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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. GRB 250530C: Enhanced Swift-XRT position
  2. GRB 250530C: Swift detection of a burst
  3. GRB 250521C/AT2025mgj: NOT optical observations of the afterglow candidate
  4. GRB 250530A: EP-FXT counterpart detection
  5. GRB 250530A: SVOM/VT optical upper limit
  6. Fermi Gamma-ray Burst Monitor trigger 770296643/250530470 is not a GRB
  7. GRB 250530B: Fermi GBM Final Real-time Localization
  8. GRB 250530A: Swift-XRT counterpart detection
  9. GRB 250530A: SVOM/COLIBRÍ (FM-GFT) optical counterpart candidate retraction and detection limit
  10. GRB 250530A: SVOM/COLIBRÍ (FM-GFT) optical counterpart candidate
  11. GRB 250530A: SVOM detection of a burst
  12. GRB 250527D: CALET Gamma-Ray Burst Monitor detection
  13. GRB 250527C: Swift/UVOT Upper Limits
  14. GRB 250527D: Swift/BAT-GUANO localization skymap of a burst
  15. EP J1350.0-8622: EP-FXT follow-up observation
  16. GRB 250529B: Fermi GBM Final Real-time Localization
  17. GRB 250527B: Swift-XRT observations
  18. EP-WXT trigger 01709177124: confirmation of a stellar flare by BOOTES-6
  19. The EP-WXT trigger 01709177124 is likely a flaring star
  20. GRB 250529A: Fermi GBM Final Real-time Localization
  21. GRB 250521C (short): Zwicky Transient Facility identification of a possible fast optical transient counterpart
  22. GRB 250520A: Swift-BAT refined analysis
  23. GRB 250527C: Swift ToO observations
  24. GRB 250527C: Swift/BAT-GUANO arcminute localization of a burst
  25. EP250526a: SVOM/VT optical upper limit
  26. GRB 250521D: SVOM/GRM analysis suggests a possible “long” duration type I burst
  27. GRB 250527B: Tiled Swift observations
  28. GRB 250520A: Gemini-South optical afterglow detection
  29. Fermi trigger No 770058372: Global MASTER-Net observations report
  30. Fermi trigger No 770047117: Global MASTER-Net observations report
  31. GRB 250527B / MAXI J1450-527 : MAXI/GSC detection
  32. GRB 250527A: Fermi GBM Final Localization
  33. EP250526a: refined analysis of the EP-WXT and EP-FXT observations
  34. GRB 250314A: CIDER NB1008 upper limit
  35. EP250526a: COLIBRÍ optical upper limits
  36. EP250526a: Global MASTER-Net observations report
  37. EP250526a: Einstein Probe detection of a fast X-ray transient
  38. EP J1350.0-8622: BOOTES-6/DPRT optical upper limit
  39. EP J1350.0-8622: Einstein Probe detection of an X-ray transient candidate
  40. EP-WXT trigger 01709176712: SVOM/C-GFT observations of blue-to-red color variation
  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. Fermi trigger No 769611916: Global MASTER-Net observations report
  45. EP-WXT trigger 01709176712: GOTO observations confirm stellar counterpart variability
  46. GRB 250521A: GRBAlpha detection
  47. GRB 250520A: GRBAlpha detection
  48. GRB 250523A: BALROG localization (Fermi Trigger 769703188 / GRB 250523602)
  49. GRB 250523A: Fermi GBM Final Real-time Localization
  50. The EP-WXT trigger 01709176712 is likely a flaring star
  51. GRB 250521B: SVOM/VT optical upper limit
  52. The EP-WXT trigger 01709176612: SVOM/VT optical observations
  53. The EP-WXT trigger 01709176612: refined analysis of the EP-FXT observation
  54. Fermi GRB 250522B: Global MASTER-Net observations report
  55. GRB 250521B: EP-FXT follow-up observation and afterglow candidates
  56. GRB 250522B: Fermi GBM Final Localization
  57. GRB 250521D: SVOM/VT optical observations
  58. GRB 250522A: Fermi GBM Final Real-time Localization
  59. EP#01709176612: Swift-XRT counterpart detection of flaring star
  60. Fermi GRB 250521D: Global MASTER-Net observations report
  61. Fermi trigger No 769533898: Global MASTER-Net observations report
  62. Fermi trigger No 769499303: Global MASTER-Net observations report
  63. GRB 250521D: DDOTI Optical Upper Limit
  64. The EP-WXT trigger 01709176612 is likely a flaring star
  65. GRB 250521D: GOTO detects LAST counterpart candidate prior to the GRB
  66. GRB 250521B: SVOM/COLIBRÍ (FM-GFT) optical upper limit
  67. GRB 250521D: LAST tentative optical counterpart candidate
  68. GRB 250520A: CALET Gamma-Ray Burst Monitor detection
  69. GRB 250520A: 10 GHz VLA radio source
  70. GRB 250521B: Swift ToO observations
  71. GRB 250521D: Fermi GBM Final Real-time Localization
  72. GRB 250521C: Fermi GBM Final Localization
  73. GRB 250521A: DDOTI Optical Upper Limit
  74. GRB 250521B: SVOM detection of a burst through offline search
  75. Konus-Wind detection of GRB 250520A (short/hard)
  76. GRB 250520A: VLT/FORS2 Optical Observation
  77. GRB 250502A: Tautenburg observations
  78. GRB 250520A: Swift/UVOT Upper Limits
  79. GRB 250521A: Fermi GBM Final Real-time Localization
  80. Konus-Wind detection of GRB 250516B
  81. IPN triangulation of GRB 250516B
  82. GRB 250520A: J-band observations with WINTER
  83. GRB 250520A: Gemini-South optical observations
  84. GRB 250520A: Swift-XRT refined Analysis
  85. GRB 250520A: REM optical/NIR early observations
  86. GRB 250520B: Fermi GBM Final Real-time Localization
  87. GRB 250520A：SVOM/VT optical candidate
  88. GRB 250520A: COLIBRÍ optical upper limit
  89. GRB 250520A: DDOTI Optical Upper Limit
  90. GRB 250520A: AstroSat CZTI detection of a short burst
  91. GRB 250516B: GRBAlpha detection
  92. GRB 250520A: SVOM/GRM observation
  93. GRB 250520A: Enhanced Swift-XRT position
  94. GRB 250520A: GOTO optical upper limit
  95. GRB 250520A: Prompt enhanced Swift-XRT position
  96. GRB 250520A: Swift detection of a burst
  97. Swift GRB 250520A: Global MASTER-Net observations report
  98. GRB 250516B: Insight-HXMT detection
  99. EP250427a/GRB250427A: VLA Detection of Radio Counterpart
  100. GRB 250516A: Swift-BAT refined analysis

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