GRB 260204A
GCN Circular 43723
Subject
GRB 260204A: SVOM/ECLAIRs refined analysis
Date
2026-02-13T14:24:15Z (7 months ago)
From
SVOM_group <svomgroup@bao.ac.cn>
Via
Web form
M. Brunet, O. Godet (IRAP), M. Pillas, M. Dennefeld (IAP) on behalf of the ECLAIRs team.
Using the event-by-event data downloaded through the X-band ground station, we report further analysis of ECLAIRs observations of GRB 260204A (SVOM burst-id sb26020403, GCN 43613), which was also detected by Fermi/GBM as a sub-threshold event (GCN 43618).
ECLAIRs started collecting data at T0-8.91 s (T0 = 2026-02-04T14:48:49 UT), the Fermi sub-threshold detection starting at T0-47 s shows that part of the burst emission has been missed by ECLAIRs.
The burst as seen by ECLAIRs is featureless in the 4-120 keV lightcurve. The burst emission is detected up to T0+220 s.
The time-averaged spectrum before the slew from T0-8.91 s to T0+36.03 s in the 4-120 keV energy range is best fitted by a power-law model with a photon index of 1.76 +0.12/-0.11. With this model, the fluence in the 4-120 keV energy band is (7.55 +0.55/-1.02)e-7 erg/cm².
After the slew, the GRB emission is still detectable below 10 keV for around 80 s, but it is rather faint. So, it is not possible to derive meaningful spectral information.
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: Marius Brunet (IRAP) (marius.brunet at irap.omp.eu)
GCN Circular 43678
Subject
GRB 260204A: Swift-XRT afterglow detection
Date
2026-02-10T08:34:30Z (8 months ago)
Edited On
2026-02-10T16:37:59Z (8 months ago)
From
Phil Evans at U of Leicester <pae9@star.le.ac.uk>
Edited By
Judith Racusin at NASA/GSFC <judith.racusin@nasa.gov> on behalf of P.A. Evans at U. Leicester <pae9@leicester.ac.uk>
Via
email
J.P. Osborne (U. Leicester), M.G. Bernardini (INAF-OAB), E. Ambrosi
(INAF-IASFPA) , M. Capalbi (INAF-OAR), D.N. Burrows (PSU), S. Lanava
(PSU), S. Dichiara (PSU), K.L. Page (U. Leicester) and P.A. Evans (U.
Leicester) reports on behalf of the Swift-XRT team:
Swift-XRT has performed a second epoch of follow-up observations of GRB
260204A (Pillas et al., GCN Circ. 43613), collecting a further 2.6 ks
between T0+363 ks and T0+458 ks. "Source 1" (Evans et al., GCN Circ.
43622), which corresponds to the fading optical counterpart (Li et al.,
GCN Circs 43620, 43623), is no longer detected and has faded with
>3-sigma significance. The upper limit is 6.97e-3 ct/sec, compared to
the previous detection level of (2.36 +/- 0.46)e-2 ct/sec, giving a
power-law decay index of alpha >0.4.
Using 1659 s of PC mode data and 1 UVOT image, we find an enhanced XRT
position (using the XRT-UVOT alignment and matching UVOT field sources
to the USNO-B1 catalogue): RA, Dec = 205.10623, +1.93075 which is
equivalent to:
RA (J2000): 13h 40m 25.49s
Dec(J2000): +01d 55' 50.7"
with an uncertainty of 4.4 arcsec (radius, 90% confidence).
The results of the XRT-team automatic analysis are available at
https://www.swift.ac.uk/xrt_products/03000405.
The results of the full analysis of the XRT observations are available
at https://www.swift.ac.uk/SVOM/SVOM_FIELD00057.
This circular is an official product of the Swift-XRT team.
GCN Circular 43669
Subject
GRB 260204A: Swift/UVOT Upper Limits
Date
2026-02-09T13:22:25Z (8 months ago)
From
Alice Breeveld at MSSL-UCL <a.breeveld@ucl.ac.uk>
Via
email
A.A. Breeveld (UCL-MSSL) and S. Laha (GSFC/UMBC) report on behalf of the Swift/UVOT team:
The Swift/UVOT began settled observations of the field of the SVOM/ECLAIRS-detected burst GRB 260204A (Pillas et al., GCN Circ. 43613) 2.3 ks after the trigger. The afterglow reported by Malesani et al. (in the r and z bands, GCN Circ. 43621) and Li et al. (GCN Circ. 43626) and consistent with XRT source 1 (Evans et al., GCN Circ. 43622) is not detected in the U-band exposures.
Preliminary 3-sigma upper limit using the UVOT photometric system (Breeveld et al. 2011, AIP Conf. Proc. 1358, 373) for the initial exposure is:
Filter T_start(s) T_stop(s) Exp(s) Mag
u 23622 25281 1634 >20.8
The magnitudes in the table are not corrected for the Galactic extinction due to the reddening of E(B-V) = 0.023 in the direction of the burst (Schlegel et al. 1998).
GCN Circular 43623
Subject
GRB 260204A: SVOM/VT confirms fading of the optical afterglow
Date
2026-02-06T04:13:44Z (8 months ago)
From
Huali Li at at NAOC, SVOM <lhl@nao.cas.cn>
Via
Web form
H. L. Li, Y. N. Ma, C. Wu, Z. H. Yao, Y. L. Qiu, L.P. Xin, X. H. Han, J. Wang, Y. Xu, P. P. Zhang, W. J. Xie, Y. J. Xiao, H. B. Cai, L. Lan, J. R. Xu, J. S. Deng, J. Y. Wei (NAOC), J. Palmerio (CEA/Irfu), R. Z. Li (YNAO), C. W. Wang (IHEP) report on behalf of the SVOM/VT team.
SVOM/VT performed ToO observation to the GRB 260204A triggered by SVOM/ECLAIRs (sb26020403, Pillas et al., GCN 43613), which was also detected by Fermi (Fermi GBM team, GCN 43618) and followed by Swift (Evan et al., GCN 43622), LCO (Turpin et al., GCN 43616; Malesani et al. GCN 43621), GOTO (Kumar et al, GCN 43617) and MASTER (Lipunov et al., GCN 43619). The observation started at 2026-02-05T07:04:40 UTC, i.e., 16.27 hour post trigger in the VT_B (400nm-650nm) and VT_R (650nm-1000nm) channels simultaneously.
By stacking images of 47*50 sec in VT_R and 44*50 sec in VT_B, the counterpart (Li et al., GCN 43620; Malesani et al. GCN 43621) was confirmed to be fading with the brightness of VT_R~23.1+/-0.3 mag and VT_B>23.3 mag at the mid time of 18.0 hours post trigger. Combined with the earlier detection (Li et al., GCN 43620), the optical decay slope was -0.90.
Our photometry was in AB magnitude and not corrected for Galactic extinction.
The Space Variable Objects Monitor (SVOM) is a China-France joint mission led by the Chinese National Space Administration (CNSA, China), National Center for Space Studies (CNES, France) and the Chinese Academy of Sciences (CAS, China), which is dedicated to observing gamma-ray bursts and other transient phenomena in the energetic universe. VT was jointly developed by Xi'an Institute of Optics and Precision Mechanics (XIOPM), CAS and National astronomical observatories (NAOC), CAS.
GCN Circular 43622
Subject
GRB 260204A: Swift-XRT observations
Date
2026-02-05T13:29:09Z (8 months 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 GRB
260204A, collecting 1.7 ks of Photon Counting (PC) mode data between T0+23 ks and
T0+25 ks after the trigger. We have detected 4 sources. These have been
automatically classified as follows:
* 0 likely counterparts
* 0 candidate counterparts
* 3 uncatalogued X-ray sources
* 1 known X-ray source
As already reported source 1 is consistent with an optical source (Li et al., GCN
Circ. 43620; Malesani et al., GCN Circ. 43621). We note that, in the X-rays, this
source is not well separated from source 3 and cannot rule out that these arise not
from point sources but from a patch of diffuse emission.
We note also the presence of a source in the XMM Slew survey XMMSL3 catalogue,
XMMSL3 J134023.8+015613 at RA,Dec = 205.0888, +1.9370 degrees (J2000), with a
1-sigma error of 4.3" (statistical) and an estimated systematic error of ~8" (see
http://xmmssc.irap.omp.eu/Catalogue/XMMSL3/XMMSL3_Catalogue_User_Guide.html#Astromet
ry). This source is 33" from the position of source 1.
Source 2 is consistent with the position of HD 118981, a high proper motion star,
while source 4 is a known quasar.
Further observations are planned.
Uncatalogued X-ray sources
--------------------------
Source 1 (SWIFT J134025.4+015552):
==================================
RA (J2000.0): 205.1060 = 13 40 25.44
Dec (J2000.0): +1.9313 = +01 55 52.7
Error: 5.0 (arcsec, radius, 90% confidence).
Detect flag: GOOD
Distance: 5.4 arcmin from the SVOM/ECLAIRs position.
Mean rate: 0.0235 +/- 0.0046 ct s^-1
Mean flux: (8.7 +/- 1.7)e-13 erg cm^-2 s^-1
Peak rate: 0.0235 +/- 0.0046 ct s^-1
Peak flux: (8.7 +/- 1.7)e-13 erg cm^-2 s^-1
ECF: 3.71e-11 erg cm^-2 ct^-1
assuming NH=1.90e+20 cm^-2, gamma=1.76
determined from a spectral fit.
RASS UL: 4.1e-02 ct s^-1 (converted to XRT; 0.3-10 keV)
so the source is not above this 3-sigma upper limit.
There is no evidence for fading.
Source 2 (SWIFT J134026.9+020905):
==================================
RA (J2000.0): 205.1125 = 13 40 27.00
Dec (J2000.0): +2.1515 = +02 09 05.4
Error: 5.0 (arcsec, radius, 90% confidence).
Detect flag: GOOD
Distance: 7.9 arcmin from the SVOM/ECLAIRs position.
Mean rate: 0.0136 +/- 0.0036 ct s^-1
Mean flux: (2.28 +/- 0.61)e-13 erg cm^-2 s^-1
Peak rate: 0.0136 +/- 0.0036 ct s^-1
Peak flux: (2.28 +/- 0.61)e-13 erg cm^-2 s^-1
ECF: 1.67e-11 erg cm^-2 ct^-1
assuming NH=1.30e+22 cm^-2, gamma=9.94
determined from a spectral fit.
RASS UL: 3.3e-02 ct s^-1 (converted to XRT; 0.3-10 keV)
so the source is not above this 3-sigma upper limit.
There is no evidence for fading.
A SIMBAD object `HD 118981' is 0.7" away.
There is 1 2MASS object within the source's 3-sigma error radius.
Source 4 (SWIFT J134043.1+020310):
==================================
RA (J2000.0): 205.1796 = 13 40 43.10
Dec (J2000.0): +2.0530 = +02 03 10.8
Error: 6.6 (arcsec, radius, 90% confidence).
Detect flag: GOOD
Distance: 4.2 arcmin from the SVOM/ECLAIRs position.
Mean rate: (7.2 [+2.9, -2.3])e-3 ct s^-1
Mean flux: (1.49 [+0.60, -0.48])e-13 erg cm^-2 s^-1
Peak rate: (7.2 [+2.9, -2.3])e-3 ct s^-1
Peak flux: (1.49 [+0.60, -0.48])e-13 erg cm^-2 s^-1
ECF: 2.07e-11 erg cm^-2 ct^-1
assuming NH=6.90e+21 cm^-2, gamma=9.20
determined from a spectral fit.
RASS UL: 2.1e-02 ct s^-1 (converted to XRT; 0.3-10 keV)
so the source is not above this 3-sigma upper limit.
There is no evidence for fading.
A SIMBAD object `[VV2006] J134042.9+020307' is 4.5" away.
Known X-ray sources
-------------------
Source 3 (SWIFT J134023.6+015612):
==================================
RA (J2000.0): 205.0984 = 13 40 23.62
Dec (J2000.0): +1.9369 = +01 56 12.8
Error: 6.1 (arcsec, radius, 90% confidence).
Detect flag: GOOD
Distance: 5.1 arcmin from the SVOM/ECLAIRs position.
Mean rate: 0.0225 +/- 0.0058 ct s^-1
Mean flux: (2.54 +/- 0.65)e-12 erg cm^-2 s^-1
Peak rate: 0.0225 +/- 0.0058 ct s^-1
Peak flux: (2.54 +/- 0.65)e-12 erg cm^-2 s^-1
ECF: 1.13e-10 erg cm^-2 ct^-1
assuming NH=1.89e+20 cm^-2, gamma=1.04
determined from a spectral fit.
This matches a catalogued X-ray source XMMSL3 J134023.8+015613
in the XMM-NEWTON/XMMSLEWCLN catalogue. Details:
Separation: 1.6" from the XRT source
Cat Rate: 4.8e-01 +/- 2.6e-01 ct s^-1
Cat Flux: 7.7e-12 +/- 4.1e-12 erg cm^-2 s^-1 (0.3-10 keV)
so the source is not above the catalogued flux.
There is no evidence for fading.
There is 1 2MASS object within the source's 3-sigma error radius.
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_FIELD00057.
This circular is an official product of the Swift-XRT team.
GCN Circular 43621
Subject
GRB 260204A: LCO optical afterglow detection
Date
2026-02-05T10:45:38Z (8 months ago)
From
SVOM_group <svomgroup@bao.ac.cn>
Via
Web form
D. B. Malesani (DAWN/NBI and Radboud), D. Turpin (CEA/Irfu), A. Saccardi (CEA/Irfu), B. Cordier (CEA/Irfu), M. Pillas, M. Dennefeld (IAP), report on behalf of the SVOM mission team:
Following the report of an optical counterpart (Li et al., GCN 43620; see also the X-ray detection at https://www.swift.ac.uk/SVOM/SVOM_FIELD00057/) of the SVOM GRB 260204A (Pillas et al. GCN 43613), we inspected again our images taken with the LCO telescope at the Siding Spring Observatory (Turpin et al., GCN 43616).
The optical counterpart is detected in our images, and we measure the following magnitudes:
r = 20.26 +- 0.21 AB (mid-time 25.7 min after the trigger);
z = 19.49 +- 0.25 AB (mid-time 38.4 min after the trigger).
We note that these measurements are close to the sensitivity limit of our images, and consistent with the 5-sigma upper limits reported in our previous circular (Turpin et al., GCN 43616). The above measurements are not corrected for Galactic extinction.
Compared to the SVOM/VT measurement (taken at a mean epoch ~74 min after the GRB), our data indicate only marginal decay between the two observations.
GCN Circular 43620
Subject
GRB 260204A: SVOM/VT optical candidate
Date
2026-02-05T02:02:27Z (8 months ago)
Edited On
2026-02-05T15:49:27Z (8 months ago)
From
Huali Li at at NAOC, SVOM <lhl@nao.cas.cn>
Edited By
Judith Racusin at NASA/GSFC <judith.racusin@nasa.gov> on behalf of Huali Li at at NAOC, SVOM <lhl@nao.cas.cn>
Via
Web form
H. L. Li , C. Wu, Y. N. Ma, Z. H. Yao, Y. L. Qiu, L.P. Xin, X. H. Han, J. Wang, Y. Xu, P. P. Zhang, W. J. Xie, Y. J. Xiao, H. B. Cai, L. Lan, J. R. Xu, J. S. Deng, J. Y. Wei (NAOC), J. Palmerio (CEA/Irfu), M. Pillas (IAP), M. Dennefeld (IAP) report on behalf of the SVOM/VT team.
SVOM/VT performed observation with auto slew to the field of GRB 260204A triggered by SVOM/ECLAIRs (sb26020403, Pillas et al., GCN 43613). The observation started at 2026-02-04T15:37:26UTC, i.e., 49 minutes post trigger in the VT_B (400nm-650nm) and VT_R (650nm-1000nm) channels simultaneously.
An uncatalogued source was detected within the error box of ECLAIRs (Pillas et al., GCN 43613) and source 1 of Swift-XRT (https://www.swift.ac.uk/SVOM/SVOM_FIELD00057), compared to the Legacy survey catalog. The position is at R.A., Dec. = 205.106167, 1.930114 degrees, equivalent to:
R.A. (J2000) = 13:40:25.48
Dec. (J2000) = +1:55:48.41
with an uncertainty of 0.5 arcsec.
The measurements in AB magnitudes are given below:
Mid_time Band Exposure Time Magnitude (AB)
1.23 hour VT_R 27*50 sec 20.5+/-0.1 mag
1.23 hour VT_B 26*50 sec 21.3+/-0.1 mag
Our photometry was not corrected for Galactic extinction.
The Space Variable Objects Monitor (SVOM) is a China-France joint mission led by the Chinese National Space Administration (CNSA, China), National Center for Space Studies (CNES, France) and the Chinese Academy of Sciences (CAS, China), which is dedicated to observing gamma-ray bursts and other transient phenomena in the energetic universe. VT was jointly developed by Xi'an Institute of Optics and Precision Mechanics (XIOPM), CAS and National astronomical observatories (NAOC), CAS.
GCN Circular 43619
Subject
GRB 260204A : MASTER Global robotic net optical observations
Date
2026-02-05T01:13:33Z (8 months ago)
From
Vladimir Lipunov at Moscow State U/Krylov Obs <lipunov@xray.sai.msu.ru>
Via
email
V.M.Lipunov (Lomonosov MSU), O.A.Gress, N.M.Budnev (ISU), V.A.Senik, I.Panchenko, P.Balanutsa,
A.Kuznetsov, E.Gorbovskoy, G.Antipov, N. Tiurina, Ya.Kechin,A.Chasovnikov, D.Vlasenko, I.Ionov,Yu.Tselik(Lomonosov MSU),
R.Mirgazov, A.Diachok, O.Ershova (Irkutsk State University),
R. Podesta, C.Francile, F. Podesta, E. Gonzalez (OAFA, San JuanUni.,Argentina);
D.Buckley (SAAO),
A. Sosnovskij (CrAO RAS),
A. Tlatov, D. Dormidontov (Kislovodsk Solar Station of the Pulkovo Observatory),
L.Carrasco, J.R.Valdes, V.Chavushyan, V.M.Patino, J.Martinez, A.R.Corella, J.G. Tanori, L. F. Villalobos, L.H.Rodriguez (INAOE, Guillermo Haro Astrophysic Observatory, Mexico)
V.M.Pillet, R.Rebolo Lopez (The Instituto de Astrofisica de Canarias,Spain)
At alert and notice time the error-box of SVOM GRB 260204A
(Pillas et al. GCN 43613, also by Fermi-GBM GCN 43618;
in optic observed by LCO (Turpin et al. GCN 43616), GOTO (Kumar et al. GCN 43617))
altitude was -8deg at MASTER-Tunka (the nearest MASTER for observation).
So we started observe it several hours later.
MASTER-Tunka robotic telescope [1-3] located in Russia (Applied Physics Institute, Irkutsk State University) was pointed to the SVOM GRB260204A (trigger No 1770219433,13h 40m 56.04s , +01d 58m 50.2s, R=0.0662) errorbox 12301 sec after notice time (13245 sec after trigger time) at 2026-02-04 19:17:57 UT, with upper limit up to 18.1 mag at single images and 19.9 at summary.
MASTER-Kislovodsk robotic telescope located in Russia (Lomonosov MSU, Kislovodsk Solar Station of Pulkovo observatory) was pointed to the SVOM GRB 260204A errorbox 16703 sec after notice time and 17647 sec after trigger time at 2026-02-04 20:31:20 UT, with upper limit up to 17.1 mag. The observations began at zenith distance = 81 deg. The sun altitude was -60.8 deg.
The galactic latitude b = 62 deg., longitude l = 331 deg.
Real time updated cover map and OT discovered available here:
https://master.sai.msu.ru/site/master2/observ.php?id=3122418
Observation and reduction will continue.
[1] Lipunov et al. 2023, Astronomical Robotic Networks and Operative Multichanel Astrophysics, Lomonosov MSU PRESS, 591pp.
http : // www.pereplet.ru/lipunov/625.html
[2] Lipunov et al. 2022, Universe, 8, id.271
[3] Lipunov et al. 2023, Astronomy Reports, 67, p.S140
GCN Circular 43618
Subject
Fermi GBM Sub-Threshold Detection of GRB 260204A
Date
2026-02-04T21:43:34Z (8 months ago)
From
Matt Godwin <msg0028@uah.edu>
Via
Web form
Matt Godwin (UAH) reports on behalf of the Fermi-GBM Team:
SVOM/ECLAIRs detected the GRB 260204A on 2026-02-04 at 14:48:49 UTC (Pillas et al. 2026, GCN 43613). There was no Fermi-GBM onboard trigger around this event time. An automated, blind search for gamma-ray bursts below the onboard triggering threshold in Fermi-GBM identified a candidate.
The GBM Targeted Search [1], the most sensitive coherent search for GRB-like signals in GBM, identified a transient starting -35 seconds before the SVOM best SNR time at 2026-02-04T14:48:28 most significantly on the 16 s timescale, with a false alarm rate of 3.8e-05 Hz. The Fermi-MET of this transient is 791909278.714 s. The Targeted Search localization is found to be spatially consistent with the ECLAIRs localization
Additionally, the GBM Targeted Search event was found with the highest significance using a "normal" spectrum (Band function with Epeak = 230 keV, alpha = -1.0, beta = -2.3) for a GRB.
[1] Goldstein et al. 2019 arXiv:1903.12597
GCN Circular 43617
Subject
GRB 260204A: GOTO optical upper limit
Date
2026-02-04T21:17:42Z (8 months ago)
From
Amit Kumar at The Open University, UK <amitkundu515@gmail.com>
Via
Web form
A. Kumar, D. O’Neill, B. P. Gompertz, R. Starling, M. Wortley, M. Kennedy, K. Ackley, M. Dyer, J. Lyman, K. Ulaczyk, D. Steeghs, D. Galloway, V. Dhillon, P. O'Brien, G. Ramsay, K. Noysena, R. Kotak, R. Breton, J. Casares, L. Nuttall, B. Godson, T. Killestein, M. Pursiainen, on behalf of 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 the SVOM/ECLAIRs GRB 260204A (Pillas et al. GCN 43613). Observations covering the localisation area began at 2026-02-04 15:39:17 UT (+0.85h post trigger) and continued through to 2026-02-04 17:08:08 UT (+2.33h post trigger) utilising GOTO-South. Each observation consisted of 4x90 s 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. Source candidates were initially filtered using a classifier (Killestein et al. 2021) and cross-matched against a variety of contextual and minor planet catalogs. Human vetting was carried out in real time on any candidates that passed the above checks.
No new transients that could be credibly associated with GRB 260204A were detected down to an average 5-sigma depth of 19.3 mag (AB).
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, the University of Birmingham and the Instituto de Astrofisica de Canarias (IAC).
GCN Circular 43616
Subject
GRB 260204A: LCO optical upper limits
Date
2026-02-04T21:16:28Z (8 months ago)
From
SVOM_group <svomgroup@bao.ac.cn>
Via
Web form
D. Turpin (CEA/Irfu), A. Saccardi (CEA/Irfu), D. B. Malesani (DAWN/NBI and Radboud), B. Cordier (CEA/Irfu), report on behalf of the SVOM mission team:
We observed the field of GRB 260204A (Pillas et al., GCN 43613) with the LCO 1-m telescope at Siding Spring Observatory equipped with the Sinistro instrument.
Our observation started on 2026-02-04 at 15:10:42 UT (about 22 min after the trigger) and we obtained 3x200 s in each of the SDSS r and Pan-STARRS z filters. In the stacked image, we do not detect any new source within the SVOM/ECLAIRs error box.
We measure the following upper limit calibrated against the PanSTARRS DR1 catalog, and not corrected for Galactic extinction:
r > 20.3 AB (5-sigma, mid-time 25.7 min after the trigger);
z > 19.4 AB (5-sigma, mid-time 38.4 min after the trigger).
This project is funded by the SVOM collaboration.
GCN Circular 43613
Subject
GRB 260204A: SVOM detection of a burst
Date
2026-02-04T15:09:47Z (8 months ago)
From
SVOM_group <svomgroup@bao.ac.cn>
Via
Web form
M. Pillas (IAP), M. Dennefeld (IAP), M. Brunet (IRAP), S. Guillot (IRAP), C. Pellouin (IAP), report on behalf of the SVOM mission team:
At 2026-02-04T14:48:49 UTC (T0), SVOM/ECLAIRs triggered and located the gamma-ray burst GRB 260204A (SVOM burst-id sb26020403).
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 6 alerts. IMT provided the alert with the best signal-to-noise-ratio in the image (SNR) of 10.87 in the [5-20] keV energy band over a time window of 40.96 seconds starting at 2026-02-04T14:48:28.
The localization of the best alert is R.A., Dec. 205.1185, 2.0200 degrees:
R.A. (J2000) = 13h40m28.44s
Dec. (J2000) = 2d01m12.14s
with a 90% confidence level (C.L.) radius of 7.36 arcmin (including systematic error of 2 arcmin added in quadrature).
SVOM slewed to the burst.
No X-ray observation could be performed by SVOM/MXT for the time being, due to Earth occultation.
SVOM/VT observations will be reported in 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 Marion Pillas: marion.pillas@iap.fr.
Please contact the BA by email if you require additional information.