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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"

36158 results found.

  1. GRB 260510C: SVOM/VT optical counterpart confirmation
  2. GRB 260511A: SVOM/VT optical observation with VHF data
  3. Fermi GRB 260511A: Global MASTER-Net observations report
  4. GRB 260511A: KAIT optical afterglow observations
  5. GRB 260511A: LCO optical afterglow detection
  6. GRB 260511A: SVOM/COLIBRÍ (FM-GFT) optical counterpart
  7. GRB 260511A: TRT optical counterpart detection
  8. GRB 260511A: SVOM detection of a bright burst
  9. GRB 260511A: BALROG localization (Fermi Trigger 800172815 / GRB 260511259)
  10. GRB 260510C: SVOM/COLIBRÍ (FM-GFT) optical counterpart candidate
  11. GRB 260511A: Fermi GBM Final Real-time Localization
  12. GRB 260510B: SVOM/VT optical upper limits
  13. GRB 260510C: SVOM/VT optical upper limits
  14. GRB 260510C: MAXI/GSC detection
  15. Fermi GBM Sub-Threshold Detection of GRB 260510B
  16. GRB 260510D: Fermi GBM Final Real-time Localization
  17. GRB 260510B: GOTO early upper limit
  18. GRB 260510C: SVOM detection of a burst
  19. GRB 260510C: Fermi GBM Final Real-time Localization
  20. GRB 260510A: GECAM-B observation
  21. GRB 260510B: LCO optical upper limits
  22. GRB 260509A: Liverpool Telescope optical observations
  23. GRB 260510B: SVOM detection of a burst
  24. GRB 260509A: NOT spectroscopic redshift upper limit z < 1.95
  25. GRB 260509A: LCO optical observations
  26. SVOM GRB 260509A: MASTER-OAFA optical observation
  27. Fermi GRB 260510A: Global MASTER-Net observations report
  28. GRB 260509A: KAIT optical observations
  29. GRB 260509A: SVOM/COLIBRÍ (FM-GFT) observations
  30. GRB 260510A: Fermi GBM Final Real-time Localization
  31. GRB 260509A: SVOM/VT optical candidate with VHF data
  32. GRB 260509A: LCO optical counterpart detection
  33. GRB 260509A: GOTO optical counterpart candidate
  34. GRB 260509A: SVOM detection of a burst
  35. GRB 260506B: AstroSat CZTI detection
  36. IceCube-260504A: Upper limits from a search for additional neutrino events in IceCube
  37. GRB 260507B / EP260507a: Fermi-GBM Sub-Threshold Detection
  38. GRB 260507A: Fermi GBM Final Real-time Localization
  39. GRB 260504B: AstroSat CZTI detection
  40. GRB 260504B: SVOM/ECLAIRs refined analysis
  41. GRB 260506B: BALROG localization (Fermi Trigger 799765648 / GRB 260506547)
  42. GRB 260506B: Fermi GBM Final Real-time Localization
  43. Fermi GRB 260506A: Global MASTER-Net observations report
  44. GRB 260506A: Fermi GBM Final Real-time Localization
  45. GRB 260503A: GECAM-B observation of a burst
  46. GRB 260430B: Glowbug gamma-ray detection
  47. GRB 260504B: SVOM/VT optical upper limits
  48. GRB 260421B: radio observation with the VLA
  49. Konus-Wind detection of GRB 260504B (short/hard)
  50. GRB 260504B: GECAM-B detection
  51. GRB 260504C: SVOM/GRM observation of short GRB
  52. GRB 260504B: SVOM/GRM spectral analysis
  53. GRB 260430B: AstroSat CZTI detection of a long burst
  54. GRB 260504B: SVOM/MXT refined analysis and potential detection
  55. GRB 260504B: EP-FXT upper limit
  56. GRB 260502A: SVOM/GRM observation of a short GRB
  57. GRB 260503A: SVOM/GRM observation of a GRB
  58. IceCube-260504A - IceCube observation of a high-energy neutrino candidate track-like event
  59. Konus-Wind detection of GRB 260415C
  60. GRB 260310A / AT2026fgk: photometric monitoring and tentative maximum of a possible SN
  61. Konus-Wind detection of GRB 260411C
  62. GRB 260504B: REM optical/NIR observations
  63. IPN triangulation of GRB 260429A
  64. IPN triangulation of GRB 260428A
  65. GRB 260504B: AST3-2 i-band upper limit
  66. GRB 260504B: LCO z-band upper limit
  67. SVOM GRB 260504B: MASTER-OAFA optical observations
  68. GRB 260504B: SVOM detection of a short burst
  69. Fermi GRB 260504A: Global MASTER-Net observations report
  70. GRB 260504A: Fermi GBM Final Real-time Localization
  71. GRB 260503A: Fermi GBM Final Real-time Localization
  72. GRB 260502A: GECAM-B observation of a short burst
  73. IPN triangulation of a bright burst from SGR 1E1841-045
  74. GRB 260502A: Fermi GBM Final Localization
  75. GRB 260429B / EP260429a: EP-FXT follow-up observation
  76. GRB 260429B / EP260429a: AstroSat CZTI detection
  77. GRB 260429A: SVOM/GRM observation of a short burst
  78. GRB 260424B: AstroSat CZTI detection
  79. GRB 260429B / EP260429a: COLIBRÍ optical upper limit
  80. GRB 260430A / EP260430a: COLIBRÍ optical upper limit
  81. GRB 260429A: Fermi GBM Detection
  82. Fermi GRB 260429A: Global MASTER-Net observations report
  83. GRB 260429A: Fermi GBM Final Real-time Localization
  84. GRB 260428A: SVOM/GRM observation of a possible short burst with extended emission
  85. GRB 260428A: GECAM-B detection of a possible long duration Type I burst
  86. IceCube-260425A: Upper limits from a search for additional neutrino events in IceCube
  87. GRB 260428A: AstroSat CZTI detection
  88. Fermi GRB 260428A: Global MASTER-Net observations report
  89. EP260416a: Mondy and Terskol optical upper limits
  90. GRB 260424B: Glowbug gamma-ray detection of a short burst
  91. GRB 260424B: COLIBRÍ optical upper limit
  92. Konus-Wind detection of GRB 260424B
  93. GRB 260428A: Fermi GBM Final Real-time Localization
  94. GRB 260424C: Fermi GBM Final Localization
  95. EP260321a/SN 2026gzf: spectroscopy at Mondy observatory
  96. IPN triangulation of GRB 260424B (short)
  97. GRB 260424B: SVOM/GRM detection of a short burst
  98. IceCube-260425A - IceCube observation of a high-energy neutrino candidate track-like event
  99. GRB 260305A: likely detection by Fermi-LAT and the LAT gamma-ray position
  100. GRB 260401A: cubesat Avion detection

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