GRB 260604A

D. Svinkin (Ioffe), D. Frederiks (Ioffe), D. Kapshtan (Geoscan), M. Orlov (Geoscan), 
V. Bazunova (Geoscan), E. Shchepin (Geoscan), E. Meltsov (Geoscan), 
K. Starikov (Geoscan, SPbSU), A. Khogoev (Geoscan), 
A. Razdobarin (SPbAU), and D. Dolmatov (SPbSU),
on behalf of the 239Alferov team, report:

The long-duration GRB 260604A
(Fermi-GBM detection: The Fermi GBM team, GCN 44812
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 ; 
Glowbug detection: Cheung et al., GCN 44845
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 ; 
SVOM-GRM detection: Yu et al., GCN 44863
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 )
was detected by 239Alferov 3U CubeSat at about 8668 s (02:24:28) UT.
The burst was also detected by Konus-Wind in the waiting mode.

The burst light curve, as measured by 239Alferov detector, 
shows a single pulse with a duration of ~5 s. 
The emission is seen up to ~500 keV.

The light curve recorded by 239Alferov is available at:
http://www.ioffe.ru/LEA/239Alferov/260604A/

239Alferov GRB detections are listed at:
http://www.ioffe.ru/LEA/239Alferov/

239Alferov is an educational 3U CubeSat mission at SSO combining amateur radio 
and space research objectives. The gamma-ray detector onboard 239Alferov contains 
a 64x72x15 mm NaI(Tl) scintillator read out by a SiPM array and covers the energy range 
from ~20 keV to ~1000 keV. 
Currently, the instrument records count rates in five energy bands:  
~20-50 keV, ~50-100 keV, ~100-500 keV, 500-1000 keV, and > 1000 keV, with 0.5 s temporal resolution.
The ground segment of the mission utilizes the SONIKS open ground station network.

SVOM/GRM team: Zheng-Hang Yu, 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 a burst GRB 260604A at 2026-06-04T02:24:27.200 UTC (T0), which is also detected by Fermi/GBM (Fermi GBM Team, GCN #44812
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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 mainly consists of multiple pulses with a T90 of 4.0 +4.2/-2.2 s in the 15-5000 keV band.

The SVOM/GRM light curve can be found here:
https://www.bursthub.cn//admin/static/svgrb260604A.png

In addition, the position of this burst, according to Fermi/GBM localization (RA = 60.4 deg, Dec = -12.8 deg, Err = 9.8 deg, Fermi GBM Team, GCN #44812
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 ), is located at about 71 degrees from the SVOM optical axis, which is outside the ECLAIRs field of view.

With this localization, the time-averaged spectrum from T0+0 to T0+4 s is fitted by a power law function. The power law index is -1.69 +0.12/-0.11. The event fluence (10-1000 keV) in this time interval is (1.01 +0.17/-0.16)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: Zheng-Hang Yu (IHEP) (zhyu@ihep.ac.cn)

C.C. Cheung, R. Woolf, M. Kerr, J.E. Grove (NRL), A. Goldstein (USRA), C.A. Wilson-Hodge, D. Kocevski (MSFC), and M.S. Briggs (UAH) report:

The Glowbug gamma-ray telescope [1,2,3], operating on the International Space Station, reports the detection of GRB 260604A, which was also detected by Fermi/GBM (GCN 44812
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 ).

Using an adaptive window with a resolution of 32-ms, the burst onset is determined to be 2026-06-04 02:24:24.648 with a duration of 4.1 s and a total significance of about 9.8 sigma.  The light curve comprises a single peak.  Note that data from ~T0-5s to +1s suffered from deadtime in various detectors.

The analysis results presented here are preliminary and use a response function that lacks a detailed characterization of the surrounding passive structure of the ISS. Glowbug is a NASA-funded technology demonstrator for sensitive, low-cost gamma-ray transient telescopes developed, built, and operated by the U.S. Naval Research Laboratory (NRL) with support from the University of Alabama in Huntsville, USRA, and NASA MSFC.  It was launched on 2023 March 15 aboard the Department of Defense Space Test Program’s STP-H9 to the ISS and operated until 2024 April when it was put in safe storage on orbit. Glowbug was removed from storage and resumed operation on 2025 September 12. 

[1] Grove, J.E. et al. 2020, Proc. Yamada Conf. LXXI, arXiv:2009.11959
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[2] Woolf, R.S. et al. 2022, Proc. SPIE, 12181, id. 121811O 
[3] Woolf, R.S. et al. 2024, Proc. SPIE, 13151, id. 1315108 

 Distribution Statement A: Approved for public release.  Distribution is unlimited.

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

At 02:24:27 UT on 4 Jun 2026, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 260604A (trigger 802232672.54125 / 260604100).

The on-ground calculated location, using the Fermi GBM trigger data, is RA = 60.4, Dec = -12.8 (J2000 degrees, equivalent to J2000 04h 01m, -12d 48'), with a statistical uncertainty of 9.3 degrees.

The angle from the Fermi LAT boresight is 94.0 degrees.

The skymap can be found here:
https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260604100/quicklook/glg_skymap_all_bn260604100.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/bn260604100/quicklook/glg_healpix_all_bn260604100.fit

The GBM light curve can be found here:
https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260604100/quicklook/glg_lc_medres34_bn260604100.gif