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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 260503A: SVOM/GRM observation of a GRB
  2. IceCube-260504A - IceCube observation of a high-energy neutrino candidate track-like event
  3. Konus-Wind detection of GRB 260415C
  4. GRB 260310A / AT2026fgk: photometric monitoring and tentative maximum of a possible SN
  5. Konus-Wind detection of GRB 260411C
  6. GRB 260504B: REM optical/NIR observations
  7. IPN triangulation of GRB 260429A
  8. IPN triangulation of GRB 260428A
  9. GRB 260504B: AST3-2 i-band upper limit
  10. GRB 260504B: LCO z-band upper limit
  11. SVOM GRB 260504B: MASTER-OAFA optical observations
  12. GRB 260504B: SVOM detection of a short burst
  13. Fermi GRB 260504A: Global MASTER-Net observations report
  14. GRB 260504A: Fermi GBM Final Real-time Localization
  15. GRB 260503A: Fermi GBM Final Real-time Localization
  16. SVOM/GRM observation of a bright burst from SGR 1E1841-045
  17. GRB 260502A: GECAM-B observation of a short burst
  18. IPN triangulation of a bright burst from SGR 1E1841-045
  19. GRB 260502A: Fermi GBM Final Localization
  20. The EP-WXT trigger 01709261576 is likely a flaring star
  21. GRB 260429B / EP260429a: EP-FXT follow-up observation
  22. EP260502a: BOOTES-7 observations of a fading catalogued source close to the X-ray position
  23. GRB 260429B / EP260429a: AstroSat CZTI detection
  24. EP260502a: BOOTES-7: early optical upper limit
  25. EP260502a: Las Cumbres upper limit
  26. EP260502a: Einstein Probe detection of an X-ray transient
  27. GRB 260429A: SVOM/GRM observation of a short burst
  28. SN 2026kid: Optical follow-up with small-aperture telescopes in Spain and China
  29. EP260429a: Global MASTER-Net observations report
  30. EP260430a: refined analysis of the EP-WXT and follow-up EP-FXT observations
  31. GRB 260424B: AstroSat CZTI detection
  32. GRB 260429B / EP260429a: COLIBRÍ optical upper limit
  33. EP260429a: LCO optical upper limits
  34. EP260430a: LCO optical upper limits
  35. GRB 260430A / EP260430a: COLIBRÍ optical upper limit
  36. GRB 260429A: Fermi GBM Detection
  37. Fermi GRB 260429A: Global MASTER-Net observations report
  38. EP260430a: Global MASTER-Net observations report
  39. EP260430a: Einstein Probe detection of an X-ray transient
  40. EP260429a: EP-WXT detection of a fast X-ray transient
  41. GRB 260429A: Fermi GBM Final Real-time Localization
  42. GRB 260428A: SVOM/GRM observation of a possible short burst with extended emission
  43. GRB 260428A: GECAM-B detection of a possible long duration Type I burst
  44. IceCube-260425A: Upper limits from a search for additional neutrino events in IceCube
  45. GRB 260428A: AstroSat CZTI detection
  46. Fermi GRB 260428A: Global MASTER-Net observations report
  47. EP260416a: Mondy and Terskol optical upper limits
  48. GRB 260424B: Glowbug gamma-ray detection of a short burst
  49. GRB 260424B: COLIBRÍ optical upper limit
  50. Konus-Wind detection of GRB 260424B
  51. GRB 260428A: Fermi GBM Final Real-time Localization
  52. Fermi-LAT Gamma-ray Observations of IceCube-260425A
  53. GRB 260424C: Fermi GBM Final Localization
  54. EP260321a/SN 2026gzf: spectroscopy at Mondy observatory
  55. IPN triangulation of GRB 260424B (short)
  56. GRB 260424B: SVOM/GRM detection of a short burst
  57. IceCube-260425A - IceCube observation of a high-energy neutrino candidate track-like event
  58. GRB 260305A: likely detection by Fermi-LAT and the LAT gamma-ray position
  59. IceCube Alert 260425A: Global MASTER-Net observations report
  60. Fermi trigger No 798737427: Global MASTER-Net observations report
  61. GRB 260401A: cubesat Avion detection
  62. GRB 260424A: AstroSat CZTI detection of a long burst
  63. EP260321a: Upper limits from ATCA radio observations
  64. GRB 260421B: Kilonova-Catcher optical afterglow detection
  65. GRB 260421B: Insight-HXMT/HE detection
  66. The EP-WXT trigger 01709258652: Mondy optical observations
  67. GRB 250328A: VLT host galaxy discovery and redshift z = 1.250
  68. EP260416a: Mondy optical observations
  69. GRB 260421B: SVOM/ECLAIRs refined analysis
  70. GRB 260421B: 3.6m DOT optical observation
  71. EP260416a: ZTSh R band observations
  72. EP-WXT trigger 01709260362: FRAM-ORM optical observations confirm flaring star G 151-9
  73. IceCube-Cascade 260418A: Upper limits from a search for additional neutrino events in IceCube
  74. EP250512a / GRB 250512B: VLT/X-shooter host galaxy identification and redshift z = 1.773
  75. GRB 250530A: VLT/X-shooter host galaxy redshift z = 1.486
  76. GRB 260419A: AstroSat CZTI detection
  77. GRB 260421B: SVOM/GRM observation
  78. GRB260421B: J band upper limit by SYSU 80cm infrared telescope
  79. GRB 260421B: EP-FXT follow-up observation
  80. The EP-WXT trigger 01709260362 is likely a flaring star
  81. GOTO26djh/AT2026jpw: ATCA radio detection
  82. GRB 260421B: J-band upper limit with WINTER
  83. GRB 260421B: LCO optical counterpart detection
  84. GRB 260421B: Fermi GBM Observation
  85. Fermi Gamma-ray Burst Monitor trigger 798482368/260421694 is not a GRB
  86. GRB 260421A: AstroSat CZTI detection
  87. GOTO26djh/AT2026jpw: radio detection at 15GHz
  88. GRB 260412A: SVOM/ECLAIRs refined analysis
  89. GRB 260421B: SVOM/VT optical observations
  90. EP260416a: J band upper limit by SYSU 80cm infrared telescope
  91. GRB 260310A: Late-time Chandra X-ray Detection
  92. GRB 260418A: Insight-HXMT/HE detection
  93. EP260416a: 1.3m DFOT optical observation
  94. GRB 260415A: CALET Gamma-Ray Burst Monitor detection
  95. GRB 260415B: CALET Gamma-Ray Burst Monitor detection
  96. Fermi GRB 260421C: Global MASTER-Net observations report
  97. GRB 260421C: Fermi GBM Final Real-time Localization
  98. GRB 260421B: VLT/X-shooter spectroscopic redshift z = 2.115
  99. Fermi GRB 260421B: Global MASTER-Net observations report
  100. GRB 260421B: BOOTES-7 early optical afterglow detection

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