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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"

35441 results found.

  1. GRB 250521C/AT2025mgj: NOT optical observations of the afterglow candidate
  2. GRB 250530A: EP-FXT counterpart detection
  3. GRB 250530A: SVOM/VT optical upper limit
  4. Fermi Gamma-ray Burst Monitor trigger 770296643/250530470 is not a GRB
  5. GRB 250530B: Fermi GBM Final Real-time Localization
  6. GRB 250530A: Swift-XRT counterpart detection
  7. GRB 250530A: SVOM/COLIBRÍ (FM-GFT) optical counterpart candidate retraction and detection limit
  8. GRB 250530A: SVOM/COLIBRÍ (FM-GFT) optical counterpart candidate
  9. GRB 250530A: SVOM detection of a burst
  10. GRB 250527D: CALET Gamma-Ray Burst Monitor detection
  11. GRB 250527C: Swift/UVOT Upper Limits
  12. GRB 250527D: Swift/BAT-GUANO localization skymap of a burst
  13. GRB 250529B: Fermi GBM Final Real-time Localization
  14. GRB 250527B: Swift-XRT observations
  15. EP-WXT trigger 01709177124: confirmation of a stellar flare by BOOTES-6
  16. GRB 250529A: Fermi GBM Final Real-time Localization
  17. GRB 250521C (short): Zwicky Transient Facility identification of a possible fast optical transient counterpart
  18. GRB 250520A: Swift-BAT refined analysis
  19. GRB 250527C: Swift ToO observations
  20. GRB 250527C: Swift/BAT-GUANO arcminute localization of a burst
  21. GRB 250521D: SVOM/GRM analysis suggests a possible “long” duration type I burst
  22. GRB 250527B: Tiled Swift observations
  23. GRB 250520A: Gemini-South optical afterglow detection
  24. GRB 250527B / MAXI J1450-527 : MAXI/GSC detection
  25. GRB 250527A: Fermi GBM Final Localization
  26. GRB 250314A: CIDER NB1008 upper limit
  27. EP J1350.0-8622: BOOTES-6/DPRT optical upper limit
  28. GRB 250520A: 3 GHz MeerKAT Detection
  29. GRB 250520A: 10 GHz VLA Afterglow Confirmation
  30. Fermi GRB 250523A: Global MASTER-Net observations report
  31. GRB 250521A: GRBAlpha detection
  32. GRB 250520A: GRBAlpha detection
  33. GRB 250523A: BALROG localization (Fermi Trigger 769703188 / GRB 250523602)
  34. GRB 250523A: Fermi GBM Final Real-time Localization
  35. GRB 250521B: SVOM/VT optical upper limit
  36. Fermi GRB 250522B: Global MASTER-Net observations report
  37. GRB 250521B: EP-FXT follow-up observation and afterglow candidates
  38. GRB 250522B: Fermi GBM Final Localization
  39. GRB 250521D: SVOM/VT optical observations
  40. GRB 250522A: Fermi GBM Final Real-time Localization
  41. Fermi GRB 250521D: Global MASTER-Net observations report
  42. GRB 250521D: DDOTI Optical Upper Limit
  43. GRB 250521D: GOTO detects LAST counterpart candidate prior to the GRB
  44. GRB 250521B: SVOM/COLIBRÍ (FM-GFT) optical upper limit
  45. GRB 250521D: LAST tentative optical counterpart candidate
  46. GRB 250520A: CALET Gamma-Ray Burst Monitor detection
  47. GRB 250520A: 10 GHz VLA radio source
  48. GRB 250521B: Swift ToO observations
  49. GRB 250521D: Fermi GBM Final Real-time Localization
  50. GRB 250521C: Fermi GBM Final Localization
  51. GRB 250521A: DDOTI Optical Upper Limit
  52. GRB 250521B: SVOM detection of a burst through offline search
  53. Konus-Wind detection of GRB 250520A (short/hard)
  54. GRB 250520A: VLT/FORS2 Optical Observation
  55. GRB 250502A: Tautenburg observations
  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: DDOTI Optical Upper Limit
  68. GRB 250520A: AstroSat CZTI detection of a short burst
  69. GRB 250516B: GRBAlpha detection
  70. GRB 250520A: SVOM/GRM observation
  71. GRB 250520A: Enhanced Swift-XRT position
  72. GRB 250520A: GOTO optical upper limit
  73. GRB 250520A: Prompt enhanced Swift-XRT position
  74. GRB 250520A: Swift detection of a burst
  75. Swift GRB 250520A: Global MASTER-Net observations report
  76. GRB 250516B: Insight-HXMT detection
  77. EP250427a/GRB250427A: VLA Detection of Radio Counterpart
  78. GRB 250516A: Swift-BAT refined analysis
  79. GRB 250516A: COLIBRÍ optical upper limit
  80. Konus-Wind detection of GRB 250516A
  81. GRB 250516B: NuSTAR Detection of the Prompt Emission
  82. Fermi GRB 250516A: Global MASTER-Net observations report
  83. GRB 250515A: Swift-XRT observations
  84. GRB 250515A: NOT classification of GOTO25cqo as a type-Ia SN
  85. Fermi Gamma-ray Burst Monitor trigger 769160489/250517320 is not a GRB
  86. GRB 250515A:COLIBRÍ optical observations of the GOTO candidate
  87. Swift GRB 250516A: Global MASTER-Net observations report
  88. GRB 250515A: 1.6m Mephisto optical detection
  89. GRB 250516A: AstroSat CZTI detection
  90. GRB 250515A/GOTO25cqo: SVOM/VT optical blue color
  91. GRB 250516A: Fermi GBM Observation
  92. GRB 250516A: Swift-XRT refined Analysis
  93. GRB 250516A: Swift/UVOT Detection
  94. GRB 250515A: Swift ToO observations
  95. GRB 250516B: GECAM-B detection of a bright long burst
  96. GRB 250516A: Enhanced Swift-XRT position
  97. GRB 250516A: Swift detection of a burst
  98. GRB 250516A: Fermi GBM Final Real-time Localization
  99. GRB 250512B / EP250512a: SVOM/GRM analysis
  100. GRB 250515A: GOTO candidate optical counterpart

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