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"2744 results found.
- GRB 250814A: Further COLIBRÍ optical upper limit
- GRB 250814A: possible optical afterglow candidate at Spanish observatories
- GRB 250814A: Possible afterglow candidate from P200/WIRC
- IceCube-250813A - IceCube observation of a high-energy neutrino candidate track-like event
- IceCube-250804A - IceCube observation of a high-energy neutrino candidate track-like event
- LIGO/Virgo/KAGRA S250727dc: DECam GW-MMADS candidates
- EP250702a/GRB250702 B,D,E: uGMRT Radio detection in 1.26 GHz
- SVOM J195836+32283/sb25072103: Liverpool Telescope detection of an extended source
- Swift Trigger 1334535: a possible GRB 250718A
- GRB 250716A: GOTO tentative optical counterpart candidate
- GRB 250713A: NOT optical upper limits
- EP250711a: COLIBRÍ refined photometry and optical confirmation of the candidate
- IceCube-250708A - IceCube observation of a high-energy neutrino candidate track-like event
- IceCube-250706A - IceCube observation of a high-energy neutrino candidate track-like event
- EP250702a/GRB 250702B,C,D,E: Archival radio observations from ASKAP VAST
- EP250704a / GRB 250704B: NOT observations of the optical afterglow
- GRB 250702D, C, E: Swift/BAT-GUANO localization skymap of a burst or galactic transient
- GRB 250702F: Ondrejov D50 optical afterglow detection
- GRB 250628A: REM optical/NIR upper limits
- GRB 250625A: SAO RAS possible optical afterglow
- GRB 250621B: SVOM/GRM detection of a possible magnetar X-ray burst
- sb25061207: SVOM detection of a X-ray transient
- GRB 250610B: REM optical/NIR observations
- GRB 250610B: SVOM/VT optical shallow decay
- GRB 250610B: Fermi/GBM sub-threshold detection of a possibly hard burst
- EP250610a: REM optical/NIR observations
- GRB 250608A: SVOM/GRM detection of a possible magnetar X-ray burst
- GRB 250605A: SVOM/VT optical upper limit
- GRB 250605A: LT optical observations
- GRB 250603A: Swift detection of a burst or new Galactic transient Swift J0839.7-3916
- GRB 250521C/ZTF25aarhkyn/AT2025mgj: COLIBRÍ optical observations
- GRB 250530C: Swift detection of a burst
- GRB 250521C (short): Zwicky Transient Facility identification of a possible fast optical transient counterpart
- GRB 250521D: SVOM/GRM analysis suggests a possible “long” duration type I burst
- GRB 250520A: REM optical/NIR early observations
- GRB 250515A/GOTO25cqo: SVOM/VT optical blue color
- GRB 250424A: COLIBRÍ detection of the associated supernova
- EP250512a/GRB 250512B: REM optical/NIR observations
- EP250511a: REM optical/NIR observations
- EP250511a: SVOM/VT optical candidate comfirmation
- EP250511a: COLIBRÍ optical counterpart candidate
- GRB 250510A: follow-up observation with EP-FXT
- GRB 250510A: SVOM possible detection of a burst
- EP250508a: REM optical/NIR observations
- GRB 250507A: REM optical/NIR observations
- IceCube-250506A - IceCube observation of a high-energy neutrino candidate track-like event
- GRB 250506A: REM optical/NIR upper limits
- GRB 250506A: Swift XRT observations and possible counterpart detection
- EP250428b: Pan-STARRS follow-up, upper limit on the optical counterpart, and possible host galaxy.
- IceCube-250429A - IceCube observation of a high-energy neutrino candidate track-like event
- EP250427a: Lesedi optical counterpart detection
- EP250427a / GRB 250427A: VLT/X-shooter redshift confirmation z = 1.520
- IceCube-250426A - IceCube observation of a high-energy neutrino candidate track-like event
- Fermi-LAT gamma-ray observations of IceCube-250421A
- LIGO/Virgo/KAGRA S250328ae: Subaru/PFS Spectroscopic Follow up and Candidates
- IceCube-250421A - IceCube observation of a high-energy neutrino candidate track-like event
- EP250416a: Swift/XRT counterpart fading
- EP250416a: refined EP-WXT and EP-FXT analysis
- IceCube-250416A - IceCube observation of a high-energy neutrino candidate track-like event
- EP250227a: Further NOT optical observations
- IceCube-250406A - IceCube observation of a high-energy neutrino candidate track-like event
- GRB 250331C Swift-BAT refined analysis
- IceCube-250330A: MASTER detection of PKS 2032+107 blazar flare with Zhirkov effect
- GRB 250322B possible detection by the AstroSat Satellite
- LIGO/Virgo/KAGRA S250328ae: DECam DESGW Candidates (Epoch 2)
- LIGO/Virgo/KAGRA S250328ae: Swift XRT observations, 34 possible X-ray sources
- IceCube-250330A - IceCube observation of a high-energy neutrino candidate track-like event
- LIGO/Virgo/KAGRA S250328ae: DECam DESGW Candidates (Epoch 1)
- GRB 250329A: SVOM/VT optical counterpart confirmation
- FRB 20250316A: Gemini Imaging and Spectroscopy of the Sub-arcsecond Localization Region of FRB 20250316A
- GRB 250317B: NOT optical observations suggest an optical plateau phase
- GRB 250314A: VLT/X-shooter dropout, redshift z ~ 7.3
- SVOM/MXT upper limit on GRB 250314A
- IceCube-250309A: MASTER detection of J140105.33-091631.6 blazar flare with Zhirkov effect
- EP trigger ID 01709061302: Lick/Kast spectroscopy with the 3 m Shane telescope
- ATCA detection of the radio counterpart of GRB 250309B-AT2025dws
- Liverpool Telecope observations of AT 2025dws / GRB 250309B
- GRB 250309B / AT2025dws: SAO RAS optical observations
- GRB250309B: One candidate counterpart from the Zwicky Transient Facility
- EP250304a: MeerKAT detection of a possible radio counterpart
- GRB250101A: Radio upper limits from VLA observations
- IceCube-250302A - IceCube observation of a high-energy neutrino candidate track-like event
- LIGO/Virgo/KAGRA S250223dk: DECam optical detections of Swift X-ray sources
- GRB 250221A: EP-FXT detection of the X-ray afterglow
- LIGO/Virgo/KAGRA S250223dk and Swift/BAT-GUANO ID 762004910: DECam GW-MMADS candidates
- LIGO/Virgo/KAGRA S250223dk: DECam DESGW Candidates
- GRB 250221A: VLT/X-shooter redshift z = 0.768
- SVOM/sb25021804: COLIBRÍ/DDRAGO Confirmation of Variability
- EP250212a: FTW optical and NIR upper limits
- LIGO/Virgo/KAGRA S250206dm: DECam GW-MMADS candidates
- GRB250101A: Radio upper limits from GMRT observations
- LIGO/Virgo/KAGRA S250206dm: continued in SOAR galaxy targeted observations and identification of one possible transient
- LIGO/Virgo/KAGRA S250206dm: Kinder confirmation of a possible artefact in AT 2025bbo
- EP250207b: Liverpool Telescope possible optical counterpart
- GRB 250209A: MAXI/GSC detection (possible detection of an X-ray flare from 1RXS J145110.3+310648)
- LIGO/Virgo/KAGRA S250206dm: COLIBRÍ/DDRAGO Observations of AT2025bbo and Galaxies in the Localization Volume
- LIGO/Virgo/KAGRA S250206dm & FRB 20250206A: MASTER observations and possible mother galaxy
- LIGO/Virgo/KAGRA S250206dm: further Pan-STARRS observations and one candidate AT2025bbo
- LIGO/Virgo/KAGRA S250206dm: COLIBRÍ/DDRAGO Observations of the DDOTI optical candidates
- EP250207a: EP-WXT detection and XRT follow-up observation