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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"

28096 results found.

  1. GRB 250521C/AT2025mgj: FTW optical and NIR observations
  2. GRB 250601A: Fermi GBM Final Real-time Localization
  3. EP#01709177494: SVOM/VT optical observations
  4. GRB 250531A: Fermi GBM Final Real-time Localization
  5. EP#01709177494: Swift-XRT counterpart detection of known source
  6. GRB 250530C: BOOTES-7 optical upper limit
  7. GRB 250530C: Swift-XRT refined Analysis
  8. GRB 250530A: TNG detection of a NIR source inside the Swift/XRT error circle
  9. GRB 250530C: Enhanced Swift-XRT position
  10. GRB 250530C: Swift detection of a burst
  11. GRB 250521C/AT2025mgj: NOT optical observations of the afterglow candidate
  12. GRB 250530A: EP-FXT counterpart detection
  13. GRB 250530A: SVOM/VT optical upper limit
  14. GRB 250530B: Fermi GBM Final Real-time Localization
  15. GRB 250530A: Swift-XRT counterpart detection
  16. GRB 250530A: SVOM/COLIBRÍ (FM-GFT) optical counterpart candidate retraction and detection limit
  17. GRB 250530A: SVOM/COLIBRÍ (FM-GFT) optical counterpart candidate
  18. GRB 250530A: SVOM detection of a burst
  19. GRB 250527D: CALET Gamma-Ray Burst Monitor detection
  20. GRB 250527C: Swift/UVOT Upper Limits
  21. EP J1350.0-8622: EP-FXT follow-up observation
  22. GRB 250529B: Fermi GBM Final Real-time Localization
  23. GRB 250527B: Swift-XRT observations
  24. EP-WXT trigger 01709177124: confirmation of a stellar flare by BOOTES-6
  25. GRB 250529A: Fermi GBM Final Real-time Localization
  26. GRB 250521C (short): Zwicky Transient Facility identification of a possible fast optical transient counterpart
  27. GRB 250527C: Swift ToO observations
  28. GRB 250527C: Swift/BAT-GUANO arcminute localization of a burst
  29. GRB 250527B: Tiled Swift observations
  30. GRB 250520A: Gemini-South optical afterglow detection
  31. GRB 250527B / MAXI J1450-527 : MAXI/GSC detection
  32. GRB 250527A: Fermi GBM Final Localization
  33. EP250526a: Einstein Probe detection of a fast X-ray transient
  34. EP J1350.0-8622: BOOTES-6/DPRT optical upper limit
  35. EP J1350.0-8622: Einstein Probe detection of an X-ray transient candidate
  36. GRB 250520A: 3 GHz MeerKAT Detection
  37. GRB 250520A: 10 GHz VLA Afterglow Confirmation
  38. GRB 250521A: GRBAlpha detection
  39. GRB 250520A: GRBAlpha detection
  40. GRB 250523A: Fermi GBM Final Real-time Localization
  41. GRB 250521B: SVOM/VT optical upper limit
  42. The EP-WXT trigger 01709176612: refined analysis of the EP-FXT observation
  43. GRB 250521B: EP-FXT follow-up observation and afterglow candidates
  44. GRB 250522B: Fermi GBM Final Localization
  45. GRB 250522A: Fermi GBM Final Real-time Localization
  46. EP#01709176612: Swift-XRT counterpart detection of flaring star
  47. GRB 250521D: GOTO detects LAST counterpart candidate prior to the GRB
  48. GRB 250521D: LAST tentative optical counterpart candidate
  49. GRB 250520A: CALET Gamma-Ray Burst Monitor detection
  50. GRB 250521B: Swift ToO observations
  51. GRB 250521D: Fermi GBM Final Real-time Localization
  52. GRB 250521C: Fermi GBM Final Localization
  53. GRB 250521B: SVOM detection of a burst through offline search
  54. Konus-Wind detection of GRB 250520A (short/hard)
  55. GRB 250520A: VLT/FORS2 Optical Observation
  56. GRB 250520A: Swift/UVOT Upper Limits
  57. GRB 250521A: Fermi GBM Final Real-time Localization
  58. Konus-Wind detection of GRB 250516B
  59. IPN triangulation of GRB 250516B
  60. GRB 250520A: J-band observations with WINTER
  61. GRB 250520A: Gemini-South optical observations
  62. GRB 250520A: Swift-XRT refined Analysis
  63. GRB 250520A: REM optical/NIR early observations
  64. GRB 250520B: Fermi GBM Final Real-time Localization
  65. GRB 250520A:SVOM/VT optical candidate
  66. GRB 250520A: COLIBRÍ optical upper limit
  67. GRB 250520A: AstroSat CZTI detection of a short burst
  68. GRB 250516B: GRBAlpha detection
  69. GRB 250520A: Enhanced Swift-XRT position
  70. GRB 250520A: GOTO optical upper limit
  71. GRB 250520A: Prompt enhanced Swift-XRT position
  72. GRB 250520A: Swift detection of a burst
  73. GRB 250516B: Insight-HXMT detection
  74. EP250427a/GRB250427A: VLA Detection of Radio Counterpart
  75. GRB 250516A: COLIBRÍ optical upper limit
  76. Konus-Wind detection of GRB 250516A
  77. GRB 250516B: NuSTAR Detection of the Prompt Emission
  78. EP-WXT trigger (ID: 01709176312): a new X-ray outburst of HMXB RX J0111.2-7317
  79. GRB 250515A: Swift-XRT observations
  80. GRB 250515A:COLIBRÍ optical observations of the GOTO candidate
  81. GRB 250515A: 1.6m Mephisto optical detection
  82. GRB 250516A: AstroSat CZTI detection
  83. GRB 250516A: Swift-XRT refined Analysis
  84. GRB 250516A: Swift/UVOT Detection
  85. GRB 250515A: Swift ToO observations
  86. GRB 250516B: GECAM-B detection of a bright long burst
  87. GRB 250516A: Enhanced Swift-XRT position
  88. GRB 250516A: Swift detection of a burst
  89. GRB 250516A: Fermi GBM Final Real-time Localization
  90. GRB 250515A: Fermi GBM Final Localization
  91. GRB 250424A: COLIBRÍ detection of the associated supernova
  92. Konus-Wind detection of GRB 250512B / EP250512a
  93. GRB 250502A: TESS observations
  94. GRB 250511A: GECAM-A detection of a short burst
  95. LIGO/Virgo/KAGRA S250328ae: DECam DESGW Candidates (Final Epochs)
  96. Konus-Wind detection of GRB 250506A
  97. EP250512a/GRB 250512B: REM optical/NIR observations
  98. GRB 250507B: AstroSat CZTI detection
  99. GRB 250507B: GRBAlpha detection
  100. GRB 250506A: GRBAlpha detection

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