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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').
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"
  1. EP250427A: COLIBRÍ Optical Detection
  2. EP250427a: TRT optical counterpart detection
  3. EP 250427a: BOOTES-7 optical afterglow candidate
  4. EP250427a: Global MASTER-Net observations report
  5. EP250427a: Einstein Probe detection of a fast X-ray transient
  6. IceCube Alert 250426.74: Global MASTER-Net observations report
  7. GRB 250424A: Swift-BAT refined analysis
  8. IceCube-250426A - IceCube observation of a high-energy neutrino candidate track-like event (duplicate submission)
  9. IceCube-250426A - IceCube observation of a high-energy neutrino candidate track-like event
  10. GRB 250424A: SVOM/GRM observation of a long burst
  11. GRB 250424A: PRIME near-infrared detection
  12. GRB 250424A: WINTER J-band detection
  13. GRB 250424A: EIRSAT-1 GMOD Detection
  14. IceCube-250416A: Upper limits from a search for additional neutrino events in IceCube
  15. IceCube-250421A: Upper limits from a search for additional neutrino events in IceCube
  16. GRB 250424A: SVOM/VT optical observation
  17. GRB 250419A: Mondy Optical Observations
  18. GRB 250424A: Swift/UVOT Detection
  19. Konus-Wind detection of GRB 250424A
  20. Fermi-LAT gamma-ray observations of IceCube-250421A
  21. GRB 250424A: Skynet Optical Observations
  22. GRB 250424A: Kilonova-Catcher optical afterglow detection
  23. GRB 250419a: Continued Liverpool Telescope observations
  24. GRB 250419A: Liverpool Telescope optical upper limit
  25. GRB 250407A: GRBAlpha detection
  26. GRB 250404A / EP250404a: GRBAlpha detection
  27. GRB 250330B: GRBAlpha detection
  28. GRB 250419A: SVOM/ECLAIRs refined analysis
  29. GRB 250424A: Swift-XRT refined Analysis
  30. GRB 250424A: Enhanced Swift-XRT position
  31. GRB 250424A: AstroSat CZTI detection of a bright long burst
  32. GRB 250424A: COLIBRÍ Detection of a Bright Optical Counterpart
  33. GRB 250424A: BlackGEM optical afterglow detection
  34. GRB 250424A: VLT/X-shooter spectroscopic redshift z = 0.310
  35. GRB 250424A: likely host galaxy
  36. GRB 250424A: DDOTI Afterglow Detection
  37. GRB 250424A: REM optical/NIR afterglow detection
  38. GRB 250424A: Swift detection of a burst with an optical counterpart
  39. Swift GRB 250424A: Global MASTER-Net observations report
  40. Swift GRB 250424A: Global MASTER-Net OT detection
  41. LIGO/Virgo/KAGRA S250328ae: Subaru/PFS Spectroscopic Follow up and Candidates
  42. EP250421a: Nickel optical upper limit
  43. EP250416a / GRB 250416C: Gemini GMOS-S likely host galaxy redshift z = 0.963
  44. EP250421a: Upper limits from Fermi-GBM Observations
  45. SVOM/sb25042207: XRT observations
  46. SVOM/sb25042207: BOOTES-2 early optical upper limit
  47. SVOM/sb25042207: GOTO optical upper limits
  48. GRB 250421A: AstroSat CZTI detection
  49. SVOM/sb25042207: SVOM detection of an X-ray transient
  50. GRB250419A: VLA radio detection
  51. IceCube-250421A: DDOTI Detection of the LAST Candidate
  52. GRB 250419A: Mephisto Multi-band Optical Detection
  53. GRB 250419A: Calapai Observatory, Massa S. Giorgio (Messina), optical observations.
  54. IC-250421A: LAST optical observations of the IceCube neutrino candidate
  55. EP250421a: NOT optical observations
  56. GRB 250419A: Optical Observations via Virtual Telescope Project
  57. EP250421a: REM optical upper limit
  58. EP250421a: Swift/XRT counterpart detection
  59. EP250421A: COLIBRÍ Optical Upper Limit
  60. GRB 250419A: Mondy Continued Optical Observations
  61. Fermi GRB 250421A: Global MASTER-Net observations report
  62. EP250421a: Global MASTER-Net observations report
  63. GRB 250421B: AstroSat CZTI detection of a bright long burst
  64. EP250421a: Einstein Probe detection of an X-ray transient
  65. EP250421a: Mephisto optical counterpart confirmation
  66. IceCube Alert 250421.71: Global MASTER-Net observations report
  67. IceCube-250421A - IceCube observation of a high-energy neutrino candidate track-like event
  68. IceCube-Cascade 250414A: Upper limits from a search for additional neutrino events in IceCube
  69. EP250421a: JinShan likely optical counterpart
  70. The EP-WXT trigger 01709135179: Kinder optical counterpart candidate
  71. GRB 250421A: Fermi GBM Final Real-time Localization
  72. GRB 250419A: Liverpool Telescope observations
  73. GRB 250419A: LCO optical observation
  74. GRB 250419A: JinShan optical observations
  75. GRB 250419A: SVOM/VT optical continuous observations
  76. GRB 250419A: SVOM/C-GFT optical observations
  77. GRB 250419A: Swift/UVOT Follow up
  78. GRB 250416C / EP250416a: SVOM/GRM observation of a burst
  79. GRB 250419A: LCO optical afterglow multi-band observations
  80. GRB 250419A: Mondy and AbAO Optical Observations
  81. GRB 250419A: Liverpool Telescope observations
  82. GRB 250419A: AKO Optical Afterglow Detection
  83. GRB 250419A: MASTER optical afterglow observation
  84. Fermi-LAT Gamma-ray Observations of IceCube-250416A
  85. GRB 250407A: rest-frame energetics from Konus-Wind observation
  86. GRB 250419A: Swift-XRT localisation
  87. GRB 250407A: GTC/OSIRIS+ spectroscopic redshift z = 1.36
  88. GRB 250419A: VLT/X-shooter spectroscopic redshift z = 0.845
  89. GRB 250419A: Swift-XRT refined Analysis
  90. GRB 250419A: GOTO optical counterpart detection
  91. GRB 250419A: KAIT optical afterglow observations
  92. GRB 250419A: SVOM/VT optical bright counterpart confirmation
  93. GRB 250419A: SVOM/COLIBRÍ (FM-GFT) Detection of the Optical Counterpart
  94. GRB 250419A: SVOM detection of a soft burst
  95. Konus-Wind detection of GRB 250416C (a counterpart of EP250416a)
  96. EP250416a: Swift/XRT counterpart fading
  97. EP250416a: refined EP-WXT and EP-FXT analysis
  98. Konus-Wind detection of GRB 250403A
  99. EP20250416a: Swift/XRT counterpart detection
  100. GRB 250403A: VLT/FORS2 spectroscopic redshift z = 1.847

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