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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"

3394 results found.

  1. GRB 260909A: Swift-XRT observations
  2. GRB 260914A: EP-FXT follow-up observation
  3. GRB 260903A: Swift-XRT observations
  4. EP260903a: EP-FXT follow-up observation
  5. EP260901a: EP-FXT follow-up observation
  6. EP260830a: EP-FXT follow-up observation
  7. GRB 260818B: Further EP-FXT observation
  8. GRB 260807A: EP-FXT follow-up observations
  9. GRB 260822A: EP/FXT follow-up observations
  10. GRB 260818B: EP-FXT follow-up observation
  11. GRB260818A: EP-FXT follow-up observation
  12. GRB260809A/EPF_J234751.2+210212: EP-FXT follow-up observation
  13. GRB 260808B / EPF_J230056.0+082842: EP-FXT follow-up observation
  14. AT 2026wki: EP/FXT follow-up observations
  15. GRB 260802A / EP J223759.5+521421: EP-FXT follow-up observation
  16. GRB 260727A: EP-FXT further follow-up observations and candidate afterglow
  17. EP260728a: EP-FXT follow-up observation
  18. GRB 260726A: EP-FXT follow-up observations
  19. GRB 260727A: EP/FXT follow-up observations
  20. EP260723a: further EP-FXT follow-up observation
  21. EP260725a: EP-WXT detection of an X-ray transient
  22. EP260723a: EP-FXT follow-up observation
  23. GRB 260718A: EP-FXT follow-up observation
  24. GRB 260310A / AT2026fgk: Late-time Chandra Detection
  25. GRB 260618B: EP-FXT follow-up observation upper limit
  26. GRB 260708A: slowly decaying X-ray emission observed by EP/FXT
  27. EP260711a: EP-FXT follow-up observation
  28. Fermi LAT GRB 260708A: MASTER OT J150237.02-435307.7 optical counterpart detection
  29. GRB 260706A: Further EP-FXT follow-up observation
  30. GRB 260706A: EP-FXT follow-up observation
  31. GRB 260704A: EP-FXT follow-up observation
  32. EP260703a: EP-FXT follow-up observation
  33. EP260628b: EP-WXT detection of an X-ray transient and EP-FXT follow-up observation
  34. EP260628a: EP-FXT follow-up observation
  35. EP260626a: EP-FXT follow-up observation
  36. GRB 260614B: EP-FXT follow-up observation
  37. EP260618a: EP-FXT follow-up observation
  38. EP260618a: EP-WXT detection of an X-ray transient
  39. EP260616a/GRB 260616B: EP-FXT follow-up observation
  40. IceCube-260610A: EP-FXT follow-up observation
  41. EP260610a: refined analysis of the EP-WXT and follow-up EP-FXT observations
  42. EP260605a: EP-FXT follow-up observation
  43. GRB 260607B: Fermi-LAT detection
  44. EP260602d: EP-FXT follow-up observation
  45. EP260602c: EP-FXT follow-up observation
  46. EP260602a: EP-FXT follow-up observation
  47. GRB 260603A: EP-FXT follow-up observation
  48. EP260601a/GRB 260601B: EP-FXT follow-up observation
  49. EP260602b: EP-FXT follow-up observation
  50. AT2026nik: EP-FXT X-ray counterpart
  51. EP260527a/GRB 260527A: EP-FXT follow-up observation
  52. EP260526a: EP-FXT follow-up observation
  53. Fermi GRB 260516C: Global MASTER-Net observations report
  54. GRB 260515A: EP-FXT follow-up observation
  55. EP260514a: refined analysis of the EP-WXT and follow-up EP-FXT observations
  56. SVOM GRB 260515A: MASTER OT J151044.43+243321.7 optical counterpart detection
  57. EP260512a: EP-FXT follow-up observation
  58. GRB 260511B: EP-FXT follow-up observation
  59. GRB 260510B: EP-FXT follow-up observation
  60. SVOM GRB 260509A: MASTER-OAFA optical observation
  61. SVOM GRB 260504B: MASTER-OAFA optical observations
  62. EP260430a: refined analysis of the EP-WXT and follow-up EP-FXT observations
  63. GRB 260310A: Late-time Chandra X-ray Detection
  64. EP260417a/GRB 260417A: refined analysis of the EP-WXT and follow-up EP-FXT observations
  65. EP260416a: refined analysis of the EP-WXT and autonomous EP-FXT observations
  66. GOTO26djh/AT2026jpw : MASTER OT observation
  67. GRB 260310A / AT2026fgk: NuSTAR detection of the rebrightening
  68. GRB 260411B: Fermi GBM Detection
  69. EP260409a: refined analysis of the EP-WXT and autonomous EP-FXT observations
  70. EP260321a: Chandra X-ray Non-detection
  71. EP260405a: Global MASTER-Net observations report
  72. EP260403a: refined analysis of the EP-WXT and EP-FXT observations
  73. GRB 260402A: MASTER optical observations
  74. EP260327a: refined analysis of the EP-WXT and autonomous EP-FXT observations
  75. GRB 260310A/AT2026fgk: Detection of temporal steepening in Einstein Probe X-ray data
  76. GRB 260310A / AT 2026fgk: FTW optical and NIR observations show no rebrightening
  77. EP260316a: refined analysis of the EP-WXT and EP-FXT observations
  78. IceCube Alert-260315A/AT2026fpm Automatic MASTER optical blue counterpart candidate
  79. GRB 260310A / AT2026fgk : MASTER OT rebrightening during 7h observations
  80. GRB 260226A: Fermi-LAT refined analysis
  81. EP260223a: EP-FXT follow-up observation
  82. EP260214b: EP-FXT follow-up observation
  83. EP260214a: refined analysis of the EP-FXT observation
  84. EP260213a: refined analysis of the EP-FXT observation
  85. GRB 260208A: Swift UVOT detection
  86. EP260210a: refined analysis of the EP-FXT observation
  87. GRB 260208B: refined analysis of the EP-FXT observation
  88. GRB 260204A: Swift-XRT afterglow detection
  89. GRB 260208B: Swift-XRT observations
  90. GRB 260204A: Swift/UVOT Upper Limits
  91. GRB 260208A: Swift-XRT observations
  92. GRB 260208B: Fermi-LAT detection
  93. GRB 260206A: Swift-XRT observations
  94. GRB 260204A: Swift-XRT observations
  95. EP260131a: refined analysis of the EP-WXT and autonomous EP-FXT observations
  96. GRB 260127B: Swift-XRT observations
  97. GRB 260127A: Swift-XRT refined Analysis
  98. GRB 260127A: Prompt enhanced Swift-XRT position
  99. GRB 260125A: Swift-XRT observations
  100. EP260126a: EP-FXT follow-up observation

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