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').
18282 results found.
- 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
- Konus-Wind detection of GRB 250306A
- GRB 250306A: Swift-BAT refined analysis
- GRB 250306A: NuSTAR detection of the prompt emission
- GRB 250306A: AstroSat CZTI detection
- Swift GRB 250306A: Global MASTER-Net observations report
- GRB 250306A: Swift detection of a burst
- IPN triangulation of GRB 250222A
- EP250304a: Swift/UVOT detection of an optical counterpart with a rising light curve
- EP250304a: Swift-XRT detection of a fading X-ray source
- LIGO/Virgo/KAGRA S250223dk and Swift/BAT-GUANO ID 762004910: Swift/UVOT Upper Limits
- EP250302a: Swift/UVOT detection
- EP250302a: Swift-XRT observations of a fading X-ray source
- EP250228a: Optical observations with Kinder and Swift/UVOT
- GRB 250225B: EIRSAT-1 GMOD Detection
- GRB 250225B: VLT/HAWKI near-infrared observations
- EP250228a: updates on the EP observations
- EP250228a: Swift/XRT localisation
- GRB 250225B: INTEGRAL SPI-ACS detection
- LIGO/Virgo/KAGRA S250223dk: Insight-HXMT/HE sub-threshold detection of a burst (HEB 250223501)
- GRB 250225B: Fermi GBM Observation
- GRB 250221A: ATCA Detections and Upper Limits
- GRB 250225B: REM NIR upper limits
- LIGO/Virgo/KAGRA S250223dk and Swift/BAT-GUANO ID 762004910: Updated Sky localization and Coincidence with External Event
- Konus-Wind detection of GRB 250225B
- LIGO/Virgo/KAGRA S250223dk: DECam optical detections of Swift X-ray sources
- GRB 250225B: VLT/FORS2 candidate optical afterglow
- GRB 250225B: SVOM/GRM observation of a long burst
- GRB 250221A: EP-FXT detection of the X-ray afterglow
- LIGO/Virgo S250223dk: Swift XRT observations, 7 X-ray sources
- Swift GRB 250225B: Global MASTER-Net observations report
- GRB 250225B: Swift detection of a burst
- GRB 250221A: Swift-BAT refined analysis
- LIGO/Virgo/KAGRA S250223dk and Swift/BAT-GUANO ID 762004910: DECam GW-MMADS candidates
- LIGO/Virgo/KAGRA S250223dk and Swift/BAT-GUANO ID 762004910: AstroSat CZTI non-detection and upper limits
- LIGO/Virgo/KAGRA S250223dk and Swift/BAT-GUANO ID 762004910: Magellan upper limits.
- GRB 250207a: ATCA Radio Upper Limits
- LIGO/Virgo/KAGRA S250223dk: DECam DESGW Candidates
- LIGO/Virgo/KAGRA S250223dk and Swift/BAT-GUANO ID 762004910: Upper limits from Fermi-GBM Observations
- GRB 250119B: VZLUSAT-2 detection
- GOTO observations of LVK S250223dk/Swift-BAT RAVEN alert
- GRB 250219A: EP-FXT afterglow detection
- EP250223a: COLIBRÍ/DDRAGO Detection of the Optical Counterpart and Slow Fading
- EP250223a: REM NIR upper limit
- EP250223a: TRT optical afterglow observation
- EP250223a: refined analysis of the EP-WXT and FXT observations
- EP250223a: SVOM/VT optical observation
- LIGO/Virgo/KAGRA S250223dk: DDOTI Upper Limits on the Optical Counterpart
- LIGO/Virgo/KAGRA S250223dk and Swift/BAT-GUANO trigger with ID 762004910: Identification of a GW compact binary merger candidate possibly associated with a sub-threshold Swift/BAT-GUANO trigger
- EP250223a: OASDG optical observations
- EP250223a: LCO detection of the afterglow
- EP250223a: early optical detection by BOOTES-4
- EP250223a: NOT redshift z = 2.756
- EP250223a: Swift/XRT localization
- GRB 250221A: VLA radio detection
- GRB 250221A: continued Assy optical observations, brightening afterglow confirmation
- GRB 250221A: continued Mondy optical observations, brightening afterglow
- GRB 250221A: Optical counterpart detection by LCO.
- GRB 250221A: Mondy optical observations
- Konus-Wind detection of GRB 250221A
- GRB 250221A: Assy optical observations