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"23095 results found.
- EP260131a: Xinglong optical upper limit
- GRB 260131A/B (AT2026bwg): COLIBRÍ optical observations and confirmation of fading
- GRB 260131A/B: GOTO candidate optical counterpart consistent with the MAXI localisation
- EP260131a: COLIBRÍ observations of slow optical fading
- GRB 260131B: MAXI/GSC detection
- EP260131a: COLIBRÍ optical observations of the counterpart
- GRB 260127B: AstroSat CZTI detection
- GRB 260130A: Fermi GBM Detection
- EP260128a / GRB 260128A: COLIBRÍ optical upper limit
- Fermi GRB 260130A: Global MASTER-Net observations report
- EP260128a / GRB 260128A: NOT and TNG optical and NIR upper limits
- GRB 260128B: SVOM/COLIBRÍ (FM-GFT) optical upper limits
- IPN triangulation of GRB 260121A
- GRB 260127A: Swift-BAT refined analysis
- GRB 260128B: SVOM detection of a burst through offline search
- IPN triangulation of GRB 260127B (short)
- GRB 260127A: INASAN-Kislovodsk, SAO RAS, and Terskol K-800 optical observations
- GRB 260128A / EP260128a: Fermi-GBM Sub-Threshold Detection
- EP260128a: NOT optical counterpart candidate
- GRB 260127A: COLIBRÍ optical observations
- EP260126a: Seimei/TriCCS optical upper limit
- GRB 260127A : MITSuME Akeno optical afterglow candidate detection
- GRB 260127B: GOTO candidate optical counterpart
- GRB 260127A: LCO optical afterglow discovery
- GRB 260127A: Swift detection of a burst
- EP260126a: Optical upper limit with Kinder observations
- EP260126a: COLIBRÍ optical upper limits
- EP260126a: NOT optical observations
- Konus-Wind detection of GRB 260120B
- GRB 260125A: GOTO candidate optical counterpart
- GRB 260114A: SVOM/VT optical upper limits
- GRB 260120A: AstroSat CZTI detection
- GRB 260122B: Swift-BAT refined analysis
- GRB 260120B: AstroSat CZTI detection
- GRB 260122B: Swift detection of a burst
- EP260119a: Assy AZT-20 optical observations
- EP260119a: Xinglong optical upper limit
- 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: Swift/UVOT Detection
- GRB 260120B: COLIBRÍ optical upper limits
- GRB 260101A: 239Alferov CubeSat detection
- EP260116a: COLIBRÍ observations of a tentative optical rebrightening
- GRB 260120B: Swift detection of a burst
- 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
- EP260119a: NOT optical observations
- 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
- GRB 260115A: AstroSat CZTI detection
- EP260119a: COLIBRÍ optical counterpart candidate
- GRB 260110A: SVOM detection of a burst through offline search
- GRB 260117A: SVOM/COLIBRÍ (FM-GFT) optical observations
- Swift trigger on the HMXB 1A 1118-61
- GRB 260117A: Swift-XRT observations
- EP 260116a: COLIBRÍ optical upper limit
- FRB 20251229A: COLIBRÍ further inspection of the updated localization
- GRB 260114A: VLT/MUSE spectroscopic observations
- GRB 260111A: COLIBRÍ fading of the optical counterpart candidate
- EP260116a: Xinglong optical upper limit
- GRB 260114A: VLT/HAWK-I further near-infrared upper limits
- GRB260114A: STEP/T80S optical limits
- GRB 251222A: radio detection with the VLA
- Konus-Wind detection of GRB 260114A
- GRB 260114A: Swift-XRT refined Analysis
- GRB 260114A: 6 GHz VLA observations
- GRB 260114A : MITSuME Akeno optical upper limits
- GRB 260114A: COLIBRÍ optical upper limits
- GRB 260114A: TNG NIR upper limit
- Konus-Wind detection of GRB 251230A / EP251230a
- GRB 260114A: Swift detection of a short burst
- EP260110a: TRT optical upper limits
- Konus-Wind detection of GRB 260101A
- GRB 260111A: Swift-XRT observations
- Swift Trigger 1439093: is probably not GRB 260113A
- GRB 260111A: COLIBRÍ optical afterglow candidate
- Swift Trigger 1434591 is not a GRB
- GRB 260111A: GOTO optical upper limits
- IceCube Alert 260111A: Global MASTER-Net observations report
- Swift trigger 1436759 is not an astrophysical event
- EP260110a: KAIT optical upper limit
- EP 260110a: COLIBRÍ optical observations
- EP260110a: BOOTES-5/JGU optical upper limit
- GRB 260109C: Kilonova-Catcher optical upper limit
- EP260105b / GRB 260105C : Fermi-GBM Sub-Threshold Detection
- Swift Trigger 1434591: possible GRB 260109C
- GRB 260102A: Swift-XRT afterglow detection
- GRB 260104A: Swift-BAT refined analysis
- GRB 260101A: Swift-BAT refined analysis
- Swift GRB 251230A: Global MASTER-Net OT detection
- EP260105b/EP-WXT trigger 01709251028: Einstein Probe detection of an X-ray transient
- The EP-WXT trigger 01709251028 is likely a flaring star
- FRB 20251229A: COLIBRÍ optical upper limits