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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. EP260405a: SVOM/VT optical upper limits
  2. EP260405a: Global MASTER-Net observations report
  3. EP260405a: Einstein Probe detection of a fast X-ray transient
  4. The EP-WXT trigger 01709259621 is likely a flaring star
  5. EP260405a / EP-WXT 11900672904: COLIBRÍ optical upper limits
  6. The EP-WXT trigger 01709259615 is likely a flaring star
  7. Fermi trigger No 797039833: Global MASTER-Net observations report
  8. GRB 260403A: GECAM-B observation of a long burst
  9. EP260324A / AT 2026hir: COLIBRÍ further optical observations
  10. Fermi Gamma-ray Burst Monitor trigger 796972356/260404217 is not a GRB
  11. EP260403a: refined analysis of the EP-WXT and EP-FXT observations
  12. The EP-WXT trigger 01709259586 is likely a flaring star
  13. GRB 260330B: SVOM/VT further optical observation
  14. Fermi Gamma-ray Burst Monitor trigger 796931884/260403749 is not a GRB
  15. GRB 260330B: SVOM/ECLAIRs refined analysis
  16. EP260403a: LCO optical observations of the counterpart
  17. GRB 260310A/AT2026fgk: Kilonova-Catcher long term optical monitoring
  18. EP260403a: LCO optical counterpart detection
  19. EP260403a: COLIBRÍ optical counterpart candidate
  20. GRB 260330B: SVOM/VT optical candidate
  21. EP260403a: Einstein Probe detection of an X-ray transient
  22. GRB 260330B: EP-FXT follow-up and identification of candidate afterglow
  23. GRB 260403A: AstroSat CZTI detection
  24. EP260402a/GRB 260402A: refined analysis of the EP-WXT and EP-FXT observations
  25. GRB 260402B: GECAM-B observation
  26. EP260402a/GRB 260402A: Jinshan near-infrared upper limit
  27. GRB 260402C: NuSTAR detection of prompt emission
  28. GRB 260402C: AstroSat CZTI detection of a long burst
  29. EP260324A / AT 2026hir: COLIBRÍ optical observations
  30. GRB 260403A: Fermi GBM Final Real-time Localization
  31. EP260324A / AT 2026hir: Spectroscopic Observations with the Next Generation Palomar Spectrograph
  32. GRB 260402B: Fermi GBM Final Real-time Localization
  33. GRB 260402A: WINTER J-band upper limit
  34. GRB260402A: GROWTH-India Telescope optical upper limit
  35. GRB 260402A / EP260402a: SVOM/VT optical upper limits
  36. EP260402a/GRB 260402A: SVOM/C-GFT upper limit
  37. GRB 260401A: SVOM/GRM observation
  38. GRB 260401A: GECAM-B observation
  39. EP260402a/GRB 260402A: Einstein Probe detection of an X-ray transient
  40. GRB 260402A: Kilonova-Catcher optical upper limit
  41. GRB 260402A: MASTER optical observations
  42. GRB 260402A: SVOM/COLIBRÍ (FM-GFT) optical upper limit
  43. GRB 260402A: SVOM/MXT candidate X-ray afterglow
  44. GRB 260402A: SVOM detection of a burst
  45. Fermi GRB 260401A: Global MASTER-Net observations report
  46. GRB 260401A: Fermi GBM Observation
  47. GRB 260401A: NuSTAR detection of prompt emission
  48. GRB 260401A: CALET Gamma-Ray Burst Monitor detection
  49. GRB 260401A: MAXI/GSC detection
  50. GRB 260401A: BALROG localization (Fermi Trigger 796733611 / GRB 260401454)
  51. GRB 260401A: Fermi GBM Final Real-time Localization
  52. EP260329b: Mondy and Assy-Turgen optical upper limits
  53. GRB 260310A / AT2026fgk: Luminance-band optical follow-up with a 28cm telescope in Daocheng
  54. EP260321a :Xinglong optical observations
  55. EP260327a: Xinglong optical upper limit
  56. EP260329b: GOTO detection of optical counterpart
  57. GRB 260330B: SVOM/VT optical upper limits
  58. Konus-Wind detection of GRB 260320A
  59. Konus-Wind detection of GRB 260316B (duplicate submission)
  60. Konus-Wind detection of GRB 260316B
  61. GRB 260321A: SVOM/ECLAIRs refined analysis
  62. EP260329b: J-band upper limits with WINTER
  63. EP260329a: J-band upper limit with WINTER
  64. GRB 260330A: Glowbug gamma-ray detection
  65. GRB 260310A: VLA Multi-frequency Radio Observations
  66. Fermi GBM Sub-Threshold Detection of GRB 260330B
  67. GRB 260330B: LCO optical upper limits
  68. GRB 260330B: SVOM detection of a burst
  69. EP260324a / AT2026hir: g- and r-band optical follow-up with the PKU 60cm Telescope
  70. EP260329b: refined analysis of the EP-WXT and EP-FXT observations
  71. EP260329a: COLIBRÍ optical upper limit
  72. EP260329a: EP-FXT follow up observation
  73. EP260329a: NOT optical counterpart candidate
  74. GRB 260330A: Fermi GBM Final Real-time Localization
  75. EP260329b: Global MASTER-Net observations report
  76. Fermi trigger No 796485221: Global MASTER-Net observations report
  77. GRB 260327A: Insight-HXMT/HE detection
  78. EP260329b: Optical follow-up with Kinder observations
  79. EP 260329b: COLIBRÍ optical observations
  80. EP260329a: Optical upper limit with Kinder observations
  81. EP260329b: LCO optical observations of the counterpart
  82. GRB 260326A: Insight-HXMT/HE detection
  83. EP260329b: Einstein Probe detection of an X-ray transient
  84. EP260329a: Einstein Probe detection of an X-ray transient
  85. EP-WXT trigger 01709259209: TRT optical counterpart detection
  86. The EP-WXT trigger 01709259209 (EP260329b?): Las Cumbres discovery of the optical counterpart
  87. GRID detection of GRB 260326A
  88. GRB 260310A: Gemini-North Spectral Confirmation of Supernova Features
  89. EP260327a: refined analysis of the EP-WXT and autonomous EP-FXT observations
  90. EP260327a: SVOM/VT optical upper limits
  91. SMA Detection of GRB 260310A / AT 2026fgk
  92. GRB 260307B: ATCA Radio Upper Limits
  93. EP260327a: WINTER J-band upper limit
  94. EP260327a: COLIBRÍ optical upper limits
  95. GRB 260327A: AstroSat CZTI detection of a long burst
  96. EP260327a: Gemini-North optical upper limits
  97. EP260324a: GROWTH-India Telescope optical observation
  98. EP260327a: Global MASTER-Net observations report
  99. EP260327a: Einstein Probe detection of an X-ray transient
  100. GRB 260310A / AT 2026fgk: COLIBRÍ photometric evidence of the emerging supernova

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