GRB 251211B
GCN Circular 43080
Subject
GRB 251211B: AstroSat CZTI detection
Date
2025-12-13T04:13:33Z (2 days ago)
From
Utkarsh Pathak at IIT Bombay <utkarshpathak.07@gmail.com>
Via
Web form
A. Arya (IITB), A. Goyal (IITB), U. Pathak (IITB), M. Tembhurnikar (IUCAA), S. Salunke (IUCAA), Harsha K. H. (IUCAA), G. Waratkar (Caltech/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 GRB 251211B, which was also detected by Fermi/GBM (Fermi GBM Team, GCN Circ. 43072).
The source was faintly detected in the CsI anticoincidence (Veto) detector in the 100-500 keV energy range. The light curve peaks at 2025-12-11 20:32:04.31 UTC. The measured peak count rate associated with the burst is 176 (+60, -53) counts/s above the background in the combined data of all quadrants, with a total of 367 (+222, -238) counts. The local mean background count rate was 1180 (+8, -8) counts/s. Due to the intrinsic 1 s binning of veto data and the relatively faint detection, we cannot reliably estimate a T90 for this burst.
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 43073
Subject
Fermi GRB 251211B: Global MASTER-Net observations report
Date
2025-12-12T00:15:55Z (3 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-Tunka robotic telescope [1] located in Russia (Applied Physics Institute, Irkutsk State University) started inspect of the Fermi GRB 251211B ( Fermi GBM team, GCN 43072) errorbox 622 sec after notice time and 629 sec after trigger time at 2025-12-11 20:42:33 UT, with upper limit up to 17.5 mag. The observations began at zenith distance = 72 deg. The sun altitude is -39.1 deg.
The galactic latitude b = 48 deg., longitude l = 279 deg.
Real time updated cover map and OT discovered available here:
https://master.sai.msu.ru/site/master2/observ.php?id=3068576
We obtain a following upper limits.
Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment
_________|_____________________|_____________________|____________________________________|_____|_______|_______|________
643 | 2025-12-11 20:42:33 | MASTER-Tunka | (11h 44m 16.21s , -11d 00m 25.5s) | C | 25 | 16.9 |
665 | 2025-12-11 20:42:33 | MASTER-Tunka | (11h 44m 16.21s , -11d 00m 25.6s) | C | 70 | 17.5 | Coadd
671 | 2025-12-11 20:43:02 | MASTER-Tunka | (11h 44m 16.37s , -11d 00m 25.6s) | C | 25 | 16.9 |
697 | 2025-12-11 20:43:30 | MASTER-Tunka | (11h 44m 16.51s , -11d 00m 25.3s) | C | 20 | 16.8 |
Filter C is a clear (unfiltred) band.
The observation and reduction will continue.
The message may be cited.
[1] - V.M. Lipunov, V.G. Kornilov, E.S. Gorbovskoy, N.A. Tiurina & A.S.Kuznetsov, 2023, Astronomical Robotic Networks and Operative Multichanel Astrophysics, Lomonosov MSU PRESS, 591pp.
http : // www.pereplet.ru/lipunov/625.html
GCN Circular 43072
Subject
GRB 251211B: Fermi GBM Final Real-time Localization
Date
2025-12-11T20:42:26Z (3 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 20:32:04 UT on 11 Dec 2025, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 251211B (trigger 787177929.268096 / 251211856).
The on-ground calculated location, using the Fermi GBM trigger data, is RA = 176.2, Dec = -11.6 (J2000 degrees, equivalent to J2000 11h 44m, -11d 35'), with a statistical uncertainty of 4.5 degrees.
The angle from the Fermi LAT boresight is 56.0 degrees.
The skymap can be found here:
https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn251211856/quicklook/glg_skymap_all_bn251211856.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/bn251211856/quicklook/glg_healpix_all_bn251211856.fit
The GBM light curve can be found here:
https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2025/bn251211856/quicklook/glg_lc_medres34_bn251211856.gif