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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"

32418 results found.

  1. GRB 250602A: Fermi GBM Final Real-time Localization
  2. GRB 250601A: Swift/BAT-GUANO arcminute localization of a likely short burst
  3. GRB 250601A: Swift ToO observations
  4. GRB 250530A: VLT/HAWK-I NIR counterpart fading
  5. GRB 250521C/AT2025mgj: FTW optical and NIR observations
  6. GRB 250601A: Fermi GBM Final Real-time Localization
  7. Fermi GRB 250531A: Global MASTER-Net observations report
  8. GRB 250531A: Fermi GBM Final Real-time Localization
  9. GRB 250530C: BOOTES-7 optical upper limit
  10. GRB 250521C/ZTF25aarhkyn/AT2025mgj: COLIBRÍ optical observations
  11. GRB 250530C: Swift-XRT refined Analysis
  12. GRB 250530A: TNG detection of a NIR source inside the Swift/XRT error circle
  13. Swift GRB 250530C: Global MASTER-Net observations report
  14. GRB 250530C: Enhanced Swift-XRT position
  15. GRB 250530C: Swift detection of a burst
  16. GRB 250521C/AT2025mgj: NOT optical observations of the afterglow candidate
  17. GRB 250530A: EP-FXT counterpart detection
  18. GRB 250530A: SVOM/VT optical upper limit
  19. Fermi Gamma-ray Burst Monitor trigger 770296643/250530470 is not a GRB
  20. GRB 250530B: Fermi GBM Final Real-time Localization
  21. GRB 250530A: Swift-XRT counterpart detection
  22. GRB 250530A: SVOM/COLIBRÍ (FM-GFT) optical counterpart candidate retraction and detection limit
  23. GRB 250530A: SVOM/COLIBRÍ (FM-GFT) optical counterpart candidate
  24. GRB 250530A: SVOM detection of a burst
  25. GRB 250527D: CALET Gamma-Ray Burst Monitor detection
  26. GRB 250527C: Swift/UVOT Upper Limits
  27. GRB 250527D: Swift/BAT-GUANO localization skymap of a burst
  28. GRB 250529B: Fermi GBM Final Real-time Localization
  29. GRB 250527B: Swift-XRT observations
  30. GRB 250529A: Fermi GBM Final Real-time Localization
  31. GRB 250521C (short): Zwicky Transient Facility identification of a possible fast optical transient counterpart
  32. GRB 250520A: Swift-BAT refined analysis
  33. GRB 250527C: Swift ToO observations
  34. GRB 250527C: Swift/BAT-GUANO arcminute localization of a burst
  35. GRB 250521D: SVOM/GRM analysis suggests a possible “long” duration type I burst
  36. GRB 250527B: Tiled Swift observations
  37. GRB 250520A: Gemini-South optical afterglow detection
  38. GRB 250527B / MAXI J1450-527 : MAXI/GSC detection
  39. GRB 250527A: Fermi GBM Final Localization
  40. GRB 250314A: CIDER NB1008 upper limit
  41. GRB 250520A: 3 GHz MeerKAT Detection
  42. GRB 250520A: 10 GHz VLA Afterglow Confirmation
  43. Fermi GRB 250523A: Global MASTER-Net observations report
  44. GRB 250521A: GRBAlpha detection
  45. GRB 250520A: GRBAlpha detection
  46. GRB 250523A: BALROG localization (Fermi Trigger 769703188 / GRB 250523602)
  47. GRB 250523A: Fermi GBM Final Real-time Localization
  48. GRB 250521B: SVOM/VT optical upper limit
  49. Fermi GRB 250522B: Global MASTER-Net observations report
  50. GRB 250521B: EP-FXT follow-up observation and afterglow candidates
  51. GRB 250522B: Fermi GBM Final Localization
  52. GRB 250521D: SVOM/VT optical observations
  53. GRB 250522A: Fermi GBM Final Real-time Localization
  54. Fermi GRB 250521D: Global MASTER-Net observations report
  55. GRB 250521D: DDOTI Optical Upper Limit
  56. GRB 250521D: GOTO detects LAST counterpart candidate prior to the GRB
  57. GRB 250521B: SVOM/COLIBRÍ (FM-GFT) optical upper limit
  58. GRB 250521D: LAST tentative optical counterpart candidate
  59. GRB 250520A: CALET Gamma-Ray Burst Monitor detection
  60. GRB 250520A: 10 GHz VLA radio source
  61. GRB 250521B: Swift ToO observations
  62. GRB 250521D: Fermi GBM Final Real-time Localization
  63. GRB 250521C: Fermi GBM Final Localization
  64. GRB 250521A: DDOTI Optical Upper Limit
  65. GRB 250521B: SVOM detection of a burst through offline search
  66. Konus-Wind detection of GRB 250520A (short/hard)
  67. GRB 250520A: VLT/FORS2 Optical Observation
  68. GRB 250502A: Tautenburg observations
  69. GRB 250520A: Swift/UVOT Upper Limits
  70. GRB 250521A: Fermi GBM Final Real-time Localization
  71. Konus-Wind detection of GRB 250516B
  72. IPN triangulation of GRB 250516B
  73. GRB 250520A: J-band observations with WINTER
  74. GRB 250520A: Gemini-South optical observations
  75. GRB 250520A: Swift-XRT refined Analysis
  76. GRB 250520A: REM optical/NIR early observations
  77. GRB 250520B: Fermi GBM Final Real-time Localization
  78. GRB 250520A：SVOM/VT optical candidate
  79. GRB 250520A: COLIBRÍ optical upper limit
  80. GRB 250520A: DDOTI Optical Upper Limit
  81. GRB 250520A: AstroSat CZTI detection of a short burst
  82. GRB 250516B: GRBAlpha detection
  83. GRB 250520A: SVOM/GRM observation
  84. GRB 250520A: Enhanced Swift-XRT position
  85. GRB 250520A: GOTO optical upper limit
  86. GRB 250520A: Prompt enhanced Swift-XRT position
  87. GRB 250520A: Swift detection of a burst
  88. Swift GRB 250520A: Global MASTER-Net observations report
  89. GRB 250516B: Insight-HXMT detection
  90. EP250427a/GRB250427A: VLA Detection of Radio Counterpart
  91. GRB 250516A: Swift-BAT refined analysis
  92. GRB 250516A: COLIBRÍ optical upper limit
  93. Konus-Wind detection of GRB 250516A
  94. GRB 250516B: NuSTAR Detection of the Prompt Emission
  95. Fermi GRB 250516A: Global MASTER-Net observations report
  96. GRB 250515A: Swift-XRT observations
  97. GRB 250515A: NOT classification of GOTO25cqo as a type-Ia SN
  98. Fermi Gamma-ray Burst Monitor trigger 769160489/250517320 is not a GRB
  99. GRB 250515A:COLIBRÍ optical observations of the GOTO candidate
  100. Swift GRB 250516A: Global MASTER-Net observations report

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