GRB 261026B
GCN Circular 46066
Subject
GRB 261026B: AstroSat CZTI detection
Date
2026-10-28T09:11:49Z (a day ago)
From
ABHINAV GOYAL at Indian Institute of Technology Bombay <abhigoyale2003@gmail.com>
Via
Web form
S. Salunke (IUCAA), Harsha K. H. (IUCAA), A. Goyal (IITB), A. Arya (IITB), S. Puri (IITB), G. Waratkar (Caltech/IITB), V. Bhalerao (IITB), A. Vibhute (IUCAA), 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 261026B which was also detected by Fermi (Fermi GBM Team, GCN Circ. 46032), NuSTAR (Waratkar et. al., GCN Circ. 46052), and SVOM/GRM (via notices).
The source was detected in the CZT detectors in the 20-200 keV energy range. The light curve peaks at 2026-10-26 07:21:19.60 UTC. The measured peak count rate associated with the burst is 244 (+36, -24) counts/s above the background in the combined data of three quadrants (out of four), with a total of 2741 (+283, -323) counts. The local mean background count rate was 216 (+2, -2) counts/s. We measure a T90 of 21 (+4, -3) s from the cumulative CZT light curve.
The source was also detected in the CsI anticoincidence (Veto) detector in the 100-500 keV energy range. The light curve showed a peak at 2026-10-26 07:21:19.60 UTC. The measured peak count rate associated with the burst is 313 (+49, -30) counts/s above the background in the combined data of three quadrants (out of four), with a total of 3030 (+347, -443) counts. The local mean background count rate was 540 (+3, -4) counts/s. We measure a T90 of 18 (+4, -3) s from the cumulative Veto light curve.
CZTI data products like interactive and downloadable light curves for this GRB can be found at:
https://astrosat.iucaa.in/cift/cift_products/ET20261026T072117/ET20261026T072117_details.html
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 46052
Subject
GRB 261026B: NuSTAR detection of prompt emission
Date
2026-10-26T22:01:21Z (2 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 261026B 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 2026-10-26T07:21:12.380 UTC shows a detection of GRB 261026B, also detected by Fermi-GBM (GCN 46032), SVOM-GRM (GCN notices), and KONUS-Wind (GCN notices).
The NuSTAR CsI shield data are recorded at 1 Hz. We detect a single-peaked burst lasting for about 20-s. The peak count rate is ~1500-cps with a baseline rate of ~1000-cps during this time period. We do not see any evidence in the signal above 100 keV in the CZT detectors.
The Fermi-GBM localization (GCN 46032) at RA = 61.8, Dec = -1.7 implies an offset from the NuSTAR boresight of 38-deg and an offset from the geocenter of 140-deg.
Lightcurves and analysis for this GRB can be found here:
https://nustarsoc.caltech.edu/NuSTAR_Public/grbs/reports/2026/261026B
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 46036
Subject
Fermi GRB 261026B: Global MASTER-Net observations report
Date
2026-10-26T09:01:29Z (3 days ago)
From
Vladimir Lipunov at Moscow State U/Krylov Obs <lipunov@xray.sai.msu.ru>
Via
email
M. Segura, F. Podesta, R.Podesta, E. Gonzalez (Observatorio Astronomico Felix Aguilar (OAFA)
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 (Lomonosov MSU)
D.Buckley (SAAO),
A. Gabovich, V.Yurkov (Blagoveschensk Educational StateUniversity)
A.Sosnovskij (Lomonosov MSU)
A. Tlatov, D. Dormidontov (Kislovodsk Solar Station of the Pulkovo Observatory)
L.Carrasco, J.R.Valdes, V.Chavushyan, V.M.Patino Alvarez, J.Martinez,
A.R.Corella, L.H.Rodriguez (INAOE, Guillermo Haro Astrophysics Observatory)
R.Rebolo (The Instituto de Astrofisica de Canarias)
O.Gress, N.Budnev(ISU)
MASTER-OAFA robotic telescope [1] located in Argentina (OAFA observatory of San Juan National University) started inspect of the Fermi GRB 261026B ( Fermi GBM team, GCN 46032) errorbox 549 sec after notice time and 581 sec after trigger time at 2026-10-26 07:30:54 UT, with upper limit up to 18.6 mag. The observations began at zenith distance = 34 deg. The sun altitude is -26.4 deg.
The galactic latitude b = -36 deg., longitude l = 193 deg.
Real time updated cover map and OT discovered available here:
https://master.sai.msu.ru/site/master2/observ.php?id=3531853
We obtain a following upper limits.
Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment
_________|_____________________|_____________________|____________________________________|_____|_______|_______|________
642 | 2026-10-26 07:30:54 | MASTER-OAFA | (04h 05m 24.25s , -01d 50m 38.1s) | C | 120 | 18.1 |
1060 | 2026-10-26 07:38:22 | MASTER-OAFA | (04h 05m 22.23s , -01d 51m 12.2s) | C | 60 | 18.1 |
1125 | 2026-10-26 07:39:27 | MASTER-OAFA | (04h 05m 21.90s , -01d 51m 14.1s) | C | 60 | 18.2 |
1190 | 2026-10-26 07:40:32 | MASTER-OAFA | (04h 05m 21.60s , -01d 51m 13.2s) | C | 60 | 18.2 |
1257 | 2026-10-26 07:41:39 | MASTER-OAFA | (04h 05m 21.28s , -01d 51m 12.8s) | C | 60 | 18.2 |
1322 | 2026-10-26 07:42:44 | MASTER-OAFA | (04h 05m 20.95s , -01d 51m 12.5s) | C | 60 | 18.2 |
1388 | 2026-10-26 07:43:50 | MASTER-OAFA | (04h 05m 20.63s , -01d 51m 12.3s) | C | 60 | 18.2 |
1454 | 2026-10-26 07:44:56 | MASTER-OAFA | (04h 05m 20.32s , -01d 51m 11.7s) | C | 60 | 18.2 |
1519 | 2026-10-26 07:46:01 | MASTER-OAFA | (04h 05m 19.98s , -01d 51m 11.1s) | C | 60 | 18.1 |
1585 | 2026-10-26 07:47:07 | MASTER-OAFA | (04h 05m 19.71s , -01d 51m 11.1s) | C | 60 | 18.2 |
1651 | 2026-10-26 07:48:13 | MASTER-OAFA | (04h 05m 19.39s , -01d 51m 10.6s) | C | 60 | 18.3 |
1717 | 2026-10-26 07:49:18 | MASTER-OAFA | (04h 05m 19.04s , -01d 51m 10.4s) | C | 60 | 18.1 |
1782 | 2026-10-26 07:50:24 | MASTER-OAFA | (04h 05m 18.75s , -01d 51m 09.9s) | C | 60 | 18.3 |
2222 | 2026-10-26 07:57:44 | MASTER-OAFA | (03h 58m 38.16s , -02d 35m 48.4s) | C | 60 | 18.2 |
2300 | 2026-10-26 07:59:02 | MASTER-OAFA | (03h 58m 38.15s , -02d 37m 13.8s) | C | 60 | 18.3 |
2376 | 2026-10-26 08:00:18 | MASTER-OAFA | (04h 06m 41.10s , -02d 35m 52.2s) | C | 60 | 18.4 |
2453 | 2026-10-26 08:01:35 | MASTER-OAFA | (03h 58m 34.59s , -02d 36m 40.6s) | C | 60 | 18.3 |
2529 | 2026-10-26 08:02:51 | MASTER-OAFA | (03h 58m 34.70s , -02d 35m 39.0s) | C | 60 | 18.3 |
2605 | 2026-10-26 08:04:07 | MASTER-OAFA | (04h 06m 41.81s , -02d 36m 27.4s) | C | 60 | 18.3 |
2680 | 2026-10-26 08:05:22 | MASTER-OAFA | (03h 58m 35.75s , -02d 37m 37.2s) | C | 60 | 18.2 |
2756 | 2026-10-26 08:06:38 | MASTER-OAFA | (03h 59m 08.63s , -04d 29m 59.6s) | C | 60 | 18.3 |
2910 | 2026-10-26 08:09:12 | MASTER-OAFA | (04h 07m 14.13s , -04d 29m 27.7s) | C | 60 | 18.2 |
2985 | 2026-10-26 08:10:27 | MASTER-OAFA | (04h 07m 06.86s , -04d 30m 21.1s) | C | 60 | 17.9 |
3060 | 2026-10-26 08:11:42 | MASTER-OAFA | (03h 59m 06.26s , -04d 29m 31.7s) | C | 60 | 17.6 |
3136 | 2026-10-26 08:12:58 | MASTER-OAFA | (04h 07m 12.88s , -04d 30m 19.6s) | C | 60 | 18.3 |
3288 | 2026-10-26 08:15:29 | MASTER-OAFA | (04h 13m 35.69s , -00d 41m 31.4s) | C | 60 | 18.4 |
3589 | 2026-10-26 08:20:31 | MASTER-OAFA | (04h 13m 32.59s , -00d 41m 07.8s) | C | 60 | 18.5 |
3740 | 2026-10-26 08:23:02 | MASTER-OAFA | (04h 13m 32.48s , -00d 43m 06.2s) | C | 60 | 18.5 |
3813 | 2026-10-26 08:24:15 | MASTER-OAFA | (04h 06m 13.81s , -01d 49m 03.4s) | C | 60 | 18.2 |
3879 | 2026-10-26 08:25:21 | MASTER-OAFA | (04h 06m 13.82s , -01d 49m 03.2s) | C | 60 | 18.4 |
3945 | 2026-10-26 08:26:27 | MASTER-OAFA | (04h 06m 13.79s , -01d 49m 02.4s) | C | 60 | 18.4 |
4011 | 2026-10-26 08:27:33 | MASTER-OAFA | (04h 06m 13.79s , -01d 49m 01.9s) | C | 60 | 18.6 |
4077 | 2026-10-26 08:28:39 | MASTER-OAFA | (04h 06m 13.76s , -01d 49m 01.4s) | C | 60 | 18.4 |
4142 | 2026-10-26 08:29:44 | MASTER-OAFA | (04h 06m 13.76s , -01d 49m 01.0s) | C | 60 | 18.2 |
4208 | 2026-10-26 08:30:50 | MASTER-OAFA | (04h 06m 13.78s , -01d 49m 00.7s) | C | 60 | 18.3 |
4274 | 2026-10-26 08:31:56 | MASTER-OAFA | (04h 06m 13.75s , -01d 49m 00.1s) | C | 60 | 18.3 |
4340 | 2026-10-26 08:33:02 | MASTER-OAFA | (04h 06m 13.74s , -01d 48m 59.6s) | C | 60 | 18.4 |
4407 | 2026-10-26 08:34:08 | MASTER-OAFA | (04h 06m 13.73s , -01d 48m 59.4s) | C | 60 | 18.4 |
4472 | 2026-10-26 08:35:14 | MASTER-OAFA | (04h 06m 13.74s , -01d 48m 59.3s) | C | 60 | 18.5 |
4537 | 2026-10-26 08:36:19 | MASTER-OAFA | (04h 06m 13.73s , -01d 48m 58.3s) | C | 60 | 18.5 |
5428 | 2026-10-26 08:51:10 | MASTER-OAFA | (04h 06m 41.96s , -02d 36m 04.5s) | C | 60 | 17.0 |
5581 | 2026-10-26 08:53:43 | MASTER-OAFA | (04h 06m 42.00s , -02d 36m 48.7s) | C | 60 | 16.4 |
5659 | 2026-10-26 08:55:00 | MASTER-OAFA | (04h 06m 38.77s , -02d 35m 19.7s) | C | 60 | 16.9 |
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 46032
Subject
GRB 261026B: Fermi GBM Final Real-time Localization
Date
2026-10-26T07:31:46Z (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 07:21:12 UT on 26 Oct 2026, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 261026B (trigger 814692077.378468 / 261026306).
The on-ground calculated location, using the Fermi GBM trigger data, is RA = 61.8, Dec = -1.7 (J2000 degrees, equivalent to J2000 04h 07m, -1d 42'), with a statistical uncertainty of 1.4 degrees.
The angle from the Fermi LAT boresight is 80.0 degrees.
The skymap can be found here:
https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn261026306/quicklook/glg_skymap_all_bn261026306.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/bn261026306/quicklook/glg_healpix_all_bn261026306.fit
The GBM light curve can be found here:
https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn261026306/quicklook/glg_lc_medres34_bn261026306.gif