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').
- FRB 250316A: NOT optical upper limit for the X ray source EP J120944.2+585060
- GRB 250322A: further NOT optical observations
- EP-WXT trigger 01709133021: Optical upper limit through Kinder observations
- GRB 250322A: Swift/UVOT Upper Limits
- EP250324A: COLIBRÍ/DDRAGO Optical Observations
- GRB 250322A: VLT/X-shooter redshift confirmation of the putative host galaxy
- FRB 250316A: COLIBRÍ/DDRAGO Optical follow up of the X ray source EP J120944.2+585060
- GRB 250322B: NuSTAR detection of the prompt emission and regular dips during the burst
- GRB 250321B: Swift-XRT observations
- GRB 250322A: Swift-XRT refined Analysis
- EP250321a: TNOT Observation of Optical Counterpart
- FRB 250316A: DDOTI Continued Optical Observations (Third Epoch)
- GRB 250322A: Gemini-North redshift of candidate host galaxy
- EP250304a: VLT/MUSE spectroscopic observation of its associated supernova SN 2025fhm
- SVOM/sb25032302: SVOM detection of a long X-ray transient
- GRB 250322A: AstroSat CZTI detection of a short burst
- GRB 250322B: AstroSat CZTI detection of a bright long burst
- GRB250322A: STEP/T80S optical limits
- GRB 250322A: Gemini-South optical observations
- GRB 250322A: VLT optical observations
- GRB 250322A: VLT near-infrared observations
- FRB 250316A: DDOTI Continued Optical Observations
- GRB 250322A: NOT optical upper limits
- GRB 250322A: Enhanced Swift-XRT position
- GRB 250321B: SVOM/COLIBRÍ (F-GFT) follow-up observations
- FRB 20250316A: Kinder optical upper limits of the Einstein Probe candidate X-ray source EP J120944.2+585060
- GRB 250322A: MASTER optical observation
- EP250321a: Liverpool Telescope optical follow-up
- EP250321a: Mondy AZT-33IK Optical Observations
- GRB 250322A: Swift detection of a short burst
- FRB 20250316A: detection of a candidate associated X-ray source EP J120944.2+585060 by Einstein Probe
- EP250321a: refined analysis of the EP-WXT and EP-FXT observations
- EP250321a: KAIT optical observations
- EP250321A: COLIBRÍ Continuing Optical Observations
- GRB 250225B: GECAM-A detection
- GRB 250312A: GECAM-A detection
- GRB 250321B: Swift ToO observations
- EP250321a: WFST optical observations
- GRB 250320B: NuSTAR detection of the prompt emission from two broad bursts and preliminary analysis
- GRB 250321C: Fermi GBM Final Real-time Localization
- GRB 250320A: NuSTAR Detection of the Prompt Emission and Preliminary Results
- GRB 250320B: Fermi GBM Observation
- EP250321a: Xinglong 216 decaying optical observations
- GRB 250321A: Swift-BAT refined analysis
- GRB 250321A: Swift-XRT refined Analysis
- GRB 250320B: Fermi-LAT detection
- GRB 250321B: SVOM detection of a sub-threshold transient event
- EP250321a: SVOM/VT optical observation
- EP 250321A: Optical counterpart detection by LCO.
- EP250321a: Kinder optical follow-up observations
- GRB 250321A: Swift/UVOT Upper Limits
- GRB 250320B: SVOM/GRM observation of a long burst
- EP250321a: LCO optical counterpart detection
- EP250321a: Swift-XRT detection of an X-ray source
- EP250321A: COLIBRÍ Optical Observations
- EP250321a: VLT/X-shooter redshift z = 4.368
- GRB 250320B: AstroSat CZTI detection
- EP250321a: REM optical/NIR afterglow detection
- Fermi GRB 250320B: Global MASTER-Net observations report
- EP250321a: BOOTES-5/JGT optical afterglow detection
- EP250321a: TRT optical counterpart detection
- EP250321a: Global MASTER-Net observations report
- Swift GRB 250321A: Global MASTER-Net observations report
- Fermi GRB 250321A: Global MASTER-Net observations report
- EP250321a: Einstein Probe detection of an X-ray transient
- GRB 250321A: GOTO optical upper limits
- GRB 250321A: Swift-XRT localisation
- GRB 250314A: Keck/NIRC2 J-band upper limit
- EP250226a/GRB 250226A: KAIT optical observations
- GRB 250321A: Fermi GBM Observation
- GRB 250321A: Swift detection of a burst
- GRB 250321A: Fermi GBM Final Real-time Localization
- GRB 250320B: Fermi GBM Final Real-time Localization
- GRB 250309B: Proof-of-concept for Joint ZTF+EP Experiment
- GRB 250317B: Mondy AZT-33IK Continued Optical Observations
- GRB 250320A: Fermi GBM Final Real-time Localization
- Fermi GRB 250319B: Global MASTER-Net observations report
- FRB 20250316A: Upper limits for gamma-ray transient from Insight-HXMT/HE observations
- GRB 250313A: GRBAlpha detection
- LIGO/Virgo/KAGRA S250206dm: LIGHETR followup observations of AT2025azn
- GRB 250317B: SVOM/COLIBRI (F-GFT) follow-up observations
- GRB 250319B: Fermi GBM Final Localization
- GRB 250319A: Fermi GBM Final Localization
- GRB 250317D: EIRSAT-1 GMOD Detection
- LIGO/Virgo/KAGRA S250319bu: Updated Sky localization
- GRB 250314A: ATCA radio upper limits
- EP250302a: VLA observations
- GRB 250317B: OHP/T193 continued follow-up
- LIGO/Virgo/KAGRA S250319bu: Identification of a GW compact binary merger candidate
- GRB 250317C: SVOM/GRM observation of a long burst
- GRB 250317B: Leavitt Observatory optical upper limit
- GRB 250309B/AT2025dws: further ATCA observations
- GRB 250317B: Mondy AZT-33IK Optical Observations
- GRB 250317C: AstroSat CZTI detection
- GRB 250317B: NOT optical observations suggest an optical plateau phase
- GRB 250317B: GTC/OSIRIS+ spectroscopic redshift z=3.44
- GRB 250317C: GECAM-B detection
- GRB 250317B: OHP/T193 optical observations
- Fermi trigger No 763933627: Global MASTER-Net observations report
- GRB250312A: Swift/UVOT Upper Limits