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"- GRB 250521D: DDOTI Optical Upper Limit
- The EP-WXT trigger 01709176612 is likely a flaring star
- GRB 250521D: GOTO detects LAST counterpart candidate prior to the GRB
- GRB 250521B: SVOM/COLIBRÍ (FM-GFT) optical upper limit
- GRB 250521D: LAST tentative optical counterpart candidate
- GRB 250520A: CALET Gamma-Ray Burst Monitor detection
- GRB 250520A: 10 GHz VLA radio source
- GRB 250521B: Swift ToO observations
- GRB 250521D: Fermi GBM Final Real-time Localization
- GRB 250521C: Fermi GBM Final Localization
- GRB 250521A: DDOTI Optical Upper Limit
- GRB 250521B: SVOM detection of a burst through offline search
- Konus-Wind detection of GRB 250520A (short/hard)
- GRB 250520A: VLT/FORS2 Optical Observation
- GRB 250502A: Tautenburg observations
- GRB 250520A: Swift/UVOT Upper Limits
- GRB 250521A: Fermi GBM Final Real-time Localization
- Konus-Wind detection of GRB 250516B
- IPN triangulation of GRB 250516B
- GRB 250520A: J-band observations with WINTER
- GRB 250520A: Gemini-South optical observations
- GRB 250520A: Swift-XRT refined Analysis
- GRB 250520A: REM optical/NIR early observations
- GRB 250520B: Fermi GBM Final Real-time Localization
- GRB 250520A：SVOM/VT optical candidate
- GRB 250520A: COLIBRÍ optical upper limit
- GRB 250520A: DDOTI Optical Upper Limit
- GRB 250520A: AstroSat CZTI detection of a short burst
- GRB 250516B: GRBAlpha detection
- GRB 250520A: SVOM/GRM observation
- GRB 250520A: Enhanced Swift-XRT position
- GRB 250520A: GOTO optical upper limit
- GRB 250520A: Prompt enhanced Swift-XRT position
- GRB 250520A: Swift detection of a burst
- Swift GRB 250520A: Global MASTER-Net observations report
- GRB 250516B: Insight-HXMT detection
- EP250427a/GRB250427A: VLA Detection of Radio Counterpart
- GRB 250516A: Swift-BAT refined analysis
- GRB 250516A: COLIBRÍ optical upper limit
- Konus-Wind detection of GRB 250516A
- GRB 250516B: NuSTAR Detection of the Prompt Emission
- EP-WXT trigger (ID: 01709176312): a new X-ray outburst of HMXB RX J0111.2-7317
- Fermi GRB 250516A: Global MASTER-Net observations report
- GRB 250515A: Swift-XRT observations
- GRB 250515A: NOT classification of GOTO25cqo as a type-Ia SN
- Fermi Gamma-ray Burst Monitor trigger 769160489/250517320 is not a GRB
- GRB 250515A:COLIBRÍ optical observations of the GOTO candidate
- Swift GRB 250516A: Global MASTER-Net observations report
- GRB 250515A: 1.6m Mephisto optical detection
- GRB 250516A: AstroSat CZTI detection
- GRB 250515A/GOTO25cqo: SVOM/VT optical blue color
- GRB 250516A: Fermi GBM Observation
- GRB 250516A: Swift-XRT refined Analysis
- GRB 250516A: Swift/UVOT Detection
- GRB 250515A: Swift ToO observations
- GRB 250516B: GECAM-B detection of a bright long burst
- GRB 250516A: Enhanced Swift-XRT position
- GRB 250516A: Swift detection of a burst
- GRB 250516A: Fermi GBM Final Real-time Localization
- GRB 250512B / EP250512a: SVOM/GRM analysis
- GRB 250515A: GOTO candidate optical counterpart
- MAXI GRB250515.65: Global MASTER-Net observations report
- GRB 250515A: Fermi GBM Final Localization
- GRB 250424A: COLIBRÍ detection of the associated supernova
- Konus-Wind detection of GRB 250512B / EP250512a
- GRB 250502A: TESS observations
- Fermi trigger No 768922089: Global MASTER-Net observations report
- GRB 250511A: GECAM-A detection of a short burst
- GRB 250509A: Swift-BAT refined analysis
- LIGO/Virgo/KAGRA S250328ae: DECam DESGW Candidates (Final Epochs)
- Fermi GRB 250512A: Global MASTER-Net observations report
- Konus-Wind detection of GRB 250506A
- EP250512a/GRB 250512B: REM optical/NIR observations
- EP250511a: Koshka Zeiss-1000 Optical Upper Limit
- GRB 250507B: AstroSat CZTI detection
- EP250511a: Gemini optical counterpart observation
- EP250512a/GRB 250512B refined analysis of the EP-WXT and EP-FXT observations
- EP250512a/GRB 250512B: FTW optical and NIR observations of the counterpart
- EP250512a: Global MASTER-Net observations report
- EP250511a: FTW optical and NIR observations
- GRB 250512B/EP250512a: SVOM/VT optical fading
- GRB 250512B/EP250512a：SVOM/VT bright optical counterpart
- EP250511a: Mephisto optical upper limits
- GRB 250507B: GRBAlpha detection
- GRB 250506A: GRBAlpha detection
- GRB 250512B: SVOM detection of a burst
- GRB 250507B: SVOM/GRM observation of a burst
- EP250512a: Einstein Probe detection of an X-ray transient
- GRB 250512A: Fermi GBM Final Real-time Localization
- EP250511a: REM optical/NIR observations
- EP250511a: Einstein Probe follow-up obsevation and refined analysis
- EP250511a: SVOM/VT optical candidate comfirmation
- EP250511a: Global MASTER-Net observations report
- EP250511a: COLIBRÍ optical counterpart candidate
- EP250511a: BOOTES-5 optical upper limit
- EP250511a: Einstein Probe detection of an X-ray transient
- EP250508a: Gemini NIR upper limits
- GRB 250510B: Fermi GBM Observation
- Fermi GRB 250510C: Global MASTER-Net observations report
- Fermi GRB 250510B: Global MASTER-Net observations report