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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. EP260402a/GRB 260402A: Xinglong optical upper limit
  2. EP260321a: Upper limits from VLA radio observations
  3. GRID detection of GRB 260401A
  4. EP260321a: uGMRT observations
  5. GRB 260407A: Fermi GBM Final Real-time Localization
  6. EP260405a: GMOS-N optical upper limits
  7. EP260405a: SVOM/VT optical upper limits
  8. EP260405a: Global MASTER-Net observations report
  9. EP260405a: Einstein Probe detection of a fast X-ray transient
  10. The EP-WXT trigger 01709259621 is likely a flaring star
  11. EP260405a / EP-WXT 11900672904: COLIBRÍ optical upper limits
  12. The EP-WXT trigger 01709259615 is likely a flaring star
  13. Fermi trigger No 797039833: Global MASTER-Net observations report
  14. GRB 260403A: GECAM-B observation of a long burst
  15. EP260324A / AT 2026hir: COLIBRÍ further optical observations
  16. Fermi Gamma-ray Burst Monitor trigger 796972356/260404217 is not a GRB
  17. EP260403a: refined analysis of the EP-WXT and EP-FXT observations
  18. The EP-WXT trigger 01709259586 is likely a flaring star
  19. GRB 260330B: SVOM/VT further optical observation
  20. Fermi Gamma-ray Burst Monitor trigger 796931884/260403749 is not a GRB
  21. GRB 260330B: SVOM/ECLAIRs refined analysis
  22. EP260403a: LCO optical observations of the counterpart
  23. GRB 260310A/AT2026fgk: Kilonova-Catcher long term optical monitoring
  24. EP260403a: LCO optical counterpart detection
  25. EP260403a: COLIBRÍ optical counterpart candidate
  26. GRB 260330B: SVOM/VT optical candidate
  27. EP260403a: Einstein Probe detection of an X-ray transient
  28. GRB 260330B: EP-FXT follow-up and identification of candidate afterglow
  29. GRB 260403A: AstroSat CZTI detection
  30. EP260402a/GRB 260402A: refined analysis of the EP-WXT and EP-FXT observations
  31. GRB 260402B: GECAM-B observation
  32. EP260402a/GRB 260402A: Jinshan near-infrared upper limit
  33. GRB 260402C: NuSTAR detection of prompt emission
  34. GRB 260402C: AstroSat CZTI detection of a long burst
  35. EP260324A / AT 2026hir: COLIBRÍ optical observations
  36. GRB 260403A: Fermi GBM Final Real-time Localization
  37. EP260324A / AT 2026hir: Spectroscopic Observations with the Next Generation Palomar Spectrograph
  38. GRB 260402B: Fermi GBM Final Real-time Localization
  39. GRB 260402A: WINTER J-band upper limit
  40. GRB260402A: GROWTH-India Telescope optical upper limit
  41. GRB 260402A / EP260402a: SVOM/VT optical upper limits
  42. EP260402a/GRB 260402A: SVOM/C-GFT upper limit
  43. GRB 260401A: SVOM/GRM observation
  44. GRB 260401A: GECAM-B observation
  45. EP260402a/GRB 260402A: Einstein Probe detection of an X-ray transient
  46. GRB 260402A: Kilonova-Catcher optical upper limit
  47. GRB 260402A: MASTER optical observations
  48. GRB 260402A: SVOM/COLIBRÍ (FM-GFT) optical upper limit
  49. GRB 260402A: SVOM/MXT candidate X-ray afterglow
  50. GRB 260402A: SVOM detection of a burst
  51. Fermi GRB 260401A: Global MASTER-Net observations report
  52. GRB 260401A: Fermi GBM Observation
  53. GRB 260401A: NuSTAR detection of prompt emission
  54. GRB 260401A: CALET Gamma-Ray Burst Monitor detection
  55. GRB 260401A: MAXI/GSC detection
  56. GRB 260401A: BALROG localization (Fermi Trigger 796733611 / GRB 260401454)
  57. GRB 260401A: Fermi GBM Final Real-time Localization
  58. EP260329b: Mondy and Assy-Turgen optical upper limits
  59. GRB 260310A / AT2026fgk: Luminance-band optical follow-up with a 28cm telescope in Daocheng
  60. EP260321a :Xinglong optical observations
  61. EP260327a: Xinglong optical upper limit
  62. EP260329b: GOTO detection of optical counterpart
  63. GRB 260330B: SVOM/VT optical upper limits
  64. Konus-Wind detection of GRB 260320A
  65. Konus-Wind detection of GRB 260316B (duplicate submission)
  66. Konus-Wind detection of GRB 260316B
  67. GRB 260321A: SVOM/ECLAIRs refined analysis
  68. EP260329b: J-band upper limits with WINTER
  69. EP260329a: J-band upper limit with WINTER
  70. GRB 260330A: Glowbug gamma-ray detection
  71. GRB 260310A: VLA Multi-frequency Radio Observations
  72. Fermi GBM Sub-Threshold Detection of GRB 260330B
  73. GRB 260330B: LCO optical upper limits
  74. GRB 260330B: SVOM detection of a burst
  75. EP260324a / AT2026hir: g- and r-band optical follow-up with the PKU 60cm Telescope
  76. EP260329b: refined analysis of the EP-WXT and EP-FXT observations
  77. EP260329a: COLIBRÍ optical upper limit
  78. EP260329a: EP-FXT follow up observation
  79. EP260329a: NOT optical counterpart candidate
  80. GRB 260330A: Fermi GBM Final Real-time Localization
  81. EP260329b: Global MASTER-Net observations report
  82. Fermi trigger No 796485221: Global MASTER-Net observations report
  83. GRB 260327A: Insight-HXMT/HE detection
  84. EP260329b: Optical follow-up with Kinder observations
  85. EP 260329b: COLIBRÍ optical observations
  86. EP260329a: Optical upper limit with Kinder observations
  87. EP260329b: LCO optical observations of the counterpart
  88. GRB 260326A: Insight-HXMT/HE detection
  89. EP260329b: Einstein Probe detection of an X-ray transient
  90. EP260329a: Einstein Probe detection of an X-ray transient
  91. EP-WXT trigger 01709259209: TRT optical counterpart detection
  92. The EP-WXT trigger 01709259209 (EP260329b?): Las Cumbres discovery of the optical counterpart
  93. GRID detection of GRB 260326A
  94. GRB 260310A: Gemini-North Spectral Confirmation of Supernova Features
  95. EP260327a: refined analysis of the EP-WXT and autonomous EP-FXT observations
  96. EP260327a: SVOM/VT optical upper limits
  97. SMA Detection of GRB 260310A / AT 2026fgk
  98. GRB 260307B: ATCA Radio Upper Limits
  99. EP260327a: WINTER J-band upper limit
  100. EP260327a: COLIBRÍ optical upper limits

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