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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. EP260321a: VLA radio detection
  2. GRB 260404A: Fermi GBM Final Localization
  3. GRB 260407A: Glowbug gamma-ray detection
  4. GRB 260402A: SVOM/ECLAIRs refined analysis
  5. GRB 260310A: Continued VLA Multi-frequency Radio Observations
  6. GRB 260310A / AT2026fgk: X-ray rebrightening
  7. EP260402a / GRB 260402A: Mephisto optical upper limits
  8. EP-WXT01709259586: Xinglong optical upper limit
  9. EP260403a: Mephisto optical upper limits
  10. EP260402a/GRB 260402A: Xinglong optical upper limit
  11. EP260321a: Upper limits from VLA radio observations
  12. GRID detection of GRB 260401A
  13. EP260321a: uGMRT observations
  14. GRB 260407A: Fermi GBM Final Real-time Localization
  15. EP260405a: GMOS-N optical upper limits
  16. EP260405a: SVOM/VT optical upper limits
  17. EP260405a: Global MASTER-Net observations report
  18. EP260405a: Einstein Probe detection of a fast X-ray transient
  19. The EP-WXT trigger 01709259621 is likely a flaring star
  20. EP260405a / EP-WXT 11900672904: COLIBRÍ optical upper limits
  21. The EP-WXT trigger 01709259615 is likely a flaring star
  22. Fermi trigger No 797039833: Global MASTER-Net observations report
  23. GRB 260403A: GECAM-B observation of a long burst
  24. EP260324A / AT 2026hir: COLIBRÍ further optical observations
  25. Fermi Gamma-ray Burst Monitor trigger 796972356/260404217 is not a GRB
  26. EP260403a: refined analysis of the EP-WXT and EP-FXT observations
  27. The EP-WXT trigger 01709259586 is likely a flaring star
  28. GRB 260330B: SVOM/VT further optical observation
  29. Fermi Gamma-ray Burst Monitor trigger 796931884/260403749 is not a GRB
  30. GRB 260330B: SVOM/ECLAIRs refined analysis
  31. EP260403a: LCO optical observations of the counterpart
  32. GRB 260310A/AT2026fgk: Kilonova-Catcher long term optical monitoring
  33. EP260403a: LCO optical counterpart detection
  34. EP260403a: COLIBRÍ optical counterpart candidate
  35. GRB 260330B: SVOM/VT optical candidate
  36. EP260403a: Einstein Probe detection of an X-ray transient
  37. GRB 260330B: EP-FXT follow-up and identification of candidate afterglow
  38. GRB 260403A: AstroSat CZTI detection
  39. EP260402a/GRB 260402A: refined analysis of the EP-WXT and EP-FXT observations
  40. GRB 260402B: GECAM-B observation
  41. EP260402a/GRB 260402A: Jinshan near-infrared upper limit
  42. GRB 260402C: NuSTAR detection of prompt emission
  43. GRB 260402C: AstroSat CZTI detection of a long burst
  44. EP260324A / AT 2026hir: COLIBRÍ optical observations
  45. GRB 260403A: Fermi GBM Final Real-time Localization
  46. EP260324A / AT 2026hir: Spectroscopic Observations with the Next Generation Palomar Spectrograph
  47. GRB 260402B: Fermi GBM Final Real-time Localization
  48. GRB 260402A: WINTER J-band upper limit
  49. GRB260402A: GROWTH-India Telescope optical upper limit
  50. GRB 260402A / EP260402a: SVOM/VT optical upper limits
  51. EP260402a/GRB 260402A: SVOM/C-GFT upper limit
  52. GRB 260401A: SVOM/GRM observation
  53. GRB 260401A: GECAM-B observation
  54. EP260402a/GRB 260402A: Einstein Probe detection of an X-ray transient
  55. GRB 260402A: Kilonova-Catcher optical upper limit
  56. GRB 260402A: MASTER optical observations
  57. GRB 260402A: SVOM/COLIBRÍ (FM-GFT) optical upper limit
  58. GRB 260402A: SVOM/MXT candidate X-ray afterglow
  59. GRB 260402A: SVOM detection of a burst
  60. Fermi GRB 260401A: Global MASTER-Net observations report
  61. GRB 260401A: Fermi GBM Observation
  62. GRB 260401A: NuSTAR detection of prompt emission
  63. GRB 260401A: CALET Gamma-Ray Burst Monitor detection
  64. GRB 260401A: MAXI/GSC detection
  65. GRB 260401A: BALROG localization (Fermi Trigger 796733611 / GRB 260401454)
  66. GRB 260401A: Fermi GBM Final Real-time Localization
  67. EP260329b: Mondy and Assy-Turgen optical upper limits
  68. GRB 260310A / AT2026fgk: Luminance-band optical follow-up with a 28cm telescope in Daocheng
  69. EP260321a :Xinglong optical observations
  70. EP260327a: Xinglong optical upper limit
  71. EP260329b: GOTO detection of optical counterpart
  72. GRB 260330B: SVOM/VT optical upper limits
  73. Konus-Wind detection of GRB 260320A
  74. Konus-Wind detection of GRB 260316B (duplicate submission)
  75. Konus-Wind detection of GRB 260316B
  76. GRB 260321A: SVOM/ECLAIRs refined analysis
  77. EP260329b: J-band upper limits with WINTER
  78. EP260329a: J-band upper limit with WINTER
  79. GRB 260330A: Glowbug gamma-ray detection
  80. GRB 260310A: VLA Multi-frequency Radio Observations
  81. Fermi GBM Sub-Threshold Detection of GRB 260330B
  82. GRB 260330B: LCO optical upper limits
  83. GRB 260330B: SVOM detection of a burst
  84. EP260324a / AT2026hir: g- and r-band optical follow-up with the PKU 60cm Telescope
  85. EP260329b: refined analysis of the EP-WXT and EP-FXT observations
  86. EP260329a: COLIBRÍ optical upper limit
  87. EP260329a: EP-FXT follow up observation
  88. EP260329a: NOT optical counterpart candidate
  89. GRB 260330A: Fermi GBM Final Real-time Localization
  90. EP260329b: Global MASTER-Net observations report
  91. Fermi trigger No 796485221: Global MASTER-Net observations report
  92. GRB 260327A: Insight-HXMT/HE detection
  93. EP260329b: Optical follow-up with Kinder observations
  94. EP 260329b: COLIBRÍ optical observations
  95. EP260329a: Optical upper limit with Kinder observations
  96. EP260329b: LCO optical observations of the counterpart
  97. GRB 260326A: Insight-HXMT/HE detection
  98. EP260329b: Einstein Probe detection of an X-ray transient
  99. EP260329a: Einstein Probe detection of an X-ray transient
  100. EP-WXT trigger 01709259209: TRT optical counterpart detection

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