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 250510A: follow-up observation with EP-FXT
- GRB 250510B: Swift/BAT-GUANO localization skymap of a burst
- GRB 250510B: Fermi GBM Final Localization
- GRB 250510A: SVOM/COLIBRÍ (FM-GFT) optical upper limit
- GRB 250509A: Swift-XRT refined Analysis
- GRB 250510A: SVOM possible detection of a burst
- GRB 250507A: J-band observations with WINTER (duplicate submission)
- GRB 250507A: J-band observations with WINTER
- EP250508a: SVOM/VT optical candidate fading
- GRB 250509A: Enhanced Swift-XRT position
- GRB 250509A: Prompt enhanced Swift-XRT position
- Fermi GRB 250509A: Global MASTER-Net observations report
- Swift GRB 250509A: Global MASTER-Net observations report
- GRB 250509A: Swift detection of a burst
- GRB 250509A: Fermi GBM Final Real-time Localization
- GRB 250506A: NOT optical upper limits
- EP250508a: Liverpool Telescope optical upper limits
- EP250508a: follow-up observation with EP-FXT
- EP250508a: SVOM/VT optical candidate
- EP250508a: KAIT optical upper limit
- GRB 250507A: KAIT optical upper limit
- EP250508a: refined analysis of the EP-WXT and EP-FXT observations
- GRB 250505B: SVOM/GRM observation of a short burst
- GRB 250502A: Calapai Observatory, Massa S. Giorgio (Messina), optical observation.
- GRB 250506A: GECAM detection
- EP250508a: REM optical/NIR observations
- GRB 250506A: Swift-XRT afterglow detection
- EP250508a: Global MASTER-Net observations report
- GRB 250506A: SVOM/VT optical upper limit
- EP250508a: COLIBRÍ Optical Limit
- EP250508a: Einstein Probe detection of an X-ray transient
- GRB 250507A: Swift-XRT refined Analysis
- IceCube-250506A: Upper limits from a search for additional neutrino events in IceCube
- GRB 250506A: Swift/UVOT Upper Limits
- GRB 250427B : SVOM detection of a burst through offline search
- GRB 250507A: follow-up observation with EP-FXT
- GRB 250430A / EP250430a: AstroSat CZTI detection
- EP#01709175213/IGR J19566+0326: Swift-XRT detection
- GRB 250506A: SVOM/COLIBRÍ (FM-GFT) optical upper limit
- GRB 250507A: refined SVOM/MXT data analysis
- GRB 250507A: REM optical/NIR observations
- GRB 250507A: SVOM/VT optical upper limit
- GRB 250506A: Swift-XRT observations
- Fermi-LAT Gamma-ray Observations of IceCube-250506A
- GRB 250507A: SVOM/COLIBRÍ (FM-GFT) optical upper limit
- EP-WXT trigger 01709175213: a new X-ray outburst of LMXB MAXI J1957+032
- GRB 250507A: SVOM detection of a long burst
- GRB 250506A: Mephisto optical upper limits
- GRB 250504A: EIRSAT-1 GMOD Detection
- GRB 250506A: Swift ToO observations
- GRB 250502A: Bassano Bresciano Observatory upper limit
- IceCube-250506A - IceCube observation of a high-energy neutrino candidate track-like event
- IceCube Alert 250506.59: Global MASTER-Net observations report
- GRB 250430A: Konus-Wind detection and joint Konus-Wind+Swift-BAT spectral analysis
- GRB 250506A: Xinglong 2.16m optical upper limit
- SVOM/sb25050601: EP-FXT observations
- GRB 250506A: SVOM improved position and MXT detection of a fading X-ray afterglow
- GRB 250506A: REM optical/NIR upper limits
- GRB 250506A: Fermi GBM Observation
- GRB 250506A: Swift XRT observations and possible counterpart detection
- GRB 250506A: TRT optical observations
- GRB 250506A: SVOM/COLIBRÍ (FM-GFT) Upper Limits on the Optical Counterpart
- GRB 250506A: SVOM detection of a burst
- GRB 250504A: Swift-BAT refined analysis
- GRB 250430A: Swift-BAT refined analysis
- GRB 250506A: Fermi GBM Final Real-time Localization
- GRB 250504A: Swift-XRT refined Analysis
- GRB 250504A: VLT/X-shooter upper limits
- Fermi GRB 250505A: Global MASTER-Net observations report
- GRB 250504A: SVOM/VT upper limit
- GRB 250504A: REM optical/NIR observations
- GRB 250502A: REM optical/NIR observations
- GRB 250505A: Fermi GBM Final Real-time Localization
- GRB 250504A: MeerLICHT optical afterglow detection
- GRB 250504A: Fermi GBM Observation
- GRB 250504A: Enhanced Swift-XRT position
- Fermi GRB 250504A: Global MASTER-Net observations report
- GRB 250504A: Swift detection of a burst
- GRB 250504A: Fermi GBM Final Real-time Localization
- Swift GRB250504.98: Global MASTER-Net observations report
- GRB 250502A: Swift/UVOT Follow up
- GRB 250502A: Mondy and Tien-Shan Optical Observations
- GRB 250502A: KAIT optical observations
- GRB 250502A: Montarrenti Observatory optical detection
- GRB 250502A: Swift-XRT afterglow detection
- Fermi trigger No 767975731: Global MASTER-Net observations report
- GRB 250502A: NOT optical observations
- GRB 250502a: Liverpool Telescope optical follow-up
- GRB 250502B: AstroSat CZTI detection
- GRB 250502A: AKO Optical Afterglow Detection
- GRB 250502A: LCO optical counterpart detection
- GRB 250502A: Swift ToO observations
- GRB 250502A: Redshift from OSIRIS+/GTC z = 2.163
- GRB 250502C: Fermi GBM Final Localization
- GRB 250407A: VZLUSAT-2 detection
- Fermi-LAT Gamma-ray Observations of IceCube-250429A
- GRB 250502B: DDOTI Optical Observations
- GRB 250430A: Swift-XRT refined Analysis
- GRB 250502A: Early optical counterpart detection by LCO.
- GRB 250430A: Swift/UVOT Detection