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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: GMOS-N optical upper limits
  2. EP260405a: SVOM/VT optical upper limits
  3. EP260405a: Global MASTER-Net observations report
  4. EP260405a: Einstein Probe detection of a fast X-ray transient
  5. The EP-WXT trigger 01709259621 is likely a flaring star
  6. EP260405.149 / EP-WXT 11900672904: COLIBRÍ optical upper limits
  7. The EP-WXT trigger 01709259615 is likely a flaring star
  8. Fermi trigger No 797039833: Global MASTER-Net observations report
  9. GRB 260403A: GECAM-B observation of a long burst
  10. EP260324A / AT 2026hir: COLIBRÍ further optical observations
  11. Fermi Gamma-ray Burst Monitor trigger 796972356/260404217 is not a GRB
  12. EP260403a: refined analysis of the EP-WXT and EP-FXT observations
  13. The EP-WXT trigger 01709259586 is likely a flaring star
  14. GRB 260330B: SVOM/VT further optical observation
  15. Fermi Gamma-ray Burst Monitor trigger 796931884/260403749 is not a GRB
  16. GRB 260330B: SVOM/ECLAIRs refined analysis
  17. EP260403a: LCO optical observations of the counterpart
  18. GRB 260310A/AT2026fgk: Kilonova-Catcher long term optical monitoring
  19. EP260403a: LCO optical counterpart detection
  20. EP260403a: COLIBRÍ optical counterpart candidate
  21. GRB 260330B: SVOM/VT optical candidate
  22. EP260403a: Einstein Probe detection of an X-ray transient
  23. GRB 260330B: EP-FXT follow-up and identification of candidate afterglow
  24. GRB 260403A: AstroSat CZTI detection
  25. EP260402a/GRB 260402A: refined analysis of the EP-WXT and EP-FXT observations
  26. GRB 260402B: GECAM-B observation
  27. EP260402a/GRB 260402A: Jinshan near-infrared upper limit
  28. GRB 260402C: NuSTAR detection of prompt emission
  29. GRB 260402C: AstroSat CZTI detection of a long burst
  30. EP260324A / AT 2026hir: COLIBRÍ optical observations
  31. GRB 260403A: Fermi GBM Final Real-time Localization
  32. EP260324A / AT 2026hir: Spectroscopic Observations with the Next Generation Palomar Spectrograph
  33. GRB 260402B: Fermi GBM Final Real-time Localization
  34. GRB 260402A: WINTER J-band upper limit
  35. GRB260402A: GROWTH-India Telescope optical upper limit
  36. GRB 260402A / EP260402a: SVOM/VT optical upper limits
  37. EP260402a/GRB 260402A: SVOM/C-GFT upper limit
  38. GRB 260401A: SVOM/GRM observation
  39. GRB 260401A: GECAM-B observation
  40. EP260402a/GRB 260402A: Einstein Probe detection of an X-ray transient
  41. GRB 260402A: Kilonova-Catcher optical upper limit
  42. GRB 260402A: MASTER optical observations
  43. GRB 260402A: SVOM/COLIBRÍ (FM-GFT) optical upper limit
  44. GRB 260402A: SVOM/MXT candidate X-ray afterglow
  45. GRB 260402A: SVOM detection of a burst
  46. Fermi GRB 260401A: Global MASTER-Net observations report
  47. GRB 260401A: Fermi GBM Observation
  48. GRB 260401A: NuSTAR detection of prompt emission
  49. GRB 260401A: CALET Gamma-Ray Burst Monitor detection
  50. GRB 260401A: MAXI/GSC detection
  51. GRB 260401A: BALROG localization (Fermi Trigger 796733611 / GRB 260401454)
  52. GRB 260401A: Fermi GBM Final Real-time Localization
  53. EP260329b: Mondy and Assy-Turgen optical upper limits
  54. GRB 260310A / AT2026fgk: Luminance-band optical follow-up with a 28cm telescope in Daocheng
  55. EP260321a :Xinglong optical observations
  56. EP260327a: Xinglong optical upper limit
  57. EP260329b: GOTO detection of optical counterpart
  58. GRB 260330B: SVOM/VT optical upper limits
  59. Konus-Wind detection of GRB 260320A
  60. Konus-Wind detection of GRB 260316B (duplicate submission)
  61. Konus-Wind detection of GRB 260316B
  62. GRB 260321A: SVOM/ECLAIRs refined analysis
  63. EP260329b: J-band upper limits with WINTER
  64. EP260329a: J-band upper limit with WINTER
  65. GRB 260330A: Glowbug gamma-ray detection
  66. GRB 260310A: VLA Multi-frequency Radio Observations
  67. Fermi GBM Sub-Threshold Detection of GRB 260330B
  68. GRB 260330B: LCO optical upper limits
  69. GRB 260330B: SVOM detection of a burst
  70. EP260324a / AT2026hir: g- and r-band optical follow-up with the PKU 60cm Telescope
  71. EP260329b: refined analysis of the EP-WXT and EP-FXT observations
  72. EP260329a: COLIBRÍ optical upper limit
  73. EP260329a: EP-FXT follow up observation
  74. EP260329a: NOT optical counterpart candidate
  75. GRB 260330A: Fermi GBM Final Real-time Localization
  76. EP260329b: Global MASTER-Net observations report
  77. Fermi trigger No 796485221: Global MASTER-Net observations report
  78. GRB 260327A: Insight-HXMT/HE detection
  79. EP260329b: Optical follow-up with Kinder observations
  80. EP 260329b: COLIBRÍ optical observations
  81. EP260329a: Optical upper limit with Kinder observations
  82. EP260329b: LCO optical observations of the counterpart
  83. GRB 260326A: Insight-HXMT/HE detection
  84. EP260329b: Einstein Probe detection of an X-ray transient
  85. EP260329a: Einstein Probe detection of an X-ray transient
  86. EP-WXT trigger 01709259209: TRT optical counterpart detection
  87. The EP-WXT trigger 01709259209 (EP260329b?): Las Cumbres discovery of the optical counterpart
  88. GRID detection of GRB 260326A
  89. GRB 260310A: Gemini-North Spectral Confirmation of Supernova Features
  90. EP260327a: refined analysis of the EP-WXT and autonomous EP-FXT observations
  91. EP260327a: SVOM/VT optical upper limits
  92. SMA Detection of GRB 260310A / AT 2026fgk
  93. GRB 260307B: ATCA Radio Upper Limits
  94. EP260327a: WINTER J-band upper limit
  95. EP260327a: COLIBRÍ optical upper limits
  96. GRB 260327A: AstroSat CZTI detection of a long burst
  97. EP260327a: Gemini-North optical upper limits
  98. EP260324a: GROWTH-India Telescope optical observation
  99. EP260327a: Global MASTER-Net observations report
  100. EP260327a: Einstein Probe detection of an X-ray transient

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