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.
Search for Circulars by submitter, subject, or body text (e.g. 'Fermi GRB').
To navigate to a specific circular, enter the associated Circular ID (e.g. 'gcn123', 'Circular 123', or '123').
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"- GRB 260511B SVOM/C-GFT optical counterpart detection
- EP260509a: LCO optical upper limits
- GRB 260511A: UTGO H50 optical afterglow observation
- GRB 260510C: AstroSat CZTI detection
- GRB 260511B: SVOM detection of a burst
- GRB 260511B: Fermi GBM Final Real-time Localization
- GRB 260510C: EP-FXT follow-up observation
- GRB 260510C: SVOM/VT optical counterpart confirmation
- EP260509a: EP-FXT non-detection and upper limit
- GRB 260511A: SVOM/VT optical observation with VHF data
- Fermi GRB 260511A: Global MASTER-Net observations report
- GRB 260511A: KAIT optical afterglow observations
- GRB 260511A: LCO optical afterglow detection
- GRB 260511A: SVOM/COLIBRÍ (FM-GFT) optical counterpart
- GRB 260511A: TRT optical counterpart detection
- GRB 260511A: SVOM detection of a bright burst
- GRB 260511A: BALROG localization (Fermi Trigger 800172815 / GRB 260511259)
- GRB 260510C: SVOM/COLIBRÍ (FM-GFT) optical counterpart candidate
- GRB 260511A: Fermi GBM Final Real-time Localization
- GRB 260510B: SVOM/VT optical upper limits
- GRB 260510C: SVOM/VT optical upper limits
- GRB 260510C: MAXI/GSC detection
- EP260509a: Global MASTER-Net observations report
- Fermi GBM Sub-Threshold Detection of GRB 260510B
- GRB 260510D: Fermi GBM Final Real-time Localization
- GRB 260510B: GOTO early upper limit
- GRB 260510C: SVOM detection of a burst
- GRB 260510C: Fermi GBM Final Real-time Localization
- GRB 260510A: GECAM-B observation
- GRB 260510B: LCO optical upper limits
- EP260509a: Einstein Probe detection of an X-ray transient
- GRB 260509A: Liverpool Telescope optical observations
- GRB 260510B: SVOM detection of a burst
- GRB 260509A: NOT spectroscopic redshift upper limit z < 1.95
- GRB 260509A: LCO optical observations
- SVOM GRB 260509A: MASTER-OAFA optical observation
- Fermi GRB 260510A: Global MASTER-Net observations report
- GRB 260509A: KAIT optical observations
- GRB 260509A: SVOM/COLIBRÍ (FM-GFT) observations
- GRB 260510A: Fermi GBM Final Real-time Localization
- GRB 260509A: SVOM/VT optical candidate with VHF data
- GRB 260509A: LCO optical counterpart detection
- GRB 260509A: GOTO optical counterpart candidate
- GRB 260509A: SVOM detection of a burst
- GRB 260506B: AstroSat CZTI detection
- IceCube-260504A: Upper limits from a search for additional neutrino events in IceCube
- EP260507a: REM optical/NIR observations
- EP260507a: refined analysis of the EP-WXT and EP-FXT observations
- GRB 260507B / EP260507a: Fermi-GBM Sub-Threshold Detection
- EP260507a: COLIBRÍ optical observations
- EP260507a: SVOM/VT optical observations
- EP260507a: NOT optical observations
- EP260507a: further Liverpool Telescope observations
- EP260507a: Liverpool Telescope optical upper limits
- GRB 260507A: Fermi GBM Final Real-time Localization
- EP260507a: GOTO optical counterpart detection
- EP260507a: TRT optical counterpart detection
- EP260507a: Kinder optical counterpart candidate
- EP260507a: LCO optical counterpart
- EP260507a: Einstein Probe detection of an X-ray transient
- GRB 260504B: AstroSat CZTI detection
- GRB 260504B: SVOM/ECLAIRs refined analysis
- GRB 260506B: BALROG localization (Fermi Trigger 799765648 / GRB 260506547)
- GRB 260506B: Fermi GBM Final Real-time Localization
- EP260502a is likely a flaring star
- Fermi GRB 260506A: Global MASTER-Net observations report
- GRB 260506A: Fermi GBM Final Real-time Localization
- GRB 260503A: GECAM-B observation of a burst
- IceCube Alert 260505A: Global MASTER-Net observations report
- GRB 260430B: Glowbug gamma-ray detection
- GRB 260504B: SVOM/VT optical upper limits
- GRB 260421B: radio observation with the VLA
- Konus-Wind detection of a burst from SGR 1E1841-045 on 2026 May 2
- Konus-Wind detection of GRB 260504B (short/hard)
- GRB 260504B: GECAM-B detection
- Fermi-LAT Gamma-ray Observations of IceCube-260504A
- GRB 260504C: SVOM/GRM observation of short GRB
- GRB 260504B: SVOM/GRM spectral analysis
- GRB 260430B: AstroSat CZTI detection of a long burst
- GRB 260504B: SVOM/MXT refined analysis and potential detection
- GRB 260504B: EP-FXT upper limit
- GRB 260502A: SVOM/GRM observation of a short GRB
- GRB 260503A: SVOM/GRM observation of a GRB
- IceCube-260504A - IceCube observation of a high-energy neutrino candidate track-like event
- Konus-Wind detection of GRB 260415C
- GRB 260310A / AT2026fgk: photometric monitoring and tentative maximum of a possible SN
- Konus-Wind detection of GRB 260411C
- GRB 260504B: REM optical/NIR observations
- IPN triangulation of GRB 260429A
- IPN triangulation of GRB 260428A
- GRB 260504B: AST3-2 i-band upper limit
- GRB 260504B: LCO z-band upper limit
- SVOM GRB 260504B: MASTER-OAFA optical observations
- GRB 260504B: SVOM detection of a short burst
- Fermi GRB 260504A: Global MASTER-Net observations report
- GRB 260504A: Fermi GBM Final Real-time Localization
- GRB 260503A: Fermi GBM Final Real-time Localization
- SVOM/GRM observation of a bright burst from SGR 1E1841-045
- GRB 260502A: GECAM-B observation of a short burst
- IPN triangulation of a bright burst from SGR 1E1841-045