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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 260407A: Fermi GBM Final Real-time Localization
  2. EP260405a: GMOS-N optical upper limits
  3. EP260405a: SVOM/VT optical upper limits
  4. EP260405a: Global MASTER-Net observations report
  5. EP260405a: Einstein Probe detection of a fast X-ray transient
  6. The EP-WXT trigger 01709259621 is likely a flaring star
  7. EP260405.149 / EP-WXT 11900672904: COLIBRÍ optical upper limits
  8. The EP-WXT trigger 01709259615 is likely a flaring star
  9. Fermi trigger No 797039833: Global MASTER-Net observations report
  10. GRB 260403A: GECAM-B observation of a long burst
  11. EP260324A / AT 2026hir: COLIBRÍ further optical observations
  12. Fermi Gamma-ray Burst Monitor trigger 796972356/260404217 is not a GRB
  13. EP260403a: refined analysis of the EP-WXT and EP-FXT observations
  14. The EP-WXT trigger 01709259586 is likely a flaring star
  15. GRB 260330B: SVOM/VT further optical observation
  16. Fermi Gamma-ray Burst Monitor trigger 796931884/260403749 is not a GRB
  17. GRB 260330B: SVOM/ECLAIRs refined analysis
  18. EP260403a: LCO optical observations of the counterpart
  19. GRB 260310A/AT2026fgk: Kilonova-Catcher long term optical monitoring
  20. EP260403a: LCO optical counterpart detection
  21. EP260403a: COLIBRÍ optical counterpart candidate
  22. GRB 260330B: SVOM/VT optical candidate
  23. EP260403a: Einstein Probe detection of an X-ray transient
  24. GRB 260330B: EP-FXT follow-up and identification of candidate afterglow
  25. GRB 260403A: AstroSat CZTI detection
  26. EP260402a/GRB 260402A: refined analysis of the EP-WXT and EP-FXT observations
  27. GRB 260402B: GECAM-B observation
  28. EP260402a/GRB 260402A: Jinshan near-infrared upper limit
  29. GRB 260402C: NuSTAR detection of prompt emission
  30. GRB 260402C: AstroSat CZTI detection of a long burst
  31. EP260324A / AT 2026hir: COLIBRÍ optical observations
  32. GRB 260403A: Fermi GBM Final Real-time Localization
  33. EP260324A / AT 2026hir: Spectroscopic Observations with the Next Generation Palomar Spectrograph
  34. GRB 260402B: Fermi GBM Final Real-time Localization
  35. GRB 260402A: WINTER J-band upper limit
  36. GRB260402A: GROWTH-India Telescope optical upper limit
  37. GRB 260402A / EP260402a: SVOM/VT optical upper limits
  38. EP260402a/GRB 260402A: SVOM/C-GFT upper limit
  39. GRB 260401A: SVOM/GRM observation
  40. GRB 260401A: GECAM-B observation
  41. EP260402a/GRB 260402A: Einstein Probe detection of an X-ray transient
  42. GRB 260402A: Kilonova-Catcher optical upper limit
  43. GRB 260402A: MASTER optical observations
  44. GRB 260402A: SVOM/COLIBRÍ (FM-GFT) optical upper limit
  45. GRB 260402A: SVOM/MXT candidate X-ray afterglow
  46. GRB 260402A: SVOM detection of a burst
  47. Fermi GRB 260401A: Global MASTER-Net observations report
  48. GRB 260401A: Fermi GBM Observation
  49. GRB 260401A: NuSTAR detection of prompt emission
  50. GRB 260401A: CALET Gamma-Ray Burst Monitor detection
  51. GRB 260401A: MAXI/GSC detection
  52. GRB 260401A: BALROG localization (Fermi Trigger 796733611 / GRB 260401454)
  53. GRB 260401A: Fermi GBM Final Real-time Localization
  54. EP260329b: Mondy and Assy-Turgen optical upper limits
  55. GRB 260310A / AT2026fgk: Luminance-band optical follow-up with a 28cm telescope in Daocheng
  56. EP260321a :Xinglong optical observations
  57. EP260327a: Xinglong optical upper limit
  58. EP260329b: GOTO detection of optical counterpart
  59. GRB 260330B: SVOM/VT optical upper limits
  60. Konus-Wind detection of GRB 260320A
  61. Konus-Wind detection of GRB 260316B (duplicate submission)
  62. Konus-Wind detection of GRB 260316B
  63. GRB 260321A: SVOM/ECLAIRs refined analysis
  64. EP260329b: J-band upper limits with WINTER
  65. EP260329a: J-band upper limit with WINTER
  66. GRB 260330A: Glowbug gamma-ray detection
  67. GRB 260310A: VLA Multi-frequency Radio Observations
  68. Fermi GBM Sub-Threshold Detection of GRB 260330B
  69. GRB 260330B: LCO optical upper limits
  70. GRB 260330B: SVOM detection of a burst
  71. EP260324a / AT2026hir: g- and r-band optical follow-up with the PKU 60cm Telescope
  72. EP260329b: refined analysis of the EP-WXT and EP-FXT observations
  73. EP260329a: COLIBRÍ optical upper limit
  74. EP260329a: EP-FXT follow up observation
  75. EP260329a: NOT optical counterpart candidate
  76. GRB 260330A: Fermi GBM Final Real-time Localization
  77. EP260329b: Global MASTER-Net observations report
  78. Fermi trigger No 796485221: Global MASTER-Net observations report
  79. GRB 260327A: Insight-HXMT/HE detection
  80. EP260329b: Optical follow-up with Kinder observations
  81. EP 260329b: COLIBRÍ optical observations
  82. EP260329a: Optical upper limit with Kinder observations
  83. EP260329b: LCO optical observations of the counterpart
  84. GRB 260326A: Insight-HXMT/HE detection
  85. EP260329b: Einstein Probe detection of an X-ray transient
  86. EP260329a: Einstein Probe detection of an X-ray transient
  87. EP-WXT trigger 01709259209: TRT optical counterpart detection
  88. The EP-WXT trigger 01709259209 (EP260329b?): Las Cumbres discovery of the optical counterpart
  89. GRID detection of GRB 260326A
  90. GRB 260310A: Gemini-North Spectral Confirmation of Supernova Features
  91. EP260327a: refined analysis of the EP-WXT and autonomous EP-FXT observations
  92. EP260327a: SVOM/VT optical upper limits
  93. SMA Detection of GRB 260310A / AT 2026fgk
  94. GRB 260307B: ATCA Radio Upper Limits
  95. EP260327a: WINTER J-band upper limit
  96. EP260327a: COLIBRÍ optical upper limits
  97. GRB 260327A: AstroSat CZTI detection of a long burst
  98. EP260327a: Gemini-North optical upper limits
  99. EP260324a: GROWTH-India Telescope optical observation
  100. EP260327a: Global MASTER-Net observations report

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