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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 260409A: Insight-HXMT/HE detection
  2. GRB 260411B: Fermi GBM Detection
  3. GRB 260411B: GOTO optical counterpart candidate
  4. EP260409a: Gemini/FLAMINGOS2 J-band counterpart
  5. GRB 260411B: BALROG localization (Fermi Trigger 797587480 / GRB 260411337)
  6. GRB 260411B: Fermi GBM Final Real-time Localization
  7. GRB 260411A: Fermi GBM Final Real-time Localization
  8. GRB 260410A: COLIBRÍ optical upper limit
  9. EP-WXT01709259790: Optical Upper limits with kinder observations
  10. GRB 260410A: Fermi GBM Observation
  11. GRB 260410B: SVOM/GRM detection of a short faint burst
  12. The EP-WXT trigger 01709259790 is likely a flaring star
  13. GRB 260410B: Fermi GBM Final Real-time Localization
  14. EP-WXT01709259790: Xinglong optical upper limit
  15. GRB 260410A: Fermi-LAT detection
  16. GRB 260410A: Fermi GBM Final Real-time Localization
  17. EP260409a: refined analysis of the EP-WXT and autonomous EP-FXT observations
  18. EP260321a: Chandra X-ray Non-detection
  19. GRB 260409A: Fermi GBM Final Real-time Localization
  20. GRB 260310A/AT2026fgk: Kilonova-Catcher SN peak identification
  21. The EP-WXT trigger 01709259773 is likely a flaring star
  22. GRB 260407A: GECAM-A detection
  23. GRB 260407A: Insight-HXMT/HE detection
  24. EP260409a: SVOM/VT optical upper limits
  25. EP260409a: COLIBRÍ optical upper limits
  26. GRB 260407A: CALET Gamma-Ray Burst Monitor detection
  27. EP260409a: Global MASTER-Net observations report
  28. EP260409a: Einstein Probe detection of an X-ray transient
  29. EP260321a: VLA radio detection
  30. GRB 260404A: Fermi GBM Final Localization
  31. GRB 260407A: Glowbug gamma-ray detection
  32. GRB 260402A: SVOM/ECLAIRs refined analysis
  33. GRB 260310A: Continued VLA Multi-frequency Radio Observations
  34. GRB 260310A / AT2026fgk: X-ray rebrightening
  35. EP260402a / GRB 260402A: Mephisto optical upper limits
  36. EP-WXT01709259586: Xinglong optical upper limit
  37. EP260403a: Mephisto optical upper limits
  38. EP260402a/GRB 260402A: Xinglong optical upper limit
  39. EP260321a: Upper limits from VLA radio observations
  40. GRID detection of GRB 260401A
  41. EP260321a: uGMRT observations
  42. GRB 260407A: Fermi GBM Final Real-time Localization
  43. EP260405a: GMOS-N optical upper limits
  44. EP260405a: SVOM/VT optical upper limits
  45. EP260405a: Global MASTER-Net observations report
  46. EP260405a: Einstein Probe detection of a fast X-ray transient
  47. The EP-WXT trigger 01709259621 is likely a flaring star
  48. EP260405a / EP-WXT 11900672904: COLIBRÍ optical upper limits
  49. The EP-WXT trigger 01709259615 is likely a flaring star
  50. Fermi trigger No 797039833: Global MASTER-Net observations report
  51. GRB 260403A: GECAM-B observation of a long burst
  52. EP260324A / AT 2026hir: COLIBRÍ further optical observations
  53. Fermi Gamma-ray Burst Monitor trigger 796972356/260404217 is not a GRB
  54. EP260403a: refined analysis of the EP-WXT and EP-FXT observations
  55. The EP-WXT trigger 01709259586 is likely a flaring star
  56. GRB 260330B: SVOM/VT further optical observation
  57. Fermi Gamma-ray Burst Monitor trigger 796931884/260403749 is not a GRB
  58. GRB 260330B: SVOM/ECLAIRs refined analysis
  59. EP260403a: LCO optical observations of the counterpart
  60. GRB 260310A/AT2026fgk: Kilonova-Catcher long term optical monitoring
  61. EP260403a: LCO optical counterpart detection
  62. EP260403a: COLIBRÍ optical counterpart candidate
  63. GRB 260330B: SVOM/VT optical candidate
  64. EP260403a: Einstein Probe detection of an X-ray transient
  65. GRB 260330B: EP-FXT follow-up and identification of candidate afterglow
  66. GRB 260403A: AstroSat CZTI detection
  67. EP260402a/GRB 260402A: refined analysis of the EP-WXT and EP-FXT observations
  68. GRB 260402B: GECAM-B observation
  69. EP260402a/GRB 260402A: Jinshan near-infrared upper limit
  70. GRB 260402C: NuSTAR detection of prompt emission
  71. GRB 260402C: AstroSat CZTI detection of a long burst
  72. EP260324A / AT 2026hir: COLIBRÍ optical observations
  73. GRB 260403A: Fermi GBM Final Real-time Localization
  74. EP260324A / AT 2026hir: Spectroscopic Observations with the Next Generation Palomar Spectrograph
  75. GRB 260402B: Fermi GBM Final Real-time Localization
  76. GRB 260402A: WINTER J-band upper limit
  77. GRB260402A: GROWTH-India Telescope optical upper limit
  78. GRB 260402A / EP260402a: SVOM/VT optical upper limits
  79. EP260402a/GRB 260402A: SVOM/C-GFT upper limit
  80. GRB 260401A: SVOM/GRM observation
  81. GRB 260401A: GECAM-B observation
  82. EP260402a/GRB 260402A: Einstein Probe detection of an X-ray transient
  83. GRB 260402A: Kilonova-Catcher optical upper limit
  84. GRB 260402A: MASTER optical observations
  85. GRB 260402A: SVOM/COLIBRÍ (FM-GFT) optical upper limit
  86. GRB 260402A: SVOM/MXT candidate X-ray afterglow
  87. GRB 260402A: SVOM detection of a burst
  88. Fermi GRB 260401A: Global MASTER-Net observations report
  89. GRB 260401A: Fermi GBM Observation
  90. GRB 260401A: NuSTAR detection of prompt emission
  91. GRB 260401A: CALET Gamma-Ray Burst Monitor detection
  92. GRB 260401A: MAXI/GSC detection
  93. GRB 260401A: BALROG localization (Fermi Trigger 796733611 / GRB 260401454)
  94. GRB 260401A: Fermi GBM Final Real-time Localization
  95. EP260329b: Mondy and Assy-Turgen optical upper limits
  96. GRB 260310A / AT2026fgk: Luminance-band optical follow-up with a 28cm telescope in Daocheng
  97. EP260321a :Xinglong optical observations
  98. EP260327a: Xinglong optical upper limit
  99. EP260329b: GOTO detection of optical counterpart
  100. GRB 260330B: SVOM/VT optical upper limits

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