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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 260507B / EP260507a: Fermi-GBM Sub-Threshold Detection
  2. EP260507a: COLIBRÍ optical observations
  3. EP260507a: SVOM/VT optical observations
  4. EP260507a: NOT optical observations
  5. EP260507a: further Liverpool Telescope observations
  6. EP260507a: Liverpool Telescope optical upper limits
  7. GRB 260507A: Fermi GBM Final Real-time Localization
  8. EP260507a: GOTO optical counterpart detection
  9. EP260507a: TRT optical counterpart detection
  10. EP260507a: Kinder optical counterpart candidate
  11. EP260507a: LCO optical counterpart
  12. EP260507a: Einstein Probe detection of an X-ray transient
  13. GRB 260504B: AstroSat CZTI detection
  14. GRB 260504B: SVOM/ECLAIRs refined analysis
  15. GRB 260506B: BALROG localization (Fermi Trigger 799765648 / GRB 260506547)
  16. GRB 260506B: Fermi GBM Final Real-time Localization
  17. EP260502a is likely a flaring star
  18. Fermi GRB 260506A: Global MASTER-Net observations report
  19. GRB 260506A: Fermi GBM Final Real-time Localization
  20. GRB 260503A: GECAM-B observation of a burst
  21. IceCube Alert 260505A: Global MASTER-Net observations report
  22. GRB 260430B: Glowbug gamma-ray detection
  23. GRB 260504B: SVOM/VT optical upper limits
  24. GRB 260421B: radio observation with the VLA
  25. Konus-Wind detection of a burst from SGR 1E1841-045 on 2026 May 2
  26. Konus-Wind detection of GRB 260504B (short/hard)
  27. GRB 260504B: GECAM-B detection
  28. Fermi-LAT Gamma-ray Observations of IceCube-260504A
  29. GRB 260504C: SVOM/GRM observation of short GRB
  30. GRB 260504B: SVOM/GRM spectral analysis
  31. GRB 260430B: AstroSat CZTI detection of a long burst
  32. GRB 260504B: SVOM/MXT refined analysis and potential detection
  33. GRB 260504B: EP-FXT upper limit
  34. GRB 260502A: SVOM/GRM observation of a short GRB
  35. GRB 260503A: SVOM/GRM observation of a GRB
  36. IceCube-260504A - IceCube observation of a high-energy neutrino candidate track-like event
  37. Konus-Wind detection of GRB 260415C
  38. GRB 260310A / AT2026fgk: photometric monitoring and tentative maximum of a possible SN
  39. Konus-Wind detection of GRB 260411C
  40. GRB 260504B: REM optical/NIR observations
  41. IPN triangulation of GRB 260429A
  42. IPN triangulation of GRB 260428A
  43. GRB 260504B: AST3-2 i-band upper limit
  44. GRB 260504B: LCO z-band upper limit
  45. SVOM GRB 260504B: MASTER-OAFA optical observations
  46. GRB 260504B: SVOM detection of a short burst
  47. Fermi GRB 260504A: Global MASTER-Net observations report
  48. GRB 260504A: Fermi GBM Final Real-time Localization
  49. GRB 260503A: Fermi GBM Final Real-time Localization
  50. SVOM/GRM observation of a bright burst from SGR 1E1841-045
  51. GRB 260502A: GECAM-B observation of a short burst
  52. IPN triangulation of a bright burst from SGR 1E1841-045
  53. GRB 260502A: Fermi GBM Final Localization
  54. The EP-WXT trigger 01709261576 is likely a flaring star
  55. GRB 260429B / EP260429a: EP-FXT follow-up observation
  56. EP260502a: BOOTES-7 observations of a fading catalogued source close to the X-ray position
  57. GRB 260429B / EP260429a: AstroSat CZTI detection
  58. EP260502a: BOOTES-7: early optical upper limit
  59. EP260502a: Las Cumbres upper limit
  60. EP260502a: Einstein Probe detection of an X-ray transient
  61. GRB 260429A: SVOM/GRM observation of a short burst
  62. SN 2026kid: Optical follow-up with small-aperture telescopes in Spain and China
  63. EP260429a: Global MASTER-Net observations report
  64. EP260430a: refined analysis of the EP-WXT and follow-up EP-FXT observations
  65. GRB 260424B: AstroSat CZTI detection
  66. GRB 260429B / EP260429a: COLIBRÍ optical upper limit
  67. EP260429a: LCO optical upper limits
  68. EP260430a: LCO optical upper limits
  69. GRB 260430A / EP260430a: COLIBRÍ optical upper limit
  70. GRB 260429A: Fermi GBM Detection
  71. Fermi GRB 260429A: Global MASTER-Net observations report
  72. EP260430a: Global MASTER-Net observations report
  73. EP260430a: Einstein Probe detection of an X-ray transient
  74. EP260429a: EP-WXT detection of a fast X-ray transient
  75. GRB 260429A: Fermi GBM Final Real-time Localization
  76. GRB 260428A: SVOM/GRM observation of a possible short burst with extended emission
  77. GRB 260428A: GECAM-B detection of a possible long duration Type I burst
  78. IceCube-260425A: Upper limits from a search for additional neutrino events in IceCube
  79. GRB 260428A: AstroSat CZTI detection
  80. Fermi GRB 260428A: Global MASTER-Net observations report
  81. EP260416a: Mondy and Terskol optical upper limits
  82. GRB 260424B: Glowbug gamma-ray detection of a short burst
  83. GRB 260424B: COLIBRÍ optical upper limit
  84. Konus-Wind detection of GRB 260424B
  85. GRB 260428A: Fermi GBM Final Real-time Localization
  86. Fermi-LAT Gamma-ray Observations of IceCube-260425A
  87. GRB 260424C: Fermi GBM Final Localization
  88. EP260321a/SN 2026gzf: spectroscopy at Mondy observatory
  89. IPN triangulation of GRB 260424B (short)
  90. GRB 260424B: SVOM/GRM detection of a short burst
  91. IceCube-260425A - IceCube observation of a high-energy neutrino candidate track-like event
  92. GRB 260305A: likely detection by Fermi-LAT and the LAT gamma-ray position
  93. IceCube Alert 260425A: Global MASTER-Net observations report
  94. Fermi trigger No 798737427: Global MASTER-Net observations report
  95. GRB 260401A: cubesat Avion detection
  96. GRB 260424A: AstroSat CZTI detection of a long burst
  97. EP260321a: Upper limits from ATCA radio observations
  98. GRB 260421B: Kilonova-Catcher optical afterglow detection
  99. GRB 260421B: Insight-HXMT/HE detection
  100. The EP-WXT trigger 01709258652: Mondy optical observations

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