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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. Fermi GRB 250531A: Global MASTER-Net observations report
  2. GRB 250531A: Fermi GBM Final Real-time Localization
  3. EP#01709177494: Swift-XRT counterpart detection of known source
  4. GRB 250530C: BOOTES-7 optical upper limit
  5. GRB 250521C/ZTF25aarhkyn/AT2025mgj: COLIBRÍ optical observations
  6. GRB 250530C: Swift-XRT refined Analysis
  7. GRB 250530A: TNG detection of a NIR source inside the Swift/XRT error circle
  8. Swift GRB 250530C: Global MASTER-Net observations report
  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. Fermi Gamma-ray Burst Monitor trigger 770296643/250530470 is not a GRB
  15. GRB 250530B: Fermi GBM Final Real-time Localization
  16. GRB 250530A: Swift-XRT counterpart detection
  17. GRB 250530A: SVOM/COLIBRÍ (FM-GFT) optical counterpart candidate retraction and detection limit
  18. GRB 250530A: SVOM/COLIBRÍ (FM-GFT) optical counterpart candidate
  19. GRB 250530A: SVOM detection of a burst
  20. GRB 250527D: CALET Gamma-Ray Burst Monitor detection
  21. GRB 250527C: Swift/UVOT Upper Limits
  22. GRB 250527D: Swift/BAT-GUANO localization skymap of a burst
  23. EP J1350.0-8622: EP-FXT follow-up observation
  24. GRB 250529B: Fermi GBM Final Real-time Localization
  25. GRB 250527B: Swift-XRT observations
  26. EP-WXT trigger 01709177124: confirmation of a stellar flare by BOOTES-6
  27. The EP-WXT trigger 01709177124 is likely a flaring star
  28. GRB 250529A: Fermi GBM Final Real-time Localization
  29. GRB 250521C (short): Zwicky Transient Facility identification of a possible fast optical transient counterpart
  30. GRB 250520A: Swift-BAT refined analysis
  31. GRB 250527C: Swift ToO observations
  32. GRB 250527C: Swift/BAT-GUANO arcminute localization of a burst
  33. EP250526a: SVOM/VT optical upper limit
  34. GRB 250521D: SVOM/GRM analysis suggests a possible “long” duration type I burst
  35. GRB 250527B: Tiled Swift observations
  36. GRB 250520A: Gemini-South optical afterglow detection
  37. Fermi trigger No 770058372: Global MASTER-Net observations report
  38. Fermi trigger No 770047117: Global MASTER-Net observations report
  39. GRB 250527B / MAXI J1450-527 : MAXI/GSC detection
  40. GRB 250527A: Fermi GBM Final Localization
  41. EP250526a: refined analysis of the EP-WXT and EP-FXT observations
  42. GRB 250314A: CIDER NB1008 upper limit
  43. EP250526a: COLIBRÍ optical upper limits
  44. EP250526a: Global MASTER-Net observations report
  45. EP250526a: Einstein Probe detection of a fast X-ray transient
  46. EP J1350.0-8622: BOOTES-6/DPRT optical upper limit
  47. EP J1350.0-8622: Einstein Probe detection of an X-ray transient candidate
  48. EP-WXT trigger 01709176712: SVOM/C-GFT observations of blue-to-red color variation
  49. GRB 250520A: 3 GHz MeerKAT Detection
  50. GRB 250520A: 10 GHz VLA Afterglow Confirmation
  51. Fermi GRB 250523A: Global MASTER-Net observations report
  52. Fermi trigger No 769611916: Global MASTER-Net observations report
  53. EP-WXT trigger 01709176712: GOTO observations confirm stellar counterpart variability
  54. GRB 250521A: GRBAlpha detection
  55. GRB 250520A: GRBAlpha detection
  56. GRB 250523A: BALROG localization (Fermi Trigger 769703188 / GRB 250523602)
  57. GRB 250523A: Fermi GBM Final Real-time Localization
  58. The EP-WXT trigger 01709176712 is likely a flaring star
  59. GRB 250521B: SVOM/VT optical upper limit
  60. The EP-WXT trigger 01709176612: SVOM/VT optical observations
  61. The EP-WXT trigger 01709176612: refined analysis of the EP-FXT observation
  62. Fermi GRB 250522B: Global MASTER-Net observations report
  63. GRB 250521B: EP-FXT follow-up observation and afterglow candidates
  64. GRB 250522B: Fermi GBM Final Localization
  65. GRB 250521D: SVOM/VT optical observations
  66. GRB 250522A: Fermi GBM Final Real-time Localization
  67. EP#01709176612: Swift-XRT counterpart detection of flaring star
  68. Fermi GRB 250521D: Global MASTER-Net observations report
  69. Fermi trigger No 769533898: Global MASTER-Net observations report
  70. Fermi trigger No 769499303: Global MASTER-Net observations report
  71. GRB 250521D: DDOTI Optical Upper Limit
  72. The EP-WXT trigger 01709176612 is likely a flaring star
  73. GRB 250521D: GOTO detects LAST counterpart candidate prior to the GRB
  74. GRB 250521B: SVOM/COLIBRÍ (FM-GFT) optical upper limit
  75. GRB 250521D: LAST tentative optical counterpart candidate
  76. GRB 250520A: CALET Gamma-Ray Burst Monitor detection
  77. GRB 250520A: 10 GHz VLA radio source
  78. GRB 250521B: Swift ToO observations
  79. GRB 250521D: Fermi GBM Final Real-time Localization
  80. GRB 250521C: Fermi GBM Final Localization
  81. GRB 250521A: DDOTI Optical Upper Limit
  82. GRB 250521B: SVOM detection of a burst through offline search
  83. Konus-Wind detection of GRB 250520A (short/hard)
  84. GRB 250520A: VLT/FORS2 Optical Observation
  85. GRB 250502A: Tautenburg observations
  86. GRB 250520A: Swift/UVOT Upper Limits
  87. GRB 250521A: Fermi GBM Final Real-time Localization
  88. Konus-Wind detection of GRB 250516B
  89. IPN triangulation of GRB 250516B
  90. GRB 250520A: J-band observations with WINTER
  91. GRB 250520A: Gemini-South optical observations
  92. GRB 250520A: Swift-XRT refined Analysis
  93. GRB 250520A: REM optical/NIR early observations
  94. GRB 250520B: Fermi GBM Final Real-time Localization
  95. GRB 250520A：SVOM/VT optical candidate
  96. GRB 250520A: COLIBRÍ optical upper limit
  97. GRB 250520A: DDOTI Optical Upper Limit
  98. GRB 250520A: AstroSat CZTI detection of a short burst
  99. GRB 250516B: GRBAlpha detection
  100. GRB 250520A: SVOM/GRM observation

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