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').
- GRB 210506A: Swift/BAT-GUANO position retraction
- IPN triangulation of GRB 210506A
- HAWC-210507A: No neutrino counterpart candidates in ANTARES search
- Fermi GRB 210507A: Global MASTER-Net observations report
- Fermi-LAT Gamma-ray Observations of IceCube-210503A and detection of a new gamma-ray source, Fermi J0931.9+3633
- ZTF21aayokph (AT2021lfa): continued Mondy optical observations
- GRB 210507A: Fermi GBM Final Real-time Localization
- Integral GRB210507.04: Global MASTER-Net observations report
- Integral GRB210506.78: Global MASTER-Net observations report
- GRB 210506A: Swift-XRT observations
- ZTF21aayokph (AT2021lfa): MASTER OT detection 3h befor ZTF
- Alert from the HAWC Burst Monitor HAWC-210507A
- HAWC GRB 210507.443: DDOTI Upper Limit
- GRB 210506A: Nanshan/NEXT optical upper limit
- GRB 210506A: TNG NIR upper limits
- ZTF21aayokph (AT2021lfa): Mondy and Koshka observatory optical observations
- ZTF21aayokph (AT2021lfa): X-ray Detection with Swift/XRT
- Lowell Discovery Telescope Observations of ZTF21aayokph (AT2021lfa)
- IceCube-210503A: IceCube observation of a high-energy neutrino candidate event
- ZTF21aayokph (AT2021lfa): Assy optical observations
- GRB 210506A: Swift ToO observations
- ZTF21aayokph (AT2021lfa): Nanshan/NEXT optical upper limit
- GRB 210506A: Swift/BAT-GUANO detection and possible arcminute localization of a short hard burst
- GRB 210504A: Lowell Discovery Telescope optical observations
- ZTF21aayokph (AT2021lfa): Redshift from Gemini South
- GRB 210504A: VLT X-shooter redshift
- GRB 210424B: AstroSat CZTI detection
- GRB 210504A: Swift-XRT refined Analysis
- RATIR Observations of ZTF21aayokph (AT2021lfa)
- DDOTI Observations of ZTF21aayokph (AT2021lfa)
- GRB 210504A: Swift-BAT refined analysis
- ZTF and LT observations of ZTF21aayokph (AT2021lfa), a fast-fading red transient
- GRB 210504A: NOT optical afterglow detection
- GRB 210504A: MITSuME Akeno optical upper limits
- Fermi GRB 210503A: DDOTI Upper Limits on the Afterglow
- GRB 210504A: AST3-3 YaoAn Optical Upper Limit
- GRB 210504A: Swift/UVOT Detection
- GRB 210504A: BOOTES-4/MET optical upper limit
- Swift GRB210504.58: Global MASTER-Net observations report
- GRB 210504A: update on the BAT trigger time and burst duration
- GRB 210504A: Swift detection of a burst
- Fermi GRB 210503A: Global MASTER-Net observations report
- GRB 210503A: Fermi GBM Final Real-time Localization
- Swift GRB210502.74: Global MASTER-Net observations report
- Swift Detection of MAXI J1803-298 including an optical counterpart
- MAXI GRB210501.83: Global MASTER-Net observations report
- Fermi GRB 210501A: Global MASTER-Net observations report
- Fermi trigger No 641601187: Global MASTER-Net observations report
- GRB 210430A: BOOTES-1 optical limit
- GRB 210424B: MITSuME Akeno optical upper limits
- GRB 210501A: Fermi GBM Final Real-time Localization
- GRB 210430A: Swift-BAT refined analysis
- Fermi GRB 210430B: Global MASTER-Net observations report
- GRB 210430B: Fermi GBM Final Real-time Localization
- Swift GRB210430.45: Global MASTER-Net observations report
- GRB 210430A: Swift detection of a burst
- GRB 210424B: CALET Gamma-Ray Burst Monitor detection
- GRB 210413B: Swift/UVOT Observations
- Konus-Wind detection of GRB 210424B
- Delayed GRB GCN Notices from Swift
- IPN triangulation of GRB 210424B (short/hard)
- GRB 210323B: Swift-XRT observations
- Swift Trigger 1045571 is not a GRB
- GRB 210427A: GECAM detection
- GRB 210427A: BALROG localization (Fermi Trigger / GRB 210427206)
- 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