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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 250530A: SVOM/COLIBRÍ (FM-GFT) optical counterpart candidate retraction and detection limit
  2. GRB 250530A: SVOM/COLIBRÍ (FM-GFT) optical counterpart candidate
  3. GRB 250530A: SVOM detection of a burst
  4. GRB 250527D: CALET Gamma-Ray Burst Monitor detection
  5. GRB 250527C: Swift/UVOT Upper Limits
  6. GRB 250527D: Swift/BAT-GUANO localization skymap of a burst
  7. EP J1350.0-8622: EP-FXT follow-up observation
  8. GRB 250529B: Fermi GBM Final Real-time Localization
  9. GRB 250527B: Swift-XRT observations
  10. EP-WXT trigger 01709177124: confirmation of a stellar flare by BOOTES-6
  11. The EP-WXT trigger 01709177124 is likely a flaring star
  12. GRB 250529A: Fermi GBM Final Real-time Localization
  13. GRB 250521C (short): Zwicky Transient Facility identification of a possible fast optical transient counterpart
  14. GRB 250520A: Swift-BAT refined analysis
  15. GRB 250527C: Swift ToO observations
  16. GRB 250527C: Swift/BAT-GUANO arcminute localization of a burst
  17. EP250526a: SVOM/VT optical upper limit
  18. GRB 250521D: SVOM/GRM analysis suggests a possible “long” duration type I burst
  19. GRB 250527B: Tiled Swift observations
  20. GRB 250520A: Gemini-South optical afterglow detection
  21. Fermi trigger No 770058372: Global MASTER-Net observations report
  22. Fermi trigger No 770047117: Global MASTER-Net observations report
  23. GRB 250527B / MAXI J1450-527 : MAXI/GSC detection
  24. GRB 250527A: Fermi GBM Final Localization
  25. EP250526a: refined analysis of the EP-WXT and EP-FXT observations
  26. GRB 250314A: CIDER NB1008 upper limit
  27. EP250526a: COLIBRÍ optical upper limits
  28. EP250526a: Global MASTER-Net observations report
  29. EP250526a: Einstein Probe detection of a fast X-ray transient
  30. EP J1350.0-8622: BOOTES-6/DPRT optical upper limit
  31. EP J1350.0-8622: Einstein Probe detection of an X-ray transient candidate
  32. EP-WXT trigger 01709176712: SVOM/C-GFT observations of blue-to-red color variation
  33. GRB 250520A: 3 GHz MeerKAT Detection
  34. GRB 250520A: 10 GHz VLA Afterglow Confirmation
  35. Fermi GRB 250523A: Global MASTER-Net observations report
  36. Fermi trigger No 769611916: Global MASTER-Net observations report
  37. EP-WXT trigger 01709176712: GOTO observations confirm stellar counterpart variability
  38. GRB 250521A: GRBAlpha detection
  39. GRB 250520A: GRBAlpha detection
  40. GRB 250523A: BALROG localization (Fermi Trigger 769703188 / GRB 250523602)
  41. GRB 250523A: Fermi GBM Final Real-time Localization
  42. The EP-WXT trigger 01709176712 is likely a flaring star
  43. GRB 250521B: SVOM/VT optical upper limit
  44. The EP-WXT trigger 01709176612: SVOM/VT optical observations
  45. The EP-WXT trigger 01709176612: refined analysis of the EP-FXT observation
  46. Fermi GRB 250522B: Global MASTER-Net observations report
  47. GRB 250521B: EP-FXT follow-up observation and afterglow candidates
  48. GRB 250522B: Fermi GBM Final Localization
  49. GRB 250521D: SVOM/VT optical observations
  50. GRB 250522A: Fermi GBM Final Real-time Localization
  51. EP#01709176612: Swift-XRT counterpart detection of flaring star
  52. Fermi GRB 250521D: Global MASTER-Net observations report
  53. Fermi trigger No 769533898: Global MASTER-Net observations report
  54. Fermi trigger No 769499303: Global MASTER-Net observations report
  55. GRB 250521D: DDOTI Optical Upper Limit
  56. The EP-WXT trigger 01709176612 is likely a flaring star
  57. GRB 250521D: GOTO detects LAST counterpart candidate prior to the GRB
  58. GRB 250521B: SVOM/COLIBRÍ (FM-GFT) optical upper limit
  59. GRB 250521D: LAST tentative optical counterpart candidate
  60. GRB 250520A: CALET Gamma-Ray Burst Monitor detection
  61. GRB 250520A: 10 GHz VLA radio source
  62. GRB 250521B: Swift ToO observations
  63. GRB 250521D: Fermi GBM Final Real-time Localization
  64. GRB 250521C: Fermi GBM Final Localization
  65. GRB 250521A: DDOTI Optical Upper Limit
  66. GRB 250521B: SVOM detection of a burst through offline search
  67. Konus-Wind detection of GRB 250520A (short/hard)
  68. GRB 250520A: VLT/FORS2 Optical Observation
  69. GRB 250502A: Tautenburg observations
  70. GRB 250520A: Swift/UVOT Upper Limits
  71. GRB 250521A: Fermi GBM Final Real-time Localization
  72. Konus-Wind detection of GRB 250516B
  73. IPN triangulation of GRB 250516B
  74. GRB 250520A: J-band observations with WINTER
  75. GRB 250520A: Gemini-South optical observations
  76. GRB 250520A: Swift-XRT refined Analysis
  77. GRB 250520A: REM optical/NIR early observations
  78. GRB 250520B: Fermi GBM Final Real-time Localization
  79. GRB 250520A：SVOM/VT optical candidate
  80. GRB 250520A: COLIBRÍ optical upper limit
  81. GRB 250520A: DDOTI Optical Upper Limit
  82. GRB 250520A: AstroSat CZTI detection of a short burst
  83. GRB 250516B: GRBAlpha detection
  84. GRB 250520A: SVOM/GRM observation
  85. GRB 250520A: Enhanced Swift-XRT position
  86. GRB 250520A: GOTO optical upper limit
  87. GRB 250520A: Prompt enhanced Swift-XRT position
  88. GRB 250520A: Swift detection of a burst
  89. Swift GRB 250520A: Global MASTER-Net observations report
  90. GRB 250516B: Insight-HXMT detection
  91. EP250427a/GRB250427A: VLA Detection of Radio Counterpart
  92. GRB 250516A: Swift-BAT refined analysis
  93. GRB 250516A: COLIBRÍ optical upper limit
  94. Konus-Wind detection of GRB 250516A
  95. GRB 250516B: NuSTAR Detection of the Prompt Emission
  96. EP-WXT trigger (ID: 01709176312): a new X-ray outburst of HMXB RX J0111.2-7317
  97. Fermi GRB 250516A: Global MASTER-Net observations report
  98. GRB 250515A: Swift-XRT observations
  99. GRB 250515A: NOT classification of GOTO25cqo as a type-Ia SN
  100. Fermi Gamma-ray Burst Monitor trigger 769160489/250517320 is not a GRB

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