GRB 260421A
GCN Circular 44380
Subject
GRB 260421A: AstroSat CZTI detection
Date
2026-04-21T15:59:15Z (3 days ago)
From
Anuraag Arya at IIT Bombay <aryaanuraag910@gmail.com>
Via
Web form
M. Tembhurnikar (IUCAA), S. Salunke (IUCAA), Harsha K. H. (IUCAA), A. Arya (IITB), A. Goyal (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 short GRB 260421A which was also detected by Fermi GBM (Fermi GBM Team, GCN Circ. 44358).
The source was detected in the CsI anticoincidence (Veto) detector in the 100-500 keV energy range. The light curve peaks at 2026-04-21 02:12:43.91 UTC. The measured peak count rate associated with the burst is 251 (+66, -70) counts/s above the background in the combined data of all quadrants, with a total of 267 (+133, -138) counts. The local mean background count rate was 1340 (+8, -10) counts/s. Due to the intrinsic 1s binning of Veto data, we cannot reliably estimate 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 44359
Subject
Fermi GRB 260421A: Global MASTER-Net observations report
Date
2026-04-21T03:16:41Z (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-OAGH robotic telescope [1] located in Mexico (OAGH National Institute for Astrophysics, Optics and Electronics) started inspect of the Fermi GRB 260421A ( Fermi GBM team, GCN 44358) errorbox 3101 sec after notice time and 3131 sec after trigger time at 2026-04-21 03:04:55 UT, with upper limit up to 19.4 mag. Observations started at twilight. The observations began at zenith distance = 47 deg. The sun altitude is -16.0 deg.
The galactic latitude b = 54 deg., longitude l = 118 deg.
Real time updated cover map and OT discovered available here:
https://master.sai.msu.ru/site/master2/observ.php?id=3262778
We obtain a following upper limits.
Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment
_________|_____________________|_____________________|____________________________________|_____|_______|_______|________
3162 | 2026-04-21 03:04:55 | MASTER-OAGH | (13h 20m 14.14s , +62d 00m 28.6s) | C | 60 | 18.8 |
3162 | 2026-04-21 03:04:55 | MASTER-OAGH | (13h 22m 34.25s , +61d 26m 33.6s) | C | 60 | 19.2 |
3234 | 2026-04-21 03:06:08 | MASTER-OAGH | (13h 37m 23.83s , +62d 00m 57.1s) | C | 60 | 18.8 |
3234 | 2026-04-21 03:06:08 | MASTER-OAGH | (13h 39m 43.36s , +61d 26m 60.0s) | C | 60 | 19.2 |
3426 | 2026-04-21 03:09:20 | MASTER-OAGH | (13h 07m 30.22s , +63d 21m 09.2s) | C | 60 | 19.4 |
3426 | 2026-04-21 03:09:20 | MASTER-OAGH | (13h 04m 59.80s , +63d 55m 03.4s) | C | 60 | 19.0 |
3497 | 2026-04-21 03:10:31 | MASTER-OAGH | (13h 25m 34.30s , +63d 20m 22.6s) | C | 60 | 19.4 |
3497 | 2026-04-21 03:10:31 | MASTER-OAGH | (13h 23m 04.46s , +63d 54m 18.8s) | C | 60 | 19.0 |
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 44358
Subject
GRB 260421A: Fermi GBM Final Real-time Localization
Date
2026-04-21T02:23:18Z (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 SHORT GRB
At 02:12:44 UT on 21 Apr 2026, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 260421A (trigger 798430369.324586 / 260421092).
The on-ground calculated location, using the Fermi GBM trigger data, is RA = 198.8, Dec = 62.9 (J2000 degrees, equivalent to J2000 13h 15m, 62d 53'), with a statistical uncertainty of 8.2 degrees.
The angle from the Fermi LAT boresight is 60.0 degrees.
The skymap can be found here:
https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260421092/quicklook/glg_skymap_all_bn260421092.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/bn260421092/quicklook/glg_healpix_all_bn260421092.fit
The GBM light curve can be found here:
https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260421092/quicklook/glg_lc_medres34_bn260421092.gif