GRB 260629A

SVOM/GRM team: Yue Wang, Chen-Wei Wang, Shi-Jie Zheng, Yue Huang, Shao-Lin Xiong, Shuang-Nan Zhang (IHEP)

SVOM/ECLAIRs team: Olivier Godet (IRAP)

Report on behalf of the SVOM team:

SVOM/GRM was triggered on-ground by GRB 260629A at 2026-06-29T15:06:59.000 (T0), which is also detected by Fermi/GBM (Fermi GBM team, GCN #45056
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 ), AstroSat CZTI (Harsha et. al., GCN #45074
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 ) and GECAM-A (Yue Wang et al., GCN #45076
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 ).

With the event-by-event data downloaded through the X-band ground station, the GRM light curve shows that this burst consists of a single pulse with a T90 of 1.20 +1.55/-0.65 s in the 15-5000 keV band.

The SVOM/GRM light curve can be found here:
https://www.bursthub.cn//admin/static/svgrb260629A.png

In addition, the position of this burst, as determined by Fermi/GBM (RA = 146.1, Dec = 70.6, Error = 10.5, GCN #45056
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 ), is located at about 138 degrees from the SVOM optical axis, which is outside the ECLAIRs field of view.

With this localization, the time-averaged spectrum from T0-1.0 to T0+2.0 s is best fitted by a power law function. The power law index is -1.89 +0.24/-0.39. The event fluence (10-1000 keV) in this time interval is (2.35 +0.42/-0.40)E-06 erg/cm^2.

The localization of GRB 260629A in the 'Amati' relation diagram is shown at: https://www.bursthub.cn//admin/static/svgrb260629A_amati.png

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: Yue Wang (IHEP) (yuewang@ihep.ac.cn)

Yue Wang, Chen-Wei Wang, Shao-Lin Xiong (IHEP) report on behalf of GECAM team: 

GECAM-A was triggered on-ground by GRB 260629A at 2026-06-29T15:06:59.000 UTC (denoted as T0), which is also detected by Fermi/GBM (Fermi GBM team, GCN #45056
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 ) and AstroSat CZTI (Harsha et. al., GCN #45074
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 ).

According to the GECAM-A light curves in about 70-6000 keV, this burst mainly consists of a single pulse with a duration (T90) of 3.20 +1.13/-1.10 s.

The GECAM-A light curve can be found here:
https://www.bursthub.cn//admin/static/gecamagrb260629A.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).

Harsha K. H. (IUCAA), S. Salunke (IUCAA), A. Arya (IITB), A. Goyal (IITB), 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 Short GRB 260629A which was also detected by Fermi (GBM Team, GCN Circ. 45056
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 ).

The source was clearly detected in the CZT detectors in the 20-200 keV energy range. The light curve peaks at 2026-06-29 15:06:59 UTC. The measured peak count rate associated with the burst is 108 (+70, -15) counts/s above the background in the combined data of three quadrants (out of four), with a total of 96 (+49, -50) counts. The local mean background count rate was 205 (+4, -6) counts/s. We measure a T90 of 0.89 (+0.45, -0.48) s from the cumulative CZT light curve.

The source was also clearly detected in the CsI anticoincidence (Veto) detector in the 100-500 keV energy range. The light curve peaks at 2026-06-29 15:06:59 UTC. The measured peak count rate associated with the burst is 378 (+65, -73) counts/s above the background in the combined data of all quadrants, with a total of 382 (+169, -188) counts. The local mean background count rate was 1283 (+7, -8) counts/s.  Due to the intrinsic 1 s binning of veto data, we cannot reliably estimate a T90 for our detection.

CZTI data products like interactive and downloadable light curves for this GRB can be found at: http://astrosat.iucaa.in/cift/cift_products/520441618.77/S520441618.77_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

The Fermi GBM team reports the detection of a likely SHORT GRB

At 15:06:58 UT on 29 Jun 2026, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 260629A (trigger 804438423.955606 / 260629630).

The on-ground calculated location, using the Fermi GBM trigger data, is RA = 146.1, Dec = 70.6 (J2000 degrees, equivalent to J2000 09h 44m, 70d 35'), with a statistical uncertainty of 10.5 degrees.

The angle from the Fermi LAT boresight is 49.0 degrees.

The skymap can be found here:
https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260629630/quicklook/glg_skymap_all_bn260629630.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/bn260629630/quicklook/glg_healpix_all_bn260629630.fit

The GBM light curve can be found here:
https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260629630/quicklook/glg_lc_medres34_bn260629630.gif