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"14824 results found.
- GRB 250823A: Swift detection of a burst
- GRB 250823A: Fermi GBM Final Real-time Localization
- Konus-Wind detection of GRB 250821B
- LIGO/Virgo/KAGRA S250818k: Rebrightening detected with Gemini/GMOS
- LIGO/Virgo/KAGRA S250818k: HST nIR detection of AT 2025ulz
- LIGO/Virgo/KAGRA S250818k: JinShan optical observations of AT2025ulz
- LIGO/Virgo/KAGRA S250818k: GTC/OSIRIS Optical Detection of AT2025ulz
- LIGO/Virgo/KAGRA S250818k: 3 GHz MeerKAT observations of AT2025ulz
- IPN triangulation of GRB 250821B (long/bright)
- GRB 250821A: GECAM-B detection
- GRB 250821C: Fermi GBM Final Real-time Localization
- LIGO/Virgo/KAGRA S250818k: Continued fading and reddening of AT2025ulz from Keck/LRIS imaging observations
- GRB 250821B: Fermi GBM Detection
- LIGO/Virgo/KAGRA S250818k: ENGRAVE observations of AT 2025ulz
- GRB 250821B: Fermi GBM Final Localization of a Bright Burst
- EP250821a: Swift XRT and UVOT counterpart detection
- LIGO/Virgo/KAGRA S250818k: 10 GHz VLA observations of AT2025ulz
- GRB 250821A: Swift detection of a burst
- LIGO/Virgo/KAGRA S250818k: WFST pre-discovery limits and follow-up observations of AT 2025ulz
- EP250821a: Einstein Probe detection of an X-ray transient
- GRB 250819A: SVOM/GRM observation of a possible “long” duration type I burst
- GRB 250819A: Insight-HXMT detection
- GRB 250818B: 10 GHz VLA detection
- LIGO/Virgo/KAGRA S250818k: Multi-band Gemini GMOS Detections
- IPN triangulation of GRB 250816A (short)
- IPN triangulation of GRB 250814C (short)
- IPN triangulation of GRB 250804B (short)
- GRB 250818B: Kilonova-Catcher optical afterglow detection
- LIGO/Virgo/KAGRA S250818k: AstroSat CZTI non-detection and upper limits
- LIGO/Virgo/KAGRA S250818k: Upper limits from Fermi-GBM Observations
- LIGO/Virgo/KAGRA S250818k: Pan-STARRS pre-detection limits for AT2025ulz
- GRB 250818A: AstroSat CZTI detection
- GRB 250818B: Swift/UVOT Detection
- GRB 250820A: Fermi GBM Final Real-time Localization
- GRB 250818B: optical afterglow detection with Lesedi (GOTO25fzq)
- GRB 250818B: TRT Optical Observation
- GRB 250818B: EP-FXT counterpart detection
- GRB 250818C: Fermi GBM Final Real-time Localization
- GRB 250818B: Swift-XRT afterglow detection
- GRB 250818B: SVOM detection of a short burst
- GRB 250818A: Swift detection of a burst
- GRB 250818A: Fermi GBM Final Real-time Localization
- SVOM/sb25081602: detection of a likely X-ray transient
- GRB 250816A: Fermi GBM Final Real-time Localization
- GRB 250815A: Fermi GBM Final Localization
- GRB 250814A: detection of the afterglow candidate with Liverpool Telescope
- GRB 250812A: SVOM/VT optical continued observation
- GRB250814A: TRT optical upper limits
- LIGO/Virgo/KAGRA S250813k: Swift XRT observations, 2 X-ray sources
- GRB 250814A: Possible afterglow candidate from P200/WIRC
- GRB 250814A: Optical observations with MDM Hiltner 2.4m telescope
- GRB 250814B: Fermi GBM Final Real-time Localization
- GRB 250813A: AstroSat CZTI detection
- GRB 250813B: VLT X-shooter spectroscopic redshift z = 1.752
- GRB 250813B: EP-FXT counterpart detection
- GRB 250813B: Swift-XRT afterglow detection
- GRB 250814A: Swift detection of a burst coincident with a subthreshold GW trigger
- GRB 250814A: Fermi GBM Final Real-time Localization
- GRB 250813B: SVOM detection of a bright long burst (Correction for GCN 41352).
- GRB 250813B: Ondrejov D50 optical afterglow detection
- GRB 250813B: SVOM detection of a bright long burst
- GRB 250812A: VLT X-shooter spectroscopic redshift confirmation z = 2.571
- GRB 250812A: NTT spectroscopic redshift z = 2.57
- GRB250812a: STEP/T80S Indication of slow decay of afterglow
- GRB 250812A: Swift/UVOT Detection
- GRB 250813A: Fermi GBM Final Localization
- EP250812a: COLIBRÍ detection of the VT candidate and evidence of flattening
- EP250812a: Liverpool Telescope upper limits
- IceCube-250813A - IceCube observation of a high-energy neutrino candidate track-like event
- GRB 250812A: EP-FXT counterpart detection
- GRB 250812A: Kilonova-Catcher optical afterglow detection
- EP250812a: Swift-XRT counterpart detection
- GRB 250812A: SVOM/COLIBRÍ (FM-GFT) optical observations
- EP250812a: Einstein Probe detection of an X-ray transient
- GRB 250812A: SVOM/VT optical afterglow confirmation
- GRB 250812A: Swift-XRT afterglow detection
- GRB 250812A: TRT likely optical counterpart detection
- GRB 250812A: SVOM detection of a faint long burst
- GRB 250809A: Swift/UVOT Detection
- GRB 250702B: Chandra X-ray Detection
- GRB 250809A: Swift detection of a gamma ray burst
- GRB 250808A: Swift-XRT candidate counterpart detection
- GRB 250808A: SVOM detection of a long burst
- GRB 250808A: Fermi GBM Final Real-time Localization
- Konus-Wind detection of GRB 250807A
- GRB 250807B: Swift/UVOT Detection
- GRB 250807B: Kilonova-Catcher optical afterglow detection
- GRB 250807A: Swift/UVOT Detection
- GRB 250806A: SVOM/MXT refined analysis
- GRB 250804B: Insight-HXMT detection
- GRB 250807A: AstroSat CZTI detection of bright long burst
- EP250807a: EP-WXT detection of a fast X-ray transient
- GRB 250807B: Swift detection of a burst with an optical counterpart.
- GRB 250806A: Swift/UVOT U-band detection
- GRB 250807A: Swift detection of a burst with an optical counterpart
- GRB 250806A: EP-FXT observation
- EP250802a: EP-FXT follow-up observation
- EP250806a: Earlier Detection of the VT Candidate by COLIBRÍ and LS
- GRB 250806A: SVOM/VT refined analysis
- GRB 250806A: Swift-XRT counterpart detection