GRB 250902B
GCN Circular 41707
Subject
GRB 250902B: CALET Gamma-Ray Burst Monitor detection
Date
2025-09-04T18:04:18Z (8 days ago)
From
Yuta Kawakubo at Aoyama Gakuin University <kawakubo@phys.aoyama.ac.jp>
Via
Web form
N. Cannady (GSFC/UMBC), A. Yoshida, T. Sakamoto, S. Sugita,
Y. Kawakubo (AGU), K. Yamaoka (Nagoya U), S. Nakahira (JAXA),
Y. Asaoka (ICRR), S. Torii, Y. Akaike, K. Kobayashi (Waseda U),
Y. Shimizu, T. Tamura (Kanagawa U), M. L. Cherry (LSU),
S. Ricciarini (U of Florence), P. S. Marrocchesi (U of Siena),
and the CALET collaboration:
The long GRB 250902B (Fermi GBM Final Real-time Localization:
Fermi GBM team, GCN Circ. 41660; SVOM/GRM observation: Wang et al.,
GCN Circ. 41668; AstroSat CZTI detection: Tembhurnikar et al., GCN Circ. 41678)
triggered the CALET Gamma-ray Burst Monitor (CGBM) at 18:45:35.15 UTC on 2 September 2025
(https://cgbm.calet.jp/cgbm_trigger/flight/1440873547/index.html).
The burst signal was seen by all CGBM detectors. Because of a problem with the ground
alert processing script, the GCN notice was not distributed automatically for this event.
The burst light curve shows a multi-peaked structure that starts
at T-2.4 sec, peaks at T+9.6 sec, and ends at T+17.4 sec.
The T90 and T50 durations measured by the SGM data are 17.4 +/- 0.7 sec
and 8.8 +/- 0.6 sec (40-1000 keV), respectively.
The ground-processed light curve is available at
https://cgbm.calet.jp/cgbm_trigger/ground/1440873547/
The CALET data used in this analysis are provided by
the Waseda CALET Operation Center located at Waseda University.
GCN Circular 41678
Subject
GRB 250902B: AstroSat CZTI detection
Date
2025-09-03T18:16:21Z (9 days ago)
From
Anuraag Arya at IIT Bombay <aryaanuraag910@gmail.com>
Via
Web form
M. Tembhurnikar (IUCAA), A. Arya, (IITB), 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 GRB 250902B which was also detected by Fermi GBM (Fermi GBM Team, GCN Circ. 41660), and SVOM GRM (Wang et. al., GCN Circ. 41668).
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 2025-09-02 18:45:45.00 UTC. The measured peak count rate associated with the burst is 47 (+17, -10) counts/s above the background in the combined data of two quadrants (out of four), with a total of 297 (+122, -145) counts. The local mean background count rate was 152 (+2, -2) counts/s. Using cumulative rates, we measure a T90 of 17.2 (+2.7, -7.6) s.
The source was also 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 2025-09-02 18:45:44.68 UTC. The measured peak count rate associated with the burst is 365 (+71, -49) counts/s above the background in the combined data of all quadrants, with a total of 1924 (+390, -422) counts. The local mean background count rate was 1405 (+5, -6) counts/s. We measure a T90 of 15.4 (+3.2, -2.4) 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
GCN Circular 41668
Subject
GRB 250902B: SVOM/GRM observation
Date
2025-09-03T11:23:57Z (9 days ago)
From
Chenwei Wang at IHEP <cwwang@ihep.ac.cn>
Via
Web form
SVOM/GRM team: Chen-Wei Wang, Yue Huang, Shi-Jie Zheng, Shao-Lin Xiong, Shuang-Nan Zhang (IHEP)
SVOM/ECLAIRs team: Feliu Lacreu (IAP)
Report on behalf of the SVOM team:
SVOM/GRM was triggered in-flight by a burst GRB 250902B (SVOM trigger reference: sb25090205) at 2025-09-02T18:45:36.000 UTC (T0), which is also detected by Fermi/GBM (Fermi GBM team, GCN #41660).
With the event-by-event data downloaded through the X-band ground station, the GRM light curve shows that this burst consists of multi-pulses with a T90 of 17.4 +1.3/-0.7 s in the 15-5000 keV band.
The SVOM/GRM light curve can be found here:
https://www.bursthub.cn//admin/static/svgrb250902B.png
In addition, the position of this burst, as determined by Fermi/GBM (RA = 82.3, Dec = -5.0, GCN #41660), is located at about 85 degrees from the SVOM optical axis, which is outside the ECLAIRs field of view.
With the localization from Fermi/GBM, the time-averaged spectrum from T0-10 to T0+20 s is best fitted by a power law function with an exponential high-energy cutoff. The power law index is -0.85 +0.18/-0.17 and the cutoff energy, parameterized as Epeak, is 146 +21/-16 keV. The event fluence (10-1000 keV) in this time interval is (1.07 +0.08/-0.07)E-05 erg/cm^2.
The 'Amati' relation diagram of GRB 250902B is shown at:
https://www.bursthub.cn//admin/static/svgrb250902B_amati.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: Chen-Wei Wang (IHEP)(cwwang@ihep.ac.cn)
GCN Circular 41664
Subject
Fermi GRB 250902B: Global MASTER-Net observations report
Date
2025-09-03T03:31:08Z (9 days ago)
From
Vladimir Lipunov at Moscow State U/Krylov Obs <lipunov@xray.sai.msu.ru>
Via
email
V.Lipunov, E.Gorbovskoy, A.Kuznetsov, K.Zhirkov, I.Panchenko, N.Tiurina, P.Balanutsa, V.Topolev, D.Vlasenko,
G.Antipov, A.Sankovich, Yu.Tselik, Ya.Kechin, V.Senik, A.Chasovnikov, K.Labsina, I. Gorbunov (Lomonosov MSU),
O.Gress, N.Budnev (ISU),
C.Francile, F. Podesta, R.Podesta, E. Gonzalez (Observatorio Astronomico Felix Aguilar (OAFA),
A. Tlatov, D. Dormidontov (Kislovodsk Solar Station of the Pulkovo Observatory),
A.Sosnovskij (CrAO),
A. Gabovich, V.Yurkov (Blagoveschensk Educational StateUniversity),
D.Buckley (SAAO),
R.Rebolo (The Instituto de Astrofisica de Canarias),
L.Carrasco, J.R.Valdes, V.Chavushyan, V.M.Patino Alvarez, J.Martinez,
A.R.Corella, L.H.Rodriguez (INAOE, Guillermo Haro Astrophysics Observatory)
MASTER-SAAO robotic telescope (Global MASTER-Net: http://observ.pereplet.ru, Lipunov et al., 2010, Advances in Astronomy, vol. 2010, 30L) located in South Africa (South African Astronomical Observatory) started inspect of the Fermi GRB 250902B ( Fermi GBM team, GCN 41660) errorbox 18838 sec after notice time and 18874 sec after trigger time at 2025-09-03 00:00:08 UT, with upper limit up to 18.6 mag. The observations began at zenith distance = 77 deg. The sun altitude is -59.1 deg.
The galactic latitude b = -20 deg., longitude l = 208 deg.
Real time updated cover map and OT discovered available here:
https://master.sai.msu.ru/site/master2/observ.php?id=2983003
We obtain a following upper limits.
Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment
_________|_____________________|_____________________|____________________________________|_____|_______|_______|________
18905 | 2025-09-03 00:00:08 | MASTER-SAAO | (05h 20m 30.13s , -04d 32m 16.8s) | C | 60 | 17.4 |
18905 | 2025-09-03 00:00:08 | MASTER-SAAO | (05h 22m 16.39s , -04d 47m 44.4s) | C | 60 | 13.4 |
19743 | 2025-09-03 00:14:07 | MASTER-SAAO | (05h 20m 31.93s , -04d 32m 23.9s) | C | 60 | 17.7 |
19743 | 2025-09-03 00:14:07 | MASTER-SAAO | (05h 22m 18.01s , -04d 47m 48.8s) | C | 60 | 16.7 |
19962 | 2025-09-03 00:17:46 | MASTER-SAAO | (05h 27m 44.14s , -04d 30m 25.1s) | C | 60 | 17.8 |
19962 | 2025-09-03 00:17:46 | MASTER-SAAO | (05h 29m 30.52s , -04d 45m 52.0s) | C | 60 | 16.8 |
20055 | 2025-09-03 00:19:19 | MASTER-SAAO | (05h 35m 39.60s , -04d 30m 43.8s) | C | 60 | 18.0 |
20055 | 2025-09-03 00:19:19 | MASTER-SAAO | (05h 37m 26.17s , -04d 46m 09.6s) | C | 60 | 15.7 |
20368 | 2025-09-03 00:24:32 | MASTER-SAAO | (05h 20m 25.60s , -04d 32m 23.1s) | C | 60 | 17.8 |
20368 | 2025-09-03 00:24:32 | MASTER-SAAO | (05h 22m 12.33s , -04d 47m 48.4s) | C | 60 | 17.1 |
20590 | 2025-09-03 00:28:14 | MASTER-SAAO | (05h 27m 42.05s , -04d 30m 33.7s) | C | 60 | 17.8 |
20590 | 2025-09-03 00:28:14 | MASTER-SAAO | (05h 29m 28.33s , -04d 45m 56.0s) | C | 60 | 17.1 |
20814 | 2025-09-03 00:31:58 | MASTER-SAAO | (05h 35m 47.86s , -04d 30m 20.8s) | C | 60 | 17.9 |
20814 | 2025-09-03 00:31:58 | MASTER-SAAO | (05h 37m 33.96s , -04d 45m 44.0s) | C | 60 | 16.9 |
21125 | 2025-09-03 00:37:08 | MASTER-SAAO | (05h 20m 30.36s , -04d 31m 31.8s) | C | 60 | 17.8 |
21125 | 2025-09-03 00:37:08 | MASTER-SAAO | (05h 22m 17.39s , -04d 46m 55.0s) | C | 60 | 17.4 |
21217 | 2025-09-03 00:38:41 | MASTER-SAAO | (05h 27m 38.90s , -04d 32m 11.0s) | C | 60 | 17.8 |
21218 | 2025-09-03 00:38:41 | MASTER-SAAO | (05h 29m 25.88s , -04d 47m 33.9s) | C | 60 | 17.3 |
21436 | 2025-09-03 00:42:19 | MASTER-SAAO | (05h 35m 42.83s , -04d 30m 02.1s) | C | 60 | 18.1 |
21436 | 2025-09-03 00:42:19 | MASTER-SAAO | (05h 37m 29.66s , -04d 45m 25.2s) | C | 60 | 17.6 |
21623 | 2025-09-03 00:45:27 | MASTER-SAAO | (05h 28m 42.64s , -06d 25m 09.3s) | C | 60 | 17.8 |
21623 | 2025-09-03 00:45:27 | MASTER-SAAO | (05h 30m 29.96s , -06d 40m 32.5s) | C | 60 | 17.5 |
21717 | 2025-09-03 00:47:00 | MASTER-SAAO | (05h 36m 44.94s , -06d 23m 48.0s) | C | 60 | 18.3 |
21717 | 2025-09-03 00:47:00 | MASTER-SAAO | (05h 38m 32.18s , -06d 39m 10.9s) | C | 60 | 17.8 |
21811 | 2025-09-03 00:48:35 | MASTER-SAAO | (05h 20m 28.96s , -04d 31m 31.0s) | C | 60 | 17.8 |
21811 | 2025-09-03 00:48:35 | MASTER-SAAO | (05h 22m 16.10s , -04d 46m 53.7s) | C | 60 | 17.6 |
21905 | 2025-09-03 00:50:09 | MASTER-SAAO | (05h 27m 37.83s , -04d 32m 12.9s) | C | 60 | 17.8 |
21905 | 2025-09-03 00:50:09 | MASTER-SAAO | (05h 29m 24.93s , -04d 47m 35.3s) | C | 60 | 17.6 |
22202 | 2025-09-03 00:55:06 | MASTER-SAAO | (05h 21m 31.95s , -06d 24m 31.1s) | C | 60 | 17.9 |
22202 | 2025-09-03 00:55:06 | MASTER-SAAO | (05h 23m 19.48s , -06d 39m 55.5s) | C | 60 | 17.9 |
22295 | 2025-09-03 00:56:39 | MASTER-SAAO | (05h 35m 39.88s , -04d 30m 50.9s) | C | 60 | 18.2 |
22295 | 2025-09-03 00:56:39 | MASTER-SAAO | (05h 37m 26.70s , -04d 46m 15.3s) | C | 60 | 17.9 |
22481 | 2025-09-03 00:59:44 | MASTER-SAAO | (05h 28m 48.06s , -06d 25m 09.7s) | C | 60 | 18.0 |
22481 | 2025-09-03 00:59:44 | MASTER-SAAO | (05h 30m 35.49s , -06d 40m 34.0s) | C | 60 | 17.9 |
22579 | 2025-09-03 01:01:23 | MASTER-SAAO | (05h 36m 44.70s , -06d 25m 51.1s) | C | 60 | 18.6 |
22579 | 2025-09-03 01:01:23 | MASTER-SAAO | (05h 38m 32.64s , -06d 41m 14.1s) | C | 60 | 18.4 |
22672 | 2025-09-03 01:02:56 | MASTER-SAAO | (05h 20m 30.08s , -04d 32m 05.7s) | C | 60 | 18.0 |
22672 | 2025-09-03 01:02:56 | MASTER-SAAO | (05h 22m 17.93s , -04d 47m 28.7s) | C | 60 | 18.0 |
22765 | 2025-09-03 01:04:29 | MASTER-SAAO | (05h 27m 40.12s , -04d 30m 40.7s) | C | 60 | 18.0 |
22765 | 2025-09-03 01:04:29 | MASTER-SAAO | (05h 29m 27.84s , -04d 46m 03.6s) | C | 60 | 17.9 |
23049 | 2025-09-03 01:09:13 | MASTER-SAAO | (05h 21m 26.00s , -06d 25m 32.3s) | C | 60 | 18.0 |
23049 | 2025-09-03 01:09:13 | MASTER-SAAO | (05h 23m 14.50s , -06d 40m 55.7s) | C | 60 | 18.0 |
23143 | 2025-09-03 01:10:46 | MASTER-SAAO | (05h 35m 38.42s , -04d 29m 57.8s) | C | 60 | 18.2 |
23143 | 2025-09-03 01:10:46 | MASTER-SAAO | (05h 37m 26.26s , -04d 45m 21.1s) | C | 60 | 18.3 |
23236 | 2025-09-03 01:12:19 | MASTER-SAAO | (05h 28m 47.39s , -06d 25m 15.1s) | C | 60 | 17.9 |
23236 | 2025-09-03 01:12:19 | MASTER-SAAO | (05h 30m 35.79s , -06d 40m 38.5s) | C | 60 | 17.9 |
23329 | 2025-09-03 01:13:52 | MASTER-SAAO | (05h 36m 43.44s , -06d 25m 56.1s) | C | 60 | 18.5 |
23329 | 2025-09-03 01:13:52 | MASTER-SAAO | (05h 38m 31.77s , -06d 41m 19.5s) | C | 60 | 18.6 |
23422 | 2025-09-03 01:15:26 | MASTER-SAAO | (05h 29m 30.58s , -04d 47m 30.8s) | C | 60 | 18.0 |
Filter C is a clear (unfiltred) band.
The observation and reduction will continue.
The message may be cited.
GCN Circular 41660
Subject
GRB 250902B: Fermi GBM Final Real-time Localization
Date
2025-09-02T18:56:35Z (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 18:45:34 UT on 2 Sep 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 250902B (trigger 778531539.099344 / 250902782).
The on-ground calculated location, using the Fermi GBM trigger data, is RA = 82.3, Dec = -5.0 (J2000 degrees, equivalent to J2000 05h 29m, -5d 00'), with a statistical uncertainty of 1.4 degrees.
The angle from the Fermi LAT boresight is 20.0 degrees.
The skymap can be found here:
https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250902782/quicklook/glg_skymap_all_bn250902782.png
The HEALPix FITS file, including the estimated localization systematic, can be found here:
https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250902782/quicklook/glg_healpix_all_bn250902782.fit
The GBM light curve can be found here:
https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250902782/quicklook/glg_lc_medres34_bn250902782.gif