GRB 260829A
GCN Circular 45496
Subject
Konus-Wind detection of GRB 260829A
Date
2026-09-02T11:12:15Z (23 days ago)
From
Anna Ridnaia at Ioffe Institute <ridnaia@mail.ioffe.ru>
Via
Web form
A. Ridnaia, D. Frederiks, A. Lysenko, V. Panteleeva,
D. Svinkin, A. Tsvetkova, M. Ulanov, and T. Cline,
on behalf of the Konus-Wind team, report:
The long-duration GRB 260829A
(Fermi-GBM detection: Fermi GBM team, GCN 45464;
Malacaria et al., GCN 45467;
BALROG localization: Preis & Greiner, GCN 45465;
GECAM-B detection: Zao et al., GCN 45470;
IPN triangulation: Kozyrev et al., GCN 45476;
AstroSat CZTI detection: Goyal et al., GCN 45485;
SVOM-GRM detection: Luo et al., GCN 45495)
triggered Konus-Wind at T0=22110.076 s UT (06:08:30.076).
The burst light curve shows an initial weak emission
episode starting at ~T0-21.3 s, followed by a brighter
multi-peaked structure. The total burst duration is ~34.8 s.
The emission is seen up to ~4 MeV.
The Konus-Wind light curve of this GRB is available at
http://www.ioffe.ru/LEA/GRBs/GRB260829_T22110/
As observed by Konus-Wind, the burst
had the total fluence of 2.05(-0.09,+0.10)x10^-5 erg/cm2,
and the 64-ms peak flux, measured from T0+2.208 s,
of 8.44(-0.91,+0.92)x10^-6 erg/cm2/s
(both in the 20 keV - 10 MeV energy range).
The time-averaged spectrum of the burst
(measured from T0 to T0+16.640 s)
is best fit in the 20 keV - 10 MeV range
by a power law with exponential cutoff model:
dN/dE ~ (E^alpha)*exp(-E*(2+alpha)/Ep)
with alpha = -0.94(-0.09,+0.09)
and Ep = 330(-24,+28) keV (chi2 = 114/98 dof).
Fitting by a GRB (Band) model yields the same alpha and Ep,
and an upper limit on the high energy photon index: beta < -2.8
(chi2 = 114/97 dof).
The spectrum near the maximum count rate
(measured from T0+0.256 to T0+8.448 s)
is best fit in the 20 keV - 10 MeV range
by a power law with exponential cutoff model:
dN/dE ~ (E^alpha)*exp(-E*(2+alpha)/Ep)
with alpha = -0.75(-0.08,+0.08)
and Ep = 314(-17,+19) keV (chi2 = 122/88 dof).
Fitting by a GRB (Band) model yields the same alpha and Ep,
and an upper limit on the high energy photon index: beta < -3.0
(chi2 = 122/87 dof).
All the quoted errors are at the 68% confidence level.
All the quoted values are preliminary.
GCN Circular 45495
Subject
GRB 260829A: SVOM/GRM observation
Date
2026-09-02T10:51:42Z (23 days ago)
From
Xinghao Luo at IHEP <2952704891@qq.com>
Via
Web form
SVOM/GRM team: Xing-Hao Luo, Yue Wang, Chen-Wei Wang, Shi-Jie Zheng, Yue Huang, Shao-Lin Xiong, Shuang-Nan Zhang (IHEP)
SVOM/ECLAIRs team: Stéphane Schanne (CEA)
Report on behalf of the SVOM team:
SVOM/GRM was triggered in-flight by GRB 260829A at 2026-08-29T06:08:29.000 (T0), which is also detected by Fermi/GBM (Fermi GBM team, GCN #45464) and GECAM-B (Xue-Yuan Zao et. al., GCN #45470).
With the event-by-event data downloaded through the X-band ground station, the GRM light curve shows that this burst consists of muplti-pulses with a T90 of 28 +3/-5 s in the 15-5000 keV band.
The SVOM/GRM light curve can be found here:
https://www.bursthub.cn/gcn/2026/svgrb260829A.png
In addition, the position of this burst, as determined by Fermi/GBM (RA = 242.3, Dec = -34.6, with a statistical uncertainty of 1.0 degrees, GCN #45464), is located at about 134 degrees from the SVOM optical axis, which is outside the ECLAIRs field of view.
With this localization, the time-averaged spectrum from T0-25 to T0+13 s is best fitted by a power law function. The power law index is -2.11 +0.07/-0.08. The event fluence (10-1000 keV) in this time interval is (6.197 +0.467/−0.406)E-05 erg/cm^2.
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. GRM is developed by the Institute of High Energy Physics (IHEP) of CAS.
The SVOM/GRM point of contact for this burst is: Xing-Hao Luo (IHEP) (luoxh@ihep.ac.cn)
GCN Circular 45485
Subject
GRB 260829A: AstroSat CZTI detection
Date
2026-09-01T11:39:37Z (24 days ago)
From
Anuraag Arya at IIT Bombay <aryaanuraag910@gmail.com>
Via
Web form
A. Goyal (IITB), A. Arya (IITB), Harsha K. H. (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 GRB 260829A which was also detected by Fermi (Fermi GBM team, GCN Circ. 45464), BALROG localization (Preis et.al., GCN Circ. 45465), GECAM-B (Hao-Xuan Guo et al., GCN Circ. 45470), and IPN triangulation (Kozyrev et.al., GCN Circ. 45476).
The source was clearly detected in the CsI anticoincidence (Veto) detector in the 100-500 keV energy range. The light curve peaks at 2026-08-29 06:08:31.7 UTC. The measured peak count rate associated with the burst is 614 (+58, -62) counts/s above the background in the combined data of all quadrants, with a total of 2357 (+429, -471) counts. The local mean background count rate was 643 (+6, -6) counts/s. We measure a T90 of 13.1 (+5.3, -6.5) s from the cumulative Veto light curve.
The source was detected in the CZT detectors in the 20-200 keV energy range. The light curve showed multiple peaks of emission with the strongest peak at 2026-08-29 06:08:30.7 UTC. The measured peak count rate associated with the burst is 213 (+34, -27) counts/s above the background in the combined data of three quadrants (out of four), with a total of 708 (+180, -194) counts. The local mean background count rate was 227 (+2, -3) counts/s. Due to poor statistics, we cannot reliably estimate the T90 from it.
CZTI data products like interactive and downloadable light curves for this GRB can be found at: https://astrosat.iucaa.in/cift/cift_products/525679702.67/S525679702.67_details.html
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 45476
Subject
IPN triangulation of GRB 260829A
Date
2026-08-31T19:15:43Z (24 days ago)
From
Anna Ridnaia at Ioffe Institute <ridnaia@mail.ioffe.ru>
Via
Web form
A.S. Kozyrev, D.V. Golovin, M.L. Litvak, I.G. Mitrofanov, and A.B. Sanin
on behalf of the HEND/Mars Odyssey team,
A. Ridnaia, D. Frederiks, A. Lysenko, D. Svinkin,
and T. Cline on behalf of the Konus-Wind team,
A. Goldstein, M. S. Briggs, C. Wilson-Hodge,
and E. Burns on behalf of the Fermi-GBM team,
and
W. Boynton, C. Fellows, K. Harshman, H. Enos, R. Starr,
and A.S. Gardner on on behalf of the GRS-Odyssey GRB team,
report:
The long-duration GRB 260829A
(Fermi-GBM detection: Fermi GBM team, GCN 45464;
Malacaria et al., GCN 45467;
BALROG localization: Preis & Greiner, GCN 45465;
GECAM-B detection: Zao et al., GCN 45470)
was detected by Fermi (GBM trigger 809676494),
Konus-Wind, GECAM-B, and Mars-Odyssey (HEND)
at about 22089 s UT (06:08:09).
We have triangulated it to the 3 sigma localization region
whose area is 5.2 sq. deg, and its maximum
dimension is 31 deg (the minimum one is 10 arcmin).
This localization may be improved.
A triangulation map and HEALPix FITS files are posted at
http://www.ioffe.ru/LEA/GRBs/GRB260829_T22110/IPN
The HEALPix triangulation map is the multi-order HEALPix in units of
probability density.
The Konus-Wind time history and spectrum will be given
in a forthcoming GCN Circular.
GCN Circular 45470
Subject
GRB 260829A: GECAM-B observation of a long burst
Date
2026-08-30T15:44:43Z (a month ago)
From
xueyuan zao <zaoxueyuan@gmail.com>
Via
Web form
Xue-Yuan Zao, Chen-Wei Wang, Shao-Lin Xiong (IHEP) report on behalf of GECAM team:
GECAM-B was triggered on-ground by GRB 260829A, at 2026-08-29T06:08:10.450 UTC, which is also detected by Fermi/GBM (Fermi GBM team, GCN #45464, GCN #45465 and GCN #45467).
According to the GECAM-B light curves in about 70-6000 keV, this burst mainly consists of a single pulse with a duration (T90) of 47.0 +/-4.0 s.
The GECAM-B light curve can be found here:
https://www.bursthub.cn/gcn/2026/gecambgrb260829A.png
The time-averaged spectrum from T0+16.0 to T0+32.0 s is best fitted by a power law function with an exponential high-energy cutoff. The power law index is -1.15 +0.18/-0.15 and the cutoff energy, parameterized as Epeak, is 466 +138/-94 keV. The event fluence (10-1000 keV) in this time interval is (2.31 +0.13/-0.16) E-05 erg/cm^2.
The localization of GRB 260829A in the 'Amati' relation diagram is shown at:
https://www.bursthub.cn/gcn/2026/gecambgrb260829A_amati.png
Gravitational wave high-energy Electromagnetic Counterpart All-sky Monitor (GECAM) mission originally consists of two micro-satellites (GECAM-A and GECAM-B) launched in Dec. 2020. As the third member of GECAM constellation, GECAM-C was launched onboard SATech-01 experimental satellite in July 2022. GECAM mission is funded by the Chinese Academy of Sciences (CAS).
GCN Circular 45467
Subject
GRB 260829A: Fermi GBM Detection
Date
2026-08-29T14:12:23Z (a month ago)
From
Christian Malacaria at INAF-OAR <cmalacaria.astro@gmail.com>
Via
Web form
C. Malacaria (INAF-OAR) reports on behalf of the Fermi Gamma-ray Burst Monitor Team:
"At 06:08:09.39 UT on 29 August 2026, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 260829A (trigger 809676494/260829256). The Final real-time localization was reported in GCN 45464.
The GBM light curve consists of a prompt emission followed by a bright peak with a duration (T90) of about 26.4 s (50-300 keV). The time-averaged spectrum from T0+18 to T0+34 s is best fit by a Band function with Epeak = 260 +/- 10 keV, alpha = -0.66 +/- 0.04, and beta = -2.17 +/- 0.08.
The event fluence (10-1000 keV) in this time interval is (1.91 +/- 0.03)E-05 erg/cm^2. The 1-sec peak photon flux measured starting from T0+22 s in the 10-1000 keV band is 19.1 +/- 0.3 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 45465
Subject
GRB 260829A: BALROG localization (Fermi Trigger 809676494 / GRB 260829256)
Date
2026-08-29T06:34:56Z (a month ago)
From
Jochen Greiner at MPE <jcgrog@mpe.mpg.de>
Via
email
T. Preis (University of Innsbruck) & J. Greiner (MPE Garching) report:
The public trigdat data of the Fermi Gamma-ray Burst Monitor (GBM) trigger
809676494 at 06:08:09 on 29 Aug. 2026 were automatically fitted for spectrum
and sky location with BALROG (Burgess et al. 2018, MNRAS 476, 1427;
Berlato et al. 2019, ApJ 873, 60).
The best-fit position is:
RA(2000.0) = 240.0 deg
Decl.(2000.0) = -30.5 deg
The 1 sigma statistical error radius is 1.5 deg.
We estimate an additional systematic error of 2 deg.
Further details are available at:
https://grb.mpe.mpg.de/grb/GRB260829256/
The Healpix map can be downloaded from:
https://grb.mpe.mpg.de/grb/GRB260829256/healpix
The location parameters are available as JSON at:
https://grb.mpe.mpg.de/grb/GRB260829256/json
GCN Circular 45464
Subject
GRB 260829A: Fermi GBM Final Real-time Localization
Date
2026-08-29T06:18:41Z (a month 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 06:08:09 UT on 29 Aug 2026, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 260829A (trigger 809676494.389126 / 260829256).
The on-ground calculated location, using the Fermi GBM trigger data, is RA = 242.3, Dec = -34.6 (J2000 degrees, equivalent to J2000 16h 09m, -34d 36'), with a statistical uncertainty of 1.0 degrees.
The angle from the Fermi LAT boresight is 47.0 degrees.
The skymap can be found here:
https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260829256/quicklook/glg_skymap_all_bn260829256.png
The HEALPix FITS file, including the estimated localization systematic, can be found here:
https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260829256/quicklook/glg_healpix_all_bn260829256.fit
The GBM light curve can be found here:
https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260829256/quicklook/glg_lc_medres34_bn260829256.gif