O I, O I*, C II, C II*, Si IV, C IV, Fe II, Al II, Zn II, Cr II, Ni II*, Fe II*, Mg II, and Mg I we infer a redshift of z = 2.178.

We acknowledge the prompt response and excellent support of the ESO observing staff in Paranal, in particular Aaron Labdon, Jonathan Smoker and Rodrigo Palominos. The analysis of this spectrum was carried out with the help of the zHunter tool (https://doi.org/10.5281/zenodo.15189495).

GCN Circular 42075

Subject
GRB 251002A: EP-FXT counterpart detection
Date
2025-10-03T06:02:41Z (5 days ago)
From
EP Team at NAOC/CAS <ep_ta@bao.ac.cn>
Via
Web form

X. X. Sun(NAO,CAS), Y.Q. Zhao(USTC,PRIC), Y. L. Wang (NAO, CAS; ICE, CSIC-IEEC)，and Z. X. Ling (NAO, CAS) on behalf of the Einstein Probe (EP) team:
 
EP-FXT performed a follow-up observation of the SVOM/ECLAIRs-detected burst GRB 251002A (SVOM/sb25100211, Saccardi et al. GCN 42060) at 2025-10-02T20:52:13Z (UTC), 2239 seconds after the SVOM/ECLAIRs trigger, with an exposure time of 2918s. One uncatalogued source is detected within the ECLAIRs error circle, and the source is spatially consistent with the counterpart reported in optical bands (Palmerio et al. GCN 42061, Turpin et al. GCN 42062, Jelinek et al. GCN 42063, Juliá-Maroto et al. GCN 42064, Moskvitin et al. GCN 42065，Perez-Garcia et al. GCN 42066, Senik et al. GCN 42067). Preliminary analysis on this source are automatically conducted, and details are listed as follows.
 
Source 1: EPF_J005537.9-053402
RA(J2000): 13.9078
Dec (J2000): -5.5669
Flux: 1.295e-11 erg/s/cm2 (observed, 0.5-10 kev)
Flux_err: 7.6399e-13 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 42067

Subject
Fermi/SVOM GRB 251002A : MASTER OT earlier detection in 2 polarization filters
Date
2025-10-03T01:27:07Z (6 days ago)
Edited On
2025-10-03T19:08:48Z (5 days ago)
From
Vladimir Lipunov at Moscow State U/Krylov Obs <lipunov@xray.sai.msu.ru>
Edited By
Vidushi Sharma at NASA GSFC/UMBC <vidushi.sharma@nasa.gov> on behalf of Vladimir Lipunov at Lomonosov Moscow State University <lipunov@sai.msu.ru>
Via
email

V.Senik, V. Lipunov, E.Gorbovskoy, A.Kuznetsov, I.Panchenko, P.Balanutsa, N.Tiurina, A.Sankovich, G.Antipov,Yu. Tselik, A. Sosnovskiy,  M.Shilova, A.Chasovnikov, V.Topolev,
K.Zhirkov, Ya.Kechin, V.Senik, D.Vlasenko(Lomonosov MSU, SAI, Moscow),
A.Sosnovskij (CrAO RAS),
R.Podesta, C.Francile,  F. Podesta, E. Gonzalez (OAFA, San Juan  Uni.,Argentina);
D.Buckley, (SAAO, South Africa)
O.Gress, N.Budnev (ISU, Irkutsk),
A. Tlatov, D. Dormidontov (Kislovodsk Solar Station of the Pulkovo Observatory),
A. Gabovich, V.Yurkov (Blagoveschensk Educational StateUniversity),
V.M.Pillet, R.Rebolo Lopez (The Instituto de Astrofisica de Canarias, Spain),
L.Carrasco, J.R.Valdes, V.Chavushyan, V.M.Patino Alvarez,J.Martinez,A.R.Corella,
L.H.Rodriguez (INAOE, Guillermo Haro  Astrophysic Observatory, Mexico)

The MASTER-Kislovodsk robotic telescope of the MASTER Global Robotic Net [1], [2]
started Fermi GRB 251002A (trigger 781128896, Ttrigger=2025-10-02 20:14:51UT)
at 2025-10-02 20:19:42 (Lipunov et al. GCN 42059, cover map and OT
https://master.sai.msu.ru/site/master2/event.php?id=3005541&action=12&SAT=SVOM&DAYS=2++  )
 in two mutually perpendicular polarization filters.

There is MASTER OT J005537.81-053401.0 since the first image with
unfiltered m_OT~17.2 at 2025-10-02 20:22:09.308(not first time)
with preliminary detected polarization.

This OT was first publishied (discovered) by SVOM (GCN 42061), and also by LCO (Turpin et al. GCN 42062), FREM-ORM (Jelinek et al. GCN 42063), SAO RAS (Moskvitin et al. GCN 42065) and BOOTES (Perez-Garcia et al. GCN 42066)

Observations and reduction will be continued.

[1] Lipunov et al., 2010, Advances in Astronomy, vol. 2010, 30L
[2] V.M. Lipunov, V.G. Kornilov, E.S. Gorbovskoy, N.A. Tiurina,A.S.Kuznetsov
 2023,  Astronomical Robotic Networks and Operative Multichanel Astrophysics, Lomonosov MSU PRESS, 591pp.
http://www.pereplet.ru/lipunov/625.html#625

GCN Circular 42066

Subject
GRB 251002A: BOOTES-6 early optical detection
Date
2025-10-02T23:27:43Z (6 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 251002A by SVOM (Saccardi et al., GCN 42060

Loading...
 
 
), the BOOTES-6/DPRT 0.6m robotic telescope at Boyden Observatory in Maselspoort (South Africa) responded to this high-energy event starting on Oct 2, 20:17:55 UT (i.e., 186 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 42061), Turpin et al. (GCN 42062), Jelinek et al. (GCN 42063), Juliá-Maroto et al. (GCN 42064) and Moskvitin et al. (GCN 42065). Using GaiaDR3 Gmag as reference we report our photometry analysis:

UT mid exposuremagerrorfilterexposure time (sec)
2025-10-02 20:18:2515.470.03clear60
2025-10-02 20:19:5315.790.03clear60
2025-10-02 20:21:2116.160.05clear60

Further analysis of the additional images is ongoing.

We thank the staff at Boyden Observatory for their excellent support.

GCN Circular 42065

Subject
GRB 251002A: SAO RAS optical observations
Date
2025-10-02T23:10:11Z (6 days ago)
From
Alexander Moskvitin at SAO RAS <mosk@sao.ru>
Via
Web form
A. S. Moskvitin (SAO RAS), V. P. Goranskij (SAI MSU), V. V. Vlasyuk, 
V. S. Shergin, V. A. Egorov, M. A. Pritychenko, I. V. Afanasieva 
(SAO RAS), report on behalf of GRB follow-up collaboration.

We observed the field of the GRB 251002A (Saccardi et al., GCN 42060)
with the 1-m SAO RAS telescope Zeiss-1000 equipped with the new 
CCD-photometer. The observations started at 20:31:30 UT, ~17 minutes 
after the trigger. 

The optical transient (Palmerio et al., GCN 42061; Turpin et al., 
GCN 42062; Jelinek et al., GCN 42063; Juliá-Maroto et al., GCN 42064)
is clearly detected in the individual images with the brightness 
of R = 17.58 +/- 0.02 (t_mid - T0 = 0.41694 hours).

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.

We are grateful to the SAO RAS staff for their technical support.

GCN Circular 42064

Subject
GRB 251002A: ULL-ASTRO-MASTER early detection of the optical afterglow with the LCO 40-cm telescope at Sutherland Observatory
Date
2025-10-02T22:16:27Z (6 days ago)
From
Ismael Perez-Fournon at Instituto de Astrofisica de Canarias <ipf@iac.es>
Via
Web form
L. Juliá-Maroto, 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, E. Lekaroz-Urriza, M. Manzano García, E. Mejía-Martínez, J. Prieto Polo, M. Pulido-Torres, M. Quintana-Ansaldo, 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). 

We report on a Las Cumbres Observatory (LCO) 40-cm telescope early observation of the Gamma-Ray Burst GRB 251002A, detected by SVOM/ECLAIRs(Saccardi et al., GCN circ. 42060). 
We observed the field of GRB 251002A with the 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 g filter, started on 2025-10-02 at 20:39:46 UT, about 24.9 minutes after the SVOM trigger.
The optical counterpart detected by SVOM/VT (Palmerio et al., GCN circ.  42061), LCO 1-m (Turpin et al., GCN circ. 42062), and FRAM-ORM (Jelinek et al., GCN circ. 42063) is clearly detected in our image with a magnitude of g = 18.13 +/- 0.09, calibrated against PanSTARRS-1 DR2 and not corrected for galactic extinction.

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 42063

Subject
GRB 251002A: FRAM-ORM afterglow detection
Date
2025-10-02T21:58:23Z (6 days ago)
From
Martin Jelinek at Astro.Inst-AVCR,Ondrejov <martin.jelinek@asu.cas.cz>
Via
email
Martin Jelinek and Jan Strobl (ASU CAS Ondrejov, CZ),
Sergey Karpov, Martin Masek, Petr Janecek, Jakub
Jurysek, Jan Ebr, Ronan Cunniffe, Petr Travnicek and
Michael Prouza (Institute of Physics, Prague, CZ)  

report:

The 25cm robotic telescope FRAM-ORM at La Palma (Spain) reacted
to the alert of GRB251002A (Saccardi et al. GCN 42060), obtaining
a series of unfiltered images starting at 20:25:24 UT, i.e.
~10.5min post trigger. 

We clearly detect the optical transient reported by Palmerio et
al. (GCN 42061) and Turpin et al. (GCN 42062). At the combination
of 9 x 60 s images (Tmid=T0+23.5min) we measure the optical
afterglow with the brightness r = 17.8 +/- 0.2 (AB) as calibrated
against Atlas-REFCAT (Tonry et al. 2018, ApJ, 867, 105).

GCN Circular 42062

Subject
GRB 251002A: LCO optical observation
Date
2025-10-02T21:05:15Z (6 days ago)
From
SVOM_group <svomgroup@bao.ac.cn>
Via
Web form
D. Turpin (CEA/Irfu), A. Saccardi (CEA/Irfu), D. Gotz (CEA/Irfu), 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 251002A (Saccardi et al. GCN 42060) with the LCO 1m telescope at South African Astronomical Observatory equipped with the Sinistro instrument. Our observation started at 2025-10-02T20:34:02.740 about 19 min after the SVOM/ECLAIRs T0 time.

We obtained 3x200 s exposures in the SDSS r filter. The optical counterpart reported by Palmerio et al. (GCN 42061) is clearly detected in our first image subtracted to the Pan-STARRS DR2 catalog image.
We measure the following magnitude:

r = 17.55 +/- 0.03 (AB), at a mid-time of 20.8 min after the trigger.

Further observations are planned.
This project is funded by the SVOM collaboration.

GCN Circular 42061

Subject
GRB 251002A: SVOM/VT optical observation
Date
2025-10-02T20:58:44Z (6 days ago)
Edited On
2025-10-02T21:42:28Z (6 days ago)
From
SVOM_group <svomgroup@bao.ac.cn>
Edited By
Vidushi Sharma at NASA GSFC/UMBC <vidushi.sharma@nasa.gov> on behalf of SVOM_group <svomgroup@bao.ac.cn>
Via
Web form
J. T. Palmerio, A. Saccardi, D. Götz (CEA/Irfu), 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 2025-10-02T20:14:54 UTC (T0), SVOM performed an automatic slew on the burst location (Saccardi et al., GCN 42060). SVOM/VT began observing the field at 2025-10-02T20:19:44, 289.75 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 36:
  This candidate was flagged as un uncatalogued source.
  The position of this candidate is R.A., Dec. 13.9082, -5.5671 degrees, corresponding to:
  R.A. (J2000) = 0h55m38.0s
  Dec. (J2000) = -5d34m01.5s
  with an uncertainty of 1 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)       |
  | -------------------- | ----------- | --------- | ----- | ------------- |
  | 2025-10-02T20:19:44  | 6.50 min    | 4*50 sec  | VT_B  | 16.81 ± 0.01  |
  | 2025-10-02T20:19:44  | 6.50 min    | 4*50 sec  | VT_R  | 16.24 ± 0.01  |
  Magnitudes were not corrected for dust extinction.
  
  Given the VT color of the counterpart, it might be a low redshift gamma-ray burst.

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.

The SVOM/VT point of contact for this burst is Jesse Palmerio: jesse.palmerio@cea.fr.

GCN Circular 42060

Subject
GRB 251002A: SVOM detection of a burst
Date
2025-10-02T20:43:05Z (6 days ago)
From
SVOM_group <svomgroup@bao.ac.cn>
Via
Web form
A. Saccardi (CEA/Irfu), D. Gotz (CEA/Irfu), S. Schanne (CEA/Irfu), M. G. Bernardini (INAF & LUPM), N. Dagoneau (CEA/Irfu), P. Maggi (ObAS), report on behalf of the SVOM mission team:

At 2025-10-02T20:14:54 UTC (T0), SVOM/ECLAIRs triggered and located the gamma-ray burst GRB 251002A (SVOM burst-id sb25100211).

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 15 alerts. CRT provided the alert with the best signal-to-noise-ratio in the image (SNR) of 22.39 in the [8-120] keV energy band over a time window of 10.20 seconds starting at 2025-10-02T20:14:49. The SVOM/ECLAIRs light curve showed a multiple peak structure with a T90 duration of 11.7 (+2.6/-1.5) s.

The localization of the best alert is R.A., Dec. 13.9059, -5.5440 degrees (J2000) with a 90% confidence level (C.L.) radius of 3.98 arcmin (including systematic error of 2 arcmin added in quadrature).

This burst also triggered SVOM/GRM at 2025-10-02T20:14:52 with an SNR of 10.40.

SVOM slewed to the burst.

SVOM/MXT began observing the field at 2025-10-02T20:17:42 UTC, 168 seconds after T0. Using onboard processed data we found an uncatalogued X-ray source located at R.A., Dec. 13.9179, -5.5679 degrees:
R.A. (J2000) = 0h55m40s
Dec. (J2000) = -5d34m04s
with a 90% C.L. radius of 81 arcseconds.

This location is 1.60 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 Andrea Saccardi: andrea.saccardi@cea.fr.
Please contact the BA by email if you require additional information.
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