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 250403A: AstroSat CZTI detection
- EP250404a: Osservatorio Astronomico "Nastro Verde" optical observations: detection of an optical counterpart
- EP250404a: REM optical/NIR observations
- EP250404a: Seimei/TriCCS optical counterpart detection
- EP250404A: COLIBRÍ/DDRAGO Optical Observations
- EP250404A / GRB250404A: Ondrejov D50 optical afterglow detection
- EP250404a: LCO optical counterpart detection
- Fermi GRB 250404A: Global MASTER-Net observations report
- EP250404a: Xinglong decaying optical counterpart
- GRB 250403A: Montarrenti Observatory optical detection
- GRB 250404A: Fermi GBM Detection
- EP250404a: Global MASTER-Net observations report
- GRB 250403A: KAIT optical observations
- EP250404a: AKO Optical Afterglow Detection
- EP250404a: LAST detection of optical counterpart
- GRB 250402A: Swift/BAT-GUANO localization skymap of a burst
- EP250404a: Xinglong-2.16m spectroscopic redshift
- GRB 250403A: Fermi GBM observations
- GRB 250327B: VIRT Optical Upper Limit
- EP250404a: Mephisto multi-band optical detection
- GRB 250331C Swift-BAT refined analysis
- GRB 250331B Swift-BAT refined analysis
- GRB 250330A Swift-BAT refined analysis
- EP250321A: J band upper limit by SYSU 80cm telescope
- EP250404a: BOOTES-4/JGT optical afterglow detection
- EP250404a: Nanshan/HMT optical counterpart detection
- EP250404a: Einstein Probe detection of an X-ray transient
- GRB 250404A: Fermi GBM Final Real-time Localization
- GRB 250402A: Mondy optical observations
- GRB 250403A: Swift/UVOT Detection
- GRB 250402A: Swift/UVOT Upper Limits
- EP250402a: Optical upper limit with Kinder observations
- GRB 250403A: SVOM/VT optical observation
- GRB 250403A: REM NIR afterglow detection
- GRB 250403A: LCO optical counterpart detection
- IceCube-250330A: MASTER detection of PKS 2032+107 blazar flare with Zhirkov effect
- GRB 250403A: JinShan optical observations
- GRB 250402A: EP-FXT afterglow detection
- GRB 250403A: Optical counterpart detection by LCO.
- EP250402a: EP-FXT follow-up observations
- GRB 250403A: Swift-XRT observations
- GRB 250322A: 10 GHz VLA radio upper limits
- Fermi GRB 250403A: Global MASTER-Net observations report
- GRB 250403A: GOTO optical counterpart follow-up observations
- GRB 250402A: NUTTelA-TAO Early Optical Limits
- GRB 250403A: GMG Optical Observation
- GRB 250403A: 1.6m Mephisto multi-band optical detection
- GRB 250402A: Fermi GBM Observation
- GRB 250403A: SVOM/C-GFT optical observations
- GRB 250403A: GOTO detection of the optical afterglow
- GRB 250402A: Swift-XRT observations
- GRB 250403A : SVOM detection of a burst
- GRB 250403A: Fermi GBM Final Real-time Localization
- GRB 250225B: VLT host galaxy redshift z = 0.950
- GRB250402A: SVOM/COLIBRÍ (FM-GFT) Detection of the Optical Counterpart
- GRB 250402A: VLT/FORS2 spectroscopic redshift z = 2.823
- GRB 250402A: REM optical/NIR upper limits
- GRB 250402A: LCO optical counterpart detection
- GRB 250402A: refined SVOM/MXT data analysis
- The EP-WXT trigger 01709133862 is a flaring star
- EP250402a: Einstein Probe detection of a fast X-ray transient
- GRB 250402B: AstroSat CZTI detection of a short burst
- GRB 250402A: SVOM/VT optical counterpart
- GRB 250402A: SVOM detection of a burst
- GRB 250331C: Calapai Observatory, Massa S. Giorgio (Messina), upper limit
- GRB 250314A: ALMA detection
- GRB 250329B: Swift/UVOT Upper Limit
- GRB 250329A: Swift/UVOT Upper Limit
- GRB 250327B: Swift/UVOT Detection
- GRB 250327A: Swift/UVOT Upper Limits
- GRB 250331E: SVOM/GRM observation
- GRB 250327B: Kilonova-Catcher Observations
- GRB250331D: AbAO optical observations
- GRB 250331D: Fermi GBM observation
- GRB 250331C: Swift/UVOT Upper Limits
- GRB 250331B: Swift/UVOT Upper Limits
- GRB 250328A: AbAO AS-32 Optical Observations
- GRB 250219A: NOT candidate host galaxy detection
- GRB 250322B: GRBAlpha detection
- GRB 250331D: Swift-XRT observations
- GRB 250331C: Swift-XRT refined Analysis
- GRB 250331B: Swift-XRT refined Analysis
- GRB 250331B: Swift-XRT refined Analysis
- GRB 250322B possible detection by the AstroSat Satellite
- GRB 250330B: SVOM/GRM observation of a short burst
- LIGO/Virgo/KAGRA S250328ae: DECam DESGW Candidates (Epoch 2)
- Fermi GRB 250331E: Global MASTER-Net observations report
- Fermi GRB 250331D: Global MASTER-Net observations report
- GRB 250330B: EIRSAT-1 GMOD Detection
- GRB 250331E: Fermi GBM Final Real-time Localization
- GRB 250327A Swift-BAT refined analysis
- LIGO/Virgo/KAGRA S250331o: Updated Sky localization
- GRB 250329A: AbAO, Mondy and SAO RAS optical upper limits
- Fermi trigger No 765078057: Global MASTER-Net observations report
- GRB 250329B: CAHA 2.2m telescope optical limit
- GRB 250331D: Swift ToO observations
- Swift GRB 250331C: Global MASTER-Net observations report
- Swift GRB 250331B: Global MASTER-Net observations report
- GRB 250331D: Swift/BAT-GUANO arcminute localization of a burst during slew
- Konus-Wind detection of GRB 250327B