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 250702B/EP250702a: JWST/NIRCam Observations
- GRB 251006A: Swift/BAT-GUANO subthreshold detection of a short burst
- GRB 251005B: Glowbug gamma-ray detection
- EP251003a: LCO and VST fading optical counterpart
- GRB 251006B/EP251006a: SVOM/VT optical candidate
- GRB 251006B/EP251006a: EP-FXT follow-up observation
- GRB 251006B: SVOM/GRM observation
- GRB 251006B: COLIBRÍ optical upper limit
- GRB 251006B/EP251006a: EP-WXT detection
- GRB 251005C: SVOM/VT optical fading
- GRB 251005C: SVOM/GRM observation of a likely short GRB
- LIGO/Virgo/KAGRA S251006dd: Identification of a GW compact binary merger candidate
- Fermi GRB 251006B: Global MASTER-Net observations report
- GRB 251006B: BALROG localization (Fermi Trigger 781473909 / GRB 251006837)
- GRB 251006B: Fermi GBM Final Real-time Localization
- GRB 251006A (short): Glowbug gamma-ray detection
- GRB 251005C: COLIBRÍ optical observations
- Fermi GRB 251006A: Global MASTER-Net observations report
- GRB 251005C: VLT/X-shooter Imaging
- GRB 251003A: LAST optical observations
- GRB 251002A: LAST optical observations
- GRB 251006A: Fermi GBM Final Real-time Localization
- GRB 251005C: SVOM/VT optical candidate
- GRB 251005C: AstroSat CZTI detection
- GRB 251005C: Swift/UVOT Upper Limits
- GRB 250902A: MSU cubesats detection
- GRB 251005C: Swift-XRT refined Analysis
- GRB 251005C: Fermi GBM Observation
- Swift GRB 251005A: Global MASTER-Net observations report
- GRB 251005C: Enhanced Swift-XRT position
- GRB 251005C: GOTO optical upper limits
- Fermi trigger No 781367244: Global MASTER-Net observations report
- GRB 251005C: Swift detection of a burst
- GRB 251005B: Fermi GBM Final Real-time Localization
- GRB 251005A: Fermi GBM Final Localization
- GRB 251002A: Mondy/AZT-33IK optical observations
- GRB 251002A: Insight-HXMT detection
- GRB 251002A: Insight-HXMT detection
- EP251003a: Einstein Probe detection of an X-ray transient
- GRB 251003A: J-band detection with WINTER
- GRB 251002A: NIR observations with WINTER
- Fermi GBM Sub-Threshold Detection of GRB 250910A
- GRB 251003A: Swift-BAT refined analysis
- GRB 251001B: NIR observations with WINTER
- GRB 251002A: Calapai Observatory, Massa S. Giorgio (Messina), optical observation.
- GRB 251003A: Swift/UVOT Upper Limits
- GRB 251002A: Swift/UVOT detection
- GRB 251001A: AstroSat CZTI detection
- GRB 251001B: COLIBRÍ further observations and evidence of a multi-wavelength shallow decay
- GRB 251003A: Swift-XRT refined Analysis
- GRB 251003A: COLIBRÍ photometric redshift
- GRB 251003A: GOTO detection of the optical counterpart
- GRB 251002A: Fermi GBM Observation
- LIGO/Virgo/KAGRA S251003at: Retraction of GW compact binary merger candidate
- GRB 251002A: GOTO detection of optical counterpart
- GRB 251001C: SVOM/GRM observation
- EP250821a: iTelescope T-59 possible detection of the optical counterpart
- GRB 251003A: Enhanced Swift-XRT position
- GRB 251002A: AKO Early Optical Afterglow Detection
- GRB 251003A: GTC/OSIRIS+ spectroscopic redshift z = 4.412
- GRB 251003A: Kilonova-Catcher optical afterglow detection
- GRB 251002A: Swift-XRT afterglow detection
- GRB 251001B: AbAO optical upper limit
- GRB 251002A: Kilonova-Catcher optical afterglow detection
- GRB 251002A: AbAO optical observations
- GRB 251002A: SVOM/COLIBRÍ (FM-GFT) optical observations
- GRB 251001C: CALET Gamma-Ray Burst Monitor detection
- GRB 251002A: J band observations by SYSU 80cm infrared telescope
- GRB 251002A: OHP/T193 MISTRAL optical afterglow detection
- GRB 251002A: VLT/X-shooter spectroscopic redshift z = 2.178
- GRB 251002A: EP-FXT counterpart detection
- GRB 251003A: LCOGT Optical Detection
- GRB 251003A: COLIBRÍ optical detection of the fading afterglow
- GRB 251003A: 1.5m OSN afterglow candidate
- GRB 251003A: Prompt enhanced Swift-XRT position
- GRB 251003A: Swift detection of a burst
- GRB 251003A: Fermi GBM Final Real-time Localization
- Swift GRB251003A: Global MASTER-Net observations report
- Fermi/SVOM GRB 251002A : MASTER OT earlier detection in 2 polarization filters
- GRB 251002A: BOOTES-6 early optical detection
- GRB 251002A: SAO RAS optical observations
- GRB 251002A: ULL-ASTRO-MASTER early detection of the optical afterglow with the LCO 40-cm telescope at Sutherland Observatory
- GRB 251002A: FRAM-ORM afterglow detection
- GRB 251002A: LCO optical observation
- GRB 251002A: SVOM/VT optical observation
- GRB 251002A: SVOM detection of a burst
- Fermi GRB 251002A: Global MASTER-Net observations report
- GRB 251001B: Swift-BAT refined analysis
- GRB 251001A: SVOM/GRM observation
- GRB 251001A: Insight-HXMT detection
- GRB 251001B: Swift/UVOT Detection
- GRB 251001B: COLIBRÍ optical observations
- GRB 251001B: GTC/OSIRIS+ spectroscopic redshift z = 2.162
- GRB 251001B: Swift-XRT refined Analysis
- GRB 251001B: SVOM/VT optical observation
- GRB 251001B: NOT optical observations
- GRB 251001C: Glowbug gamma-ray detection
- Swift GRB 251001B: Global MASTER-Net observations report
- GRB 251001B: Fermi GBM Observation
- GRB 251001B: Further GOTO observations of optical counterpart.