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

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