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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. EP260409a: COLIBRÍ optical upper limits
  2. GRB 260407A: CALET Gamma-Ray Burst Monitor detection
  3. EP260409a: Global MASTER-Net observations report
  4. EP260409a: Einstein Probe detection of an X-ray transient
  5. EP260321a: VLA radio detection
  6. GRB 260404A: Fermi GBM Final Localization
  7. GRB 260407A: Glowbug gamma-ray detection
  8. GRB 260402A: SVOM/ECLAIRs refined analysis
  9. GRB 260310A: Continued VLA Multi-frequency Radio Observations
  10. GRB 260310A / AT2026fgk: X-ray rebrightening
  11. EP260402a / GRB 260402A: Mephisto optical upper limits
  12. EP-WXT01709259586: Xinglong optical upper limit
  13. EP260403a: Mephisto optical upper limits
  14. EP260402a/GRB 260402A: Xinglong optical upper limit
  15. EP260321a: Upper limits from VLA radio observations
  16. GRID detection of GRB 260401A
  17. EP260321a: uGMRT observations
  18. GRB 260407A: Fermi GBM Final Real-time Localization
  19. EP260405a: GMOS-N optical upper limits
  20. EP260405a: SVOM/VT optical upper limits
  21. EP260405a: Global MASTER-Net observations report
  22. EP260405a: Einstein Probe detection of a fast X-ray transient
  23. The EP-WXT trigger 01709259621 is likely a flaring star
  24. EP260405.149 / EP-WXT 11900672904: COLIBRÍ optical upper limits
  25. The EP-WXT trigger 01709259615 is likely a flaring star
  26. Fermi trigger No 797039833: Global MASTER-Net observations report
  27. GRB 260403A: GECAM-B observation of a long burst
  28. EP260324A / AT 2026hir: COLIBRÍ further optical observations
  29. Fermi Gamma-ray Burst Monitor trigger 796972356/260404217 is not a GRB
  30. EP260403a: refined analysis of the EP-WXT and EP-FXT observations
  31. The EP-WXT trigger 01709259586 is likely a flaring star
  32. GRB 260330B: SVOM/VT further optical observation
  33. Fermi Gamma-ray Burst Monitor trigger 796931884/260403749 is not a GRB
  34. GRB 260330B: SVOM/ECLAIRs refined analysis
  35. EP260403a: LCO optical observations of the counterpart
  36. GRB 260310A/AT2026fgk: Kilonova-Catcher long term optical monitoring
  37. EP260403a: LCO optical counterpart detection
  38. EP260403a: COLIBRÍ optical counterpart candidate
  39. GRB 260330B: SVOM/VT optical candidate
  40. EP260403a: Einstein Probe detection of an X-ray transient
  41. GRB 260330B: EP-FXT follow-up and identification of candidate afterglow
  42. GRB 260403A: AstroSat CZTI detection
  43. EP260402a/GRB 260402A: refined analysis of the EP-WXT and EP-FXT observations
  44. GRB 260402B: GECAM-B observation
  45. EP260402a/GRB 260402A: Jinshan near-infrared upper limit
  46. GRB 260402C: NuSTAR detection of prompt emission
  47. GRB 260402C: AstroSat CZTI detection of a long burst
  48. EP260324A / AT 2026hir: COLIBRÍ optical observations
  49. GRB 260403A: Fermi GBM Final Real-time Localization
  50. EP260324A / AT 2026hir: Spectroscopic Observations with the Next Generation Palomar Spectrograph
  51. GRB 260402B: Fermi GBM Final Real-time Localization
  52. GRB 260402A: WINTER J-band upper limit
  53. GRB260402A: GROWTH-India Telescope optical upper limit
  54. GRB 260402A / EP260402a: SVOM/VT optical upper limits
  55. EP260402a/GRB 260402A: SVOM/C-GFT upper limit
  56. GRB 260401A: SVOM/GRM observation
  57. GRB 260401A: GECAM-B observation
  58. EP260402a/GRB 260402A: Einstein Probe detection of an X-ray transient
  59. GRB 260402A: Kilonova-Catcher optical upper limit
  60. GRB 260402A: MASTER optical observations
  61. GRB 260402A: SVOM/COLIBRÍ (FM-GFT) optical upper limit
  62. GRB 260402A: SVOM/MXT candidate X-ray afterglow
  63. GRB 260402A: SVOM detection of a burst
  64. Fermi GRB 260401A: Global MASTER-Net observations report
  65. GRB 260401A: Fermi GBM Observation
  66. GRB 260401A: NuSTAR detection of prompt emission
  67. GRB 260401A: CALET Gamma-Ray Burst Monitor detection
  68. GRB 260401A: MAXI/GSC detection
  69. GRB 260401A: BALROG localization (Fermi Trigger 796733611 / GRB 260401454)
  70. GRB 260401A: Fermi GBM Final Real-time Localization
  71. EP260329b: Mondy and Assy-Turgen optical upper limits
  72. GRB 260310A / AT2026fgk: Luminance-band optical follow-up with a 28cm telescope in Daocheng
  73. EP260321a :Xinglong optical observations
  74. EP260327a: Xinglong optical upper limit
  75. EP260329b: GOTO detection of optical counterpart
  76. GRB 260330B: SVOM/VT optical upper limits
  77. Konus-Wind detection of GRB 260320A
  78. Konus-Wind detection of GRB 260316B (duplicate submission)
  79. Konus-Wind detection of GRB 260316B
  80. GRB 260321A: SVOM/ECLAIRs refined analysis
  81. EP260329b: J-band upper limits with WINTER
  82. EP260329a: J-band upper limit with WINTER
  83. GRB 260330A: Glowbug gamma-ray detection
  84. GRB 260310A: VLA Multi-frequency Radio Observations
  85. Fermi GBM Sub-Threshold Detection of GRB 260330B
  86. GRB 260330B: LCO optical upper limits
  87. GRB 260330B: SVOM detection of a burst
  88. EP260324a / AT2026hir: g- and r-band optical follow-up with the PKU 60cm Telescope
  89. EP260329b: refined analysis of the EP-WXT and EP-FXT observations
  90. EP260329a: COLIBRÍ optical upper limit
  91. EP260329a: EP-FXT follow up observation
  92. EP260329a: NOT optical counterpart candidate
  93. GRB 260330A: Fermi GBM Final Real-time Localization
  94. EP260329b: Global MASTER-Net observations report
  95. Fermi trigger No 796485221: Global MASTER-Net observations report
  96. GRB 260327A: Insight-HXMT/HE detection
  97. EP260329b: Optical follow-up with Kinder observations
  98. EP 260329b: COLIBRÍ optical observations
  99. EP260329a: Optical upper limit with Kinder observations
  100. EP260329b: LCO optical observations of the counterpart

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