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').
- Trigger 1062273: Swift detection of 4U 1700-377
- GRB 210730A: Campo Imperatore optical observations
- GRB 210730A: BOOTES-5/JGT and 2.2m CAHA telescopes optical limit
- Swift GRB 210730A: Global MASTER-Net observations report
- Fermi trigger No 649390368: Global MASTER-Net observations report
- GRB 210730A: TNG optical observations
- IceCube-210730A - IceCube observation of a high-energy neutrino candidate track-like event
- GRB 210726A: Chandra detection of the X-ray afterglow
- GRB 210730A: Fermi GBM observation
- Fermi trigger No 649313854: Global MASTER-Net observations report
- GRB 210730A: AstroSat CZTI detection
- GRB 210730A: Swift-BAT refined analysis
- GRB 210730A: Swift-XRT refined Analysis
- GRB 210730A: Swift/UVOT Upper Limits
- GRB 210724A: Early CAHA 2.2m limit
- GRB 210730A: Enhanced Swift-XRT position
- GRB 210727A: AstroSat CZTI detection
- GRB 210730A: Swift detection of a burst near M82
- GRB 210724A: Corrected Swift-XRT enhanced position
- Fermi GBM Sub-Threshold Detection of GRB 210725B
- GRB 210726A: OSIRIS/GTC observations
- GRB 210727A: CALET Gamma-Ray Burst Monitor detection
- GRB 210726A: Deep CAHA 2.2m limit
- GRB 210726A: 6 GHz VLA radio upper limit
- IPN triangulation of GRB 210727A (short)
- Fermi GBM Sub-Threshold Detection of GRB 210726A
- GRB 210714A: Fermi GBM observation
- GRB 210702A: MeerKAT radio detection
- GRB 210726A: Swift-XRT refined Analysis
- GRB 210726A: Swift-BAT refined analysis
- GRB 210726A: Likely a short burst
- GRB 210726A: RATIR Optical Upper Limits and Candidate Host Galaxy
- GRB 210727A: AGILE/MCAL detection
- Fermi trigger No 649072251: Global MASTER-Net observations report
- GRB 210727A: BALROG localization (Fermi Trigger 649072251 / GRB 210727410)
- GRB 210725A: AbAO optical upper limit
- GRB 210724A: Swift/UVOT Upper Limits
- GRB 210723A: Swift/UVOT Upper Limits
- GRB 210725A: Swift/UVOT Upper Limits
- GRB 210725B: Swift/UVOT Upper Limits
- GRB 210726A: CAHA 2.2m telescope optical limit
- GRB 210726A: Enhanced Swift-XRT position
- GRB 210726A: Swift detection of a burst
- Swift GRB210726.80: Global MASTER-Net observations report
- Fermi trigger No 648959581: Global MASTER-Net observations report
- GRB 210725B: Swift-XRT refined Analysis
- GRB 210725A: Fermi GBM detection
- GRB 210724A: Zeiss-1000 of Koshka observatory, optical upper limit
- GRB 210725A: Swift-XRT refined Analysis
- GRB 210725B: Swift-BAT refined analysis
- GRB 210724A: Swift-XRT refined Analysis
- GRB 210725A: Swift-BAT refined analysis
- GRB 210724A: Swift-BAT refined analysis
- Swift GRB 210725B: Global MASTER-Net observations report
- GRB 210724A: Afterglow candidate from OSIRIS/GTC
- GRB 210725B: Enhanced Swift-XRT position
- GRB 210725A: MITSuME Akeno optical upper limits
- GRB 210725B: Swift detection of a burst
- GRB 210725A: CALET Gamma-Ray Burst Monitor detection
- GRB 210723A: CALET Gamma-Ray Burst Monitor detection
- GRB 210722A: continued Assy optical observations
- GRB 210722A: Nanshan/NEXT further optical observations
- GRB 210725A: KAIT Optical Upper Limit
- Fermi trigger No 648868114: Global MASTER-Net observations report
- GRB 210725A: Swift detection of a burst
- Swift GRB210725.16: Global MASTER-Net observations report
- GRB 210723A: Fermi GBM Observation
- GRB210724A: MeerLICHT upper limits
- GRB 210724A: Swift detection of a burst
- Swift GRB210724.84: Global MASTER-Net observations report
- GRB 210723A: Swift-BAT refined analysis
- GRB 210722A: continued Assy optical observations
- GRB 210723A: Swift-XRT refined Analysis
- GRB 210722A: D50 optical detection
- Swift GRB 210723A: Global MASTER-Net observations report
- GRB 210722A: Fermi GBM observation
- GRB 210722A: Swift-BAT refined analysis
- GRB 210722A: Kitab optical observations, light curve
- GRB 210722A: Redshift from OSIRIS/GTC
- GRB 210723A: Prompt enhanced Swift-XRT position
- GRB 210723A: Swift detection of a burst
- GRB 210722A: RATIR Optical Observations
- GRB 210722A: Swift-XRT refined Analysis
- GRB 210722A: Swift/UVOT Detection
- GRB 210722A: GIT optical detection and preliminary analysis
- Swift GRB 210722A: Global MASTER-Net observations report
- GRB 210702A: ALMA detection of mm-band rebrightening
- GRB 210722A: Assy optical detection
- GRB 210702A: ATCA detection of radio rebrightening
- GRB 210722A: Nanshan/NEXT optical afterglow observations
- GRB 210722A: Swift detection of a burst with a bright optical counterpart
- Fermi trigger No 648602917: Global MASTER-Net observations report
- Fermi-LAT Gamma-ray Observations of IceCube-210717A
- GRB 210719A: GECAM detection
- IceCube-210717A: No counterpart candidates in INTEGRAL SPI-ACS and IBIS prompt observation
- Fermi trigger No 648359752: Global MASTER-Net observations report
- Fermi trigger No 648278666: Global MASTER-Net observations report
- IceCube-210717A: IceCube observation of a high-energy neutrino candidate track-like event
- Konus-Wind detection of GRB 210714A
- Fermi trigger No 647942198: MASTER optical afterglow detection