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 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
- GRB 250331C: Enhanced Swift-XRT position
- IceCube-250330A: Upper limits from a search for additional neutrino events in IceCube
- LIGO/Virgo/KAGRA S250331o: NED Galaxies in the 3-Initial Localization Volume
- GRB 250331B: Enhanced Swift-XRT position
- GRB 250320C : SVOM detection of a burst through offline search
- LIGO/Virgo/KAGRA S250328ae: Swift XRT observations, 34 possible X-ray sources
- GRB 250329B: Swift-XRT confirmation of fading
- GRB 250330A: VLT/FORS2 Afterglow Detection
- GRB20250327B: 45th Parallel Observatory upper limit
- GRB 250328A: Swift/UVOT Detection
- GRB 250328A: Swift-XRT refined Analysis
- Fermi-LAT gamma-ray observations of IceCube-250330A
- SVOM/sb25033102 is a false trigger
- GRB 250330A: Fermi GBM Observation
- GRB 250331C: COLIBRÍ/DDRAGO optical upper limit
- GRB 250331B: COLIBRÍ/DDRAGO optical upper limit
- GRB 250331D: Fermi GBM Final Real-time Localization
- GRB 250331C: Prompt enhanced Swift-XRT position
- GRB 250331C: Swift detection of a burst
- GRB 250331B: Swift detection of a burst
- GRB 250330A: SVOM/VT optical upper limit
- GRB 250331A: MAXI/GSC detection
- SVOM/sb25033102: SVOM detection of an X-ray transient
- GRB 250314A: VLA detection
- LIGO/Virgo/KAGRA S250331o: Identification of a GW compact binary merger candidate
- Fermi GRB 250330B: Global MASTER-Net observations report
- GRB 250330B: Fermi GBM Final Real-time Localization
- Fermi GRB 250330A: Global MASTER-Net observations report
- GRB 250330A: BOOTES-7 early optical upper limit
- GRB 250330A: Swift/UVOT Upper Limits
- GRB 250330A: Swift-XRT afterglow detection
- GRB 250328A: 1.6m Mephisto optical observations
- GRB 250329B: SVOM/COLIBRÍ (F-GFT) optical upper limit
- GRB 250330A: Fermi GBM Final Localization
- IceCube-250330A - IceCube observation of a high-energy neutrino candidate track-like event
- IceCube Alert 250330.35: Global MASTER-Net observations report
- GRB 250330A: VLT/FORS2 Optical Observations
- GRB 250330A: Prompt Swift-XRT position
- GRB 250329B: Swift-XRT afterglow detection
- GRB 250330A: Swift detection of a burst
- Swift GRB250330.26: Global MASTER-Net observations report
- GRB 250328A: A fading optical afterglow confirmed by SVOM/VT
- GRB 250329B: SVOM/C-GFT optical upper limit
- LIGO/Virgo/KAGRA S250328ae: DECam DESGW Candidates (Epoch 1)
- GRB 250327B: ALMA detection
- GRB 250327B: VLA detection
- GRB 250329B: SVOM/VT optical upper limit
- GRB 250327B: SVOM/COLIBRÍ (F-GFT) Further Observations
- GRB 250329B: 1.6m Mephisto Optical Upper Limits
- LIGO/Virgo/KAGRA S250329fl: 2 counterpart neutrino candidate events from an IceCube neutrino search
- GRB250329A: REM optical afterglow detection
- GRB 250329B: GWAC-F50A optical upper limit
- GRB 250329B: SVOM detection of a faint transient
- GRB 250329A: Swift-XRT afterglow detection
- GRB 250328A: SVOM/VT optical observation
- GRB 250329A: Fading optical counterpart detection by LCO.
- GRB 250328A: SVOM/C-GFT optical upper limit
- GRB 250328A: SVOM/COLIBRÍ (F-GFT) optical afterglow candidate
- GRB 250328A: VLT/HAWK-I near-infrared afterglow candidate
- GRB 250329A: VLT/X-shooter redshift z = 2.921
- GRB 250329A: SVOM/VT optical counterpart confirmation
- GRB 250329A: SVOM detection of a burst
- GRB 250329A: SVOM/COLIBRÍ (F-GFT) Detection of a Bright Optical Counterpart Candidate
- GRB 250327B: J-band observations with WINTER
- GRB 250327B: MASTER detection of OT rebrightening
- GRB 250327B: LCO optical counterpart detection