GRB 260616B, EP260616a
GCN Circular 45011
Subject
GRB 260616B/EP260616a: SVOM/GRM detection of a burst
Date
2026-06-20T04:00:46Z (19 hours ago)
Edited On
2026-06-20T14:22:57Z (8 hours ago)
From
yzh807926@163.com
Edited By
Judith Racusin at NASA/GSFC <judith.racusin@nasa.gov> on behalf of yzh807926@163.com
Via
Web form
SVOM/GRM team: Zheng-Hang Yu, Chen-Wei Wang, Yue Huang, Shi-Jie Zheng, Shao-Lin Xiong, Shuang-Nan Zhang (IHEP)
SVOM/ECLAIRs team: Ulysse Jacob (LUPM), Olivier GODET, Jean-Luc Atteia (IRAP)
Report on behalf of the SVOM team:
SVOM/GRM was triggered in-flight by a burst GRB 260616B/EP260616a (SVOM trigger reference: sb26061603) at 2026-06-16T07:05:16.900 UTC (T0), which is also detected by Fermi/GBM (C. Malacaria et al., GCN #44953).
With the event-by-event data downloaded through the X-band ground station, the GRM light curve shows that this burst consists of a main episode with two peaks a T90 of 13.30 +0.8/-0.4 s in the 15-5000 keV band.
The SVOM/GRM light curve can be found here:
https://www.bursthub.cn//admin/static/svgrb260616B.png
In addition, the position of this burst, as determined by EP/WXT (RA= 256.059 deg, DEC= -32.305 deg, ERR=2.2 arcmin, GCN#44956), is located at about 67 degrees from the SVOM optical axis, which is outside the ECLAIRs field of view, and ECLAIRs was totally blocked by the Earth. Nevertheless, ECLAIRs detected this burst clearly over the 4-120 keV via atmospheric reflection.
With this localization, the time-averaged spectrum from T0-2 to T0+14 s is best fitted by a power law function with an exponential high-energy cutoff. The power law index is -1.11 +/-0.04 and the cutoff energy, parameterized as Epeak, is 622 +80/-66 keV. The event fluence (10-1000 keV) in this time interval is (2.29 +/-0.06)E-05 erg/cm^2.
The 1s peak spectrum, measured from T0+9.8 to T0+10.8 s, if fitted by a power law function with an exponential high-energy cutoff, the power law index is -0.90 +0.05/-0.06 and the cutoff energy, parameterized as Epeak, is 472 +52/-44 keV. The flux (10-1000 keV) in this time interval is (4.85 +/-0.17)E-06 erg/cm^2/s.
The localization of GRB 260616B in the 'Amati' relation diagram is shown at: https://www.bursthub.cn//admin/static/svgrb260616B_amati.png
The localization of GRB 260616B in the 'Yonetoku' relation diagram is shown at:
https://www.bursthub.cn//admin/static/svgrb260616B_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: Zheng-Hang Yu(IHEP)(zhyu@ihep.ac.cn)
GCN Circular 44997
Subject
GRB 260616B: AstroSat CZTI detection
Date
2026-06-19T12:22:02Z (a day ago)
From
Anuraag Arya at IIT Bombay <aryaanuraag910@gmail.com>
Via
Web form
A. Arya (IITB), A. Goyal (IITB), Harsha K. H. (IUCAA), S.Salunke(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 CIFT framework (Sharma et al., 2021, JApA, 42, 73) showed the detection of a long GRB 260616B which was also detected by Fermi/GBM (Fermi GBM team, GCN Circ. 44953), EP-WXT (D. Y. Li et. al., GCN Circ. 44956), CALET (Y. Asaoka et. al., GCN Circ. 44966), Konus-Wind (A. Ridnaia et. al., GCN Circ. 44968).
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 07:05:27.69. The measured peak count rate associated with the burst is 543 (+46, -48) counts/s above the background in the combined data of all quadrants, with a total of 2787 (+162, -177) counts. The local mean background count rate was 277 (+2, -3) counts/s. We measure a T90 of 13 (+2, -1) 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 07:05:27.10. The measured peak count rate associated with the burst is 1249 (+80, -86) counts/s above the background in the combined data of all quadrants, with a total of 5848 (+333, -346) counts. The local mean background count rate was 1225 (+5, -6) counts/s. We measure a T90 of 13 (+3, -1) s from the cumulative Veto light curve.
CZTI data products like interactive and downloadable light curves for this GRB can be found at:
https://astrosat.iucaa.in/cift/cift_products/ET20260616T070516/ET20260616T070516_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 44976
Subject
EP260616a/GRB 260616B: EP-FXT follow-up observation
Date
2026-06-18T10:37:23Z (2 days ago)
From
EP Team at NAOC/CAS <ep_ta@bao.ac.cn>
Via
Web form
D. Y. Li, T. Y. Liu (NAO, CAS), J. H. WU(GZHU), Z. X. Ling (NAO, CAS) on behalf of the Einstein Probe team
EP-FXT performed a follow-up observation of EP260616a/GRB 260616B (Li et al., GCN 44956; Preis & Greiner, GCN 44951; Malacaria et al., GCN 44953; Asaoka et al., GCN 44966) about 25.5 hours after the WXT detection, with an exposure time of 6.2 ks. An uncatalogued source was detected within the WXT error circle at R.A. = 256.0839, DEC = -32.3007 (J2000) with an uncertainty of 10 arcsec (radius, 90% C.L. statistical and systematic). The FXT spectrum can be fitted with an absorbed powerlaw with a hydrogen column density fixed at the Galactic value of 3.4 x 10^21 cm^-2 and a photon index of 1.62 (+0.27, -0.26). The derived unabsorbed 0.5-10 keV flux is approximately 8.7 (+2.2, -1.7) x 10^-13 erg/s/cm^2. The uncertainties are at the 90% confidence level for the above parameters.
No optical counterpart have been detected (Mandarakas et al., GCN 44965). Further EP-FXT follow-up observations will be arranged.
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 Circular 44968
Subject
Konus-Wind detection of GRB 260616B/EP260616a
Date
2026-06-17T15:37:56Z (3 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 260616B
(BALROG localization: Preis & Greiner, GCN 44951;
Fermi-GBM detection: Malacaria et al., GCN 44953;
EP-WXT detection: Li et al., GCN 44956;
CALET-GBM detection: Asaoka et al., GCN 44966)
triggered Konus-Wind at T0=25522.793 s UT (07:05:22.793).
The burst light curve shows two multi-peaked emission pulses.
The total duration of the burst is ~13 s.
The emission is seen up to ~2 MeV.
The Konus-Wind light curve of this GRB is available at
http://www.ioffe.ru/LEA/GRBs/GRB260616_T25522/
As observed by Konus-Wind, the burst
had the total fluence of 2.52(-0.29,+0.30)x10^-5 erg/cm2,
and the 64-ms peak flux, measured from T0+9.760 s,
of 8.62(-1.09,+1.12)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+16.832 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 = -0.78(-0.18,+0.23),
the high energy photon index beta = -2.25(-0.28,+0.16),
the peak energy Ep = 279(-49,+62) keV
(chi2 = 101/97 dof).
The spectrum near the maximum count rate
(measured from T0+8.640 to T0+16.832 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 = -1.05(-0.10,+0.11)
and Ep = 382(-41,+52) keV (chi2 = 87/85 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 = 87/84 dof).
All the quoted errors are at the 68% confidence level.
All the quoted values are preliminary.
GCN Circular 44966
Subject
GRB 260616B: CALET Gamma-Ray Burst Monitor detection
Date
2026-06-17T15:25:21Z (3 days ago)
From
Yuta Kawakubo at Aoyama Gakuin University <kawakubo@phys.aoyama.ac.jp>
Via
Web form
Y. Asaoka (ICRR), A. Yoshida, T. Sakamoto, S. Sugita, Y. Kawakubo (AGU),
K. Yamaoka (Nagoya U), S. Nakahira (JAXA), S. Torii, Y. Akaike,
K. Kobayashi (Waseda U), Y. Shimizu, T. Tamura (Kanagawa U),
N. Cannady (GSFC), M. L. Cherry (LSU), S. Ricciarini (U of Florence),
P. S. Marrocchesi (U of Siena),
and the CALET collaboration:
The CALET Gamma-ray Burst Monitor (CGBM) detected GRB 260616B
at 07:05:24.65 UTC on 16 June 2026 (trigger #1465628601;
https://cgbm.calet.jp/cgbm_trigger/flight/1465628601/index.html).
A CGBM Notice was distributed in near real time.
This event was also reported by Fermi GBM (Preis et al., GCN #44951;
Malacaria et al., GCN #44953).
The burst signal was seen by HXM2 and SGM. The burst light curve shows a double-peaked structure starting
at T-7.7 s, peaking at T+2.6 s, and ending at T+4.1 s.
The T90 and T50 durations measured with the SGM data are 11.2 +/- 0.3 s
and 8.1 +/- 0.2 s in the 40-1000 keV band, respectively.
Einstein Probe/WXT detected an X-ray transient, EP 260616a
(Li et al., GCN #44956), about 9 s before the CGBM trigger.
The position of EP 260616a was marginally above the Earth horizon
as seen from CALET/ISS at the trigger time, at an incident angle
of 110 degrees.
The ground-processed light curve is available at:
https://cgbm.calet.jp/cgbm_trigger/ground/1465628601/
The CALET data used in this analysis were provided by
the Waseda CALET Operation Center located at Waseda University.
GCN Circular 44965
Subject
EP260616a/GRB260616B: COLIBRÍ optical upper limit
Date
2026-06-17T14:44:26Z (3 days ago)
From
nikos.mandarakas@lam.fr
Via
Web form
Nikos Mandarakas (LAM), Diego López-Cámara (UNAM), Stéphane Basa (UAR Pytheas), William H. Lee (UNAM), Edilberto Aguilar-Ruiz (UNAM), Jean-Luc Atteia (IRAP), Camila Angulo (UNAM), Dalya Akl (NYUAD), Sarah Antier (IJCLAB), Rosa L. Becerra (UNAM), Nathaniel R. Butler (ASU), Damien Dornic (CPPM), Jean-Grégoire Ducoin (CPPM), Francis Fortin (IRAP), Leonardo García García (UNAM), Ramandeep Gill (UNAM), Noémie Globus (UNAM), Marion Guelfand (CPPM), Asuka Kuwata (UNAM), Massimiliano Lincetto (CPPM), Francesco Magnani (CPPM), Enrique Moreno Méndez (UNAM), Margarita Pereyra (UNAM), Fredd Sánchez Álvarez (UNAM), Benjamin Schneider (LAM), Antonio de Ugarte Postigo (LAM), and Alan M. Watson (UNAM) report:
We imaged the field of the EP 260616a (Li et al., GCN Circ. 44956), which is consistent in time and location with GRB 260616B (Malacaria et al., GCN Circ. 44953), using the DDRAGO two-channel wide-field imager on the COLIBRÍ telescope. We observed from 2026-06-17 05:56:39 to 07:16:28 UTC (from 22.86 to 24.20 hours after the trigger) and obtained 48 minutes of simultaneous exposure in the r and z filters.
The data were reduced, coadded and analysed with the ASU COLIBRÍ pipeline. The photometry was calibrated using nearby stars from the PanSTARRS DR1 catalog, is in the AB system, and is not corrected for Galactic extinction.
In the stacked image, we do not detect any new source at the WXT source position (Li et al., GCN Circ. 44956) down to the following 5-sigma limit:
r > 22.76 mag
z > 22.20 mag
We thank the staff of the Observatorio Astronómico Nacional at Sierra de San Pedro Mártir, as well as the technical and engineering teams at CEA, CPPM, IRAP, LAM, OHP, OSU Pytheas, and UNAM.
COLIBRÍ is an astronomical observatory developed and operated jointly by France (AMU, CNES and CNRS) and Mexico (UNAM and SECIHTI). It is located at the Observatorio Astronómico Nacional on the Sierra de San Pedro Mártir, Baja California, Mexico.
GCN Circular 44956
Subject
EP260616a: EP-WXT detection of a fast X-ray transient
Date
2026-06-16T16:27:09Z (4 days ago)
From
EP Team at NAOC/CAS <ep_ta@bao.ac.cn>
Via
Web form
D. Y. Li (NAO, CAS), J. H. Wu (GZHU), T. Y. Liu, Z. X. Ling (NAO, CAS) on behalf of the Einstein Probe team:
We report on the detection of a fast X-ray transient, designated EP260616a, by the Wide-field X-ray Telescope (WXT) on board the Einstein Probe (EP) mission. The transient event started at 2026-06-16T07:05:16 (UTC). The position of the source is R.A. = 256.059 deg, DEC = -32.305 deg (J2000) with an uncertainty of 2.2 arcmin in radius (90% C.L. statistical and systematic). No onboard alert or automated X-ray follow-up observation was triggered at this position due to the low Galactic latitude. The start time and the position of the transient is consistent with that of GRB 260616B detected by Fermi/GBM (GCN 44953).
The average 0.5-4 keV spectrum can be fitted by an absorbed power law with a photon index of 1.8 (+0.3/-0.3). The column density is fixed at the Galactic value of 3.4 x 10^21 cm^-2. The derived average unabsorbed 0.5-4 keV flux is 4.1 (+/-0.5) x 10^-10 erg/s/cm^2. The peak flux is around 3.4 x 10^-9 erg/s/cm^2. The uncertainties are at the 90% confidence level for the above parameters.
Follow-up observations by EP-FXT will be arranged.
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 Circular 44953
Subject
GRB 260616B: Fermi GBM Detection
Date
2026-06-16T14:20:47Z (4 days 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 07:05:16.39 UT on 16 June 2026, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 260616B (trigger 803286321/260616295).
The on-ground calculated location, using the Fermi GBM trigger data, is RA = 257.49, Dec = -32.62 (J2000 degrees, equivalent to J2000 17h 9m, -32d 37'), with a statistical uncertainty of 1.70 degrees. (radius, 1-sigma containment, statistical only; there is additionally a systematic error which we have characterized as a core-plus-tail model, with 90% of GRBs having a 3.7 deg error and a small tail suffering a larger than 10 deg systematic error [Connaughton et al. 2015, ApJS, 216, 32]).
The angle from the Fermi LAT boresight is 76 degrees.
The GBM light curve consists of two main pulses with a duration (T90) of about 13.8 s (50-300 keV). The time-averaged spectrum from T0+0.002 to T0+14.464 s is best fit by a Band function with Epeak = 240 +/- 10 keV, alpha = -0.63 +/- 0.04, and beta = -2.09 +/- 0.06.
The event fluence (10-1000 keV) in this time interval is (2.03 +/- 0.03)E-05 erg/cm^2. The 1-sec peak photon flux measured starting from T0+10 s in the 10-1000 keV band is 21.3 +/- 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 44951
Subject
GRB 260616B: BALROG localization (Fermi Trigger 803286321 / GRB 260616295)
Date
2026-06-16T09:17:04Z (5 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
803286321 at 07:05:16 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) = 255.8 deg
Decl.(2000.0) = -32.1 deg
The 1 sigma statistical error radius is 1.5 deg.
We estimate an additional systematic error of 1 deg.
Further details are available at:
https://grb.mpe.mpg.de/grb/GRB260616295/
The Healpix map can be downloaded from:
https://grb.mpe.mpg.de/grb/GRB260616295/healpix
The location parameters are available as JSON at:
https://grb.mpe.mpg.de/grb/GRB260616295/json