GCN 44202: GRB 260403A: AstroSat CZTI detection
2026-04-03T10:09:38.346Z | rev 0
A. Goyal (IITB), A. Arya (IITB), M. Tembhurnikar (IUCAA), Harsha K. H. (IUCAA), S. Salunke (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 a long-duration GRB 260403A which was also detected by Fermi GBM team (GCN Circ. 44195).
The source was clearly detected in the CZT detectors in the 20-200 keV energy range. The light curve peaks at 2026-04-03 02:31:28.51 UTC. The measured peak count rate associated with the burst is 53 (+33, -2) counts/s above the background in the combined data of three quadrants (out of four), with a total of 604 (+338, -211) counts. The local mean background count rate was 221 (+2, -3) counts/s. Using cumulative rates, we measure a T90 of 34 (+4, -14) 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 44195: GRB 260403A: Fermi GBM Final Real-time Localization
2026-04-03T02:41:58.495Z | rev 0
The Fermi GBM team reports the detection of a likely LONG GRB
At 02:31:27 UT on 3 Apr 2026, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 260403A (trigger 796876292.704364 / 260403105).
The on-ground calculated location, using the Fermi GBM trigger data, is RA = 236.2, Dec = -31.0 (J2000 degrees, equivalent to J2000 15h 44m, -31d 00'), with a statistical uncertainty of 5.0 degrees.
The angle from the Fermi LAT boresight is 86.0 degrees.
The skymap can be found here:
https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260403105/quicklook/glg_skymap_all_bn260403105.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/bn260403105/quicklook/glg_healpix_all_bn260403105.fit
The GBM light curve can be found here:
https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260403105/quicklook/glg_lc_medres34_bn260403105.gif