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.
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"
4882 results found.
- Fermi GRB 250512A: Global MASTER-Net observations report
- GRB 250507B: AstroSat CZTI detection
- EP250512a: Global MASTER-Net observations report
- GRB 250507B: GRBAlpha detection
- EP250511a: COLIBRÍ optical counterpart candidate
- EP250511a: BOOTES-5 optical upper limit
- Fermi GRB 250510C: Global MASTER-Net observations report
- GRB 250509A: Fermi GBM Observation
- Fermi GRB 250509A: Global MASTER-Net observations report
- Swift GRB 250509A: Global MASTER-Net observations report
- GRB 250509A: Swift detection of a burst
- Fermi-LAT Gamma-ray Observations of IceCube-250506A
- IceCube Alert 250506.59: Global MASTER-Net observations report
- GRB 250506A: SVOM improved position and MXT detection of a fading X-ray afterglow
- GRB 250504A: REM optical/NIR observations
- GRB 250502A: SVOM/COLIBRÍ (FM-GFT) Detection of a Bright Optical Counterpart Candidate
- Fermi trigger No 767623859: Global MASTER-Net observations report
- EP250427A: COLIBRÍ Continuing Optical Observations
- EP250427A: COLIBRÍ Optical Detection
- EP 250427a: BOOTES-7 optical afterglow candidate
- EP250427a: Global MASTER-Net observations report
- GRB 250424A: SVOM/VT optical observation
- Fermi-LAT gamma-ray observations of IceCube-250421A
- GRB 250424A: BlackGEM optical afterglow detection
- IceCube Alert 250421.71: Global MASTER-Net observations report
- Fermi-LAT Gamma-ray Observations of IceCube-250416A
- EP250225a: SVOM/VT optical brightening
- IceCube 250414.324: DDOTI Optical Observations
- Fermi trigger No 766148493: Global MASTER-Net observations report
- Fermi trigger No 766173972: Global MASTER-Net observations report
- GRB 250411A: Fermi GBM Final Real-time Localization
- GRB 250407A: Continued KAIT/Nickel optical observations
- GRB 250407A: Mondy and AbAO Optical Observations
- AMON Coincidence Alert from the sub-threshold IceCube-HAWC search NuEm-250409A
- IPN triangulation of GRB 250407A
- Fermi GRB 250407A: Global MASTER-Net observations report
- IceCube 250406.951: COLIBRÍ/DDRAGO Optical Upper Limit
- Fermi trigger No 765619921: Global MASTER-Net observations report
- GRB 250404A / EP250404a: Mondy optical observations
- GRB 250404A / EP250404a: NOT optical observations
- Fermi GRB 250404A: Global MASTER-Net observations report
- EP250404a: Global MASTER-Net observations report
- GRB 250402B: AstroSat CZTI detection of a short burst
- Fermi GRB 250331E: Global MASTER-Net observations report
- LIGO/Virgo/KAGRA S250331o: NED Galaxies in the 3-Initial Localization Volume
- GRB 250331C: Swift detection of a burst
- GRB 250331A: MAXI/GSC detection
- Fermi GRB 250330A: Global MASTER-Net observations report
- IceCube Alert 250330.35: Global MASTER-Net observations report
- GRB 250329A: SVOM/VT optical counterpart confirmation
- GRB 250327B: LCO optical counterpart detection
- EP250321a: LCO optical counterpart detection
- EP250321a: Einstein Probe detection of an X-ray transient
- EP250226a/GRB 250226A: KAIT optical observations
- Fermi trigger No 763933627: Global MASTER-Net observations report
- Fermi GRB 250316A: Global MASTER-Net observations report
- GRB 250314A: Swift XRT Detection
- EP250315a: optical counterpart candidate detected by Gemini North
- IceCube-250309A: MASTER detection of J140105.33-091631.6 blazar flare with Zhirkov effect
- Fermi GRB 250313A: Global MASTER-Net observations report
- GRB 250309B/AT2025dws: Daochen/RC-10 optical counterpart observation
- GRB 250312A: Swift detection of a burst
- IceCube-250309A: Upper limits from a search for additional neutrino events in IceCube
- IceCube-250309A: MITSuME Akeno and Seimei/TriCCS optical observations
- GRB 250309B / AT2025dws: KMTNet-CTIO optical observations
- GRB 250309B / IceCube-250309A: GECAM-B observations
- GRB 250309B / AT2025dws: SAO RAS optical observations
- GRB 250309B / AT2025dws: Swift-UVOT detection
- AT 2025dws, likely optical counterpart of GRB 250309B: LCO confirmation of fast fading
- GRB 250309B: Fermi GBM Observation
- Fermi GRB 250309B: Global MASTER-Net observations report
- Fermi GRB 250309A: Global MASTER-Net observations report
- GRB250309B: One candidate counterpart from the Zwicky Transient Facility
- IceCube-250309A: No candidates from the Zwicky Transient Facility
- Fermi-LAT gamma-ray observations of IceCube-250309A
- GRB 250309B: Fermi GBM Final Localization
- IceCube-250309A - IceCube observation of a high-energy neutrino candidate track-like event
- IceCube Alert 250309.32: Global MASTER-Net observations report
- GRB 250309B: BALROG localization (Fermi Trigger 763198715 / GRB 250309318)
- EP250308a: Global MASTER-Net observations report
- Fermi GRB 250307A: Global MASTER-Net observations report
- Fermi trigger No 762963055: Global MASTER-Net observations report
- The EP-WXT trigger 01709132323 is likely a flaring star
- Fermi GRB 250305A: Global MASTER-Net observations report
- Fermi-LAT Gamma-ray Observations of IceCube-250302A
- EP250302a: SAO RAS optical observations
- EP250302a: Nanshan/HMT optical counterpart detection
- GRB 250225B: VLT/HAWKI near-infrared observations
- EP250228a: updates on the EP observations
- EP250228a: Einstein Probe detection of an X-ray transient
- EP250225a: NOT optical candidate counterpart
- EP250226a/GRB 250226A: COLIBRÍ/DDRAGO Detection of the Optical Counterpart
- Fermi GRB 250225A: Global MASTER-Net observations report
- GOTO observations of LVK S250223dk/Swift-BAT RAVEN alert
- EP250223a: GOTO optical afterglow detections
- LIGO/Virgo/KAGRA S250223dk and Swift/BAT-GUANO trigger with ID 762004910: Identification of a GW compact binary merger candidate possibly associated with a sub-threshold Swift/BAT-GUANO trigger
- GRB 250221A: Assy optical observations
- EP250220a: EP-FXT follow-up observations
- Fermi Gamma-ray Burst Monitor trigger 761782146/250220923 is not a GRB
- GRB 250220A: Fermi GBM Final Real-time Localization