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"- Konus-Wind detection of GRB 260209B
- GRB 260208A: Swift UVOT detection
- Konus-Wind detection of GRB 260127B
- EP260209a: COLIBRÍ optical upper limit
- Fermi GRB 260210C: Global MASTER-Net observations report
- EP260209a: LCO optical upper limits
- EP260210a: Global MASTER-Net observations report
- EP260210a: refined analysis of the EP-FXT observation
- EP260209a: Global MASTER-Net observations report
- GRB 260208A: LCO detection of the optical counterpart
- EP260209a: Einstein Probe detection of a fast X-ray transient
- EP260210a: Optical upper limits with Kinder observations
- IPN triangulation of GRB 260207B (short/hard with EE)
- GRB 260210C: Fermi GBM Final Real-time Localization
- GRB 260210A: Glowbug gamma-ray detection
- GRB 260210B: Fermi GBM Final Real-time Localization
- EP260210a: SVOM/VT optical upper limit
- GRB 260210A: AstroSat CZTI detection
- GRB 260208C: AstroSat CZTI detection
- EP260210a: COLIBRÍ optical upper limit
- EP260210a: SVOM/C-GFT upper limit
- GRB 260208B: refined analysis of the EP-FXT observation
- EP260210a: Einstein Probe detection of an X-ray transient
- GRB 260207B: AstroSat CZTI detection
- GRB 260208C: SVOM/GRM observation
- GRB 260204A: Swift-XRT afterglow detection
- GRB 260208B: AstroSat CZTI detection of a bright long burst
- GRB260208A: Liverpool Telescope optical follow-up observations
- GRB 260208A: Glowbug gamma-ray detection
- GRB 260208A: NuSTAR detection of prompt emission
- GRB 260208A: Fermi GBM Observation
- Fermi GRB 260209A: Global MASTER-Net observations report
- GRB 260208B: Swift-XRT observations
- GRB 260131A/B: continued Mondy optical observations
- GRB 260204A: Swift/UVOT Upper Limits
- GRB 260208B: COLIBRÍ optical observations
- GRB 260208A: Mondy optical observations (duplicate submission)
- GRB 260208A: Mondy optical observations
- GRB 260208A: 1.3m DFOT optical detection
- GRB 260208A: COLIBRÍ optical observations
- GRB 260208B: EP-FXT observation
- GRB 260208A: NOT spectroscopic redshift z = 2.36
- GRB 260208A: Liverpool Telescope optical detection
- Fermi GRB 260208C: Global MASTER-Net observations report
- GRB 260208B: SVOM/VT optical candidate
- GRB 260208A: GECAM-B observation of a bright burst
- GRB 260208A: Zwicky Transient Facility Follow-Up of a Fermi GRB (Trigger 792220053)
- GRB 260209A: Fermi GBM Final Real-time Localization
- GRB 260208A: SVOM/VT optical observation
- Fermi GRB 260208D: Global MASTER-Net observations report
- GRB 260208D: Fermi GBM Final Real-time Localization
- GRB 260208A: Swift-XRT observations
- GRB 260208B: Swift ToO observations
- GRB 260208B: SVOM/GRM observation of a bright burst
- GRB 260208B: Fermi GBM Detection
- LAT GRB 260208B: Global MASTER-Net observations report
- GRB 260208B: Fermi-LAT detection
- GRB 260208C: Fermi GBM Final Real-time Localization
- GRB 260208A: Fermi-LAT detection
- GRB 260207B: GECAM-B observation
- GRB 260208A: Swift ToO observations
- GRB 260208A: Fermi GBM Classification Correction
- GRB 260208A: GOTO detection of a potential optical counterpart (GOTO26aob)
- GRB 260208A : MASTER bright optical transient inside retracted Fermi error-box
- GRB 260208B: BALROG localization (Fermi Trigger 792237169 / GRB 260208412)
- GRB 260208B: Fermi GBM Final Real-time Localization
- Fermi GRB 260208A: Global MASTER-Net observations report
- Fermi Gamma-ray Burst Monitor trigger 792220053/260208214 is not a GRB
- GRB 260208A: Fermi GBM Final Real-time Localization
- GRB 260207B: Fermi GBM Detection of a Short Burst with Extended Emission
- GRB 260207A : MASTER optical counterpart discovery
- GRB 260131A/B: Mondy and Terskol optical observations
- Fermi GRB 260207B: Global MASTER-Net observations report
- GRB 260206A: Swift-XRT observations
- GRB 260207B: Fermi GBM Final Real-time Localization
- GRB 260207A: Fermi GBM Final Localization
- Fermi trigger No 792135758: Global MASTER-Net observations report
- EP260131a: VLA detection
- GRB 260206A: Tiled Swift observations
- GRB 260206A (or XRB from 4U 0513-40): MAXI/GSC detection
- GRB 260204A: SVOM/VT confirms fading of the optical afterglow
- GRB 260204A: Swift-XRT observations
- GRB 260204A: LCO optical afterglow detection
- GRB 260204A: SVOM/VT optical candidate
- GRB 260204A : MASTER Global robotic net optical observations
- Fermi GBM Sub-Threshold Detection of GRB 260204A
- GRB 260204A: GOTO optical upper limit
- GRB 260204A: LCO optical upper limits
- EP260110a: Late GTC/EMIR near-infrared observations
- GRB 260204B: Fermi GBM Final Real-time Localization
- GRB 260204A: SVOM detection of a burst
- GRB 260121A: 239Alferov CubeSat detection
- Konus-Wind detection of GRB 260121A
- GRB 260131A/B: OHP/T193 optical observations
- GRB 260131A: KAIT optical observations
- GRB 251230A: MeerLICHT afterglow detection
- GRB 260131A: FTW optical and NIR observations
- GRB 260131A/AT2026bwg: Observations by the Zwicky Transient Facility
- GRID detection of GRB 260131A/B
- GRB 260131A/B: GTC/OSIRIS+ redshift confimation