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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 260411B: Fermi GBM Detection
  2. GRB 260411B: GOTO optical counterpart candidate
  3. EP260409a: Gemini/FLAMINGOS2 J-band counterpart
  4. GRB 260411B: BALROG localization (Fermi Trigger 797587480 / GRB 260411337)
  5. GRB 260411B: Fermi GBM Final Real-time Localization
  6. GRB 260411A: Fermi GBM Final Real-time Localization
  7. GRB 260410A: COLIBRÍ optical upper limit
  8. EP-WXT01709259790: Optical Upper limits with kinder observations
  9. GRB 260410A: Fermi GBM Observation
  10. GRB 260410B: SVOM/GRM detection of a short faint burst
  11. The EP-WXT trigger 01709259790 is likely a flaring star
  12. GRB 260410B: Fermi GBM Final Real-time Localization
  13. EP-WXT01709259790: Xinglong optical upper limit
  14. GRB 260410A: Fermi-LAT detection
  15. GRB 260410A: Fermi GBM Final Real-time Localization
  16. EP260409a: refined analysis of the EP-WXT and autonomous EP-FXT observations
  17. EP260321a: Chandra X-ray Non-detection
  18. GRB 260409A: Fermi GBM Final Real-time Localization
  19. GRB 260310A/AT2026fgk: Kilonova-Catcher SN peak identification
  20. The EP-WXT trigger 01709259773 is likely a flaring star
  21. GRB 260407A: GECAM-A detection
  22. GRB 260407A: Insight-HXMT/HE detection
  23. EP260409a: SVOM/VT optical upper limits
  24. EP260409a: COLIBRÍ optical upper limits
  25. GRB 260407A: CALET Gamma-Ray Burst Monitor detection
  26. EP260409a: Global MASTER-Net observations report
  27. EP260409a: Einstein Probe detection of an X-ray transient
  28. EP260321a: VLA radio detection
  29. GRB 260404A: Fermi GBM Final Localization
  30. GRB 260407A: Glowbug gamma-ray detection
  31. GRB 260402A: SVOM/ECLAIRs refined analysis
  32. GRB 260310A: Continued VLA Multi-frequency Radio Observations
  33. GRB 260310A / AT2026fgk: X-ray rebrightening
  34. EP260402a / GRB 260402A: Mephisto optical upper limits
  35. EP-WXT01709259586: Xinglong optical upper limit
  36. EP260403a: Mephisto optical upper limits
  37. EP260402a/GRB 260402A: Xinglong optical upper limit
  38. EP260321a: Upper limits from VLA radio observations
  39. GRID detection of GRB 260401A
  40. EP260321a: uGMRT observations
  41. GRB 260407A: Fermi GBM Final Real-time Localization
  42. EP260405a: GMOS-N optical upper limits
  43. EP260405a: SVOM/VT optical upper limits
  44. EP260405a: Global MASTER-Net observations report
  45. EP260405a: Einstein Probe detection of a fast X-ray transient
  46. The EP-WXT trigger 01709259621 is likely a flaring star
  47. EP260405a / EP-WXT 11900672904: COLIBRÍ optical upper limits
  48. The EP-WXT trigger 01709259615 is likely a flaring star
  49. Fermi trigger No 797039833: Global MASTER-Net observations report
  50. GRB 260403A: GECAM-B observation of a long burst
  51. EP260324A / AT 2026hir: COLIBRÍ further optical observations
  52. Fermi Gamma-ray Burst Monitor trigger 796972356/260404217 is not a GRB
  53. EP260403a: refined analysis of the EP-WXT and EP-FXT observations
  54. The EP-WXT trigger 01709259586 is likely a flaring star
  55. GRB 260330B: SVOM/VT further optical observation
  56. Fermi Gamma-ray Burst Monitor trigger 796931884/260403749 is not a GRB
  57. GRB 260330B: SVOM/ECLAIRs refined analysis
  58. EP260403a: LCO optical observations of the counterpart
  59. GRB 260310A/AT2026fgk: Kilonova-Catcher long term optical monitoring
  60. EP260403a: LCO optical counterpart detection
  61. EP260403a: COLIBRÍ optical counterpart candidate
  62. GRB 260330B: SVOM/VT optical candidate
  63. EP260403a: Einstein Probe detection of an X-ray transient
  64. GRB 260330B: EP-FXT follow-up and identification of candidate afterglow
  65. GRB 260403A: AstroSat CZTI detection
  66. EP260402a/GRB 260402A: refined analysis of the EP-WXT and EP-FXT observations
  67. GRB 260402B: GECAM-B observation
  68. EP260402a/GRB 260402A: Jinshan near-infrared upper limit
  69. GRB 260402C: NuSTAR detection of prompt emission
  70. GRB 260402C: AstroSat CZTI detection of a long burst
  71. EP260324A / AT 2026hir: COLIBRÍ optical observations
  72. GRB 260403A: Fermi GBM Final Real-time Localization
  73. EP260324A / AT 2026hir: Spectroscopic Observations with the Next Generation Palomar Spectrograph
  74. GRB 260402B: Fermi GBM Final Real-time Localization
  75. GRB 260402A: WINTER J-band upper limit
  76. GRB260402A: GROWTH-India Telescope optical upper limit
  77. GRB 260402A / EP260402a: SVOM/VT optical upper limits
  78. EP260402a/GRB 260402A: SVOM/C-GFT upper limit
  79. GRB 260401A: SVOM/GRM observation
  80. GRB 260401A: GECAM-B observation
  81. EP260402a/GRB 260402A: Einstein Probe detection of an X-ray transient
  82. GRB 260402A: Kilonova-Catcher optical upper limit
  83. GRB 260402A: MASTER optical observations
  84. GRB 260402A: SVOM/COLIBRÍ (FM-GFT) optical upper limit
  85. GRB 260402A: SVOM/MXT candidate X-ray afterglow
  86. GRB 260402A: SVOM detection of a burst
  87. Fermi GRB 260401A: Global MASTER-Net observations report
  88. GRB 260401A: Fermi GBM Observation
  89. GRB 260401A: NuSTAR detection of prompt emission
  90. GRB 260401A: CALET Gamma-Ray Burst Monitor detection
  91. GRB 260401A: MAXI/GSC detection
  92. GRB 260401A: BALROG localization (Fermi Trigger 796733611 / GRB 260401454)
  93. GRB 260401A: Fermi GBM Final Real-time Localization
  94. EP260329b: Mondy and Assy-Turgen optical upper limits
  95. GRB 260310A / AT2026fgk: Luminance-band optical follow-up with a 28cm telescope in Daocheng
  96. EP260321a :Xinglong optical observations
  97. EP260327a: Xinglong optical upper limit
  98. EP260329b: GOTO detection of optical counterpart
  99. GRB 260330B: SVOM/VT optical upper limits
  100. Konus-Wind detection of GRB 260320A

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