GRB 260316B — All Circulars

GCN Circular 44166 is a duplicate of GCN Circular 44165.

GCN Circular 44166 is a duplicate of GCN Circular 44165.

V. Panteleeva, D. Frederiks, A. Lysenko, A. Ridnaia, D. Svinkin,
A. Tsvetkova,  M. Ulanov, and T. Cline,
on behalf of the Konus-Wind team, report:

The long-duration GRB 260316B
(Fermi-GBM detection: The Fermi GBM team, GCN 44031;
AstroSat CZTI detection: Harsha et al., GCN 44035,
SVOM/GRM detection: Wang et al., GCN 44039,
GECAM-B detection: Wang et al., GCN 44040,
CALET-GBM detection: Tamura et al., GCN 44100,
IPN triangulation: Kozyrev et al., GCN 44111)
triggered Konus-Wind at T0=61972.457 s UT (17:12:52.457).

The burst light curve shows a single pulse
which starts at ~T0-0.9 s and has a total duration of ~2.5 s.
The emission is seen up to ~5 MeV.

The Konus-Wind light curve of this GRB is available at
http://www.ioffe.ru/LEA/GRBs/GRB260316_T61972/

As observed by Konus-Wind, the burst
had the total fluence of 2.66(-0.45,+0.56)x10^-6 erg/cm2,
and the 64-ms peak flux, measured from T0+0.230 s,
of 2.87(-0.74,+0.85)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+8.448 s)
is best fit in the 20 keV - 10 MeV range
by the GRB (Band) model with the following parameters:
the low-energy photon index alpha = -0.24(-0.65,+0.76),
the high energy photon index beta = -2.64(-7.36,+0.34),
the peak energy Ep = 123(-22,+58) keV
(chi2 = 64/77 dof).

All the quoted errors are at the 68% confidence level.
All the quoted values are preliminary.

A.S. Kozyrev, D.V. Golovin, M.L. Litvak, I.G. Mitrofanov, and A.B. Sanin
on behalf of the HEND/Mars Odyssey team,

D. Svinkin, D. Frederiks, A. Lysenko, A. Ridnaia,
and T. Cline on behalf of the Konus-Wind team,

A. Goyal, A. Arya, M. Tembhurnikar, G. Waratkar, V. Bhalerao, 
D. Bhattacharya, and S. Vadawale, on behalf of the Astrosat-CZTI 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 260316B
(Ferm-GBM detection: The Fermi GBM team, GCN 44031;
AstroSat-CZTI detection: Harsha et al., GCN 44035;
SVOM-GRM detection: Zhang et al., GCN 44039;
GECAM-B detection: Zhang et al., GCN 44040;
CALET-GBM detection: Tamura et al., GCN 44100)
was detected by Fermi (GBM trigger 795373977),
Konus-Wind, Astrosat (CZTI), SVOM (GRM), GECAM-B, CALET (GBM),
and Mars-Odyssey (HEND) at about 61973 s UT (17:12:53).

We have triangulated it to a preliminary, 3 sigma error box
whose coordinates are:
 ---------------------------------------------
  RA(2000), deg                 Dec(2000), deg
 ---------------------------------------------
 Center:
  345.026 (23h 00m 06s) -80.127 (-80d 07' 37")
 Corners:
  292.551 (19h 30m 12s) -74.130 (-74d 07' 48")
  293.015 (19h 32m 04s) -74.416 (-74d 24' 57")
   32.817 (02h 11m 16s) -74.223 (-74d 13' 24")
   32.021 (02h 08m 05s) -74.386 (-74d 23' 10")
 ---------------------------------------------
The error box area is 1.7 sq. deg, and its maximum
dimension is 24.2 deg (the minimum one is 4.3 arcmin).
The Sun distance was 75 deg.

This localization may be improved.

A triangulation map and HEALPix FITS file are posted at
http://www.ioffe.ru/LEA/GRBs/GRB260316_T61972/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. 

T. Tamura (Kanagawa U), A. Yoshida, T. Sakamoto, S. Sugita, Y. Kawakubo (AGU),
K. Yamaoka (Nagoya U), S. Nakahira (JAXA), Y. Asaoka (ICRR), S. Torii,
Y. Akaike, K. Kobayashi (Waseda U), Y. Shimizu (Kanagawa U),
N. Cannady (GSFC/UMBC), M. L. Cherry (LSU), S. Ricciarini (U of Florence),
P. S. Marrocchesi (U of Siena),
and the CALET collaboration:

The GRB 260316B (Fermi GBM Final Real-time Localization: Fermi GBM 
team, GCN Circ. 44031; AstroSat CZTI detection: Harsha et al., GCN Circ. 
44035; SVOM/GRM observation: Wang et al., GCN Circ. 44039; GECAM-B 
observation: Wang et al., GCN Circ. 44040) triggered the CALET Gamma-ray
Burst Monitor (CGBM) at 17:12:52.15 UTC on 16 March 2026
(https://cgbm.calet.jp/cgbm_trigger/flight/1457716347/index.html).
The burst signal was seen by all CGBM detectors.  

The burst light curve shows a single pulse that starts
at T+0.38 sec, peaks at T+1.25 sec, and ends at T+2.37 sec.
The T90 and T50 durations measured by the SGM data are 1.75 +/- 0.18 sec
and 0.75 +/- 0.13 sec (40-1000 keV), respectively.

The ground-processed light curve is available at

https://cgbm.calet.jp/cgbm_trigger/ground/1457716347/

The CALET data used in this analysis are provided by
the Waseda CALET Operation Center located at Waseda University.

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

GECAM-B was triggered in-flight by GRB 260316B at 2026-03-16T17:12:53.100 UTC (denoted as T0), which is also detected by Fermi/GBM (Fermi GBM team, GCN #44031), AstroSat CZTI (Harsha K. H. et. al., GCN
#44035) and SVOM/GRM (Yue Wang et. al., GCN #44039).

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 2.4 +0.4/-0.4 s.

The GECAM-B light curve can be found here:
https://www.bursthub.cn//admin/static/gecambgrb260316B.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).

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

SVOM/ECLAIRs team: Sebastien Guillot, Hui Yang (IRAP)

Report on behalf of the SVOM team:

SVOM/GRM was triggered in-flight by GRB 260316B at 2026-03-16T17:12:54.000 (T0), which is also detected by Fermi/GBM (Fermi GBM team, GCN #44031) and AstroSat CZTI (Harsha K. H. et. al., GCN #44035). 

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 1.6 +1.6/-0.8 s in the 15-5000 keV band.

The SVOM/GRM light curve can be found here:
https://www.bursthub.cn//admin/static/svgrb260316B.png

In addition, the position of this burst, as determined by Fermi/GBM (RA = 305.5, Dec = -79.3, Error = 3.2, GCN #44031), is located at about 113 degrees from the SVOM optical axis, which is outside the ECLAIRs field of view. 

With this localization, the time-averaged spectrum from T0-1.2 to T0+0.6 s is best fitted by a power law function. The power law index is -2.23 +0.17/-0.16. The event fluence (10-1000 keV) in this time interval is (3.21 +0.50/-0.51)E-06 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: Yue Wang (IHEP) (yuewang@ihep.ac.cn)

Harsha K. H. (IUCAA), M. Tembhurnikar (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 GRB 260316B which was also detected by Fermi GBM (Fermi GBM Team, GCN Circ. 44031), Calet (Trigger Num. 1457716347), and SVOM (Trigger Num. sb26031602).

The source was clearly detected in the CZT detectors in the 20-200 keV energy range. The light curve peaks at 2026-03-16 17:12:53.75 UTC. The measured peak count rate associated with the burst is 524 (+158, -53) counts/s above the background in the combined data of all quadrants, with a total of 818 (+139, -151) counts. The local mean background count rate was 306 (+5, -8) counts/s. Using cumulative rates, we measure a T90 of 4.9 (+1.7, -2.5) s. 

The source was also faintly detected in the CsI anticoincidence (Veto) detector in the 100-500 keV energy range.

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 LONG GRB

At 17:12:52 UT on 16 Mar 2026, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 260316B (trigger 795373977.681026 / 260316717).

The on-ground calculated location, using the Fermi GBM trigger data, is RA = 305.5, Dec = -79.3 (J2000 degrees, equivalent to J2000 20h 22m, -79d 17'), with a statistical uncertainty of 3.2 degrees.

The angle from the Fermi LAT boresight is 81.0 degrees.

The skymap can be found here:
https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260316717/quicklook/glg_skymap_all_bn260316717.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/bn260316717/quicklook/glg_healpix_all_bn260316717.fit

The GBM light curve can be found here:
https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260316717/quicklook/glg_lc_medres34_bn260316717.gif