GRB 260616A
GCN Circular 44996
Subject
GRB 260616A: AstroSat CZTI detection
Date
2026-06-19T11:50:15Z (7 days ago)
From
Anuraag Arya at IIT Bombay <aryaanuraag910@gmail.com>
Via
Web form
S.Salunke(IUCAA), Utkarsh Pathak(IITB), A. Goyal (IITB), A. Arya (IITB), Harsha K. H. (IUCAA), G. Waratkar (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 ML pipeline (Abraham et al., 2021, MNRAS, 504, 3084) and the CIFT framework (Sharma et al., 2021, JApA, 42, 73) showed the detection of a long, bright GRB 260616A which was also detected by Fermi/GBM (Fermi GBM team, GCN Circ. 44948), Fermi/LAT (S. Lopez et al., GCN Circ. 44960), GECAM-B (Hao-Xuan Guo et al., GCN Circ. 44964), Konus-Wind (A. Ridnaia et al., GCN Circ. 44967), Insight HXMT (Chen-Wei Wang et al., GCN Circ. 44980), NuSTAR(G. Waratkar et al., 44987).
The source was clearly 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 2026-06-16 03:22:46.024. The measured peak count rate associated with the burst is 241 (+20, -9) counts/s above the background in the combined data of three quadrants (out of four), with a total of 16061 (+515, -588) counts. The local mean background count rate was 203 (+1, -2) counts/s. We measure a T90 of 113 (+5, -5) s from the cumulative CZT light curve.
The source was clearly detected in the CsI anticoincidence (Veto) detector in the 100-500 keV energy range. The light curve showed multiple peaks of emission with the strongest peak at 2026-06-16 03:22:44.598. The measured peak count rate associated with the burst is 724 (+35, -35) counts/s above the background in the combined data of all quadrants, with a total of 45925.00 (+1118, -1178) counts.
The local mean background count rate was 1290 (+2, -3) counts/s. We measure a T90 of 112 (+3, -4) s from the cumulative Veto light curve.
In the preliminary analysis, we find 2989 Compton events associated with this event.
CZTI data products like interactive and downloadable light curves for this GRB can be found at:https://astrosat.iucaa.in/cift/cift_products/ET20260616T032154/ET20260616T032154_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 44995
Subject
GRB 260616A: SVOM/GRM observation
Date
2026-06-19T11:49:27Z (7 days ago)
From
guohx@ihep.ac.cn
Via
Web form
SVOM/GRM team: Hao-Xuan Guo, Chen-Wei Wang, Zheng-Hang Yu, Chao Zheng, Shi-Jie Zheng, Yue Huang, Shao-Lin Xiong, Shuang-Nan Zhang (IHEP)
SVOM/ECLAIRs team: Ulysse Jacob (LUPM)
Report on behalf of the SVOM team:
SVOM/GRM was triggered in-flight by GRB 260616A (SVOM burst-id sb26061602) at 2026-06-16T03:21:30.000 UTC (T0), which is also detected by Fermi/GBM (Fermi/GBM team, GCN #44948, Matt Godwin et al., GCN #44971), Fermi/LAT (S. Lopez et al., GCN #44960), GECAM-B (Hao-Xuan Guo et al., GCN #44964), Konus-Wind (A. Ridnaia et al., GCN #44967), Insight-HXMT (Chen-Wei Wang et al., GCN #44980) and NuSTAR (G. Waratkar et al., GCN #44987).
With the event-by-event data downloaded through the X-band ground station, the GRM light curve shows that this burst consists of multiple pulses with a T90 of 143 +5/-4 s in the 15-5000 keV band.
The SVOM/GRM light curve can be found here:
https://www.bursthub.cn//admin/static/svgrb260616A.png
In addition, the position of this burst, as determined by Fermi/LAT (RA = 93.53, Dec = -32.07, GCN #44960), is located at about 97 degrees from the SVOM optical axis, which is outside the ECLAIRs field of view.
With this localization, the time-averaged spectrum from T0-62 to T0+130 s is best fitted by a power law function with an exponential high-energy cutoff. The power law index is -1.38 +0.05/-0.04 and the cutoff energy, parameterized as Epeak, is 573 +61/-52 keV. The event fluence (10-1000 keV) in this time interval is (2.14 +/-0.03)E-04 erg/cm^2.
The 1s peak spectrum, measured from T0+75 to T0+76 s, if fitted by a power law function with an exponential high-energy cutoff, the power law index is -1.45 +0.11/-0.07 and the cutoff energy, parameterized as Epeak, is (2.00 +1.47/-0.85)E+03 keV. The flux (10-1000 keV) in this time interval is (4.48 +0.15/-0.14)E-06 erg/cm^2/s.
The localization of GRB 260616A in the 'Amati' relation diagram is shown at:
https://www.bursthub.cn//admin/static/svgrb260616A_amati.png
The localization of GRB 260616A in the 'Yonetoku' relation diagram is shown at:
https://www.bursthub.cn//admin/static/svgrb260616A_yonetoku.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 point of contact for this burst is: Hao-Xuan Guo (IHEP)(guohx@ihep.ac.cn)
GCN Circular 44987
Subject
GRB 260616A: NuSTAR detection of prompt emission
Date
2026-06-19T03:34:34Z (7 days ago)
From
Gaurav Waratkar at Caltech <gauravwaratkar@iitb.ac.in>
Via
Web form
G. Waratkar (Caltech) and B. Grefenstette (Caltech) report on behalf of the NuSTAR Search for INteresting Gamma-ray Signals (SINGS) working group:
The NuSTAR SINGS working group reports the detection of prompt emission from the long-duration GRB 260616A in both the NuSTAR CsI anti-coincidence shields. Details of the search algorithm will be described in a future paper.
The NuSTAR SINGS algorithm, triggered at 2026-06-16T03:21:25.62 UTC, shows a detection of GRB 260616A, also detected by Fermi-GBM (Fermi GBM Team, GCN 44948), GECAM-B (Guo et al., GCN 44964), Konus-Wind (Ridnaia et al., GCN 44967), and Insight-HXMT (Wang et al., GCN 44980).
The NuSTAR CsI shield data are recorded at 1 Hz. We detect a burst lasting for about 100-s. The peak count rate is ~1500-cps with a baseline rate of ~1000-cps during this time period. We do not see any evidence in the signal above 100 keV in the CZT detectors.
The Fermi-LAT localization (Lopez et al., GCN 44960) at RA = 93.53, Dec = -32.07 implies an offset from the NuSTAR boresight of 133-deg (i.e. from the backside) and an offset from the geocenter of 86-deg.
Lightcurves and analysis for this GRB can be found here:
https://nustarsoc.caltech.edu/NuSTAR_Public/grbs/reports/2026/260616A
Information on NuSTAR SINGS can be found here:
https://nustarsoc.caltech.edu/NuSTAR_Public/grbs/
NuSTAR is a NASA Small Explorer mission led by Caltech and managed by JPL for NASA's Science Mission Directorate in Washington.
GCN Circular 44980
Subject
GRB 260616A: Insight-HXMT detection
Date
2026-06-18T18:19:26Z (8 days ago)
From
Chenwei Wang at IHEP <cwwang@ihep.ac.cn>
Via
Web form
Chen-Wei Wang, Hao-Xuan Guo, Zheng-Hang Yu, Shao-Lin Xiong, Cheng-Kui Li, and Chao Zheng report on behalf of the Insight-HXMT team:
At 2026-06-16T03:22:29.650 (T0), Insight-HXMT/HE detected GRB 260616A, which is also detected by Fermi/GBM (Fermi GBM team, GCN#44948), Fermi/LAT (S. Lopez et al., GCN #44960), GECAM-B (Hao-Xuan Guo et al., GCN #44964), Konus-Wind (A. Ridnaia et al., GCN#44976) and SVOM/GRM.
The Insight-HXMT/HE light curve mainly consists of a set of dense spikes with a T90 of 76.0 +4.5/-4.0 s. The 1s peak rate, measured from T0+14.8 s, is 5435 cnts/sec. The total counts from this burst is 178317 counts.
The HXMT/HE light curve can be found here:
https://www.bursthub.cn//admin/static/hxmtgrb260616A.png
All measurements above are made with the CsI detectors operating in the regular mode with the energy range of about 60-900 keV (deposited energy). Only gamma-rays with energy greater than about 200 keV can penetrate the spacecraft and leave signals in the CsI detectors installed inside of the telescope.
Insight-HXMT is the first Chinese space X-ray telescope, which was funded jointly by the China National Space Administration (CNSA) and the Chinese Academy of Sciences (CAS). More information about it could be found at: http://www.hxmt.org.
GCN Circular 44971
Subject
GRB 260616A: Fermi GBM Observation
Date
2026-06-18T02:49:59Z (8 days ago)
From
Matt Godwin <msg0028@uah.edu>
Via
Web form
Matt Godwin (UAH) and C. Meegan (UAH) report on behalf of
the Fermi Gamma-ray Burst Monitor Team:
"At 03:21:54.33 UT on 16 June 2026, the Fermi Gamma-ray Burst Monitor (GBM)
triggered and located GRB 260616A (trigger 803272919/260616140),
which was also detected by Fermi-LAT ( et al. 2026, GCN 44960).
The Fermi GBM on-ground location is consistent with the Fermi-LAT position.
The angle from the Fermi LAT boresight is 111 degrees.
The GBM light curve consists of one long burst with a duration (T90)
of about 69 s (50-300 keV). The time-averaged spectrum
from T0+0.3 to T0+74.1 s is best fit by
a Band function with Epeak = 246 +/- 1 keV,
alpha = -0.63 +/- 0.01, and beta = -2.00 +/- 0.01.
The event fluence (10-1000 keV) in this time interval is
(1.22 +/- 0.02)E-04 erg/cm^2. The 1-sec peak photon flux measured
starting from T0+50 s in the 10-1000 keV band is 16.9 +/- 0.4 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 44967
Subject
Konus-Wind detection of GRB 260616A
Date
2026-06-17T15:37:03Z (9 days ago)
From
Anna Ridnaia at Ioffe Institute <ridnaia@mail.ioffe.ru>
Via
Web form
A. Ridnaia, D. Frederiks, A. Lysenko, D. Svinkin,
A. Tsvetkova, M. Ulanov, and T. Cline,
on behalf of the Konus-Wind team, report:
The long-duration GRB 260616A
(Fermi-GBM detection: Fermi GBM team, GCN 44948;
BALROG localization: Preis & Greiner, GCN 44949;
Fermi-LAT detection: Lopez et al., GCN 44960;
GECAM-B detection: Guo et al., GCN 44964)
triggered Konus-Wind at T0=12085.625 s UT (03:21:25.625).
The burst light curve shows a bright, multipeaked pulse,
which starts at ~T0-63 s and has a total duration of ~292 s.
A weaker possible precursor is clearly visible in the KW waiting mode
data around ~T0-422 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/GRB260616_T12085/
As observed by Konus-Wind, the burst
had the total fluence of 2.77(-0.09,+0.09)x10^-4 erg/cm2,
and the 64-ms peak flux, measured from T0+82.880 s,
of 7.35(-1.24,+1.23)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+105.984 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 = -0.76(-0.03,+0.04),
the high energy photon index beta = -2.28(-0.06,+0.05),
the peak energy Ep = 295(-10,+11) keV
(chi2 = 118/97 dof).
The spectrum near the maximum count rate
(measured from T0+81.408 to T0+89.600 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 = -0.97(-0.08,+0.09),
the high energy photon index beta = -2.23(-0.25,+0.15),
the peak energy Ep = 379(-49,+57) keV
(chi2 = 87/87 dof).
All the quoted errors are at the 68% confidence level.
All the quoted values are preliminary.
GCN Circular 44964
Subject
GRB 260616A: GECAM-B observation
Date
2026-06-17T14:27:22Z (9 days ago)
From
guohx@ihep.ac.cn
Via
Web form
Hao-Xuan Guo, Zheng-Hang Yu, Chen-Wei Wang, Chao Zheng, Shao-Lin Xiong (IHEP) report on behalf of GECAM team:
GECAM-B was triggered in-flight by GRB 260616A, at 2026-06-16T03:21:40.040 UTC (denoted as T0), which is also detected by Fermi/GBM (Fermi/GBM team, GCN #44948), BALROG (T. Preis et al., GCN #44949), Fermi/LAT (S. Lopez et al., GCN #44960).
According to the GECAM-B light curves in about 70-6000 keV, this burst mainly consists of multiple pulses with a duration (T90) of 117 +/-3 s.
The GECAM-B light curve can be found here:
https://www.bursthub.cn//admin/static/gecambgrb260616A.png
Using the localization reported by Fermi/LAT (R.A. = 93.53 deg, Dec = -32.07 deg, Err = 0.54 deg, GCN #44960) , the time-averaged spectrum from T0-77.5 s to T0+133.5 s is best fitted by a power law function with an exponential high-energy cutoff. The power law index is -1.35 +0.08/-0.07 and the cutoff energy, parameterized as Epeak, is 679 +141/-121 keV. The event fluence (10-1000 keV) in this time interval is (2.02 +0.05/-0.06)E-04 erg/cm^2.
The 'Amati' relation diagram of GRB 260616A is shown at:
https://www.bursthub.cn//admin/static/gecambgrb260616A_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 44960
Subject
GRB 260616A: Fermi-LAT detection
Date
2026-06-16T23:28:45Z (10 days ago)
From
N. Di Lalla at Stanford University <niccolo.dilalla@stanford.edu>
Via
email
S. Lopez (CNRS / IN2P3), N. Di Lalla (Stanford University), R. Gupta (NASA/GSFC), F. Longo (University and INFN, Trieste), D. Depalo (Politecnico & INFN Bari), N. Omodei (Stanford University), and J. Valverde (Marquette University) report on behalf of the Fermi-LAT collaboration:
At 03:21:54 UT on 16 June 2026, Fermi-LAT detected high-energy emission from GRB 260616A, which was also detected by Fermi-GBM (trigger 803272919/ 260616140, GCN #44948).
The best LAT on-ground location is found to be
RA, Dec = 93.53, -32.07 (J2000)
with an error radius of 0.54 deg (90 % containment, statistical error only).
This was 111 deg from the LAT boresight at the time of the trigger.
The data from the Fermi-LAT show a significant increase in the event rate that is spatially and temporally correlated with the trigger with high significance. The photon flux above 100 MeV in the time interval 500 - 3000 s after the GBM trigger is (1.8 ± 0.6)E-6 ph/cm2/s. The estimated photon index above 100 MeV is -2.4 ± 0.4. The highest energy photon has an energy of 724 MeV and occurs at 1690 s after trigger time.
The Fermi-LAT point of contact for this burst is Samantha López (lpsamy18@gmail.com).
The Fermi-LAT is a pair conversion telescope designed to cover the energy band from 20 MeV to greater than 300 GeV. It is the product of an international collaboration between NASA and DOE in the U.S. and many scientific institutions across France, Italy, Japan and Sweden.
GCN Circular 44949
Subject
GRB 260616A: BALROG localization (Fermi Trigger 803272919 / GRB 260616140)
Date
2026-06-16T03:56:27Z (10 days 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
803272919 at 03:21:54 on 16 June 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) = 94.4 deg
Decl.(2000.0) = -32.1 deg
The 1 sigma statistical error radius is 1.7 deg.
We estimate an additional systematic error of 1 deg.
Further details are available at:
https://grb.mpe.mpg.de/grb/GRB260616140/
The Healpix map can be downloaded from:
https://grb.mpe.mpg.de/grb/GRB260616140/healpix
The location parameters are available as JSON at:
https://grb.mpe.mpg.de/grb/GRB260616140/json
GCN Circular 44948
Subject
GRB 260616A: Fermi GBM Final Real-time Localization
Date
2026-06-16T03:34:02Z (10 days 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 03:21:54 UT on 16 Jun 2026, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 260616A (trigger 803272919.330008 / 260616140).
The on-ground calculated location, using the Fermi GBM trigger data, is RA = 95.0, Dec = -31.9 (J2000 degrees, equivalent to J2000 06h 19m, -31d 53'), with a statistical uncertainty of 1.4 degrees.
The angle from the Fermi LAT boresight is 111.0 degrees.
The skymap can be found here:
https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260616140/quicklook/glg_skymap_all_bn260616140.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/bn260616140/quicklook/glg_healpix_all_bn260616140.fit
The GBM light curve can be found here:
https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260616140/quicklook/glg_lc_medres34_bn260616140.gif