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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 260412A: SVOM detection of a long burst
  2. GRB 260412A: Fermi GBM Final Real-time Localization
  3. GRB 260411B: COLIBRÍ optical observations
  4. GRB 260410B: Fermi GBM Observation
  5. GRB 260411B: Ondrejov D50 optical afterglow detection
  6. GRB260411B: 3.6m DOT optical observation
  7. GRB 260411A: SVOM/GRM observation
  8. GRB 260407B: SVOM/GRM detection of a possible magnetar X-ray burst
  9. GRB 260411B: SVOM/GRM observation of a long burst
  10. GRB 260409A: Insight-HXMT/HE detection
  11. GRB 260411B: Fermi GBM Detection
  12. GRB 260411B: GOTO optical counterpart candidate
  13. EP260409a: Gemini/FLAMINGOS2 J-band counterpart
  14. GRB 260411B: BALROG localization (Fermi Trigger 797587480 / GRB 260411337)
  15. GRB 260411B: Fermi GBM Final Real-time Localization
  16. GRB 260411A: Fermi GBM Final Real-time Localization
  17. GRB 260410A: COLIBRÍ optical upper limit
  18. EP-WXT01709259790: Optical Upper limits with kinder observations
  19. GRB 260410A: Fermi GBM Observation
  20. GRB 260410B: SVOM/GRM detection of a short faint burst
  21. The EP-WXT trigger 01709259790 is likely a flaring star
  22. GRB 260410B: Fermi GBM Final Real-time Localization
  23. EP-WXT01709259790: Xinglong optical upper limit
  24. GRB 260410A: Fermi-LAT detection
  25. GRB 260410A: Fermi GBM Final Real-time Localization
  26. EP260409a: refined analysis of the EP-WXT and autonomous EP-FXT observations
  27. EP260321a: Chandra X-ray Non-detection
  28. GRB 260409A: Fermi GBM Final Real-time Localization
  29. GRB 260310A/AT2026fgk: Kilonova-Catcher SN peak identification
  30. The EP-WXT trigger 01709259773 is likely a flaring star
  31. GRB 260407A: GECAM-A detection
  32. GRB 260407A: Insight-HXMT/HE detection
  33. EP260409a: SVOM/VT optical upper limits
  34. EP260409a: COLIBRÍ optical upper limits
  35. GRB 260407A: CALET Gamma-Ray Burst Monitor detection
  36. EP260409a: Global MASTER-Net observations report
  37. EP260409a: Einstein Probe detection of an X-ray transient
  38. EP260321a: VLA radio detection
  39. GRB 260404A: Fermi GBM Final Localization
  40. GRB 260407A: Glowbug gamma-ray detection
  41. GRB 260402A: SVOM/ECLAIRs refined analysis
  42. GRB 260310A: Continued VLA Multi-frequency Radio Observations
  43. GRB 260310A / AT2026fgk: X-ray rebrightening
  44. EP260402a / GRB 260402A: Mephisto optical upper limits
  45. EP-WXT01709259586: Xinglong optical upper limit
  46. EP260403a: Mephisto optical upper limits
  47. EP260402a/GRB 260402A: Xinglong optical upper limit
  48. EP260321a: Upper limits from VLA radio observations
  49. GRID detection of GRB 260401A
  50. EP260321a: uGMRT observations
  51. GRB 260407A: Fermi GBM Final Real-time Localization
  52. EP260405a: GMOS-N optical upper limits
  53. EP260405a: SVOM/VT optical upper limits
  54. EP260405a: Global MASTER-Net observations report
  55. EP260405a: Einstein Probe detection of a fast X-ray transient
  56. The EP-WXT trigger 01709259621 is likely a flaring star
  57. EP260405.149 / EP-WXT 11900672904: COLIBRÍ optical upper limits
  58. The EP-WXT trigger 01709259615 is likely a flaring star
  59. Fermi trigger No 797039833: Global MASTER-Net observations report
  60. GRB 260403A: GECAM-B observation of a long burst
  61. EP260324A / AT 2026hir: COLIBRÍ further optical observations
  62. Fermi Gamma-ray Burst Monitor trigger 796972356/260404217 is not a GRB
  63. EP260403a: refined analysis of the EP-WXT and EP-FXT observations
  64. The EP-WXT trigger 01709259586 is likely a flaring star
  65. GRB 260330B: SVOM/VT further optical observation
  66. Fermi Gamma-ray Burst Monitor trigger 796931884/260403749 is not a GRB
  67. GRB 260330B: SVOM/ECLAIRs refined analysis
  68. EP260403a: LCO optical observations of the counterpart
  69. GRB 260310A/AT2026fgk: Kilonova-Catcher long term optical monitoring
  70. EP260403a: LCO optical counterpart detection
  71. EP260403a: COLIBRÍ optical counterpart candidate
  72. GRB 260330B: SVOM/VT optical candidate
  73. EP260403a: Einstein Probe detection of an X-ray transient
  74. GRB 260330B: EP-FXT follow-up and identification of candidate afterglow
  75. GRB 260403A: AstroSat CZTI detection
  76. EP260402a/GRB 260402A: refined analysis of the EP-WXT and EP-FXT observations
  77. GRB 260402B: GECAM-B observation
  78. EP260402a/GRB 260402A: Jinshan near-infrared upper limit
  79. GRB 260402C: NuSTAR detection of prompt emission
  80. GRB 260402C: AstroSat CZTI detection of a long burst
  81. EP260324A / AT 2026hir: COLIBRÍ optical observations
  82. GRB 260403A: Fermi GBM Final Real-time Localization
  83. EP260324A / AT 2026hir: Spectroscopic Observations with the Next Generation Palomar Spectrograph
  84. GRB 260402B: Fermi GBM Final Real-time Localization
  85. GRB 260402A: WINTER J-band upper limit
  86. GRB260402A: GROWTH-India Telescope optical upper limit
  87. GRB 260402A / EP260402a: SVOM/VT optical upper limits
  88. EP260402a/GRB 260402A: SVOM/C-GFT upper limit
  89. GRB 260401A: SVOM/GRM observation
  90. GRB 260401A: GECAM-B observation
  91. EP260402a/GRB 260402A: Einstein Probe detection of an X-ray transient
  92. GRB 260402A: Kilonova-Catcher optical upper limit
  93. GRB 260402A: MASTER optical observations
  94. GRB 260402A: SVOM/COLIBRÍ (FM-GFT) optical upper limit
  95. GRB 260402A: SVOM/MXT candidate X-ray afterglow
  96. GRB 260402A: SVOM detection of a burst
  97. Fermi GRB 260401A: Global MASTER-Net observations report
  98. GRB 260401A: Fermi GBM Observation
  99. GRB 260401A: NuSTAR detection of prompt emission
  100. GRB 260401A: CALET Gamma-Ray Burst Monitor detection

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