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').
18345 results found.
- GRB 250330A: Swift detection of a burst
- Swift GRB250330.26: Global MASTER-Net observations report
- GRB 250329B: SVOM/C-GFT optical upper limit
- GRB 250329B: SVOM/VT optical upper limit
- GRB 250329A: Swift-XRT afterglow detection
- GRB 250328A: SVOM/C-GFT optical upper limit
- GRB 250328A: VLT/HAWK-I near-infrared afterglow candidate
- GRB 250327B: LCO optical counterpart detection
- GRB 250322A: GRANDMA/TNOT optical upper limits
- GRB 250327A: SVOM/VT upper limits on the XRT position
- GRB 250327B: Swift-XRT detection of the X-ray afterglow
- GRB 250327A: Swift-XRT refined Analysis
- FRB 20250316A: The sub-arcsecond localization of FRB 20250316A using CHIME/FRB Outriggers coincides with reported X-ray counterparts
- GRB 250327A: J-band observations with WINTER
- GRB 250327A: SVOM/VT optical candidate
- GRB 250327A: Fermi GBM observation
- Swift GRB 250327A: Global MASTER-Net observations report
- GRB 250327A: DDOTI Optical Observations
- GRB 250327A: COLIBRÍ optical upper limit
- GRB 250327A: Swift detection of a burst
- Konus-Wind detection of GRB 250322A (short)
- IPN triangulation of GRB 250322B
- Swift follow-up observations of FRB250316A and EP J120944.2+585060
- GRB 250322A: Swift-BAT refined analysis
- GRB 250322A: Swift/UVOT Upper Limits
- GRB 250321B: Swift-XRT observations
- GRB 250322A: Swift-XRT refined Analysis
- GRB 250322A: AstroSat CZTI detection of a short burst
- GRB250322A: STEP/T80S optical limits
- GRB 250322A: VLT optical observations
- GRB 250322A: VLT near-infrared observations
- GRB 250322A: NOT optical upper limits
- GRB 250322A: Enhanced Swift-XRT position
- GRB 250322A: MASTER optical observation
- GRB 250322A: Swift detection of a short burst
- EP250321a: refined analysis of the EP-WXT and EP-FXT observations
- GRB 250225B: GECAM-A detection
- GRB 250312A: GECAM-A detection
- GRB 250321B: Swift ToO observations
- GRB 250321A: Swift-BAT refined analysis
- GRB 250321A: Swift-XRT refined Analysis
- GRB 250320B: Fermi-LAT detection
- GRB 250321A: Swift/UVOT Upper Limits
- EP250321a: LCO optical counterpart detection
- EP250321a: Swift-XRT detection of an X-ray source
- Swift GRB 250321A: Global MASTER-Net observations report
- GRB 250321A: GOTO optical upper limits
- GRB 250321A: Swift-XRT localisation
- GRB 250321A: Fermi GBM Observation
- GRB 250321A: Swift detection of a burst
- GRB250312A: Swift/UVOT Upper Limits
- GRB 250317B: Swift-XRT observations
- GRB 250316A: Swift/UVOT Upper Limits
- GRB 250314A: REM optical/NIR upper limits
- GRB 250316A: AbAO AS-32 Optical Upper Limit
- GRB 250316A: Swift-XRT afterglow detection
- GRB 250316A: Fermi GBM Observation
- GRB 250316A: Swift-XRT observations
- GRB 250316A: Swift ToO observations
- GRB 250316A: Swift/BAT-GUANO arcminute localization of a burst
- GRB 250314A: EP-FXT afterglow detection
- GRB 250314A: Swift/UVOT Upper Limits
- GRB 250312B: GRBAlpha detection
- GRB 250314A: Swift XRT Detection
- GRB 250314A: NOT near-infrared candidate counterpart
- GRB 250312B: Fermi GBM Observation
- GRB 250313A: Swift-XRT observations
- Konus-Wind detection of GRB 250308A
- GRB 250313A: Fermi-LAT detection
- GRB 250313A: Swift ToO observations
- GRB 250312B: Swift/BAT-GUANO localization skymap of a burst
- EP250304a: SVOM/VT optical observation
- EP250302a: Chandra X-ray Detection
- GRB 250312A: Swift-XRT refined Analysis
- GRB 250312A: Enhanced Swift-XRT position
- LIGO/Virgo/KAGRA S250304cb: Upper limits from Swift/BAT-GUANO
- GRB 250226B: Fermi GBM Observation
- Swift GRB 250312A: Global MASTER-Net observations report
- GRB 250302A: Fermi GBM Observation
- GRB 250312A: Swift detection of a burst
- GRB 250223B: Fermi GBM Observation
- GRB 250311A: Swift-XRT observations
- GRB 250228A: Fermi GBM Observation
- GRB 230509B: 1.3m DFOT Optical observations
- GRB 250308A: Swift/BAT-GUANO localization skymap of a short burst
- GRB 250302A: Swift/BAT-GUANO localization skymap of a burst
- GRB 250228A: Swift/BAT-GUANO localization skymap of a likely short burst
- GRB 250226B: Swift/BAT-GUANO localization skymap of a likely long GRB
- GRB 250226A: Swift/BAT-GUANO localization skymap of a long GRB
- GRB 250223B: Swift/BAT-GUANO localization skymap of a short burst
- EP250304a: Chandra detection
- GRB 250225B: Swift-BAT refined analysis
- GRB 250311A: Tiled Swift observations
- IPN triangulation of GRB 250308A (short)
- GRB 250309B: Swift-XRT refined Analysis
- GRB 250309B / AT2025dws: Swift-UVOT detection
- GRB250309B: One candidate counterpart from the Zwicky Transient Facility
- Correction to GCN 39633 - Swift is observing GRB 250309B/IceCube-250309A!
- GRB 230509B: Tiled Swift observations
- GRB 250306A: EIRSAT-1 GMOD detection