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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: BALROG localization (Fermi Trigger 797587480 / GRB 260411337)
  2. GRB 260411B: Fermi GBM Final Real-time Localization
  3. GRB 260411A: Fermi GBM Final Real-time Localization
  4. GRB 260410A: COLIBRÍ optical upper limit
  5. EP-WXT01709259790: Optical Upper limits with kinder observations
  6. GRB 260410A: Fermi GBM Observation
  7. GRB 260410B: SVOM/GRM detection of a short faint burst
  8. The EP-WXT trigger 01709259790 is likely a flaring star
  9. GRB 260410B: Fermi GBM Final Real-time Localization
  10. EP-WXT01709259790: Xinglong optical upper limit
  11. GRB 260410A: Fermi-LAT detection
  12. GRB 260410A: Fermi GBM Final Real-time Localization
  13. EP260409a: refined analysis of the EP-WXT and autonomous EP-FXT observations
  14. EP260321a: Chandra X-ray Non-detection
  15. GRB 260409A: Fermi GBM Final Real-time Localization
  16. GRB 260310A/AT2026fgk: Kilonova-Catcher SN peak identification
  17. The EP-WXT trigger 01709259773 is likely a flaring star
  18. GRB 260407A: GECAM-A detection
  19. GRB 260407A: Insight-HXMT/HE detection
  20. EP260409a: SVOM/VT optical upper limits
  21. EP260409a: COLIBRÍ optical upper limits
  22. GRB 260407A: CALET Gamma-Ray Burst Monitor detection
  23. EP260409a: Global MASTER-Net observations report
  24. EP260409a: Einstein Probe detection of an X-ray transient
  25. EP260321a: VLA radio detection
  26. GRB 260404A: Fermi GBM Final Localization
  27. GRB 260407A: Glowbug gamma-ray detection
  28. GRB 260402A: SVOM/ECLAIRs refined analysis
  29. GRB 260310A: Continued VLA Multi-frequency Radio Observations
  30. GRB 260310A / AT2026fgk: X-ray rebrightening
  31. EP260402a / GRB 260402A: Mephisto optical upper limits
  32. EP-WXT01709259586: Xinglong optical upper limit
  33. EP260403a: Mephisto optical upper limits
  34. EP260402a/GRB 260402A: Xinglong optical upper limit
  35. EP260321a: Upper limits from VLA radio observations
  36. GRID detection of GRB 260401A
  37. EP260321a: uGMRT observations
  38. GRB 260407A: Fermi GBM Final Real-time Localization
  39. EP260405a: GMOS-N optical upper limits
  40. EP260405a: SVOM/VT optical upper limits
  41. EP260405a: Global MASTER-Net observations report
  42. EP260405a: Einstein Probe detection of a fast X-ray transient
  43. The EP-WXT trigger 01709259621 is likely a flaring star
  44. EP260405a / EP-WXT 11900672904: COLIBRÍ optical upper limits
  45. The EP-WXT trigger 01709259615 is likely a flaring star
  46. Fermi trigger No 797039833: Global MASTER-Net observations report
  47. GRB 260403A: GECAM-B observation of a long burst
  48. EP260324A / AT 2026hir: COLIBRÍ further optical observations
  49. Fermi Gamma-ray Burst Monitor trigger 796972356/260404217 is not a GRB
  50. EP260403a: refined analysis of the EP-WXT and EP-FXT observations
  51. The EP-WXT trigger 01709259586 is likely a flaring star
  52. GRB 260330B: SVOM/VT further optical observation
  53. Fermi Gamma-ray Burst Monitor trigger 796931884/260403749 is not a GRB
  54. GRB 260330B: SVOM/ECLAIRs refined analysis
  55. EP260403a: LCO optical observations of the counterpart
  56. GRB 260310A/AT2026fgk: Kilonova-Catcher long term optical monitoring
  57. EP260403a: LCO optical counterpart detection
  58. EP260403a: COLIBRÍ optical counterpart candidate
  59. GRB 260330B: SVOM/VT optical candidate
  60. EP260403a: Einstein Probe detection of an X-ray transient
  61. GRB 260330B: EP-FXT follow-up and identification of candidate afterglow
  62. GRB 260403A: AstroSat CZTI detection
  63. EP260402a/GRB 260402A: refined analysis of the EP-WXT and EP-FXT observations
  64. GRB 260402B: GECAM-B observation
  65. EP260402a/GRB 260402A: Jinshan near-infrared upper limit
  66. GRB 260402C: NuSTAR detection of prompt emission
  67. GRB 260402C: AstroSat CZTI detection of a long burst
  68. EP260324A / AT 2026hir: COLIBRÍ optical observations
  69. GRB 260403A: Fermi GBM Final Real-time Localization
  70. EP260324A / AT 2026hir: Spectroscopic Observations with the Next Generation Palomar Spectrograph
  71. GRB 260402B: Fermi GBM Final Real-time Localization
  72. GRB 260402A: WINTER J-band upper limit
  73. GRB260402A: GROWTH-India Telescope optical upper limit
  74. GRB 260402A / EP260402a: SVOM/VT optical upper limits
  75. EP260402a/GRB 260402A: SVOM/C-GFT upper limit
  76. GRB 260401A: SVOM/GRM observation
  77. GRB 260401A: GECAM-B observation
  78. EP260402a/GRB 260402A: Einstein Probe detection of an X-ray transient
  79. GRB 260402A: Kilonova-Catcher optical upper limit
  80. GRB 260402A: MASTER optical observations
  81. GRB 260402A: SVOM/COLIBRÍ (FM-GFT) optical upper limit
  82. GRB 260402A: SVOM/MXT candidate X-ray afterglow
  83. GRB 260402A: SVOM detection of a burst
  84. Fermi GRB 260401A: Global MASTER-Net observations report
  85. GRB 260401A: Fermi GBM Observation
  86. GRB 260401A: NuSTAR detection of prompt emission
  87. GRB 260401A: CALET Gamma-Ray Burst Monitor detection
  88. GRB 260401A: MAXI/GSC detection
  89. GRB 260401A: BALROG localization (Fermi Trigger 796733611 / GRB 260401454)
  90. GRB 260401A: Fermi GBM Final Real-time Localization
  91. EP260329b: Mondy and Assy-Turgen optical upper limits
  92. GRB 260310A / AT2026fgk: Luminance-band optical follow-up with a 28cm telescope in Daocheng
  93. EP260321a :Xinglong optical observations
  94. EP260327a: Xinglong optical upper limit
  95. EP260329b: GOTO detection of optical counterpart
  96. GRB 260330B: SVOM/VT optical upper limits
  97. Konus-Wind detection of GRB 260320A
  98. Konus-Wind detection of GRB 260316B (duplicate submission)
  99. Konus-Wind detection of GRB 260316B
  100. GRB 260321A: SVOM/ECLAIRs refined analysis

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