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"21793 results found.
- EP250908b/EP#01709240653: Swift/UVOT Detection
- EP#01709240653: Swift-XRT observations
- EP250908c: refined analysis of the EP-WXT and EP-FXT observations
- EP250908c: Global MASTER-Net observations report
- Fermi GRB 250909A: Global MASTER-Net observations report
- EP#01709240652 (possibly EP250908a): FTW optical and NIR observations
- Fermi-LAT Gamma-ray Observations of IceCube-250905A
- GRB 250903A: Swift-XRT afterglow detection
- LIGO/Virgo/KAGRA S250830bp: DECam/SOAR GW-MMADS updates
- EP250905b: EP-FXT follow-up observation
- LIGO/Virgo/KAGRA S250830bp: DECam DESGW Epoch 2 Candidates
- EP250905a: Liverpool Telescope observations
- EP250905a: refined analysis of the EP-WXT and EP-FXT observations
- EP250905b: Global MASTER-Net observations report
- EP250905b: EP-WXT detection of a fast X-ray transient
- EP250905a: FTW one optical and multiple NIR counterpart candidates
- EP250905a: JinShan likely optical counterpart detection
- IceCube Alert 250905.84: Global MASTER-Net observations report
- GRB 250905A: Swift/UVOT Upper Limits
- EP250905a: Global MASTER-Net observations report
- GRB 250901A - SVOM/ECLAIRs refined analysis
- GRB 250904A: Swift/UVOT Detection
- GRB 250903A: Swift/UVOT detection
- Swift GRB250905.09: Global MASTER-Net observations report
- Swift GRB 250904A: Global MASTER-Net observations report
- GRB 250904A: TRT optical counterpart detection
- EP250827a and EP250827b: Upper limit from Fermi-GBM Observations
- EP250827b: Gemini Spectroscopic Confirmation of AT2025wkm as a Ic-BL Supernova
- GRB 250903A: Swift-XRT observations
- EP250903a: Swift-XRT observations
- EP#01709201209: Swift-XRT observations
- EP250903a: retraction of the LCO candidate, and discovery of the likely counterpart
- EP250903a: refined analysis of the EP-WXT and EP-FXT observations
- GRB 250903A: VLT X-shooter spectroscopic redshift z = 1.590
- GRB 250903A: LCO optical afterglow detection
- EP250903a: SVOM/VT optical confirmation
- EP250903a: LCO candidate counterpart discovery
- GRB 250903A: TRT optical counterpart detection
- EP250903a: Global MASTER-Net observations report
- EP250903a: TRT optical observations
- EP 250827B: Detection of supernova counterpart by LCO.
- EP/WXT01709201159: GOTO optical follow-up
- EP250827b / AT 2025wkm: TRT optical observations
- EP250827b: NOT spectroscopic observations and AT 2025wkm classification as a broad-lined type-Ic supernova
- EP250827b: continued Liverpool Telescope observations
- LIGO/VIRGO/KAGRA S250818k: No evidence for radio variability of AT2025ulz in MeerKAT 3 GHz data
- GRB 250831A (SVOM trigger sb25083102): KAIT confirmation of stellar flare
- Fermi GRB 250902B: Global MASTER-Net observations report
- Fermi-LAT Gamma-ray Observations of IceCube-250831A
- GRB 250901A: Swift/UVOT Upper Limit
- GRB 250830B: Swift-XRT afterglow detection
- EP250827b: Liverpool Telescope observations
- EP250828a: Early near-infrared follow-up with MIRAGE on the MDM 1.3m telescope
- EP250901a: refined analysis of the EP-WXT and EP-FXT observations
- GRB 250901A: NOT optical observations
- GRB 250901A: Swift-XRT afterglow detection
- EP250901a: Swift-XRT observations
- LIGO/Virgo/KAGRA S250830bp: DECam GW-MMADS candidates
- EP250827b: Swift observations of AT 2025wkm
- LIGO/Virgo/KAGRA S250830bp: DECam DESGW Epoch 1 Candidates
- EP250827b: Gemini Spectroscopy of AT 2025wkm
- EP250831a: NOT optical observations and tentative afterglow candidate
- EP250827b: FTW Observations of AT 2025wkm
- EP250827b: Contemporaneous detection of EP X-ray flare EP250827b and ZTF transient ZTF25abmpngy/AT2025wkm
- EP250901a: Mephisto optical upper limits
- EP250901a: Global MASTER-Net observations report
- EP250831a: Swift-XRT observations
- LIGO/Virgo/KAGRA S250831cc: Coverage and upper limits from MAXI/GSC observations
- IceCube Alert 250831.75: Global MASTER-Net observations report
- EP250831a: Global MASTER-Net observations report
- EP250831a: EP-WXT detection of a fast X-ray transient
- GRB 250831A: Swift-XRT counterpart detection
- GRB 250830B: Swift-XRT observations
- EP250830a: Global MASTER-Net observations report
- LIGO/Virgo/KAGRA S250830bp: Coverage and upper limits from MAXI/GSC observations
- LIGO/Virgo/KAGRA S250830bp GLADEnet Completeness: Potential Host Galaxies in the 90% Credible Volume
- LIGO/Virgo/KAGRA S250830bp: NED Galaxies in the 4-Update Localization Volume
- GRB 250830B: Swift ToO observations
- EP250821a: SOAR observations
- EP250827a: very early ATLAS detections, starting 43 sec after the EP trigger
- LIGO/Virgo/KAGRA S250725j: Observations with the NSF-DOE Vera C. Rubin Observatory
- LIGO/Virgo/KAGRA S250818k: MeerKAT detection of an increase in radio flux from AT2025ulz
- EP250828a: refined analysis of the EP-WXT and EP-FXT observations
- EP250828a: Optical counterpart detection with Kinder observations
- Swift GRB 250828B: Global MASTER-Net observations report
- EP250828a: Global MASTER-Net observations report
- EP-WXT trigger 01709200800 : KAIT optical observations
- EP250827a: Swift/UVOT Detection
- EP250828a: NOT optical counterpart confirmation
- EP250827a: STEP/T80S Confirmation of fading optical counterpart
- EP250828a: Optical upper limit with Kinder observations
- LIGO/Virgo/KAGRA S250818k: uGMRT 1.3 GHz observations of AT2025ulz
- EP250827a: LCO observations show fading optical counterpart
- EP250827a: Preliminary analysis of the EP-WXT and EP-FXT observations
- EP250827A: VLT/X-shooter redshift confirmation
- Fermi GRB 250827A: Global MASTER-Net observations report
- EP250827a: confirmation of optical rebrightening with LCO
- EP250827a: GOTO observation of the optical afterglow
- EP250827A: An optical rebrightening was detected by LCO.
- EP250827a: Swift-XRT counterpart detection