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[vsnet-grb-info 43258] MASS-Cube (GRID 2.0) detection of GRB 260616B
by GCN Circulars 25 Jun '26

25 Jun '26

TITLE: GCN CIRCULAR NUMBER: 45043 SUBJECT: MASS-Cube (GRID 2.0) detection of GRB 260616B DATE: 26/06/25 08:24:21 GMT FROM: GRID Student Team at Tsinghua University <grid(a)tsinghua.edu.cn> Jiahuan Zhu, Chenyu Wang, Xutao Zheng, Hao Chang, Zirui Yang report on behalf of the MASS-Cube Collaboration: MASS-Cube reports the detection of the long-duration GRB 260616B, which was also detected by Fermi/GBM (GCN #44953), EP (GCN #44956 and #44976), CALET (GCN #44966), SVOM (GCN #45011), HXMT (GCN #45023) and GRID-09. The event was triggered by MASS-Cube on 2026-06-16 at 07:05:14.5 UTC. The measured burst duration (T90) in the 50-10000 keV range is approximately 14.1 +/- 1.6 seconds. The MASS-Cube light curve of this event can be found at https://mirrors.tuna.tsinghua.edu.cn/GRID/data/GRID-GCN/GRB260616B/MASS_Cub…. MASS-Cube is a pathfinder for a 3D position-sensitive Compton telescope in space, currently considered the next generation of the GRID constellation in the era of multi-messenger astronomy. For more information about MASS-Cube, please refer to the following reference: https://doi.org/10.1007/s10686-024-09920-4. View this GCN Circular online at https://gcn.nasa.gov/circulars/45043. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 43257] EP260623a: FTW optical and NIR observations
by GCN Circulars 25 Jun '26

25 Jun '26

TITLE: GCN CIRCULAR NUMBER: 45042 SUBJECT: EP260623a: FTW optical and NIR observations DATE: 26/06/25 08:19:33 GMT FROM: Malte Busmann at Ludwig-Maximilians-Universität München <m.busmann(a)physik.lmu.de> Malte Busmann (LMU), Julius Gassert (LMU/CMU), Xander Hall (CMU), Brendan O'Connor (CMU), Daniel Gruen (LMU), and Antonella Palmese (CMU) report: We observed the counterpart of EP260623a (Wang et al., GCNs 45020 and 45035; Li et al., GCN 45021; Izzo et al., GCN 45022; Angulo et al., GCN 45024; Brivio et al., GCN 45025; Jiang et al., GCN 45026; Li et al., GCN 45027; Jelinek et al., GCN 45029; Lee et al., GCN 45030; Saikia et al., GCN 45034; Bochenek & Perley, GCN 45040) with the Three Channel Imager (3KK) at the Fraunhofer Telescope at Wendelstein Observatory (FTW) in the r, i and J band simultaneously for 20 x 180 s starting at 2026-06-24T23:13:34 UT (1.85 days after the trigger). We detect the counterpart in all bands and measure an r-band magnitude of r = 23.93 ± 0.22 AB mag. The magnitude is calibrated against the PS1 catalog and not corrected for Galactic extinction. We thank Christoph Ries from the Wendelstein Observatory for obtaining these observations. View this GCN Circular online at https://gcn.nasa.gov/circulars/45042. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 43256] GRB 260619A: SVOM/ECLAIRs refined analysis
by GCN Circulars 24 Jun '26

24 Jun '26

TITLE: GCN CIRCULAR NUMBER: 45041 SUBJECT: GRB 260619A: SVOM/ECLAIRs refined analysis DATE: 26/06/24 20:31:19 GMT FROM: SVOM_group <svomgroup(a)bao.ac.cn> Nicolas Dagoneau (CEA), Marius Brunet (IRAP), Wenjin Xie (NAOC) Using the event-by-event data downloaded through the X-band ground station, we report further analysis of ECLAIRs observations of GRB 260619A (SVOM burst-id sb26061901). The burst that triggered ECLAIRs onboard (GCN 44985) consists of a faint single peak lightcurve with a duration of about 40 sec in the 8-50 keV energy band. The time-averaged spectrum (from T0-40.96 s to T0) in the energy range 5-120 keV is best fit by a blackbody model with a temperature kT = 6.6 -1.3/+1.6 keV. With this model, the 4-120 keV fluence is (2.03 +/- 0.63)*E-7 erg/cm² and the 4-120 keV photon flux is (2.02 +/- 0.33)*E-1 ph/cm²/s. All the quoted errors are at the 68% confidence level. The Space-based multi-band astronomical Variable Objects Monitor (SVOM) is a China-France joint mission led by the Chinese National Space Administration (CNSA), French Space Agency (CNES), and the Chinese Academy of Sciences (CAS), which is dedicated to observing gamma-ray bursts and other transient phenomena in the energetic universe. The SVOM/ECLAIRs point of contact for this burst is: N. Dagoneau (nicolas.dagoneau at cea.fr) View this GCN Circular online at https://gcn.nasa.gov/circulars/45041. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 43255] EP260623a: Liverpool Telescope optical observations
by GCN Circulars 24 Jun '26

24 Jun '26

TITLE: GCN CIRCULAR NUMBER: 45040 SUBJECT: EP260623a: Liverpool Telescope optical observations DATE: 26/06/24 17:59:07 GMT FROM: A. Bochenek at Liverpool John Moores University <a.m.bochenek(a)2023.ljmu.ac.uk> A. Bochenek, D. A. Perley (LJMU), report: We observed the field of EP260623a (Waang et al., GCN 45020; Wang et al., GCN 45035) using the IO:O optical camera on the 2m robotic Liverpool Telescope. We obtained 6x120s exposures in SDSS griz filters, starting at 2026-06-24 01:15:57 UT, approximately 22.4 hours after EP trigger. Multiple exposures across all filters had to be discarded prior to stacking due to an issue with the telescope rotator. We detect a source in the images in all filters at the position reported by Li et al. (GCN 45021), also Izzo et al. (GCN 45022); Angulo et al. (GCN 45024); Brivio et al. (GCN 45025); Jiang et al. (GCN 45026); Li et al. (GCN 45027); Jelinek et al. (GCN 45029); Lee et al. (GCN 45030); Saikia et al. (GCN 45034). The preliminary photometry is: | MJD (mid) | T_mid-T_0 | Filter | Mag. (AB) | |---------------|-------------|-----------|---------------| | 61215.05694 | 22.49 h | g | > 21.44 | | 61215.06840 | 22.76 h | r | 21.96 ± 0.23 | | 61215.08921 | 23.26 h | i | 21.59 ± 0.13 | | 61215.09872 | 23.50 h | z | 21.06 ± 0.16 | The photometry is in the AB magnitude system, was calibrated using nearby PanSTARRS secondary standards and was not corrected for extinction. View this GCN Circular online at https://gcn.nasa.gov/circulars/45040. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 43254] Fermi GBM trigger 804010507/260624677 is not a GRB
by GCN Circulars 24 Jun '26

24 Jun '26

TITLE: GCN CIRCULAR NUMBER: 45039 SUBJECT: Fermi GBM trigger 804010507/260624677 is not a GRB DATE: 26/06/24 17:44:48 GMT FROM: rhamburg(a)usra.edu R. Hamburg (USRA) reports report on behalf of the Fermi Gamma-ray Burst Monitor Team: "The Fermi Gamma-ray Burst Monitor (GBM) trigger 804010507/260624677 at 16:15:02.91 UT on 24 June 2026, tentatively classified as a GRB, is in fact not due to a GRB. This trigger is likely due to particle activity." View this GCN Circular online at https://gcn.nasa.gov/circulars/45039. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 43253] Konus-Wind detection of GRB 260618B
by GCN Circulars 24 Jun '26

24 Jun '26

TITLE: GCN CIRCULAR NUMBER: 45038 SUBJECT: Konus-Wind detection of GRB 260618B DATE: 26/06/24 17:14:43 GMT FROM: Anna Ridnaia at Ioffe Institute <ridnaia(a)mail.ioffe.ru> 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 260618B (Fermi-GBM detection: Fermi GBM team, GCN 44979; Veres & Meegan, GCN 45010; Fermi-LAT detection: Gupta et al., GCN 44983) triggered Konus-Wind at T0=60907.637 s UT (16:55:07.637). The burst light curve shows a multipeaked structure which starts at ~T0-1.6 s and has a total duration of ~61.2 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/GRB260618_T60907/ As observed by Konus-Wind, the burst had the total fluence of 2.26(-0.34,+0.43)x10^-5 erg/cm2, and the 64-ms peak flux, measured from T0+0.378 s, of 4.90(-0.98,+1.01)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+57.600 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 = -0.83(-0.16,+0.19) and Ep = 1066(-241,+365) keV (chi2 = 94/98 dof). Fitting by a GRB (Band) model yields the same alpha and Ep, and an upper limit on the high energy photon index: beta < -2.7 (chi2 = 94/97 dof). The spectrum near the maximum count rate (measured from T0 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 = -0.39(-0.14,+0.15) and Ep = 817(-97,+119) keV (chi2 = 96/88 dof). Fitting by a GRB (Band) model yields the same alpha and Ep, and an upper limit on the high energy photon index: beta < -3.2 (chi2 = 96/87 dof). All the quoted errors are at the 68% confidence level. All the quoted values are preliminary. View this GCN Circular online at https://gcn.nasa.gov/circulars/45038. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 43252] GRB 260624A: Fermi GBM Final Real-time Localization
by GCN Circulars 24 Jun '26

24 Jun '26

TITLE: GCN CIRCULAR NUMBER: 45037 SUBJECT: GRB 260624A: Fermi GBM Final Real-time Localization DATE: 26/06/24 16:09:12 GMT FROM: Fermi GBM Team at MSFC/Fermi-GBM <do_not_reply(a)GIOC.nsstc.nasa.gov> The Fermi GBM team reports the detection of a likely LONG GRB At 15:54:14 UT on 24 Jun 2026, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 260624A (trigger 804009259.148196 / 260624663). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 54.1, Dec = -21.0 (J2000 degrees, equivalent to J2000 03h 36m, -21d 00'), with a statistical uncertainty of 4.4 degrees. The angle from the Fermi LAT boresight is 73.0 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260624663/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260624663/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260624663/… View this GCN Circular online at https://gcn.nasa.gov/circulars/45037. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 43251] GRB 260624A: Fermi GBM Final Real-time Localization
by GCN Circulars 24 Jun '26

24 Jun '26

TITLE: GCN CIRCULAR NUMBER: 45036 SUBJECT: GRB 260624A: Fermi GBM Final Real-time Localization DATE: 26/06/24 16:06:42 GMT FROM: Fermi GBM Team at MSFC/Fermi-GBM <do_not_reply(a)GIOC.nsstc.nasa.gov> The Fermi GBM team reports the detection of a likely LONG GRB At 15:54:14 UT on 24 Jun 2026, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 260624A (trigger 804009259.148196 / 260624663). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 54.1, Dec = -21.0 (J2000 degrees, equivalent to J2000 03h 36m, -21d 00'), with a statistical uncertainty of 4.4 degrees. The angle from the Fermi LAT boresight is 73.0 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260624663/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260624663/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260624663/… View this GCN Circular online at https://gcn.nasa.gov/circulars/45036. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 43250] EP260623a:refined analysis of the EP-WXT and EP-FXT observation
by GCN Circulars 24 Jun '26

24 Jun '26

TITLE: GCN CIRCULAR NUMBER: 45035 SUBJECT: EP260623a:refined analysis of the EP-WXT and EP-FXT observation DATE: 26/06/24 09:06:30 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> B.T. Wang (YNAO, CAS), Y. L. Hua (PMO, CAS) and C. C. Jin (NAO, CAS) on behalf of the Einstein Probe (EP) team: The fast X-ray transient EP260623a triggered the Wide-field X-ray Telescope (WXT) on board the Einstein Probe (EP) mission (Wang et al., GCN 45020) and followed by several optical telescopes (Li et al., GCN 45021; Angulo et al., GCN 45024; Brivio et al., GCN 45025; Jiang et al., GCN 45026; Li et al., GCN 45027; Jelinek et al., GCN 45029; Lee et al., GCN 45030; Saikia et al., GCN 45034) with the redshift confirmed at z=0.703 (Izzo et al., GCN 45022). The refined analysis of the WXT data shows that the event started at T0=2026-06-23T02:52:27Z (UTC) and lasted for 103 s before the observation was interrupted by the autonomous follow-up observation. The average WXT 0.5–4 keV spectrum can be fitted with an absorbed power-law model (tbabs*ztbabs*powerlaw) with a fixed Galactic hydrogen column density of 8.1 × 10^20 cm^-2 and a fixed redshift of z = 0.703. The best-fit photon index is 1.83 (-0.56/+0.63), and the intrinsic hydrogen column density is 2.25 (-0.97/+1.21) × 10^22 cm^-2. The derived average unabsorbed 0.5–4 keV flux is 3.17 (-0.74/+1.39) × 10^-9 erg/s/cm^2. The estimated peak flux is 1.0 × 10^-8 erg/s/cm^2, corresponding to a peak luminosity of 2.2 × 10^49 erg/s. The autonomous observation by the Follow-up X-ray Telescope (FXT) was performed at 2026-06-23T02:56:08 (UTC), about 3.7 minutes after T0. The exposure time of this observation is 3211 s. The on-ground analysis shows that an uncatalogued source was detected at R.A., Dec. = 328.2698, 12.7938 deg (J2000) with an uncertainty of about 10 arcsec (radius, 90% C.L. statistical and systematic). The FXT light curve displays two pulses structure lasting for around 210 s. The average FXT 0.5-10 keV spectrum can be fitted with an absorbed power law with a fixed Galactic equivalent hydrogen column density of 8.1 × 10^20 cm^-2 and a photon index of 1.96 (-/+ 0.03), and the intrinsic hydrogen column density is 0.94 (-/+ 0.04) × 10^22 cm^-2. The derived average unabsorbed 0.5-10 keV flux is 7.33 (-/+ 0.10) × 10^-9 erg/s/cm^2. The uncertainties are at the 90% confidence level for the above parameters. 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). View this GCN Circular online at https://gcn.nasa.gov/circulars/45035. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 43249] EP260623a: WINTER J-band observations
by GCN Circulars 23 Jun '26

23 Jun '26

TITLE: GCN CIRCULAR NUMBER: 45034 SUBJECT: EP260623a: WINTER J-band observations DATE: 26/06/23 22:37:06 GMT FROM: Geoffrey Mo at Caltech / Carnegie Observatories <gmo(a)mit.edu> Aditya Pawan Saikia (IITB), Geoffrey Mo (Caltech/Carnegie), Tomas Ahumada (NOIRLab), Benjamin Schneider (LAM), Robert Stein (UMD), Viraj Karambelkar (Columbia), Danielle Frostig (CfA), Nathan Lourie (MIT), Robert Simcoe (MIT), and Mansi Kasliwal (Caltech) report: We observed the field of EP260623a (Wang et al., GCN 45020) in the near-infrared J band with the Palomar 1-m telescope, equipped with the 1.2-square degree WINTER camera (Lourie et al. 2020, Frostig et al. 2024). Observations began at 2026-06-23T07:00:29 UTC in the J band (4.1 hr after the EP trigger), consisting of 30*120 sec exposures. The images were processed using the WINTER data reduction pipeline implemented with MIRAR (https://github.com/winter-telescope/mirar, https://doi.org/10.5281/zenodo.13352565) We detect a source at the optical counterpart location (Li et al., GCN 45021; Izzo et al., GCN 45022; Angulo et al., GCN 45024; Brivio et al., GCN 45025; Jiang et al., GCN 45026; Li et al., GCN 45027; Jelinek et al., GCN 45029; Lee et al., GCN 45030), with magnitude J = 17.9 ± 0.1 mag (AB). WINTER (Wide-field INfrared Transient ExploreR) is a partnership between MIT and Caltech, housed at Palomar Observatory, and funded by NSF MRI, NSF AAG, the David and Lucile Packard Foundation, and the MIT Kavli Institute for Astrophysics and Space Research. View this GCN Circular online at https://gcn.nasa.gov/circulars/45034. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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