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').
- 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
- GRB 250317B: REM optical/NIR observations
- 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
- EP 250317B: Fading optical counterpart detection by LCO
- GRB 250316A: Swift-XRT afterglow detection
- GRB 250317B: LCO detection of the fading optical afterglow
- GRB 250317B: refined SVOM/MXT analysis
- GRB250317B: SVOM/VT detection of an optical candidate from VHF data
- GRB 250317B: SVOM/F-GFT (COLIBRÍ) Detection of a Fading Optical Counterpart
- GRB 250317B: SVOM detection of a burst / correction to GRB name of GCN 39752
- GRB 250317B: SVOM detection of a burst
- GRB 250316A: Fermi GBM Observation
- GRB 250316A: Swift-XRT observations
- Fermi trigger No 763862734: Global MASTER-Net observations report
- GRB 250317A: Fermi GBM Final Real-time Localization
- Fermi GRB 250316A: Global MASTER-Net observations report
- GRB 250314A: SVOM/GRM analysis
- GRB 250316A: Swift ToO observations
- GRB 250316A: Swift/BAT-GUANO arcminute localization of a burst
- GRB 250314A: GTC z-band upper limit and updated photo-z ~ 7.27
- The EP-WXT trigger 01709132801 is likely a flaring star
- GRB 250316A: Fermi GBM Final Real-time Localization
- GRB 250315A/EP250315A: Fermi-GBM Sub-Threshold Detection
- GRB 250314A: EP-FXT afterglow detection
- EP250315a: refined analysis of the EP-WXT and EP-FXT observations
- GRB 250314A: Swift/UVOT Upper Limits
- GRB 250312B: GRBAlpha detection
- GRB 250313.89 / Fermi trigger 763594063: bright OT AT 2025ehi detection
- GRB 250314A: Swift XRT Detection
- EP250315a: optical counterpart candidate detected by Gemini North
- GRB 250314A: VLT/X-shooter dropout, redshift z ~ 7.3
- EP250315a: Einstein Probe detection of an X-ray transient
- GRB 250226A: Mondy AZT-33IK and Koshka Zeiss-1000 Optical Upper Limits
- SVOM/MXT upper limit on GRB 250314A
- GRB 250314A: SVOM/VT upper limit
- GRB 250314A: NOT near-infrared candidate counterpart
- GRB 250313A: Fermi GBM Detection
- GRB 250313A: CALET Gamma-Ray Burst Monitor detection
- GRB 250312B: Fermi GBM Observation
- GRB 250313A: Swift-XRT observations
- GRB250314A: SVOM/VT lack of bright optical candidate from VHF data
- Konus-Wind detection of GRB 250313A
- Konus-Wind detection of GRB 250308A
- GRB 250314A: SVOM detection of a burst
- EP250311a/GRB 250311A: Correction to EP-WXT detection time
- GRB 250313B: SVOM/GRM observation of a soft bright short burst
- GRB 250313A: SVOM/GRM observation of a bright long burst
- FRB 20250206A: Nondetection of Repeating Bursts from FRB 20250206A with FAST
- GRB 250313A: AstroSat CZTI detection of a bright long burst
- IceCube-250309A: MASTER detection of J140105.33-091631.6 blazar flare with Zhirkov effect
- Fermi trigger No 763581136: Global MASTER-Net observations report
- GRB 250313A: Fermi-LAT detection
- GRB 250313A: Swift ToO observations
- EP250304a: Pan-STARRS r and i-band imaging and photometry
- GRB 250312B: Swift/BAT-GUANO localization skymap of a burst
- EP trigger ID 01709061302: Lick/Kast spectroscopy with the 3 m Shane telescope
- Fermi GRB 250313A: Global MASTER-Net observations report
- GRB 250309B: PRIME near-infrared upper limits in 2nd epoch
- GRB 250313A???: BALROG localization (Fermi Trigger / GRB 250313607)
- GRB 250313A: Fermi GBM Final Real-time Localization
- The EP-WXT trigger 01709132551 is not a real source
- EP250304a: SVOM/VT optical observation
- EP250311a/GRB 250311A: EP-FXT follow-up observation
- ATCA detection of the radio counterpart of GRB 250309B-AT2025dws
- EP250302a: Chandra X-ray Detection
- GRB 250312A: Swift-XRT refined Analysis
- Fermi Gamma-ray Burst Monitor trigger 763509110/250312911 is not a GRB
- Fermi trigger No 763509110: Global MASTER-Net observations report
- Fermi GRB 250312B: Global MASTER-Net observations report
- GRB 250312A: Enhanced Swift-XRT position
- GRB 250312B: Fermi GBM Final Localization
- LIGO/Virgo/KAGRA S250304cb: Upper limits from Swift/BAT-GUANO
- GRB 250226B: Fermi GBM Observation