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"- EP260126a: Liverpool Telescope optical upper limits
- EP260126a: Further NOT optical upper limits
- EP260126a: COLIBRÍ optical upper limits
- EP260126a: NOT optical observations
- EP260126a: Einstein Probe detection of a fast X-ray transient
- Fermi-LAT Gamma-ray Observations of IceCube-260125A
- GRB 260125A: NOT optical observations on GOTO26acv / AT 2026bjf
- Konus-Wind detection of GRB 260120B
- GRB 251222A: SVOM/ECLAIRs refined analysis
- GRB 260125A: Swift ToO observations
- GRB 260125A: GOTO candidate optical counterpart
- Fermi GRB 260125B: Global MASTER-Net observations report
- IceCube-260125A - IceCube observation of a high-energy neutrino candidate track-like event
- GRB 260125B: Fermi GBM Final Real-time Localization
- GRB 260125A: Fermi GBM Final Real-time Localization
- GRB 260114A: SVOM/VT optical upper limits
- GRB 260120A: AstroSat CZTI detection
- GRB 260122B: Swift-BAT refined analysis
- GRB 260120B: SVOM/GRM observation
- GRB 260120A: GECAM-B observation
- GRB 260120B: AstroSat CZTI detection
- GRB 260114A: Insight-HXMT/HE detection
- GRB 260122B: Swift detection of a burst
- Swift GRB260122.97: Global MASTER-Net observations report
- EP260119a: Assy AZT-20 optical observations
- EP260119a: Mondy and SAO RAS optical upper limits
- GRB 260122A: Fermi GBM Final Real-time Localization
- IceCube-260115A: No Candidate Transients from the Zwicky Transient Facility
- EP260119a: Xinglong optical upper limit
- The EP-WXT trigger 01709251871 is likely a flaring star
- Fermi GRB 260120C: Global MASTER-Net observations report
- GRB 260120B: Swift-BAT refined analysis
- GRB 260120B: Swift-XRT refined Analysis
- EP260116a: COLIBRÍ further observations
- GRB 251122A / EP251122a: VLT/X-shooter host redshift z = 1.765
- GRB 260120B: Fermi GBM Observation
- EP260105a: GTC/HiPERCAM optical observations
- GRB 260120B: Swift/UVOT Detection
- GRB 260120B: COLIBRÍ optical upper limits
- SVOM GRB260121.06: Global MASTER-Net observations report
- GRB 260120B: Enhanced Swift-XRT position
- GRB 260120B: SVOM/C-GFT optical counterpart detection
- GRB 260120C: Fermi GBM Final Real-time Localization
- GRB 260101A: 239Alferov CubeSat detection
- EP260116a: COLIBRÍ observations of a tentative optical rebrightening
- GRB 260120B: Swift detection of a burst
- Swift GRB260120B: Global MASTER-Net observations report
- GRB 260120B: Fermi GBM Final Real-time Localization
- EP260119A: Mondy I-Band Observations
- Fermi trigger No 790601190: Global MASTER-Net observations report
- Fermi trigger No 790570272: Global MASTER-Net observations report
- GRB 260114A: Swift/UVOT Upper Limits
- EP260119a: Liverpool Telescope optical follow-up observations
- GRB 251202A: further radio observations with the VLA
- Trigger 1442421: Swift detection of HMXB 1A 1118-61
- EP260119A: GTC/OSIRIS+ spectroscopic redshift z = 5.47
- EP260119a: KAIT optical observations
- GRB 260120A: Fermi GBM Final Real-time Localization
- EP260119a: SVOM/VT optical observation
- EP260119a: update of EP-FXT follow-up observation
- EP260119a: NOT optical observations
- EP260119a: SAO RAS optical observations
- SVOM GRB260119.92: Global MASTER-Net observations report
- SVOM GRB260119.92: Global MASTER-Net observations report
- SVOM GRB260119.90: Global MASTER-Net observations report
- EP260116a: COLIBRÍ detection of a fading optical source
- GRB 251208D: SVOM/ECLAIRs refined analysis
- GRB 251208D: SVOM/ECLAIRs refined analysis
- GRB 260117A: Swift-XRT afterglow detection
- EP260119a: COLIBRÍ photometric redshift z ≈ 5.6
- EP260119a: Global MASTER-Net observations report
- GRB 260115A: AstroSat CZTI detection
- EP260119a: LCO optical observations
- GRB 260117A: ZTSh optical upper limit
- EP260119a: COLIBRÍ optical counterpart candidate
- EP260119a: preliminary result from the EP-FXT observation
- GRB 260110A: SVOM detection of a burst through offline search
- EP260119a: EP-WXT detection of a fast X-ray transient
- Swift GRB260118.48: Global MASTER-Net observations report
- GRB 260117A: SVOM/COLIBRÍ (FM-GFT) optical observations
- SVOM GRB260117.82: Global MASTER-Net observations report
- Fermi-LAT Gamma-ray Observations of IceCube-260115A
- Swift trigger on the HMXB 1A 1118-61
- GRB 260117A: SVOM/VT optical candidate
- GRB 260117A: SVOM/C-GFT upper limit
- GRB 260117A: Swift-XRT observations
- GRB 260117A: Swift ToO observations
- GRB 260117A: SVOM detection of a long faint burst
- EP 260116a: COLIBRÍ optical upper limit
- Swift triggered on the HMXB 1A 1118-61
- GRB 260115A: GECAM-B observation
- FRB 20251229A: COLIBRÍ further inspection of the updated localization
- EP260116a: Liverpool Telescope upper limits
- FRB 20251229A: Updated CHIME/FRB Baseband Localization of FRB 20251229A
- EP260116A: 1.3m DFOT optical upper limit
- GRB 260114A: VLT/MUSE spectroscopic observations
- IceCube-260115A: Upper limits from a search for additional neutrino events in IceCube
- EP260116a: Global MASTER-Net observations report
- GRB 260111A: COLIBRÍ fading of the optical counterpart candidate
- EP260116a: Xinglong optical upper limit