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"37048 results found.
- EP-WXT trigger 01709200800 : KAIT optical observations
- EP250828a: KAIT optical upper limit
- EP250827a: Swift/UVOT Detection
- GRB 250828B: Swift detection of a burst
- GRB 250828A: Fermi GBM Final Localization
- GRID detection of GRB 250824A
- Fermi GRB 250827A: Global MASTER-Net observations report
- EP250827a: confirmation of optical rebrightening with LCO
- EP250827a: GOTO observation of the optical afterglow
- GRB 250826A: SVOM/GRM observation
- GRB 250827A: Fermi GBM Final Real-time Localization
- EP250827A: An optical rebrightening was detected by LCO.
- EP250827a: Swift-XRT counterpart detection
- EP250827a / GRB 250827A: MASTER-OAFA OT observation
- Fermi GRB 250826A: Global MASTER-Net observations report
- GRB 250806A: HiPERCAM/GTC limits on a possible supernova
- LIGO/Virgo/KAGRA S250818k: SAO RAS BTA z-band observations of AT2025ulz
- Fermi Gamma-ray Burst Monitor trigger 777883624/250826283 is not a GRB
- GRB 250826A: Fermi GBM Final Real-time Localization
- Fermi GRB 250824B: Global MASTER-Net observations report
- GRB 250823A: Swift-BAT refined analysis
- GRB 250821B: AstroSat CZTI detection
- GRB 250819A: AstroSat CZTI detection
- GRB 250821B: Insight-HXMT detection
- GRB 250823A: Swift-XRT refined Analysis
- LIGO/Virgo/KAGRA S250818k: Swift Observations of AT 2025ulz - Second Epoch
- GRB 250824B: Fermi GBM Final Real-time Localization
- GRB 250823A: COLIBRÍ optical observations
- GRB 250823A: SVOM/VT optical observation
- GRB 250824A: Fermi GBM Final Real-time Localization
- GRB 250823A: Swift/UVOT Detection
- GRB 250823A: NOT optical observations
- GRB 250823A: Fermi GBM Observation
- GRB 250818B: MeerKAT Detection
- GRB 250823A: Enhanced Swift-XRT position
- GRB 250823A: LCOGT Optical Detection
- GRB 250823A: BOOTES6/DPRT early optical detection
- GRB 250823A: Liverpool Telescope optical detection
- GRB 250823A: Swift detection of a burst
- GRB 250823A: Fermi GBM Final Real-time Localization
- Swift GRB250823.84: Global MASTER-Net observations report
- Konus-Wind detection of GRB 250821B
- GRB 250806A: Gemini observations of host galaxy candidate
- IPN triangulation of GRB 250821B (long/bright)
- GRB 250821A: Kilonova-Catcher optical upper limits
- EP250821a: Swift/XRT counterpart fading
- GRB 250812A: SVOM/ECLAIRs refined analysis
- GRB 250821A: Swift-BAT refined analysis
- EP250821a: Swift/UVOT further observations.
- GRB 250821A: VLT/FORS2 Optical Observation
- GRB 250821A: GECAM-B detection
- GRB 250821B: SVOM/GRM observation
- EP250821a: SVOM/VT optical observation
- Fermi GRB 250821B: Global MASTER-Net observations report
- GRB 250821A: NOT z-band upper limit
- GRB 250821C: Fermi GBM Final Real-time Localization
- GRB 250821A: KAIT optical upper limit
- GRB 250821A: Swift-XRT refined Analysis
- Swift GRB 250821A: Global MASTER-Net observations report
- GRB 250821B: Fermi GBM Detection
- GRB 250821B: BALROG localization (Fermi Trigger / GRB 250821672)
- GRB 250821B: Fermi GBM Final Localization of a Bright Burst
- GRB 250821A: Enhanced Swift-XRT position
- GRB 250821A: Swift/UVOT Upper Limits
- EP250821a: Rapidly fading optical source detected in Las Cumbres followup
- EP250821a: Swift XRT and UVOT counterpart detection
- GRB 250821A: LCOGT Optical Upper Limits
- GRB 250814A: CMO SAI and SAO RAS izJ observations.
- GRB 250821A: Prompt enhanced Swift-XRT position
- GRB 250821A: Swift detection of a burst
- 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: Swift observations of AT 2025ulz
- GRB 250814A: Swift/UVOT Upper Limits
- GRB 250813B: Swift/UVOT Upper Limit
- IPN triangulation of GRB 250816A (short)
- IPN triangulation of GRB 250814C (short)
- IPN triangulation of GRB 250804B (short)
- GRB 250818B: FTW optical and NIR observations show reddening of the counterpart
- GRB 250818B: Kilonova-Catcher optical afterglow detection
- GRB 250818B: Liverpool Telescope optical detections
- LIGO/Virgo/KAGRA S250818k: Upper limits from Fermi-GBM Observations
- GRB 250818A: AstroSat CZTI detection
- GRB 250818B: Swift/UVOT Detection
- Fermi Gamma-ray Burst Monitor trigger 777342746/250820022 is not a GRB
- GRB 250820A: Fermi GBM Final Real-time Localization
- GRB 250818B: optical afterglow detection with Lesedi (GOTO25fzq)
- GRB 250818B: TRT Optical Observation
- Fermi GRB 250816A: Global MASTER-Net observations report
- GRB 250818B: SAO RAS optical observations
- Swift GRB 250818A: Global MASTER-Net observations report
- GRB 250818B: NOT optical observations
- GRB 250818A: Swift-XRT refined Analysis
- GRB 250818B: EP-FXT counterpart detection
- GRB 250818A: Swift-BAT refined analysis
- Fermi Gamma-ray Burst Monitor trigger 777251788/250818970 is not a GRB
- GRB 250818C: Fermi GBM Final Real-time Localization
- GRB 250818B: Keck redshift of the optical afterglow
- GRB 250818B: KAIT optical observations