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 250920C: ULL-ASTRO-MASTER early detection of the optical afterglow with LCO 40-cm telescope at Siding Spring Observatory
- GRB 250926A: AstroSat CZTI detection
- GRB 250925A: Swift/UVOT Upper Limits
- GRB 250925A: Swift-BAT refined analysis
- GRB 250925A: Mondy and AbAO optical observations
- GRB 250925A: COLIBRÍ photometric redshift
- IceCube-250926A - IceCube observation of a high-energy neutrino candidate track-like event
- GRB 250925A: SVOM/GWAC-F60A upper limit
- GRB 250925A/EP250925a: EP-WXT detection
- GRB 250926A: DDOTI Optical Observations and Spatial Coincidence with the Orion Nebula
- GRB 250925A : MITSuME Akeno optical upper limits
- GRB 250925A: JinShan optical observations
- GRB 250925A: 1.5m OSN optical detection and redshift with the 10.4m GTC/OSIRIS+
- GRB 250919A / EP250919a: Global MASTER Net before, during and after trigger optical observations
- GRB 250925A: COLIBRÍ optical photometry of the afterglow
- Fermi GRB 250926A: Global MASTER-Net observations report
- GRB 250926A: Fermi GBM Final Real-time Localization
- GRB 250925A: Optical Observations via Virtual Telescope Project, Italy
- GRB250925A: Liverpool Telescope optical observations
- GRB 250925A: NOT optical afterglow candidate
- GRB 250925A: Leavitt Observatory optical upper limit
- GRB 250925A: Enhanced Swift-XRT position
- GRB 250924A: Swift-BAT refined analysis
- GRB 250925A: GROWTH-India Telescope Upper Limits
- GRB 250925A: Swift detection of a burst
- Swift GRB 250925A: Global MASTER-Net observations report
- GRB 250922A: SVOM/GRM observation
- GRB 250924A: 1.6m Mephisto optical upper limits
- GRB 250924A: SAO RAS optical observations
- GRB 250924A: NOT optical observations
- GRB 250924A: AstroSat CZTI detection
- GRB 250914A: AstroSat CZTI detection
- GRB 250920B: AstroSat CZTI detection
- GRB 250924A: SVOM/VT optical observation
- GRB 250924A: Swift/UVOT Detection
- GRB 250924A: Swift-XRT refined Analysis
- GRB 250924A: Enhanced Swift-XRT position
- GRB 250924A: J-band detection with WINTER
- GRB 250924A: GROWTH-India Telescope Upper Limits
- GRB 250924A: KAIT optical observations
- GRB 250924A: Mondy optical observations, afterglow fading
- GRB 250924A: Kilonova-Catcher optical afterglow detection
- GRB 250920C: Kilonova-Catcher optical afterglow detection
- GRB 250922B: SVOM/GRM observation
- GRB 250920C: TRT optical observation
- GRB 250924B: Fermi GBM Final Localization
- GRB 250924A: COLIBRÍ optical observations
- Swift GRB 250924A: Global MASTER-Net observations report
- GRB 250919A / EP250919a: further LCO optical observation
- GRB 250924A: DDOTI Detection of the Optical Counterpart
- GRB 250924A: Swift detection of a burst with an optical counterpart
- GRB 250920B: AbAO optical upper limits
- Konus-Wind detection of GRB 250920C
- GRB 250920C: KAIT optical observations
- GRB 250920C: VLT redshift confirmation z = 1.399
- EP250911a: e-MERLIN radio observations
- GRB 250920B: CrAO ZTSH optical observations
- GRB 250920C: SALT redshift confirmation
- GRB 250920C: COLIBRÍ optical observations
- GRB 250922C: AstroSat CZTI detection of a short burst
- Fermi GRB 250922B: Global MASTER-Net observations report
- GRB 250920B: SAO RAS optical observations
- GRB 250920C: NIR observations with WINTER
- GRB 250920B: NIR observations with WINTER
- Fermi trigger No 780156732: Global MASTER-Net observations report
- GRB 250922B: Fermi GBM Final Real-time Localization
- GRB 250920C: PRIME near-infrared detection
- Konus-Wind detection of GRB 250920B
- Konus-Wind detection of GRB 250920A
- IPN triangulation of GRB 250920A (long/bright)
- Konus-Wind detection of GRB 250911A
- GRB 250916A: Swift/UVOT Detection
- GRB 250920B: Glowbug gamma-ray detection
- GRB 250916A: CrAO ZTSh R-band optical observations
- GRB 250920C: Swift-XRT refined Analysis
- GRB 250916A: SAO RAS Zeiss-1000 optical observations
- GRB 250922A: Fermi GBM Final Localization
- GRB 250920B: Asiago optical observations
- GRB 250920B: Kitab-ISON optical upper limit
- GRB 250917B: Mondy and Zeiss-1000 SAO RAS optical observations, optical observations, afterglow candidate
- GRB 250920C: SVOM/GRM observation
- GRB 250920C: GTC/OSIRIS+ spectroscopic redshift z = 1.40
- GRB 250917B: KAIT optical upper limit
- GRB 250920A: NuSTAR detection of bright prompt emission
- GRB 250920C: GROWTH-India Telescope optical observations
- GRB 250920C: Swift-BAT refined analysis
- GRB 250920B: Swift-BAT refined analysis
- GRB 250920C: Enhanced Swift-XRT position
- GRB 250916A: FTW optical and NIR observations of the counterpart
- GRB 250920C: Swift/UVOT Detection
- GRB 250920B: Fermi GBM Observation
- GRB 250920A: Fermi GBM Detection
- GRB 250920C: Fermi GBM Observation
- Swift GRB 250920C: Global MASTER-Net observations report
- GRB 250920B: Swift/UVOT Detection
- GRB 250920B: FTW optical and NIR observations of the counterpart
- GRB 250920C: Optical counterpart detection by LCO
- GRB 250920A: SVOM/GRM observation
- GRB250920C: LCOGT Optical Detection
- GRB 250920B: Enhanced Swift-XRT position