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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 260410A: Glowbug gamma-ray detection of a short burst
  2. GRB 260413A: Fermi GBM Final Real-time Localization
  3. GRB 260410B: Insight-HXMT/HE detection
  4. GRB 260410A: Insight-HXMT/HE detection
  5. Konus-Wind detection of GRB 260410A (short/hard)
  6. GRB 260411B: GECAM-B observation of a long burst
  7. EP260321a: SVOM/VT optical observations and color changes around peak
  8. GRB 260410A: CALET Gamma-Ray Burst Monitor detection
  9. The EP-WXT trigger 01709260010 is likely a flaring star
  10. GRB 260412A: GECAM-B observation of a long burst
  11. Fermi GRB 260412A: Global MASTER-Net observations report
  12. GRB 260412A: Fermi GBM Observation
  13. GRB 260310A / AT2026fgk: NuSTAR detection of the rebrightening
  14. GRB 260411B: Fermi-LAT detection
  15. GRB 260412A: SVOM detection of a long burst
  16. GRB 260412A: Fermi GBM Final Real-time Localization
  17. GRB 260411B: COLIBRÍ optical observations
  18. GRB 260410B: Fermi GBM Observation
  19. GRB 260411B: Ondrejov D50 optical afterglow detection
  20. GRB260411B: 3.6m DOT optical observation
  21. GRB 260411A: SVOM/GRM observation
  22. GRB 260407B: SVOM/GRM detection of a possible magnetar X-ray burst
  23. GRB 260411B: SVOM/GRM observation of a long burst
  24. GRB 260409A: Insight-HXMT/HE detection
  25. GRB 260411B: Fermi GBM Detection
  26. GRB 260411B: GOTO optical counterpart candidate
  27. EP260409a: Gemini/FLAMINGOS2 J-band counterpart
  28. GRB 260411B: BALROG localization (Fermi Trigger 797587480 / GRB 260411337)
  29. GRB 260411B: Fermi GBM Final Real-time Localization
  30. GRB 260411A: Fermi GBM Final Real-time Localization
  31. GRB 260410A: COLIBRÍ optical upper limit
  32. EP-WXT01709259790: Optical Upper limits with kinder observations
  33. GRB 260410A: Fermi GBM Observation
  34. GRB 260410B: SVOM/GRM detection of a short faint burst
  35. The EP-WXT trigger 01709259790 is likely a flaring star
  36. GRB 260410B: Fermi GBM Final Real-time Localization
  37. EP-WXT01709259790: Xinglong optical upper limit
  38. GRB 260410A: Fermi-LAT detection
  39. GRB 260410A: Fermi GBM Final Real-time Localization
  40. EP260409a: refined analysis of the EP-WXT and autonomous EP-FXT observations
  41. EP260321a: Chandra X-ray Non-detection
  42. GRB 260409A: Fermi GBM Final Real-time Localization
  43. GRB 260310A/AT2026fgk: Kilonova-Catcher SN peak identification
  44. The EP-WXT trigger 01709259773 is likely a flaring star
  45. GRB 260407A: GECAM-A detection
  46. GRB 260407A: Insight-HXMT/HE detection
  47. EP260409a: SVOM/VT optical upper limits
  48. EP260409a: COLIBRÍ optical upper limits
  49. GRB 260407A: CALET Gamma-Ray Burst Monitor detection
  50. EP260409a: Global MASTER-Net observations report
  51. EP260409a: Einstein Probe detection of an X-ray transient
  52. EP260321a: VLA radio detection
  53. GRB 260404A: Fermi GBM Final Localization
  54. GRB 260407A: Glowbug gamma-ray detection
  55. GRB 260402A: SVOM/ECLAIRs refined analysis
  56. GRB 260310A: Continued VLA Multi-frequency Radio Observations
  57. GRB 260310A / AT2026fgk: X-ray rebrightening
  58. EP260402a / GRB 260402A: Mephisto optical upper limits
  59. EP-WXT01709259586: Xinglong optical upper limit
  60. EP260403a: Mephisto optical upper limits
  61. EP260402a/GRB 260402A: Xinglong optical upper limit
  62. EP260321a: Upper limits from VLA radio observations
  63. GRID detection of GRB 260401A
  64. EP260321a: uGMRT observations
  65. GRB 260407A: Fermi GBM Final Real-time Localization
  66. EP260405a: GMOS-N optical upper limits
  67. EP260405a: SVOM/VT optical upper limits
  68. EP260405a: Global MASTER-Net observations report
  69. EP260405a: Einstein Probe detection of a fast X-ray transient
  70. The EP-WXT trigger 01709259621 is likely a flaring star
  71. EP260405a / EP-WXT 11900672904: COLIBRÍ optical upper limits
  72. The EP-WXT trigger 01709259615 is likely a flaring star
  73. Fermi trigger No 797039833: Global MASTER-Net observations report
  74. GRB 260403A: GECAM-B observation of a long burst
  75. EP260324A / AT 2026hir: COLIBRÍ further optical observations
  76. Fermi Gamma-ray Burst Monitor trigger 796972356/260404217 is not a GRB
  77. EP260403a: refined analysis of the EP-WXT and EP-FXT observations
  78. The EP-WXT trigger 01709259586 is likely a flaring star
  79. GRB 260330B: SVOM/VT further optical observation
  80. Fermi Gamma-ray Burst Monitor trigger 796931884/260403749 is not a GRB
  81. GRB 260330B: SVOM/ECLAIRs refined analysis
  82. EP260403a: LCO optical observations of the counterpart
  83. GRB 260310A/AT2026fgk: Kilonova-Catcher long term optical monitoring
  84. EP260403a: LCO optical counterpart detection
  85. EP260403a: COLIBRÍ optical counterpart candidate
  86. GRB 260330B: SVOM/VT optical candidate
  87. EP260403a: Einstein Probe detection of an X-ray transient
  88. GRB 260330B: EP-FXT follow-up and identification of candidate afterglow
  89. GRB 260403A: AstroSat CZTI detection
  90. EP260402a/GRB 260402A: refined analysis of the EP-WXT and EP-FXT observations
  91. GRB 260402B: GECAM-B observation
  92. EP260402a/GRB 260402A: Jinshan near-infrared upper limit
  93. GRB 260402C: NuSTAR detection of prompt emission
  94. GRB 260402C: AstroSat CZTI detection of a long burst
  95. EP260324A / AT 2026hir: COLIBRÍ optical observations
  96. GRB 260403A: Fermi GBM Final Real-time Localization
  97. EP260324A / AT 2026hir: Spectroscopic Observations with the Next Generation Palomar Spectrograph
  98. GRB 260402B: Fermi GBM Final Real-time Localization
  99. GRB 260402A: WINTER J-band upper limit
  100. GRB260402A: GROWTH-India Telescope optical upper limit

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