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"26359 results found.
- GRB 250809A: LCOGT Optical Upper Limits
- GRB 250808A: VLT X-shooter candidate counterpart
- GRB 250809A: Swift detection of a gamma ray burst
- GRB 250808A: SVOM/COLIBRÍ (FM-GFT) optical upper limit
- GRB 250808A: Fermi GBM Observation
- GRB 250808A: Swift-XRT candidate counterpart detection
- GRB 250807B: Swift/UVOT Detection
- GRB 250807B: Kilonova-Catcher optical afterglow detection
- IceCube-250804A: Upper limits from a search for additional neutrino events in IceCube
- GRB 250807A: Swift/UVOT Detection
- GRB 250807A: Swift-XRT refined Analysis
- GRB 250806A: SVOM/MXT refined analysis
- EP250807a: NTT z-band optical upper limit
- GRB 250806A: Mondy optical observations, and nearby bright galaxy photometry
- GRB 250807A: SVOM/GRM observation
- GRB 250807A: AstroSat CZTI detection of bright long burst
- GRB 250807B: Swift-XRT refined Analysis
- EP250807a: EP-WXT detection of a fast X-ray transient
- EP 250807.979: GOTO optical upper limit
- EP250807a: COLIBRÍ optical upper limit
- EP250806a: Upper limit from Fermi-GBM Observations
- GRB 250807B: Enhanced Swift-XRT position
- GRB 250807A: Enhanced Swift-XRT position
- IceCube-Cascade 250804A: Upper limits from a search for additional neutrino events in IceCube
- GRB 250807B: Swift detection of a burst with an optical counterpart.
- GRB 250805A: Kilonova-Catcher optical upper limits
- GRB 250805A: Swift/UVOT Upper Limits
- GRB 250806A: Swift/UVOT U-band detection
- EP250806a: Liverpool telescope optical upper limit
- GRB 250807A: Swift detection of a burst with an optical counterpart
- EP250802a: EP-FXT follow-up observation
- EP250806a: refined analysis of the EP-WXT and EP-FXT observations
- EP250806a: SVOM /VT optical candidate
- GRB 250806A: J-band upper limit from WINTER
- GRB 250805A: Swift-BAT refined analysis
- GRB 250806A: KAIT optical upper limit
- GRB 250806A: Swift-XRT counterpart detection
- EP250806a: COLIBRÍ optical upper limit
- GRB 250806A: Kilonova-Catcher optical upper limits
- EP250806a: Einstein Probe detection of an X-ray transient
- GRB 250806A: SVOM/COLIBRÍ (FM-GFT) optical upper limit
- GRB 250806A: SVOM/VT optical upper limit
- GRB 250806A: SVOM detection of a soft burst
- GRB 250805A: SVOM/VT optical counterpart
- GRB 250805A: Swift-XRT refined Analysis
- GRB 250804B: Swift-XRT observations
- GRB 250805A: Enhanced Swift-XRT position
- GRB 250805A: TRT optical upper limits
- GRB 250805A: Swift-XRT observations
- GRB 250804B: SVOM/GRM observation of a short burst
- GRB 250804A: Fermi GBM Final Localization
- EP250802a: additional Liverpool Telescope upper limits
- EP250730a: SVOM/VT optical upper limit
- EP250802a: Liverpool Telescope optical upper limits
- EP250802a: Global MASTER-Net observations report
- EP250802a: GROWTH-India Telescope optical upper limit
- LIGO/Virgo/KAGRA S250802dn: Updated Sky localization
- LIGO/Virgo/KAGRA S250802dn: Identification of a GW compact binary merger candidate
- LIGO/Virgo/KAGRA S250727dc: GRANDMA/OPD observations of AT2025smm
- LIGO/Virgo/KAGRA S250727dc: DECam GW-MMADS candidates
- LIGO/Virgo/KAGRA S250725j: GOTO pre-trigger detection of AT2025sib
- EP250711a: CrAO and Assy optical observations
- LIGO/Virgo/KAGRA S250727dc: DECam DESGW Epoch 1 Candidates
- EP250730a: COLIBRÍ optical upper limit
- GRB 250727A: Swift-XRT afterglow confirmation and refined analysis
- LIGO/Virgo/KAGRA S250725j: DECam DESGW Epoch 1-2 Candidates
- LIGO/Virgo/KAGRA S250726ak: Upper limits from Swift/BAT-GUANO
- LIGO/Virgo/KAGRA S250725l: Upper limits from Swift/BAT-GUANO
- LIGO/Virgo/KAGRA S250727dc: Upper limits from Swift/BAT-GUANO
- LIGO/Virgo/KAGRA S250727dc: Swift-XRT observations, 8 X-ray sources
- GRB 250727A: EP-FXT follow-up observation
- GRB 250725A: PRIME near-infrared observations
- LIGO/Virgo/KAGRA S250727dc: DECam GW-MMADS upper limits of AT 2025smm
- LIGO/Virgo/KAGRA S250727dc: PRIME J-band upper limits of AT 2025smm
- GRB 250728A: Swift-XRT observations
- GRB 250728A: COLIBRÍ optical upper limit
- LIGO/Virgo/KAGRA S250727dc: Updated Sky localization
- GRB 250728A: Swift/BAT-GUANO arcminute localization of a short burst
- LIGO/Virgo/KAGRA S250727cl: Updated Sky localization
- GRB 250727A: EP-FXT counterpart detection
- GRB 250727A: Swift-XRT observations
- LIGO/Virgo/KAGRA S250727dc: Identification of a GW compact binary merger candidate
- LIGO/Virgo/KAGRA S250727cl: Identification of a GW compact binary merger candidate
- LIGO/Virgo/KAGRA S250725j: DECam GW-MMADS candidates
- LIGO/Virgo/KAGRA S250725l: Updated Sky localization
- LIGO/Virgo/KAGRA S250726ak: Updated Sky localization
- LIGO/Virgo/KAGRA S250726ak: Identification of a GW compact binary merger candidate
- GRB 250725A: Swift-XRT refined Analysis
- GRB 250725A: Fermi GBM Observation
- LIGO/Virgo/KAGRA S250725j: Updated Sky localization
- GRB 250725A: Swift-BAT refined analysis
- LIGO/Virgo/KAGRA S250725j: NED Galaxies in the 3-Initial Localization Volume
- GRB 250725A: SVOM/GRM observation
- GRB 250725A: Global MASTER-Net: First Optical Synchronous Observatios of Short GRB.
- GRB 250725A: Swift/UVOT Upper Limits
- GRB 250725A: Fermi-LAT detection
- GRB 250725A: BOOTES-7 early optical detection
- GRB 250725A: SVOM/VT optical candidate
- GRB 250725A: MASTER-OAFA optical detection of very fast afterglow
- LIGO/Virgo/KAGRA S250725l: Identification of a GW compact binary merger candidate