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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: GECAM-A detection
  2. GRB 260407A: Insight-HXMT/HE detection
  3. EP260409a: SVOM/VT optical upper limits
  4. EP260409a: COLIBRÍ optical upper limits
  5. GRB 260407A: CALET Gamma-Ray Burst Monitor detection
  6. EP260409a: Global MASTER-Net observations report
  7. EP260409a: Einstein Probe detection of an X-ray transient
  8. EP260321a: VLA radio detection
  9. GRB 260404A: Fermi GBM Final Localization
  10. GRB 260407A: Glowbug gamma-ray detection
  11. GRB 260402A: SVOM/ECLAIRs refined analysis
  12. GRB 260310A: Continued VLA Multi-frequency Radio Observations
  13. GRB 260310A / AT2026fgk: X-ray rebrightening
  14. EP260402a / GRB 260402A: Mephisto optical upper limits
  15. EP-WXT01709259586: Xinglong optical upper limit
  16. EP260403a: Mephisto optical upper limits
  17. EP260402a/GRB 260402A: Xinglong optical upper limit
  18. EP260321a: Upper limits from VLA radio observations
  19. GRID detection of GRB 260401A
  20. EP260321a: uGMRT observations
  21. GRB 260407A: Fermi GBM Final Real-time Localization
  22. EP260405a: GMOS-N optical upper limits
  23. EP260405a: SVOM/VT optical upper limits
  24. EP260405a: Global MASTER-Net observations report
  25. EP260405a: Einstein Probe detection of a fast X-ray transient
  26. The EP-WXT trigger 01709259621 is likely a flaring star
  27. EP260405a / EP-WXT 11900672904: COLIBRÍ optical upper limits
  28. The EP-WXT trigger 01709259615 is likely a flaring star
  29. Fermi trigger No 797039833: Global MASTER-Net observations report
  30. GRB 260403A: GECAM-B observation of a long burst
  31. EP260324A / AT 2026hir: COLIBRÍ further optical observations
  32. Fermi Gamma-ray Burst Monitor trigger 796972356/260404217 is not a GRB
  33. EP260403a: refined analysis of the EP-WXT and EP-FXT observations
  34. The EP-WXT trigger 01709259586 is likely a flaring star
  35. GRB 260330B: SVOM/VT further optical observation
  36. Fermi Gamma-ray Burst Monitor trigger 796931884/260403749 is not a GRB
  37. GRB 260330B: SVOM/ECLAIRs refined analysis
  38. EP260403a: LCO optical observations of the counterpart
  39. GRB 260310A/AT2026fgk: Kilonova-Catcher long term optical monitoring
  40. EP260403a: LCO optical counterpart detection
  41. EP260403a: COLIBRÍ optical counterpart candidate
  42. GRB 260330B: SVOM/VT optical candidate
  43. EP260403a: Einstein Probe detection of an X-ray transient
  44. GRB 260330B: EP-FXT follow-up and identification of candidate afterglow
  45. GRB 260403A: AstroSat CZTI detection
  46. EP260402a/GRB 260402A: refined analysis of the EP-WXT and EP-FXT observations
  47. GRB 260402B: GECAM-B observation
  48. EP260402a/GRB 260402A: Jinshan near-infrared upper limit
  49. GRB 260402C: NuSTAR detection of prompt emission
  50. GRB 260402C: AstroSat CZTI detection of a long burst
  51. EP260324A / AT 2026hir: COLIBRÍ optical observations
  52. GRB 260403A: Fermi GBM Final Real-time Localization
  53. EP260324A / AT 2026hir: Spectroscopic Observations with the Next Generation Palomar Spectrograph
  54. GRB 260402B: Fermi GBM Final Real-time Localization
  55. GRB 260402A: WINTER J-band upper limit
  56. GRB260402A: GROWTH-India Telescope optical upper limit
  57. GRB 260402A / EP260402a: SVOM/VT optical upper limits
  58. EP260402a/GRB 260402A: SVOM/C-GFT upper limit
  59. GRB 260401A: SVOM/GRM observation
  60. GRB 260401A: GECAM-B observation
  61. EP260402a/GRB 260402A: Einstein Probe detection of an X-ray transient
  62. GRB 260402A: Kilonova-Catcher optical upper limit
  63. GRB 260402A: MASTER optical observations
  64. GRB 260402A: SVOM/COLIBRÍ (FM-GFT) optical upper limit
  65. GRB 260402A: SVOM/MXT candidate X-ray afterglow
  66. GRB 260402A: SVOM detection of a burst
  67. Fermi GRB 260401A: Global MASTER-Net observations report
  68. GRB 260401A: Fermi GBM Observation
  69. GRB 260401A: NuSTAR detection of prompt emission
  70. GRB 260401A: CALET Gamma-Ray Burst Monitor detection
  71. GRB 260401A: MAXI/GSC detection
  72. GRB 260401A: BALROG localization (Fermi Trigger 796733611 / GRB 260401454)
  73. GRB 260401A: Fermi GBM Final Real-time Localization
  74. EP260329b: Mondy and Assy-Turgen optical upper limits
  75. GRB 260310A / AT2026fgk: Luminance-band optical follow-up with a 28cm telescope in Daocheng
  76. EP260321a :Xinglong optical observations
  77. EP260327a: Xinglong optical upper limit
  78. EP260329b: GOTO detection of optical counterpart
  79. GRB 260330B: SVOM/VT optical upper limits
  80. Konus-Wind detection of GRB 260320A
  81. Konus-Wind detection of GRB 260316B (duplicate submission)
  82. Konus-Wind detection of GRB 260316B
  83. GRB 260321A: SVOM/ECLAIRs refined analysis
  84. EP260329b: J-band upper limits with WINTER
  85. EP260329a: J-band upper limit with WINTER
  86. GRB 260330A: Glowbug gamma-ray detection
  87. GRB 260310A: VLA Multi-frequency Radio Observations
  88. Fermi GBM Sub-Threshold Detection of GRB 260330B
  89. GRB 260330B: LCO optical upper limits
  90. GRB 260330B: SVOM detection of a burst
  91. EP260324a / AT2026hir: g- and r-band optical follow-up with the PKU 60cm Telescope
  92. EP260329b: refined analysis of the EP-WXT and EP-FXT observations
  93. EP260329a: COLIBRÍ optical upper limit
  94. EP260329a: EP-FXT follow up observation
  95. EP260329a: NOT optical counterpart candidate
  96. GRB 260330A: Fermi GBM Final Real-time Localization
  97. EP260329b: Global MASTER-Net observations report
  98. Fermi trigger No 796485221: Global MASTER-Net observations report
  99. GRB 260327A: Insight-HXMT/HE detection
  100. EP260329b: Optical follow-up with Kinder observations

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