GCN Circulars
GCN Circulars are rapid bulletins submitted by and distributed to the community. 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').
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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.
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subject:"Swift"body:"GRB"submitter:"Judith Racusin"- Fermi GRB 250824B: Global MASTER-Net observations report
- LIGO/Virgo/KAGRA S250818k: VLA upper limits on AT2025ulz
- LIGO/Virgo/KAGRA S250818k: nature of the AT2025ulz/ZTF25abjmnnps OT
- LIGO/Virgo/KAGRA S250818k: Pan-STARRS imaging confirms re-brightening of SN2025ulz
- GRB 250823A: Swift-BAT refined analysis
- LIGO/Virgo/KAGRA S250818k: Continued Keck I LRIS spectroscopy of ZTF25abjmnps (AT2025ulz)
- GRB 250821B: AstroSat CZTI detection
- GRB 250819A: AstroSat CZTI detection
- LIGO/Virgo/KAGRA S250818k: FTW Observations Show Continued Reddening of AT 2025ulz
- LIGO/Virgo/KAGRA S250818k: MASTER predicovery limits of the AT2025ulz/ZTF25abjmnps KN candidate
- GRB 250821B: Insight-HXMT detection
- LIGO/Virgo/KAGRA S250818k: ENGRAVE observations of SN 2025ulz as a type II supernova
- GRB 250823A: Swift-XRT refined Analysis
- EP250821a: MeerKAT radio counterpart
- EP triggers 01709200706 and 01709200707: GOTO confirmation of flaring stars
- LIGO/Virgo/KAGRA S250818k: Swift Observations of AT 2025ulz - Second Epoch
- GRB 250824B: Fermi GBM Final Real-time Localization
- The EP-WXT trigger 01709200707 is likely a flaring star
- GRB 250823A: COLIBRÍ optical observations
- The EP-WXT trigger 01709200706 is likely a flaring star
- GRB 250823A: SVOM/VT optical observation
- GRB 250824A: Fermi GBM Final Real-time Localization
- GRB 250823A: Swift/UVOT Detection
- GRB 250823A: NOT optical observations
- LIGO/Virgo/KAGRA S250818k: CFH/MegaCam follow-up observation for AT2025ulz
- LIGO/Virgo/KAGRA S250818k: COLIBRÍ confirmation of rebrightening of AT2025ulz
- 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
- LIGO/Virgo/KAGRA S250818k: Rebrightening detected with Gemini/GMOS
- LIGO/Virgo/KAGRA S250818k: HST nIR detection of AT 2025ulz
- LIGO/Virgo/KAGRA S250818k: J-GEM follow-up observation for AT2025ulz
- LIGO/Virgo/KAGRA S250818k: PRIME nIR observations of AT2025ulz
- LIGO/Virgo/KAGRA S250818k: JinShan optical observations of AT2025ulz
- LIGO/Virgo/KAGRA S250818k: GTC/OSIRIS Optical Detection of AT2025ulz
- LIGO/Virgo/Kagra S250818k: STEP/T80N upper limits on 2025ulz
- LIGO/Virgo/KAGRA S250818k: 3 GHz MeerKAT observations of AT2025ulz
- 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
- LIGO/Virgo/KAGRA S250818k: Pan-STARRS coverage of the skymap and candidate counterparts
- LIGO/Virgo/KAGRA S250818k: NOT optical observations of AT2025ulz
- EP250821a: Swift/UVOT further observations.
- EP250821a: VLT X-shooter spectroscopic redshift z = 0.577
- LIGO/Virgo/KAGRA S250818k: GRAWITA TNG NIR observations of AT2025ulz
- 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
- LIGO/Virgo/KAGRA S250818k: Continued fading and reddening of AT2025ulz from Keck/LRIS imaging observations
- GRB 250821A: Swift-XRT refined Analysis
- Swift GRB 250821A: Global MASTER-Net observations report
- GRB 250821B: Fermi GBM Detection
- LIGO/Virgo/KAGRA S250818k: ENGRAVE observations of AT 2025ulz
- GRB 250821B: BALROG localization (Fermi Trigger / GRB 250821672)
- LIGO/Virgo/KAGRA S250818k : Tautenburg observations, upper limits
- 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
- LIGO/Virgo/KAGRA S250818k: GOTO counterpart search and upper limits
- EP250821a: Preliminary analysis of the EP-WXT and EP-FXT observations
- GRB 250821A: LCOGT Optical Upper Limits
- GRB 250814A: CMO SAI and SAO RAS izJ observations.
- LIGO/Virgo/KAGRA S250818k: 10 GHz VLA observations of AT2025ulz
- GRB 250821A: Prompt enhanced Swift-XRT position
- GRB 250821A: Swift detection of a burst
- LIGO/Virgo/KAGRA S250818k: WFST pre-discovery limits and follow-up observations of AT 2025ulz
- LIGO/Virgo/KAGRA S250818k: EP/FXT observation of AT 2025ulz
- EP250821a: Einstein Probe detection of an X-ray transient
- GRB 250819A: SVOM/GRM observation of a possible “long” duration type I burst
- GRB 250819A: Insight-HXMT detection
- LIGO/Virgo/KAGRA S250818k: WINTER J-band observations of AT 2025ulz
- GRB 250818B: 10 GHz VLA detection
- LIGO/Virgo/KAGRA S250818k: Pan-STARRS grizy-band imaging and photometry of AT2025ulz
- LIGO/Virgo/KAGRA S250818k: Swift observations of AT 2025ulz
- LIGO/Virgo/KAGRA S250818k: Multi-band Gemini GMOS Detections
- LIGO/Virgo/KAGRA S250818k: ATLAS pre-discovery limits for AT2025ulz
- 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