GCN 45207: GRB 260718A: SVOM/ECLAIRs refined analysis
2026-07-24T16:33:19.012Z | rev 0
M. Brunet, O. Godet (IRAP), R. Hamburg (USRA), W. Zhang (PMO), Y. Ma (NAOC),
report on behalf of the SVOM/ECLAIRs team
Using the event-by-event data downloaded through the X-band ground station, we report further analysis of SVOM/ECLAIRs observations of GRB 260718A (SVOM burst-id sb26071802 – GCN 45177, trigger time T0 = 2026-07-18T11:16:34 UTC), which was also detected by Fermi/GBM (GCN 45181).
The burst that triggered ECLAIRs onboard shows a single peak lightcurve. The burst duration is T90 = 17.4 -2.0/+4.1 s in the 4-120 keV energy band.
The time-averaged spectrum from T0-2.15 s s to T0+15.0 s in the 5-120 keV energy range is best fitted by a powerlaw model with alpha = -1.95 +/- 0.05. With this model, the 4-120 keV fluence is (8.4 +/- 0.4)e-7 erg/cm^2 and the 4-120 keV photon flux is (2.16 ± 0.06) ph/cm^2/s.
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: M. Brunet (IRAP) (marius.brunet at utoulouse.fr).
GCN 45187: GRB 260718A: EP-FXT follow-up observation
2026-07-19T02:45:20.174Z | rev 0
A.Li (BNU), C. Y. Wang (THU), Y. Q. Zhao (USTC,PRIC), J. P. Chen (SYSU), W.Chen and H. Sun (NAO, CAS) on behalf of the Einstein Probe (EP) team:
EP-FXT performed a follow-up observation of GRB 260718A detected by SVOM/ECLAIRs (Antier et al., GCN 45177), which also triggered Fermi-GBM (Holzmann Airasca et al., GCN 45181). The follow-up observation started at 2026-07-18T12:09:38 (UTC), about 53 min after the SVOM-ECLAIRs trigger, with a total exposure time of around 6.2 ks. An uncatalogued source was found within the ECLAIRs error circle. The position of the source is at R.A., Dec. = 37.3004, -56.1050 deg (J2000) with an uncertainty of 10 arcsec (radius, 90% C.L. statistical and systematic). The average unabsorbed flux is 2.16(+0.62/-0.33) x 10^(-12) erg/s/cm^2 in the 0.5-10 keV energy band.
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 45185: Fermi GRB 260718A: Global MASTER-Net observations report
2026-07-18T20:46:39.605Z | rev 0
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),
M. Segura, 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 [1] located in South Africa (South African Astronomical Observatory) started inspect of the Fermi GRB 260718A ( A. Holzmann Airasca et al., GCN 45181) errorbox 30093 sec after notice time and 30129 sec after trigger time at 2026-07-18 19:38:45 UT, with upper limit up to 16.1 mag. The observations began at zenith distance = 79 deg. The sun altitude is -47.9 deg.
The galactic latitude b = -70 deg., longitude l = 272 deg.
Real time updated cover map and OT discovered available here:
https://master.sai.msu.ru/site/master2/observ.php?id=3433050
We obtain a following upper limits.
Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment
_________|_____________________|_____________________|____________________________________|_____|_______|_______|________
30160 | 2026-07-18 19:38:45 | MASTER-SAAO | (00h 43m 50.40s , -54d 15m 03.4s) | C | 60 | 15.0 |
30564 | 2026-07-18 19:45:29 | MASTER-SAAO | (01h 17m 13.48s , -58d 01m 45.8s) | C | 60 | 16.1 |
30772 | 2026-07-18 19:48:57 | MASTER-SAAO | (00h 41m 49.87s , -52d 21m 34.2s) | C | 60 | 14.7 |
31386 | 2026-07-18 19:59:10 | MASTER-SAAO | (00h 40m 00.33s , -50d 27m 42.3s) | C | 60 | 15.5 |
31486 | 2026-07-18 20:00:50 | MASTER-SAAO | (01h 13m 14.66s , -56d 07m 02.2s) | C | 60 | 15.4 |
31895 | 2026-07-18 20:07:40 | MASTER-SAAO | (01h 09m 43.51s , -54d 13m 28.2s) | C | 60 | 13.7 |
32004 | 2026-07-18 20:09:28 | MASTER-SAAO | (01h 09m 45.18s , -54d 14m 59.8s) | C | 60 | 15.1 |
32521 | 2026-07-18 20:18:06 | MASTER-SAAO | (01h 06m 29.78s , -52d 20m 35.2s) | C | 60 | 12.7 |
32725 | 2026-07-18 20:21:29 | MASTER-SAAO | (01h 03m 42.42s , -50d 26m 49.3s) | C | 60 | 14.7 |
33229 | 2026-07-18 20:29:53 | MASTER-SAAO | (01h 40m 19.62s , -56d 07m 30.7s) | C | 60 | 13.7 |
33327 | 2026-07-18 20:31:31 | MASTER-SAAO | (01h 35m 37.77s , -54d 14m 35.3s) | C | 60 | 12.8 |
33429 | 2026-07-18 20:33:14 | MASTER-SAAO | (01h 35m 33.23s , -54d 13m 49.2s) | C | 60 | 14.4 |
33947 | 2026-07-18 20:41:51 | MASTER-SAAO | (01h 31m 17.62s , -52d 21m 15.0s) | C | 60 | 13.6 |
Filter C is a clear (unfiltred) band.
The observation and reduction will continue.
The message may be cited.
[1] - 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
GCN 45184: GRB 260718A: LCO optical upper limits
2026-07-18T19:44:16.318Z | rev 0
D. Turpin, A. Saccardi (CEA/Irfu), S.-J. Yin (GXU), C. Wu, L.-P. Xin (NAOC), W. Zhang (PMO), Y. Ma (NAOC) report on behalf of the SVOM mission team:
We observed the field of GRB 260718A detected by SVOM (Antier et al., GCN 45177) and Fermi/GBM (Holzmann Airasca et al., GCN 45181) with the LCO 1m telescope at the Siding Spring Observatory (SAAO) equipped with the Sinistro instrument.
Our observation started at 2026-07-18T18:35:32 about 7.3 hours after the SVOM/ECLAIRs trigger time. We obtained 3x200 s exposures in the PanSTARRS z filters.
No any uncatalogued source was identified in our stacked frames in the ECLAIRs localisation region as also reported by SVOM/VT (Ma et al., GCN 45178; Li et al., GCN 45179) and GRANDMA/KNC (Jacquesson et al., GCN 45180) .
We measure the following upper limits (5 sigma) calibrated against the SkyMapper DR4 catalog, and not corrected for Galactic extinction:
z = 20.1 (AB) T_mid - T0 = 7.4hr
This project is funded by the SVOM collaboration.
GCN 45181: GRB 260718A: Fermi GBM Observation
2026-07-18T17:24:01.173Z | rev 0
A. Holzmann Airasca (UniTrento and INFN Bari) reports on behalf of the Fermi Gamma-ray Burst Monitor Team:
"At 11:16:35.01 UT on 18 July 2026, the Fermi Gamma-ray Burst Monitor (GBM)
triggered and located GRB 260718A (trigger 806066200/260718470),
which was also detected by SVOM/ECLAIRs (S. Antier et al. 2026, GCN 45177).
The Fermi GBM on-ground location is consistent with the SVOM/ECLAIRs position.
The angle from the Fermi LAT boresight is 31 degrees.
The GBM light curve consists of a single emission episode with a duration (T90)
of about 19 s (50-300 keV). The time-averaged spectrum
from T0-3.8 to T0+16.3 s is best fit by
a power law function with an exponential high-energy cutoff.
The power law index is -1.29 +/- 0.05 and the cutoff energy,
parameterized as Epeak, is 68 +/- 3 keV.
The event fluence (10-1000 keV) in this time interval is
(6.8 +/- 0.6)E-07 erg/cm^2. The 1-sec peak photon flux measured
starting from T0-2.4 s in the 10-1000 keV band is 2.1 +/- 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 45180: GRB 260718A : GRANDMA and KNC upper limits
2026-07-18T17:08:36.815Z | rev 0
GRB 260718A : GRANDMA and KNC upper limits
A. Jacquesson (IJCLab), S. Antier (IJCLab), D. Turpin (CEA/Irfu), P. Hello (IJCLab), M. Freeberg (KNC), N. Kochiashvili (Ilia State University), M. Molham (NRIAG), C. Douzet (IJCLab), N. Jasmin (IJCLab), R. Le Montagner (IJCLab), K. Agabi (OCA), L. Abe (OCA), T. Guillot (OCA) on behalf of GRANDMA.
We observed the field of GRB 260718A detected by SVOM/ECLAIRs (GCN 45177). The observations started with ASTEP at 2026-07-18T14-47-18 UTC on the 18th of July 2026 about 4h post ECLAIRs T0.
We didn't detect any optical counterpart within a region centered on ECLAIRs localization error box and with a radius above 8 arcmin with the GRANDMA network with ASTEP at Concordia and KNC-T30. We reported our upper limit in the public ACME service Skyportal/ICARE https://skyportal-icare.ijclab.in2p3.fr/source/GCN-260718_111632. To access, one simply needs to create an account using your ORCID id.
Our upper limit are coherent with SVOM/VT (GCN 45178 and 45179)
The data were 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.
The observations are performed under the P7 campaign of GRANDMA to monitor SVOM alerts and LSST alerts from explosive fast transients filtered by BOOM/Babamul and FINK.
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/). Astrophysics Center for Multimessenger studies in Europe is supported Skyportal/ICARE (contact camille.douzet@ijclab.in2p3.fr, skyportal.io).
GCN 45179: GRB 260718A: SVOM/VT optical upper limits
2026-07-18T16:56:45.670Z | rev 0
H. L. Li, Y. N. Ma, C. Wu, Y. L. Qiu, L. P. Xin, Z. H. Yao, J. R. Xu, X. H. Han, J. Wang, Y. Xu, P. P. Zhang, W. J. Xie, Y. J. Xiao, H. B. Cai, J. S. Deng, J. Y. Wei (NAOC), J. Palmerio (CEA/Irfu), W. L. Zhang (PMO) report on behalf of the SVOM/VT team.
SVOM/VT performed observations with automatic slew to the field of GRB 260718A triggered by SVOM/ECLAIRs (sb26071802, Antier et al., GCN 45177). The observations started at 2026-07-18T12:00:14 UTC, about 44.08 minutes post trigger in the VT_B (400-650 nm) and VT_R (650-1000 nm) channels simultaneously.
No credible sources were detected within the error box of ECLAIRs (Antier et al., GCN 45177), compared to the Legacy Survey catalog. The 3σ upper limits of AB magnitudes without corrections for Galactic extinction are as follows:
Mid time | Band | Exposure Time | 3 sigma upper limit
1.05 hr VT_B 42*50 s > 23.2 mag
1.05 hr VT_R 38*50 s > 23.0 mag
This non-detection is consistent with VT VHF upper limits (Ma et al., GCN 45178).
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 45178: GRB 260718A: SVOM/VT optical upper limits from VHF data
2026-07-18T14:52:36.281Z | rev 2
Y. N. Ma (NAOC), W. L. Zhang (PMO), C. Wu, L. P. Xin, Y.L. Qiu (NAOC), D. Turpin, A. Saccardi, J. T. Palmerio (CEA/Irfu) report on behalf of the SVOM/VT team.
After the trigger by SVOM/ECLAIRs at 2026-07-18T11:16:34 UTC (T0), SVOM performed an automatic slew on the burst location (Antier et al., GCN 45177). SVOM/VT took images of the field 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, no uncatalogued optical source was detected at the ECLAIRs position (Antier et al., GCN 45177) in our two sequence images, compared to Pan-STARRS1 DR1. The 5-sigma upper limits are:
Mid time | Band | Exposure Time | 5 sigma upper limit
44.5 min | VT_B | 6*50 sec | > 21.5 mag
44.5 min | VT_R | 6*50 sec | > 21.5 mag
49.5 min | VT_R | 6*50 sec | > 21.5 mag
The subimage and source list cover 100% of the SVOM/ECLAIRs R90 uncertainty region. Given the lack of detection in VT_B and VT_R at an early phase, deeper or redder follow-ups are encouraged to investigate the nature of the 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 Burst Advocate (BA) on shift for this alert is Yinuo Ma: mayn@bao.ac.cn.
Please contact the BA by email if you require additional information.
GCN 45178: GRB 260718A: SVOM/VT optical upper limits from VHF data
2026-07-18T14:52:36.281Z | rev 2
Y. N. Ma (NAOC), W. L. Zhang (PMO), C. Wu, L. P. Xin, Y.L. Qiu (NAOC), D. Turpin, A. Saccardi, J. T. Palmerio (CEA/Irfu) report on behalf of the SVOM/VT team.
After the trigger by SVOM/ECLAIRs at 2026-07-18T11:16:34 UTC (T0), SVOM performed an automatic slew on the burst location (Antier et al., GCN 45177). SVOM/VT took images of the field 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, no uncatalogued optical source was detected at the ECLAIRs position (Antier et al., GCN 45177) in our two sequence images, compared to Pan-STARRS1 DR1. The 5-sigma upper limits are:
Mid time | Band | Exposure Time | 5 sigma upper limit
44.5 min | VT_B | 6*50 sec | > 21.5 mag
44.5 min | VT_R | 6*50 sec | > 21.5 mag
49.5 min | VT_R | 6*50 sec | > 21.5 mag
The subimage and source list cover 100% of the SVOM/ECLAIRs R90 uncertainty region. Given the lack of detection in VT_B and VT_R at an early phase, deeper or redder follow-ups are encouraged to investigate the nature of the 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 Burst Advocate (BA) on shift for this alert is Yinuo Ma: mayn@bao.ac.cn.
Please contact the BA by email if you require additional information.
GCN 45177: GRB 260718A: SVOM detection of a burst
2026-07-18T11:57:28.227Z | rev 0
S. Antier (IJCLAB), D. Zhao (NAOC), W. Zhang (PMO), Y. Ma (NAOC), C. Wang (IHEP) report on behalf of the SVOM mission team:
At 2026-07-18T11:16:34 UTC (T0), SVOM/ECLAIRs triggered and located the gamma-ray burst GRB 260718A (SVOM burst-id sb26071802).
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 19 alerts. CRT provided the alert with the best signal-to-noise-ratio in the image (SNR) of 20.86 in the [5-20] keV energy band over a time window of 20.40 seconds starting at 2026-07-18T11:16:31.
The localization of the best alert is R.A., Dec. 37.2660, -56.0993 degrees:
R.A. (J2000) = 2h29m03.85s
Dec. (J2000) = -56d05m57.31s
with a 90% confidence level (C.L.) radius of 4.20 arcmin (including systematic error of 2 arcmin added in quadrature).
The SVOM/ECLAIRs light curve showed a broad peak structure.
This burst was also detected by SVOM/GRM. : https://www.bursthub.cn/gcn/2026/svgrb260718A.png
SVOM slewed to the burst. No immediate MXT and VT observation could be carried out due to Earth occultation. Later observations will be reported in future GCN Circulars.
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 Wenlong Zhang: wlzhang@pmo.ac.cn.
Please contact the BA by email if you require additional information.