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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. Konus-Wind detection of GRB 260411C
  2. GRB 260504B: REM optical/NIR observations
  3. IPN triangulation of GRB 260429A
  4. IPN triangulation of GRB 260428A
  5. GRB 260504B: AST3-2 i-band upper limit
  6. GRB 260504B: LCO z-band upper limit
  7. SVOM GRB 260504B: MASTER-OAFA optical observations
  8. GRB 260504B: SVOM detection of a short burst
  9. Fermi GRB 260504A: Global MASTER-Net observations report
  10. GRB 260504A: Fermi GBM Final Real-time Localization
  11. GRB 260503A: Fermi GBM Final Real-time Localization
  12. SVOM/GRM observation of a bright burst from SGR 1E1841-045
  13. GRB 260502A: GECAM-B observation of a short burst
  14. IPN triangulation of a bright burst from SGR 1E1841-045
  15. GRB 260502A: Fermi GBM Final Localization
  16. The EP-WXT trigger 01709261576 is likely a flaring star
  17. GRB 260429B / EP260429a: EP-FXT follow-up observation
  18. EP260502a: BOOTES-7 observations of a fading catalogued source close to the X-ray position
  19. GRB 260429B / EP260429a: AstroSat CZTI detection
  20. EP260502a: BOOTES-7: early optical upper limit
  21. EP260502a: Las Cumbres upper limit
  22. EP260502a: Einstein Probe detection of an X-ray transient
  23. GRB 260429A: SVOM/GRM observation of a short burst
  24. SN 2026kid: Optical follow-up with small-aperture telescopes in Spain and China
  25. EP260429a: Global MASTER-Net observations report
  26. EP260430a: refined analysis of the EP-WXT and follow-up EP-FXT observations
  27. GRB 260424B: AstroSat CZTI detection
  28. GRB 260429B / EP260429a: COLIBRÍ optical upper limit
  29. EP260429a: LCO optical upper limits
  30. EP260430a: LCO optical upper limits
  31. GRB 260430A / EP260430a: COLIBRÍ optical upper limit
  32. GRB 260429A: Fermi GBM Detection
  33. Fermi GRB 260429A: Global MASTER-Net observations report
  34. EP260430a: Global MASTER-Net observations report
  35. EP260430a: Einstein Probe detection of an X-ray transient
  36. EP260429a: EP-WXT detection of a fast X-ray transient
  37. GRB 260429A: Fermi GBM Final Real-time Localization
  38. GRB 260428A: SVOM/GRM observation of a possible short burst with extended emission
  39. GRB 260428A: GECAM-B detection of a possible long duration Type I burst
  40. IceCube-260425A: Upper limits from a search for additional neutrino events in IceCube
  41. GRB 260428A: AstroSat CZTI detection
  42. Fermi GRB 260428A: Global MASTER-Net observations report
  43. EP260416a: Mondy and Terskol optical upper limits
  44. GRB 260424B: Glowbug gamma-ray detection of a short burst
  45. GRB 260424B: COLIBRÍ optical upper limit
  46. Konus-Wind detection of GRB 260424B
  47. GRB 260428A: Fermi GBM Final Real-time Localization
  48. Fermi-LAT Gamma-ray Observations of IceCube-260425A
  49. GRB 260424C: Fermi GBM Final Localization
  50. EP260321a/SN 2026gzf: spectroscopy at Mondy observatory
  51. IPN triangulation of GRB 260424B (short)
  52. GRB 260424B: SVOM/GRM detection of a short burst
  53. IceCube-260425A - IceCube observation of a high-energy neutrino candidate track-like event
  54. GRB 260305A: likely detection by Fermi-LAT and the LAT gamma-ray position
  55. IceCube Alert 260425A: Global MASTER-Net observations report
  56. Fermi trigger No 798737427: Global MASTER-Net observations report
  57. GRB 260401A: cubesat Avion detection
  58. GRB 260424A: AstroSat CZTI detection of a long burst
  59. EP260321a: Upper limits from ATCA radio observations
  60. GRB 260421B: Kilonova-Catcher optical afterglow detection
  61. GRB 260421B: Insight-HXMT/HE detection
  62. The EP-WXT trigger 01709258652: Mondy optical observations
  63. GRB 250328A: VLT host galaxy discovery and redshift z = 1.250
  64. EP260416a: Mondy optical observations
  65. GRB 260421B: SVOM/ECLAIRs refined analysis
  66. GRB 260421B: 3.6m DOT optical observation
  67. EP260416a: ZTSh R band observations
  68. EP-WXT trigger 01709260362: FRAM-ORM optical observations confirm flaring star G 151-9
  69. IceCube-Cascade 260418A: Upper limits from a search for additional neutrino events in IceCube
  70. EP250512a / GRB 250512B: VLT/X-shooter host galaxy identification and redshift z = 1.773
  71. GRB 250530A: VLT/X-shooter host galaxy redshift z = 1.486
  72. GRB 260419A: AstroSat CZTI detection
  73. GRB 260421B: SVOM/GRM observation
  74. GRB260421B: J band upper limit by SYSU 80cm infrared telescope
  75. GRB 260421B: EP-FXT follow-up observation
  76. The EP-WXT trigger 01709260362 is likely a flaring star
  77. GOTO26djh/AT2026jpw: ATCA radio detection
  78. GRB 260421B: J-band upper limit with WINTER
  79. GRB 260421B: LCO optical counterpart detection
  80. GRB 260421B: Fermi GBM Observation
  81. Fermi Gamma-ray Burst Monitor trigger 798482368/260421694 is not a GRB
  82. GRB 260421A: AstroSat CZTI detection
  83. GOTO26djh/AT2026jpw: radio detection at 15GHz
  84. GRB 260412A: SVOM/ECLAIRs refined analysis
  85. GRB 260421B: SVOM/VT optical observations
  86. EP260416a: J band upper limit by SYSU 80cm infrared telescope
  87. GRB 260310A: Late-time Chandra X-ray Detection
  88. GRB 260418A: Insight-HXMT/HE detection
  89. EP260416a: 1.3m DFOT optical observation
  90. GRB 260415A: CALET Gamma-Ray Burst Monitor detection
  91. GRB 260415B: CALET Gamma-Ray Burst Monitor detection
  92. Fermi GRB 260421C: Global MASTER-Net observations report
  93. GRB 260421C: Fermi GBM Final Real-time Localization
  94. GRB 260421B: VLT/X-shooter spectroscopic redshift z = 2.115
  95. Fermi GRB 260421B: Global MASTER-Net observations report
  96. GRB 260421B: BOOTES-7 early optical afterglow detection
  97. GRB 260421B: LCO optical afterglow confirmation
  98. GRB 260421B: SVOM/COLIBRÍ (FM-GFT) optical detection of a candidate counterpart
  99. GRB 260421B: TRT optical counterpart detection
  100. GRB 260421B: SVOM detection of a long burst

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