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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"

4223 results found.

  1. IceCube Alert 260825A: Global MASTER-Net observations report
  2. GRB 260818B: VLA radio observations
  3. GRB 260818B: SVOM/GRM observation
  4. EP260812a: AZT-22 optical upper limit
  5. GRB260809A/EPF_J234751.2+210212: EP-FXT follow-up observation
  6. GRB 260808B: SVOM/COLIBRÍ (FM-GFT) optical observation
  7. GRB 260809A: NOT optical observations
  8. EP260809a: J-band upper limit with WINTER
  9. GRB 260808B: LCO optical observations
  10. Fermi GRB 260808A: Global MASTER-Net observations report
  11. SN 2026stf / GRB 260708A: ATLAS forced photometry
  12. Fermi GRB 260802B: Global MASTER-Net observations report
  13. GRB 260802A / EP J223759.5+531421: SVOM/VT optical upper limit
  14. EP 260729a: Ondrejov D50 optical detection supports stellar flare origin
  15. EP260723a: SVOM/VT optical observation
  16. Fermi GRB 260718A: Global MASTER-Net observations report
  17. GRB 260310A / AT2026fgk: Late-time Chandra Detection
  18. EP260711a: EP-FXT follow-up observation
  19. GRB 260629A: AstroSat CZTI detection
  20. GRB 260703A: Fermi GBM Final Localization
  21. Fermi trigger No 804552016: Global MASTER-Net observations report
  22. GRB 260629A: Fermi GBM Final Real-time Localization
  23. Fermi GRB 260628A: Global MASTER-Net observations report
  24. EP260623a: TNG NIR afterglow detection
  25. EP260623a: WINTER J-band observations
  26. GRB 260619A: SVOM possible detection of a faint burst
  27. GRB 260506B: cubesat Avion detection
  28. GRB 260429A: cubesat Avion detection
  29. GRB 260610B: further Liverpool Telescope optical observations
  30. GRB 260610B / AT2026owq: GRANDMA optical observations
  31. EP260605a: COLIBRÍ optical upper limits
  32. EP260610b: Liverpool Telescope optical upper limits
  33. GRB 260610B / AT2026owq: SVOM/VT optical observations
  34. GRB 260604C: SVOM/C-GFT upper limit
  35. EP260602a: COLIBRÍ optical observations
  36. SVOM GRB260603.23: Global MASTER-Net observations report
  37. Fermi GRB 260602B: Global MASTER-Net observations report
  38. Fermi GRB 260602B: Global MASTER-Net observations report
  39. GRB 260602A: Fermi GBM Final Real-time Localization
  40. EP260530a/AT 2026nwl: COLIBRÍ optical observations
  41. AT2026nik: EP-FXT X-ray counterpart
  42. Fermi trigger No 801900520: Global MASTER-Net observations report
  43. EP260527a/GRB 260527A: further FTW optical and NIR observations
  44. GRB 260527A / EP260527a: VLA radio detection
  45. GRB 260529A: GOTO tentative optical afterglow candidate
  46. Fermi GRB 260529A: Global MASTER-Net observations report
  47. GRB 260529A: Fermi GBM Final Real-time Localization
  48. GRB 260527A/EP260527a: Gemini GMOS-S Optical Observations
  49. EP260527a: SVOM/VT optical observation
  50. Fermi trigger No 801580882: Global MASTER-Net observations report
  51. EP260526.405: COLIBRÍ optical upper limits
  52. EP-WXT 01709266106: NOT optical upper limits
  53. GRB 260515A: OHP/T193 optical observations
  54. SVOM GRB 260515A: Global MASTER-Net observations report
  55. GRB 260511B: Mephisto multi-band optical followup
  56. Fermi GRB 260514A: Global MASTER-Net observations report
  57. GRB 260511B SVOM/C-GFT optical counterpart detection
  58. Fermi GRB 260511A: Global MASTER-Net observations report
  59. GRB 260510C: MAXI/GSC detection
  60. EP260509a: Global MASTER-Net observations report
  61. SVOM GRB 260509A: MASTER-OAFA optical observation
  62. Konus-Wind detection of a burst from SGR 1E1841-045 on 2026 May 2
  63. SVOM GRB 260504B: MASTER-OAFA optical observations
  64. SVOM/GRM observation of a bright burst from SGR 1E1841-045
  65. IPN triangulation of a bright burst from SGR 1E1841-045
  66. GRB 260429B / EP260429a: AstroSat CZTI detection
  67. SN 2026kid: Optical follow-up with small-aperture telescopes in Spain and China
  68. GRB 260429A: Fermi GBM Detection
  69. EP260429a: EP-WXT detection of a fast X-ray transient
  70. GRB 260429A: Fermi GBM Final Real-time Localization
  71. Fermi GRB 260428A: Global MASTER-Net observations report
  72. IceCube-Cascade 260418A: Upper limits from a search for additional neutrino events in IceCube
  73. Fermi GRB 260421C: Global MASTER-Net observations report
  74. Fermi GRB 260421B: Global MASTER-Net observations report
  75. GRB 260421B: LCO optical afterglow confirmation
  76. Fermi GRB 260417B: Global MASTER-Net observations report
  77. EP260417a: Global MASTER-Net observations report
  78. EP260416a: GMG Optical Observation
  79. Fermi GRB 260417A: Global MASTER-Net observations report
  80. GRB 260417A: AstroSat CZTI detection
  81. IPN triangulation of GRB 260411B
  82. EP260416a: Einstein Probe detection of an X-ray transient
  83. Fermi trigger No 797912738: Global MASTER-Net observations report
  84. EP260321a: CMO SAI J,K observations
  85. Fermi GRB 260412A: Global MASTER-Net observations report
  86. GRB260411B: 3.6m DOT optical observation
  87. Fermi trigger No 797039833: Global MASTER-Net observations report
  88. EP260403a: COLIBRÍ optical counterpart candidate
  89. EP260403a: Einstein Probe detection of an X-ray transient
  90. EP260402a/GRB 260402A: refined analysis of the EP-WXT and EP-FXT observations
  91. Fermi GRB 260401A: Global MASTER-Net observations report
  92. EP260329b: Mondy and Assy-Turgen optical upper limits
  93. EP260329b: GOTO detection of optical counterpart
  94. EP260329a: COLIBRÍ optical upper limit
  95. EP260329b: Global MASTER-Net observations report
  96. Fermi trigger No 796485221: Global MASTER-Net observations report
  97. EP 260329b: COLIBRÍ optical observations
  98. EP260329b: LCO optical observations of the counterpart
  99. EP-WXT trigger 01709259209: TRT optical counterpart detection
  100. EP260321A: Mondy optical observations

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