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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 260411B: Ondrejov D50 optical afterglow detection
  2. GRB260411B: 3.6m DOT optical observation
  3. GRB 260411A: SVOM/GRM observation
  4. GRB 260407B: SVOM/GRM detection of a possible magnetar X-ray burst
  5. GRB 260411B: SVOM/GRM observation of a long burst
  6. GRB 260409A: Insight-HXMT/HE detection
  7. GRB 260411B: Fermi GBM Detection
  8. GRB 260411B: GOTO optical counterpart candidate
  9. EP260409a: Gemini/FLAMINGOS2 J-band counterpart
  10. GRB 260411B: BALROG localization (Fermi Trigger 797587480 / GRB 260411337)
  11. GRB 260411B: Fermi GBM Final Real-time Localization
  12. GRB 260411A: Fermi GBM Final Real-time Localization
  13. GRB 260410A: COLIBRÍ optical upper limit
  14. EP-WXT01709259790: Optical Upper limits with kinder observations
  15. GRB 260410A: Fermi GBM Observation
  16. GRB 260410B: SVOM/GRM detection of a short faint burst
  17. The EP-WXT trigger 01709259790 is likely a flaring star
  18. GRB 260410B: Fermi GBM Final Real-time Localization
  19. EP-WXT01709259790: Xinglong optical upper limit
  20. GRB 260410A: Fermi-LAT detection
  21. GRB 260410A: Fermi GBM Final Real-time Localization
  22. EP260409a: refined analysis of the EP-WXT and autonomous EP-FXT observations
  23. EP260321a: Chandra X-ray Non-detection
  24. GRB 260409A: Fermi GBM Final Real-time Localization
  25. GRB 260310A/AT2026fgk: Kilonova-Catcher SN peak identification
  26. The EP-WXT trigger 01709259773 is likely a flaring star
  27. GRB 260407A: GECAM-A detection
  28. GRB 260407A: Insight-HXMT/HE detection
  29. EP260409a: SVOM/VT optical upper limits
  30. EP260409a: COLIBRÍ optical upper limits
  31. GRB 260407A: CALET Gamma-Ray Burst Monitor detection
  32. EP260409a: Global MASTER-Net observations report
  33. EP260409a: Einstein Probe detection of an X-ray transient
  34. EP260321a: VLA radio detection
  35. GRB 260404A: Fermi GBM Final Localization
  36. GRB 260407A: Glowbug gamma-ray detection
  37. GRB 260402A: SVOM/ECLAIRs refined analysis
  38. GRB 260310A: Continued VLA Multi-frequency Radio Observations
  39. GRB 260310A / AT2026fgk: X-ray rebrightening
  40. EP260402a / GRB 260402A: Mephisto optical upper limits
  41. EP-WXT01709259586: Xinglong optical upper limit
  42. EP260403a: Mephisto optical upper limits
  43. EP260402a/GRB 260402A: Xinglong optical upper limit
  44. EP260321a: Upper limits from VLA radio observations
  45. GRID detection of GRB 260401A
  46. EP260321a: uGMRT observations
  47. GRB 260407A: Fermi GBM Final Real-time Localization
  48. EP260405a: GMOS-N optical upper limits
  49. EP260405a: SVOM/VT optical upper limits
  50. EP260405a: Global MASTER-Net observations report
  51. EP260405a: Einstein Probe detection of a fast X-ray transient
  52. The EP-WXT trigger 01709259621 is likely a flaring star
  53. EP260405.149 / EP-WXT 11900672904: COLIBRÍ optical upper limits
  54. The EP-WXT trigger 01709259615 is likely a flaring star
  55. Fermi trigger No 797039833: Global MASTER-Net observations report
  56. GRB 260403A: GECAM-B observation of a long burst
  57. EP260324A / AT 2026hir: COLIBRÍ further optical observations
  58. Fermi Gamma-ray Burst Monitor trigger 796972356/260404217 is not a GRB
  59. EP260403a: refined analysis of the EP-WXT and EP-FXT observations
  60. The EP-WXT trigger 01709259586 is likely a flaring star
  61. GRB 260330B: SVOM/VT further optical observation
  62. Fermi Gamma-ray Burst Monitor trigger 796931884/260403749 is not a GRB
  63. GRB 260330B: SVOM/ECLAIRs refined analysis
  64. EP260403a: LCO optical observations of the counterpart
  65. GRB 260310A/AT2026fgk: Kilonova-Catcher long term optical monitoring
  66. EP260403a: LCO optical counterpart detection
  67. EP260403a: COLIBRÍ optical counterpart candidate
  68. GRB 260330B: SVOM/VT optical candidate
  69. EP260403a: Einstein Probe detection of an X-ray transient
  70. GRB 260330B: EP-FXT follow-up and identification of candidate afterglow
  71. GRB 260403A: AstroSat CZTI detection
  72. EP260402a/GRB 260402A: refined analysis of the EP-WXT and EP-FXT observations
  73. GRB 260402B: GECAM-B observation
  74. EP260402a/GRB 260402A: Jinshan near-infrared upper limit
  75. GRB 260402C: NuSTAR detection of prompt emission
  76. GRB 260402C: AstroSat CZTI detection of a long burst
  77. EP260324A / AT 2026hir: COLIBRÍ optical observations
  78. GRB 260403A: Fermi GBM Final Real-time Localization
  79. EP260324A / AT 2026hir: Spectroscopic Observations with the Next Generation Palomar Spectrograph
  80. GRB 260402B: Fermi GBM Final Real-time Localization
  81. GRB 260402A: WINTER J-band upper limit
  82. GRB260402A: GROWTH-India Telescope optical upper limit
  83. GRB 260402A / EP260402a: SVOM/VT optical upper limits
  84. EP260402a/GRB 260402A: SVOM/C-GFT upper limit
  85. GRB 260401A: SVOM/GRM observation
  86. GRB 260401A: GECAM-B observation
  87. EP260402a/GRB 260402A: Einstein Probe detection of an X-ray transient
  88. GRB 260402A: Kilonova-Catcher optical upper limit
  89. GRB 260402A: MASTER optical observations
  90. GRB 260402A: SVOM/COLIBRÍ (FM-GFT) optical upper limit
  91. GRB 260402A: SVOM/MXT candidate X-ray afterglow
  92. GRB 260402A: SVOM detection of a burst
  93. Fermi GRB 260401A: Global MASTER-Net observations report
  94. GRB 260401A: Fermi GBM Observation
  95. GRB 260401A: NuSTAR detection of prompt emission
  96. GRB 260401A: CALET Gamma-Ray Burst Monitor detection
  97. GRB 260401A: MAXI/GSC detection
  98. GRB 260401A: BALROG localization (Fermi Trigger 796733611 / GRB 260401454)
  99. GRB 260401A: Fermi GBM Final Real-time Localization
  100. EP260329b: Mondy and Assy-Turgen optical upper limits

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