GRB 250830C

J. Ripa, M. Dafcikova (Masaryk U.), A. Pal (Konkoly Observatory), N. Werner  (Masaryk U.), M. Ohno (Hiroshima U.),  L. Meszaros, B. Csak (Konkoly Observatory), H. Takahashi (Hiroshima U.), F. Munz , M. Topinka, F. Hroch, N. Husarikova, J.-P. Breuer (Masaryk U.), J. Hudec, J. Kapus, M. Frajt, M. Rezenov (Spacemanic s.r.o), R. Laszlo (Needronix), G. Galgoczi (Wigner Research Center/Eotvos U.), N. Uchida (ISAS/JAXA), T. Enoto (Kyoto U.), Zs. Frei (Eotvos U.), Y. Fukazawa, K. Hirose, H. Matake (Hiroshima U.), S. Hisadomi (Nagoya U.), Y. Ichinohe (Rikkyo U.), L. L. Kiss (Konkoly Observatory),  T. Mizuno (Hiroshima U.), K. Nakazawa (Nagoya U.), H. Odaka (Univ of Tokyo), K. Torigoe (Hiroshima U.), P. Svoboda, V. Daniel, J. Dudas, M. Junas, J. Gromes (VZLU), I. Vertat (FEL ZCU)  -- the VZLUSAT-2/GRB payload collaboration.

The long-duration GRB 250830C (Konus-Wind detection trigger at 2025-08-30 14:52:17.865 UT; AstroSat detection: GCN 41628
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 ; GECAM-B detection: 41630; Insight-HXMT detection: 41632) was detected by the GRB detectors on board the VZLUSAT-2 3U CubeSat (https://www.vzlusat2.cz/en/).

The data acquisition was performed by the GRB detector units no. 0 and no. 1. The detection was confirmed at the peak time 2025-08-30 14:52:19 UTC. The T90 duration is 9 s (8 s) and the significance during T90 reaches 32 sigma (18 sigma) for detector unit no. 0 (no. 1).

The light curve obtained by VZLUSAT-2 is available here:
https://vzlusat2.konkoly.hu/static/share/GRB250830C_GCN_VZLUSAT2.pdf

All VZLUSAT-2 detections are listed at: https://monoceros.physics.muni.cz/hea/VZLUSAT-2/
The GRB detectors on VZLUSAT-2 are a demonstration payload for a future CubeSat constellation (Werner et al. Proc. SPIE 2018). Two GRB modules of VZLUSAT-2 are placed in a perpendicular manner and each consists of a 75 x 75 x 5 mm3 CsI scintillator read out by a SiPM array, covering the energy range from ~30 keV to ~1000 keV. VZLUSAT-2 was launched on 2022 January 13 from Cape Canaveral.

Chen-Wei Wang, Shao-Lin Xiong, and Chao Zheng report on behalf of the Insight-HXMT team:

At 2025-08-30T14:51:55.100 (T0), Insight-HXMT/HE detected the burst GRB 250830C, which is also detected by GECAM-B (Wang et al., GCN #41630
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 ).

The Insight-HXMT/HE light curve mainly consists of multi-pulses with a T90 of 12.6 +8.2/-3.6 s. The 1s peak rate, measured from T0+26.300 s, is 2735 cnts/sec. The total counts from this burst is 10641 counts.

The HXMT/HE light curve can be found here:
https://www.bursthub.cn//admin/static/hxmtgrb250830C.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.

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

GECAM-B was triggered in-flight by a bright long burst GRB 250830C at 2025-08-30T14:51:55.100 UTC (denoted as T0). According to the GECAM-B light curves in about 40-6000 keV, this burst mainly consists of a precursor followed by multiple pulses main emission with a duration (T90) of 23.6 +12.0/-8.4 s.

The GECAM-B light curve can be found here:
https://www.bursthub.cn//admin/static/gecamgrb250830C.png

GECAM-B localized this burst to the following position (J2000): 
Ra: 240.1 deg 
Dec: 40.5 deg
Err: 1.1 deg (1-sigma, statistical only)

The time-averaged spectrum from T0-2 s to T0+40 s is best fitted by a power law function with an exponential high-energy cutoff. The power law index is -1.06 +0.23/-0.24 and the cutoff energy, parameterized as Epeak, is 255 +121/-46 keV. The event fluence (10-1000 keV) in this time interval is (2.41 +/-0.36)E-05 erg/cm^2. The 'Amati' relation diagram of GRB 250830C is shown at: 
https://www.bursthub.cn//admin/static/grb250830C_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).

Harsha K H (IUCAA), A. Arya (IITB), M. Tembhurnikar (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-duration bright GRB 250830C which was also detected by Konus-Wind (IPN notices). We note that this burst is towards the tail end of solar activity as seen in GOES data.

The source was clearly detected in the CZT detectors in the 20-200 keV energy range. The light curve peaks at 2025-08-30 14:52:21.50 UTC. The measured peak count rate associated with the burst is 248 (+42, -14) counts/s above the background in the combined data of two quadrants (out of four), with a total of 1394 (+282, -55) counts. The local mean background count rate was 135 (+5, -9) counts/s. Using cumulative rates, we measure a T90 of 9.5 (+4.8, -0.7) s. 

The source was also clearly detected in the CsI anticoincidence (Veto) detector in the 100-500 keV energy range. The light curve peaks at 2025-08-30 14:52:21.29 UTC. The measured peak count rate associated with the burst is 1516 (+85, -91) counts/s above the background in the combined data of all quadrants, with a total of 7100 (+323, -375) counts. The local mean background count rate was 1307 (+5, -4) counts/s. We measure a T90 of 9.2 (+1.5, -0.9) s from the cumulative Veto light curve.

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