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"- Fermi GRB 210427A: Global MASTER-Net observations report
- GRB 210427A: Fermi GBM Final Real-time Localization
- GRB 210422B: Fermi GBM Final Localization
- GRB 210420B: Assy optical observations
- Fermi trigger No 640975205: Global MASTER-Net observations report
- GRB 210425A: GECAM detection
- GRB 210424.694: DDOTI Upper Limits on the Afterglow
- GRB 210422A: Swift-BAT refined analysis
- GRB 210424A: Fermi GBM Final Real-time Localization
- GRB 210420B: follow-up photometry of optical afterglow at INASAN/Simeiz
- GRB 210420B: Zeiss-1000 of Koshka optical observations
- GRB 210421A: Swift-BAT refined analysis
- GRB 210421B: Swift-XRT observations
- GRB 210421B: AstroSat CZTI detection
- GRB 210420B: continued Tautenburg observations
- GRB 210421A: GECAM detection
- GRB 210421B: AstroSat CZTI detection
- Swift GRB210422.74: Global MASTER-Net observations report
- GRB 210422A: Swift detection of a burst
- GRB 210421A: Swift/UVOT Upper Limits
- GRB 210420B: Correction to AST3-3 YaoAn magnitude
- GRB 210420B: follow-up photometry of the optical afterglow at Konkoly
- GRB 210421A: MITSuME Akeno optical upper limits
- GRB 210419B: AstroSat CZTI detection
- Fermi Gamma-ray Burst Monitor trigger 210421C is not a GRB
- GRB 210420B: Swift-BAT refined analysis
- GRB 210421B: Swift ToO observations
- GRB 210421B: Swift/BAT-GUANO detection and arcminute localization
- GRB 210420B: Swift-XRT refined Analysis
- GRB 210421A: Swift-XRT refined Analysis
- GRB 210421B: Correction of GRB Type to "Likely Long GRB"
- Fermi GRB 210421C: Global MASTER-Net observations report
- GRB 210420B: Montarrenti Observatory follow-up observations
- GRB 210421C: Fermi GBM Final Real-time Localization
- GRB 210421B: Fermi GBM Final Localization
- Fermi trigger No 640695289: Global MASTER-Net observations report
- GRB 210419C: Swift/UVOT Upper Limits
- GRB 210420B: Correction to DDOTI Magnitude
- GRB 210420B: Ondrejov D50 optical afterglow detection
- GRB 210421A: Enhanced Swift-XRT position
- GRB 210420B: RATIR Optical and NIR Observations
- GRB 210420B: Tautenburg observations
- GRB 210420B: Swift/UVOT Detection
- GRB 210420B: KAIT Optical Observations
- GRB 210413B: MITSuME Okayama optical upper limits
- GRB 210419C: MITSuME Akeno optical upper limits
- GRB 210420B: DDOTI Detection of the Afterglow
- GRB 210421A: DDOTI Upper Limit
- GRB 210419C: Swift-BAT refined analysis
- Fermi GRB 210420A: Global MASTER-Net observations report
- GRB 210420B: update on the BAT trigger time
- GRB 210420B: Redshift from GTC
- GRB 210420B: Multiband photometry from NOT
- GRB 210420B: Montarrenti Observatory optical afterglow detection
- Swift GRB 210421A: Global MASTER-Net observations report
- GRB 210421A: Swift detection of a burst
- GRB 210420B: AST3-3 YaoAn Optical Observation
- GRB 210420B: BOOTES-4/MET optical afterglow detection
- GRB 210420B: Optical observations
- GRB 210420B: MASTER optical counterpart detection
- GRB 210420B: Swift detection of a burst
- GRB 210419C: RATIR Optical and NIR Upper Limits
- GRB 210419C: Montarrenti Observatory Upper Limit
- GRB 210419A: Swift/UVOT Upper Limits
- GRB 210419C: KAIT Optical Upper Limit
- GRB 210419C: Enhanced Swift-XRT position
- GRB 210419A: Swift-BAT refined analysis
- GRB 210420A: Fermi GBM Final Real-time Localization
- Swift GRB210419.98: Global MASTER-Net observations report
- GRB 210419A: Swift-XRT refined Analysis
- GRB 210419C: Swift detection of a burst
- Fermi GRB 210419B: Global MASTER-Net observations report
- Swift GRB 210419A: Global MASTER-Net observations report
- GRB 210419B: Fermi GBM Final Real-time Localization
- GRB 210419A: Enhanced Swift-XRT position
- GRB 210419A: LCO Optical Upper Limit
- GRB 210419A: Swift detection of a burst
- GRB 210413B: Swift-XRT observations
- Fermi GBM trigger 640353092/210417494 is not a GRB
- GRB 210413B: LOAO optical upper limit
- Fermi Gamma-ray Burst Monitor trigger 640303939/210416925 is not a GRB
- GRB 210411C: A very significant early X-ray afterglow
- IceCube Alert 210416.09: Global MASTER-Net observations report
- GRB 210413B: Swift ToO observations
- IceCubeCascade-210416a: Kanata Optical Imaging of 3C 279
- GRB 210413B: Swift/BAT detection and probable localization of a short burst
- GRB 210411B: AstroSat CZTI detection
- GRB 210410A: AstroSat CZTI detection
- GRB 210410A: A twin of short GRB 090510 with complementary observations
- Fermi GRB 210415A: Global MASTER-Net observations report
- GRB 210415A: Fermi GBM Final Real-time Localization
- GRB 210413A: GECAM detection
- GRB 210410A: Swift/UVOT Upper Limits (revision)
- GRB 210411C: Swift/UVOT Detection
- GRB 210411C: Swift-BAT refined analysis
- GRB 210411C: Chilescope optical observations
- GRB 210411C: ePESSTO+ NTT optical observations
- GRB 210411C: Swift-XRT refined Analysis
- GRB 210411C: VLT/X-shooter redshift
- GRB 210410A: MITSuME Akeno optical upper limits