GRB 260303B
GCN Circular 43919
Subject
GRB 260303B: AstroSat CZTI detection
Date
2026-03-04T19:43:04Z (8 days ago)
From
Anuraag Arya at IIT Bombay <aryaanuraag910@gmail.com>
Via
Web form
M. Tembhurnikar (IUCAA), Harsha K. H. (IUCAA), S. Salunke (IUCAA), A. Arya (IITB), A. Goyal (IITB), 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 a long GRB 260303B which was also detected by Fermi GBM (Fermi GBM Team., GCN Circ. 43907), and NuSTAR (Waratkar et. al. , GCN Circ. 43914).
The source was clearly detected in the CZT detectors in the 20-200 keV energy range. The light curve peaks at 2026-03-03 13:24:23.50 UTC. The measured peak count rate associated with the burst is 59 (+29, -5) counts/s above the background in the combined data of two quadrants (out of four), with a total of 504 (+69, -193) counts. The local mean background count rate was 167 (+1, -5) counts/s. We measure a T90 of 11 (+1, -3) s.
The source was also faintly detected in the CsI anticoincidence (Veto) detector in the 100-500 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 43914
Subject
GRB 260303B: NuSTAR detection of prompt emission
Date
2026-03-03T19:20:30Z (9 days ago)
From
Gaurav Waratkar at Caltech <gauravwaratkar@iitb.ac.in>
Via
Web form
G. Waratkar (Caltech) and B. Grefenstette (Caltech) report on behalf of the NuSTAR Search for INteresting Gamma-ray Signals (SINGS) working group:
The NuSTAR SINGS working group reports the detection of prompt emission from the long-duration GRB 260303B in both the NuSTAR CsI anti-coincidence shields. This GRB was identified through a blind search using the CsI shield rates. Details of the search algorithm will be described in a future paper.
The NuSTAR SINGS algorithm triggered at 2026-03-03 13:24:32.0 (with a resolution ~5-seconds). This is consistent with the detection of GRB 260303B by Fermi/GBM (Fermi GBM Team, GCN Circ. 43907).
The NuSTAR CsI shield data are recorded at 1 Hz. We see a single-peak detection lasting for ~20-s, consistent with the detections of Fermi/GBM. The peak count rate is ~1500-cps with a baseline rate of ~1000-cps during this time period. We don’t see any evidence in the signal above 100 keV in the CdZnTe detectors.
The GBM localization center (GCN Circ. 43907) at RA = 9.3, Dec = -26.7 implies an offset from the NuSTAR boresight of 92-deg (i.e. from the side of the instrument) and an offset from the geocenter of 159-deg.
Lightcurves and analysis for this GRB can be found here:
https://nustarsoc.caltech.edu/NuSTAR_Public/grbs/reports/2026/260303B
Information on NuSTAR SINGS can be found here:
https://nustarsoc.caltech.edu/NuSTAR_Public/grbs/
NuSTAR is a NASA Small Explorer mission led by Caltech and managed by JPL for NASA's Science Mission Directorate in Washington.
GCN Circular 43912
Subject
Fermi GRB 260303B: Global MASTER-Net observations report
Date
2026-03-03T19:17:13Z (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 [1] located in South Africa (South African Astronomical Observatory) started inspect of the Fermi GRB 260303B ( Fermi GBM team, GCN 43907) errorbox 20103 sec after notice time and 20130 sec after trigger time at 2026-03-03 18:59:50 UT, with upper limit up to 16.5 mag. The observations began at zenith distance = 82 deg. The sun altitude is -22.8 deg.
The galactic latitude b = -87 deg., longitude l = 48 deg.
Real time updated cover map and OT discovered available here:
https://master.sai.msu.ru/site/master2/observ.php?id=3166705
We obtain a following upper limits.
Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment
_________|_____________________|_____________________|____________________________________|_____|_______|_______|________
20160 | 2026-03-03 18:59:50 | MASTER-SAAO | (00h 37m 01.21s , -26d 50m 03.0s) | C | 60 | 16.2 |
20252 | 2026-03-03 19:01:22 | MASTER-SAAO | (00h 37m 03.97s , -26d 48m 23.8s) | C | 60 | 16.5 |
20344 | 2026-03-03 19:02:54 | MASTER-SAAO | (00h 36m 56.33s , -26d 49m 08.6s) | C | 60 | 16.4 |
20466 | 2026-03-03 19:04:26 | MASTER-SAAO | (00h 36m 55.39s , -26d 48m 01.6s) | C | 120 | 15.8 |
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 43908
Subject
GRB 260303B: BALROG localization (Fermi Trigger 794237065 / GRB 260303559)
Date
2026-03-03T14:05:07Z (10 days ago)
From
Jochen Greiner at MPE <jcgrog@mpe.mpg.de>
Via
email
T. Preis (University of Innsbruck) & J. Greiner (MPE Garching) report:
The public trigdat data of the Fermi Gamma-ray Burst Monitor (GBM) trigger
794237065 at 13:24:20 on 03 March 2026 were automatically fitted for spectrum
and sky location with BALROG (Burgess et al. 2018, MNRAS 476, 1427;
Berlato et al. 2019, ApJ 873, 60).
The best-fit position is:
RA(2000.0) = 13.0 deg
Decl.(2000.0) = -27.8 deg
The 1 sigma statistical error radius is 1.3 deg.
We estimate an additional systematic error of 1 deg.
Further details are available at:
https://grb.mpe.mpg.de/grb/GRB260303559/
The Healpix map can be downloaded from:
https://grb.mpe.mpg.de/grb/GRB260303559/healpix
The location parameters are available as JSON at:
https://grb.mpe.mpg.de/grb/GRB260303559/json
GCN Circular 43907
Subject
GRB 260303B: Fermi GBM Final Real-time Localization
Date
2026-03-03T13:34:53Z (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 13:24:20 UT on 3 Mar 2026, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 260303B (trigger 794237065.456588 / 260303559).
The on-ground calculated location, using the Fermi GBM trigger data, is RA = 9.3, Dec = -26.7 (J2000 degrees, equivalent to J2000 00h 37m, -26d 41'), with a statistical uncertainty of 1.6 degrees.
The angle from the Fermi LAT boresight is 67.0 degrees.
The skymap can be found here:
https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260303559/quicklook/glg_skymap_all_bn260303559.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/bn260303559/quicklook/glg_healpix_all_bn260303559.fit
The GBM light curve can be found here:
https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260303559/quicklook/glg_lc_medres34_bn260303559.gif