GRB 250909A
GCN Circular 41771
Subject
GRB 250909A: AstroSat CZTI detection
Date
2025-09-10T06:35:24Z (3 days ago)
From
Anuraag Arya at IIT Bombay <aryaanuraag910@gmail.com>
Via
Web form
A. Goyal (IITB), A. Arya (IITB), M. Tembhurnikar (IUCAA), 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-duration GRB 250909A which was also detected by Fermi GBM (Fermi GBM Team, GCN Circ. 41753).
The source was detected in the CsI anticoincidence (Veto) detector in the 100-500 keV energy range. The light curve showed a burst peak of emission at 2025-09-09 02:33:32.44 UTC. The measured peak count rate associated with the burst is 228 (+61, -66) counts/s above the background in the combined data of all quadrants, with a total of 663 (+255, -303) counts. The local mean background count rate was 1258 (+7, -5) counts/s. We measure a T90 of 8.2 (+2.5, -4.0) s from the cumulative Veto light curve.
The source was also faintly detected in the CZT detectors in the 20-200 keV energy range.
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 41755
Subject
Fermi GRB 250909A: Global MASTER-Net observations report
Date
2025-09-09T02:45:32Z (4 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-Tavrida robotic telescope (Global MASTER-Net: http://observ.pereplet.ru, Lipunov et al., 2010, Advances in Astronomy, vol. 2010, 30L) located in Russia (Lomonosov MSU, SAI Crimea astronomical station) started inspect of the Fermi GRB 250909A ( Fermi GBM team, GCN 41753) errorbox 31 sec after notice time and 68 sec after trigger time at 2025-09-09 02:34:37 UT, with upper limit up to 15.3 mag. Observations started at twilight. The observations began at zenith distance = 17 deg. The sun altitude is -7.8 deg.
The galactic latitude b = 1 deg., longitude l = 168 deg.
Real time updated cover map and OT discovered available here:
https://master.sai.msu.ru/site/master2/observ.php?id=2987637
We obtain a following upper limits.
Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment
_________|_____________________|_____________________|____________________________________|_____|_______|_______|________
74 | 2025-09-09 02:34:37 | MASTER-Tavrida | (05h 35m 20.66s , +41d 15m 12.7s) | C | 10 | 14.4 |
91 | 2025-09-09 02:34:50 | MASTER-Tavrida | (05h 35m 20.96s , +41d 15m 12.4s) | C | 20 | 15.1 |
124 | 2025-09-09 02:35:22 | MASTER-Tavrida | (05h 23m 43.51s , +41d 45m 12.1s) | C | 20 | 15.2 |
154 | 2025-09-09 02:35:22 | MASTER-Tavrida | (05h 23m 43.50s , +41d 45m 12.1s) | C | 80 | 15.3 | Coadd
199 | 2025-09-09 02:35:22 | MASTER-Tavrida | (05h 23m 43.51s , +41d 45m 12.2s) | C | 170 | 15.3 | Coadd
152 | 2025-09-09 02:35:45 | MASTER-Tavrida | (05h 23m 43.26s , +41d 45m 11.6s) | C | 30 | 15.0 |
184 | 2025-09-09 02:36:17 | MASTER-Tavrida | (05h 23m 43.04s , +41d 45m 10.9s) | C | 30 | 14.6 |
221 | 2025-09-09 02:36:50 | MASTER-Tavrida | (05h 23m 42.76s , +41d 45m 10.4s) | C | 40 | 15.1 |
276 | 2025-09-09 02:36:50 | MASTER-Tavrida | (05h 23m 42.74s , +41d 45m 10.4s) | C | 150 | 14.7 | Coadd
269 | 2025-09-09 02:37:32 | MASTER-Tavrida | (05h 23m 42.35s , +41d 45m 09.7s) | C | 50 | 15.1 |
327 | 2025-09-09 02:38:25 | MASTER-Tavrida | (05h 23m 41.85s , +41d 45m 08.4s) | C | 60 | 14.7 |
395 | 2025-09-09 02:39:28 | MASTER-Tavrida | (05h 23m 41.29s , +41d 45m 06.9s) | C | 70 | 14.5 |
Filter C is a clear (unfiltred) band.
The observation and reduction will continue.
The message may be cited.
GCN Circular 41753
Subject
GRB 250909A: Fermi GBM Final Real-time Localization
Date
2025-09-09T02:43:59Z (4 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 02:33:28 UT on 9 Sep 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 250909A (trigger 779078013.882702 / 250909107).
The on-ground calculated location, using the Fermi GBM trigger data, is RA = 78.8, Dec = 39.5 (J2000 degrees, equivalent to J2000 05h 15m, 39d 30'), with a statistical uncertainty of 3.3 degrees.
The angle from the Fermi LAT boresight is 85.0 degrees.
The skymap can be found here:
https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250909107/quicklook/glg_skymap_all_bn250909107.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/bn250909107/quicklook/glg_healpix_all_bn250909107.fit
The GBM light curve can be found here:
https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn250909107/quicklook/glg_lc_medres34_bn250909107.gif