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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. Fermi-LAT Gamma-ray Observations of IceCube-260504A
  2. GRB 260504C: SVOM/GRM observation of short GRB
  3. GRB 260504B: SVOM/GRM spectral analysis
  4. GRB 260430B: AstroSat CZTI detection of a long burst
  5. GRB 260504B: SVOM/MXT refined analysis and potential detection
  6. GRB 260504B: EP-FXT upper limit
  7. GRB 260502A: SVOM/GRM observation of a short GRB
  8. GRB 260503A: SVOM/GRM observation of a GRB
  9. IceCube-260504A - IceCube observation of a high-energy neutrino candidate track-like event
  10. Konus-Wind detection of GRB 260415C
  11. GRB 260310A / AT2026fgk: photometric monitoring and tentative maximum of a possible SN
  12. Konus-Wind detection of GRB 260411C
  13. GRB 260504B: REM optical/NIR observations
  14. IPN triangulation of GRB 260429A
  15. IPN triangulation of GRB 260428A
  16. GRB 260504B: AST3-2 i-band upper limit
  17. GRB 260504B: LCO z-band upper limit
  18. SVOM GRB 260504B: MASTER-OAFA optical observations
  19. GRB 260504B: SVOM detection of a short burst
  20. Fermi GRB 260504A: Global MASTER-Net observations report
  21. GRB 260504A: Fermi GBM Final Real-time Localization
  22. GRB 260503A: Fermi GBM Final Real-time Localization
  23. SVOM/GRM observation of a bright burst from SGR 1E1841-045
  24. GRB 260502A: GECAM-B observation of a short burst
  25. IPN triangulation of a bright burst from SGR 1E1841-045
  26. GRB 260502A: Fermi GBM Final Localization
  27. The EP-WXT trigger 01709261576 is likely a flaring star
  28. GRB 260429B / EP260429a: EP-FXT follow-up observation
  29. EP260502a: BOOTES-7 observations of a fading catalogued source close to the X-ray position
  30. GRB 260429B / EP260429a: AstroSat CZTI detection
  31. EP260502a: BOOTES-7: early optical upper limit
  32. EP260502a: Las Cumbres upper limit
  33. EP260502a: Einstein Probe detection of an X-ray transient
  34. GRB 260429A: SVOM/GRM observation of a short burst
  35. SN 2026kid: Optical follow-up with small-aperture telescopes in Spain and China
  36. EP260429a: Global MASTER-Net observations report
  37. EP260430a: refined analysis of the EP-WXT and follow-up EP-FXT observations
  38. GRB 260424B: AstroSat CZTI detection
  39. GRB 260429B / EP260429a: COLIBRÍ optical upper limit
  40. EP260429a: LCO optical upper limits
  41. EP260430a: LCO optical upper limits
  42. GRB 260430A / EP260430a: COLIBRÍ optical upper limit
  43. GRB 260429A: Fermi GBM Detection
  44. Fermi GRB 260429A: Global MASTER-Net observations report
  45. EP260430a: Global MASTER-Net observations report
  46. EP260430a: Einstein Probe detection of an X-ray transient
  47. EP260429a: EP-WXT detection of a fast X-ray transient
  48. GRB 260429A: Fermi GBM Final Real-time Localization
  49. GRB 260428A: SVOM/GRM observation of a possible short burst with extended emission
  50. GRB 260428A: GECAM-B detection of a possible long duration Type I burst
  51. IceCube-260425A: Upper limits from a search for additional neutrino events in IceCube
  52. GRB 260428A: AstroSat CZTI detection
  53. Fermi GRB 260428A: Global MASTER-Net observations report
  54. EP260416a: Mondy and Terskol optical upper limits
  55. GRB 260424B: Glowbug gamma-ray detection of a short burst
  56. GRB 260424B: COLIBRÍ optical upper limit
  57. Konus-Wind detection of GRB 260424B
  58. GRB 260428A: Fermi GBM Final Real-time Localization
  59. Fermi-LAT Gamma-ray Observations of IceCube-260425A
  60. GRB 260424C: Fermi GBM Final Localization
  61. EP260321a/SN 2026gzf: spectroscopy at Mondy observatory
  62. IPN triangulation of GRB 260424B (short)
  63. GRB 260424B: SVOM/GRM detection of a short burst
  64. IceCube-260425A - IceCube observation of a high-energy neutrino candidate track-like event
  65. GRB 260305A: likely detection by Fermi-LAT and the LAT gamma-ray position
  66. IceCube Alert 260425A: Global MASTER-Net observations report
  67. Fermi trigger No 798737427: Global MASTER-Net observations report
  68. GRB 260401A: cubesat Avion detection
  69. GRB 260424A: AstroSat CZTI detection of a long burst
  70. EP260321a: Upper limits from ATCA radio observations
  71. GRB 260421B: Kilonova-Catcher optical afterglow detection
  72. GRB 260421B: Insight-HXMT/HE detection
  73. The EP-WXT trigger 01709258652: Mondy optical observations
  74. GRB 250328A: VLT host galaxy discovery and redshift z = 1.250
  75. EP260416a: Mondy optical observations
  76. GRB 260421B: SVOM/ECLAIRs refined analysis
  77. GRB 260421B: 3.6m DOT optical observation
  78. EP260416a: ZTSh R band observations
  79. EP-WXT trigger 01709260362: FRAM-ORM optical observations confirm flaring star G 151-9
  80. IceCube-Cascade 260418A: Upper limits from a search for additional neutrino events in IceCube
  81. EP250512a / GRB 250512B: VLT/X-shooter host galaxy identification and redshift z = 1.773
  82. GRB 250530A: VLT/X-shooter host galaxy redshift z = 1.486
  83. GRB 260419A: AstroSat CZTI detection
  84. GRB 260421B: SVOM/GRM observation
  85. GRB260421B: J band upper limit by SYSU 80cm infrared telescope
  86. GRB 260421B: EP-FXT follow-up observation
  87. The EP-WXT trigger 01709260362 is likely a flaring star
  88. GOTO26djh/AT2026jpw: ATCA radio detection
  89. GRB 260421B: J-band upper limit with WINTER
  90. GRB 260421B: LCO optical counterpart detection
  91. GRB 260421B: Fermi GBM Observation
  92. Fermi Gamma-ray Burst Monitor trigger 798482368/260421694 is not a GRB
  93. GRB 260421A: AstroSat CZTI detection
  94. GOTO26djh/AT2026jpw: radio detection at 15GHz
  95. GRB 260412A: SVOM/ECLAIRs refined analysis
  96. GRB 260421B: SVOM/VT optical observations
  97. EP260416a: J band upper limit by SYSU 80cm infrared telescope
  98. GRB 260310A: Late-time Chandra X-ray Detection
  99. GRB 260418A: Insight-HXMT/HE detection
  100. EP260416a: 1.3m DFOT optical observation

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