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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 260310A / AT2026fgk: X-ray rebrightening
  2. EP260402a / GRB 260402A: Mephisto optical upper limits
  3. EP-WXT01709259586: Xinglong optical upper limit
  4. EP260403a: Mephisto optical upper limits
  5. EP260402a/GRB 260402A: Xinglong optical upper limit
  6. EP260321a: Upper limits from VLA radio observations
  7. GRID detection of GRB 260401A
  8. EP260321a: uGMRT observations
  9. GRB 260407A: Fermi GBM Final Real-time Localization
  10. EP260405a: GMOS-N optical upper limits
  11. EP260405a: SVOM/VT optical upper limits
  12. EP260405a: Global MASTER-Net observations report
  13. EP260405a: Einstein Probe detection of a fast X-ray transient
  14. The EP-WXT trigger 01709259621 is likely a flaring star
  15. EP260405.149 / EP-WXT 11900672904: COLIBRÍ optical upper limits
  16. The EP-WXT trigger 01709259615 is likely a flaring star
  17. Fermi trigger No 797039833: Global MASTER-Net observations report
  18. GRB 260403A: GECAM-B observation of a long burst
  19. EP260324A / AT 2026hir: COLIBRÍ further optical observations
  20. Fermi Gamma-ray Burst Monitor trigger 796972356/260404217 is not a GRB
  21. EP260403a: refined analysis of the EP-WXT and EP-FXT observations
  22. The EP-WXT trigger 01709259586 is likely a flaring star
  23. GRB 260330B: SVOM/VT further optical observation
  24. Fermi Gamma-ray Burst Monitor trigger 796931884/260403749 is not a GRB
  25. GRB 260330B: SVOM/ECLAIRs refined analysis
  26. EP260403a: LCO optical observations of the counterpart
  27. GRB 260310A/AT2026fgk: Kilonova-Catcher long term optical monitoring
  28. EP260403a: LCO optical counterpart detection
  29. EP260403a: COLIBRÍ optical counterpart candidate
  30. GRB 260330B: SVOM/VT optical candidate
  31. EP260403a: Einstein Probe detection of an X-ray transient
  32. GRB 260330B: EP-FXT follow-up and identification of candidate afterglow
  33. GRB 260403A: AstroSat CZTI detection
  34. EP260402a/GRB 260402A: refined analysis of the EP-WXT and EP-FXT observations
  35. GRB 260402B: GECAM-B observation
  36. EP260402a/GRB 260402A: Jinshan near-infrared upper limit
  37. GRB 260402C: NuSTAR detection of prompt emission
  38. GRB 260402C: AstroSat CZTI detection of a long burst
  39. EP260324A / AT 2026hir: COLIBRÍ optical observations
  40. GRB 260403A: Fermi GBM Final Real-time Localization
  41. EP260324A / AT 2026hir: Spectroscopic Observations with the Next Generation Palomar Spectrograph
  42. GRB 260402B: Fermi GBM Final Real-time Localization
  43. GRB 260402A: WINTER J-band upper limit
  44. GRB260402A: GROWTH-India Telescope optical upper limit
  45. GRB 260402A / EP260402a: SVOM/VT optical upper limits
  46. EP260402a/GRB 260402A: SVOM/C-GFT upper limit
  47. GRB 260401A: SVOM/GRM observation
  48. GRB 260401A: GECAM-B observation
  49. EP260402a/GRB 260402A: Einstein Probe detection of an X-ray transient
  50. GRB 260402A: Kilonova-Catcher optical upper limit
  51. GRB 260402A: MASTER optical observations
  52. GRB 260402A: SVOM/COLIBRÍ (FM-GFT) optical upper limit
  53. GRB 260402A: SVOM/MXT candidate X-ray afterglow
  54. GRB 260402A: SVOM detection of a burst
  55. Fermi GRB 260401A: Global MASTER-Net observations report
  56. GRB 260401A: Fermi GBM Observation
  57. GRB 260401A: NuSTAR detection of prompt emission
  58. GRB 260401A: CALET Gamma-Ray Burst Monitor detection
  59. GRB 260401A: MAXI/GSC detection
  60. GRB 260401A: BALROG localization (Fermi Trigger 796733611 / GRB 260401454)
  61. GRB 260401A: Fermi GBM Final Real-time Localization
  62. EP260329b: Mondy and Assy-Turgen optical upper limits
  63. GRB 260310A / AT2026fgk: Luminance-band optical follow-up with a 28cm telescope in Daocheng
  64. EP260321a :Xinglong optical observations
  65. EP260327a: Xinglong optical upper limit
  66. EP260329b: GOTO detection of optical counterpart
  67. GRB 260330B: SVOM/VT optical upper limits
  68. Konus-Wind detection of GRB 260320A
  69. Konus-Wind detection of GRB 260316B (duplicate submission)
  70. Konus-Wind detection of GRB 260316B
  71. GRB 260321A: SVOM/ECLAIRs refined analysis
  72. EP260329b: J-band upper limits with WINTER
  73. EP260329a: J-band upper limit with WINTER
  74. GRB 260330A: Glowbug gamma-ray detection
  75. GRB 260310A: VLA Multi-frequency Radio Observations
  76. Fermi GBM Sub-Threshold Detection of GRB 260330B
  77. GRB 260330B: LCO optical upper limits
  78. GRB 260330B: SVOM detection of a burst
  79. EP260324a / AT2026hir: g- and r-band optical follow-up with the PKU 60cm Telescope
  80. EP260329b: refined analysis of the EP-WXT and EP-FXT observations
  81. EP260329a: COLIBRÍ optical upper limit
  82. EP260329a: EP-FXT follow up observation
  83. EP260329a: NOT optical counterpart candidate
  84. GRB 260330A: Fermi GBM Final Real-time Localization
  85. EP260329b: Global MASTER-Net observations report
  86. Fermi trigger No 796485221: Global MASTER-Net observations report
  87. GRB 260327A: Insight-HXMT/HE detection
  88. EP260329b: Optical follow-up with Kinder observations
  89. EP 260329b: COLIBRÍ optical observations
  90. EP260329a: Optical upper limit with Kinder observations
  91. EP260329b: LCO optical observations of the counterpart
  92. GRB 260326A: Insight-HXMT/HE detection
  93. EP260329b: Einstein Probe detection of an X-ray transient
  94. EP260329a: Einstein Probe detection of an X-ray transient
  95. EP-WXT trigger 01709259209: TRT optical counterpart detection
  96. The EP-WXT trigger 01709259209 (EP260329b?): Las Cumbres discovery of the optical counterpart
  97. GRID detection of GRB 260326A
  98. GRB 260310A: Gemini-North Spectral Confirmation of Supernova Features
  99. EP260327a: refined analysis of the EP-WXT and autonomous EP-FXT observations
  100. EP260327a: SVOM/VT optical upper limits

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