GCN Circulars
GCN Circulars are rapid astronomical bulletins submitted by and distributed to community members worldwide. They are used to share discoveries, observations, quantitative near-term predictions, requests for follow-up observations, or future observing plans related to high-energy, multi-messenger, and variable or transient astrophysical events. See the documentation for help with subscribing to or submitting Circulars.
To navigate to a specific circular, enter the associated Circular ID (e.g. 'gcn123', 'Circular 123', or '123').
Advanced Search
To narrow the search results, use advanced search syntax. This allows for specifying which circular field to search (submitter, subject, and/or body). For additional information, refer to the advanced search documentation.
Advanced Search Examples (click to copy):
subject:"Swift"body:"GRB"submitter:"Judith Racusin"32486 results found.
- GOTO26djh/AT2026jpw transient: SAO RAS optical observations
- NOT r-band observations of the transient GOTO26djh/AT2026jpw
- GRB 260415B: NuSTAR detection of long prompt emission
- GRB 260414A: Glowbug gamma-ray detection
- EP260409a: Early NIR limits from MIRAGE on the MDM 1.3m telescope
- EP260321a: CMO SAI J,K observations
- GRB 260412A: Insight-HXMT/HE detection
- Fermi GRB 260413A: Global MASTER-Net observations report
- GRB 260410A: Glowbug gamma-ray detection of a short burst
- GRB 260410B: Insight-HXMT/HE detection
- GRB 260410A: Insight-HXMT/HE detection
- Konus-Wind detection of GRB 260410A (short/hard)
- GRB 260411B: GECAM-B observation of a long burst
- EP260321a: SVOM/VT optical observations and color changes around peak
- GRB 260410A: CALET Gamma-Ray Burst Monitor detection
- GRB 260412A: GECAM-B observation of a long burst
- Fermi GRB 260412A: Global MASTER-Net observations report
- GRB 260412A: Fermi GBM Observation
- GRB 260310A / AT2026fgk: NuSTAR detection of the rebrightening
- GRB 260411B: Fermi-LAT detection
- GRB 260412A: SVOM detection of a long burst
- GRB 260411B: COLIBRÍ optical observations
- GRB 260410B: Fermi GBM Observation
- GRB 260411B: Ondrejov D50 optical afterglow detection
- GRB260411B: 3.6m DOT optical observation
- GRB 260411A: SVOM/GRM observation
- GRB 260411B: SVOM/GRM observation of a long burst
- GRB 260409A: Insight-HXMT/HE detection
- GRB 260411B: Fermi GBM Detection
- GRB 260411B: GOTO optical counterpart candidate
- EP260409a: Gemini/FLAMINGOS2 J-band counterpart
- GRB 260410A: COLIBRÍ optical upper limit
- EP-WXT01709259790: Optical Upper limits with kinder observations
- GRB 260410A: Fermi GBM Observation
- GRB 260410B: SVOM/GRM detection of a short faint burst
- GRB 260410A: Fermi-LAT detection
- EP260409a: refined analysis of the EP-WXT and autonomous EP-FXT observations
- EP260321a: Chandra X-ray Non-detection
- GRB 260310A/AT2026fgk: Kilonova-Catcher SN peak identification
- GRB 260407A: GECAM-A detection
- GRB 260407A: Insight-HXMT/HE detection
- EP260409a: SVOM/VT optical upper limits
- EP260409a: COLIBRÍ optical upper limits
- GRB 260407A: CALET Gamma-Ray Burst Monitor detection
- EP260409a: Global MASTER-Net observations report
- EP260321a: VLA radio detection
- GRB 260407A: Glowbug gamma-ray detection
- GRB 260402A: SVOM/ECLAIRs refined analysis
- GRB 260310A: Continued VLA Multi-frequency Radio Observations
- GRB 260310A / AT2026fgk: X-ray rebrightening
- EP260402a / GRB 260402A: Mephisto optical upper limits
- EP-WXT01709259586: Xinglong optical upper limit
- EP260403a: Mephisto optical upper limits
- EP260402a/GRB 260402A: Xinglong optical upper limit
- EP260321a: Upper limits from VLA radio observations
- GRID detection of GRB 260401A
- EP260321a: uGMRT observations
- EP260405a: GMOS-N optical upper limits
- EP260405a: SVOM/VT optical upper limits
- EP260405a: Global MASTER-Net observations report
- EP260405a: Einstein Probe detection of a fast X-ray transient
- GRB 260403A: GECAM-B observation of a long burst
- EP260324A / AT 2026hir: COLIBRÍ further optical observations
- EP260403a: refined analysis of the EP-WXT and EP-FXT observations
- GRB 260330B: SVOM/VT further optical observation
- GRB 260330B: SVOM/ECLAIRs refined analysis
- EP260403a: LCO optical observations of the counterpart
- GRB 260310A/AT2026fgk: Kilonova-Catcher long term optical monitoring
- EP260403a: LCO optical counterpart detection
- EP260403a: COLIBRÍ optical counterpart candidate
- GRB 260330B: SVOM/VT optical candidate
- GRB 260330B: EP-FXT follow-up and identification of candidate afterglow
- GRB 260403A: AstroSat CZTI detection
- EP260402a/GRB 260402A: refined analysis of the EP-WXT and EP-FXT observations
- GRB 260402B: GECAM-B observation
- EP260402a/GRB 260402A: Jinshan near-infrared upper limit
- GRB 260402C: NuSTAR detection of prompt emission
- EP260324A / AT 2026hir: COLIBRÍ optical observations
- EP260324A / AT 2026hir: Spectroscopic Observations with the Next Generation Palomar Spectrograph
- GRB 260402A: WINTER J-band upper limit
- GRB260402A: GROWTH-India Telescope optical upper limit
- GRB 260402A / EP260402a: SVOM/VT optical upper limits
- EP260402a/GRB 260402A: SVOM/C-GFT upper limit
- GRB 260401A: SVOM/GRM observation
- GRB 260401A: GECAM-B observation
- EP260402a/GRB 260402A: Einstein Probe detection of an X-ray transient
- GRB 260402A: Kilonova-Catcher optical upper limit
- GRB 260402A: MASTER optical observations
- GRB 260402A: SVOM/COLIBRÍ (FM-GFT) optical upper limit
- GRB 260402A: SVOM/MXT candidate X-ray afterglow
- Fermi GRB 260401A: Global MASTER-Net observations report
- GRB 260401A: Fermi GBM Observation
- GRB 260401A: NuSTAR detection of prompt emission
- GRB 260401A: CALET Gamma-Ray Burst Monitor detection
- GRB 260401A: MAXI/GSC detection
- EP260329b: Mondy and Assy-Turgen optical upper limits
- GRB 260310A / AT2026fgk: Luminance-band optical follow-up with a 28cm telescope in Daocheng
- EP260321a :Xinglong optical observations
- EP260327a: Xinglong optical upper limit
- EP260329b: GOTO detection of optical counterpart