General information
GRB 260421B triggered Fermi/GBM at 04:13:21 UT on 2026-04-21 and was also detected by SVOM (ECLAIRs/GRM), with a well-identified afterglow position consistent across optical, X-ray, and later radio observations.
Wavelength coverage
- Gamma-ray: Fermi/GBM; SVOM/ECLAIRs; SVOM/GRM; Insight-HXMT/HE.
- X-ray: SVOM/MXT detection; Einstein Probe/FXT detection with measured 0.5–10 keV flux.
- Optical: Multiple detections (SVOM/VT, SVOM/COLIBRÍ, TRT, LCO, BOOTES-7, VLT imaging; plus later limits from DOT and GRANDMA reports).
- Near-IR: J-band non-detections/limits (WINTER; SYSU 80cm).
- Radio: VLA non-detections at ~1–3 d and detection at 8.92 d.
No observations were mentioned in UV, sub-mm/mm, or TeV bands.
Lightcurve and spectrum
Redshift
VLT/X-shooter spectroscopy measured absorption features at a common redshift z=2.115, interpreted as the GRB redshift.
What’s special vs typical
GCN 44665: GRB 260421B: radio detection with the VLA
2026-05-19T13:17:22.540Z | rev 0
GCN 44476: GRB 260421B: radio observation with the VLA
2026-05-05T15:50:44.521Z | rev 0
GCN 44402: GRB 260421B: Kilonova-Catcher optical afterglow detection
2026-04-23T15:46:39.663Z | rev 0
GCN 44401: GRB 260421B: Insight-HXMT/HE detection
2026-04-23T14:06:52.265Z | rev 0
GCN 44397: GRB 260421B: SVOM/ECLAIRs refined analysis
2026-04-23T10:06:59.073Z | rev 2
GCN 44396: GRB 260421B: 3.6m DOT optical observation
2026-04-23T10:00:19.621Z | rev 0
2026-04-22T08:31:00.313Z | rev 0
GCN 44388: GRB260421B: J band upper limit by SYSU 80cm infrared telescope
2026-04-22T07:24:57.600Z | rev 0
GCN 44387: GRB 260421B: EP-FXT follow-up observation
2026-04-22T02:42:41.802Z | rev 0
GCN 44384: GRB 260421B: J-band upper limit with WINTER
2026-04-21T23:32:26.010Z | rev 0
GCN 44383: GRB 260421B: LCO optical counterpart detection
2026-04-21T23:18:19.092Z | rev 0
GCN 44382: GRB 260421B: Fermi GBM Observation
2026-04-21T19:36:16.903Z | rev 0
GCN 44377: GRB 260421B: SVOM/VT optical observations
2026-04-21T11:53:36.227Z | rev 0
GCN 44368: GRB 260421B: VLT/X-shooter spectroscopic redshift z = 2.115
2026-04-21T06:41:33.314Z | rev 0
GCN 44367: Fermi GRB 260421B: Global MASTER-Net observations report
2026-04-21T05:45:38.348Z | rev 0
GCN 44366: GRB 260421B: BOOTES-7 early optical afterglow detection
2026-04-21T05:37:53.205Z | rev 0
GCN 44365: GRB 260421B: LCO optical afterglow confirmation
2026-04-21T05:32:17.597Z | rev 0
GCN 44364: GRB 260421B: SVOM/COLIBRÍ (FM-GFT) optical detection of a candidate counterpart
2026-04-21T05:28:06.522Z | rev 0
GCN 44363: GRB 260421B: TRT optical counterpart detection
2026-04-21T05:26:32.010Z | rev 0
GCN 44362: GRB 260421B: SVOM detection of a long burst
2026-04-21T05:20:23.010Z | rev 0
GCN 44361: GRB 260421B: BALROG localization (Fermi Trigger 798437606 / GRB 260421176)
2026-04-21T04:54:24.252Z | rev 0
GCN 44360: GRB 260421B: Fermi GBM Final Real-time Localization
2026-04-21T04:22:36.864Z | rev 0