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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. sb25061207: Mephisto optical upper limits
  2. IceCube alert 141029_8144692 retraction
  3. Fermi Gamma-ray Burst Monitor trigger 771596290/250614513 is not a GRB
  4. GRB 250614A: Fermi GBM Final Real-time Localization
  5. EP250612a / GRB 250612B: NOT optical observations of the afterglow candidate
  6. Fermi Gamma-ray Burst Monitor trigger 771547945/250613953 is not a GRB
  7. Fermi Gamma-ray Burst Monitor trigger 771541927/250613883 is not a GRB
  8. sb25061218: SVOM/COLIBRÍ (FM-GFT) optical upper limits
  9. sb25061207: SVOM/COLIBRÍ (FM-GFT) optical upper limit
  10. Fermi trigger No 771494087: Global MASTER-Net observations report
  11. sb25061218: Swift-XRT observations
  12. EP250612a: refined analysis of the EP-WXT and EP-FXT observations
  13. GRB 250610B: J band upper limit by SYSU 80cm infrared telescope
  14. sb25061207: EP-FXT follow-up observation and afterglow candidate
  15. GRB 250612B: Fermi GBM Observation
  16. EP250612a: SVOM/VT optical candidate
  17. Fermi trigger No 771424081: Global MASTER-Net observations report
  18. EP250612a: Global MASTER-Net observations report
  19. GRB 250612C: Fermi GBM Observation
  20. sb25061218: SVOM detection of a X-ray transient
  21. sb25061207: Swift-XRT observations
  22. EP250612a/GRB 250612B: JinShan optical upper limit
  23. EP 250612a: AST3-3 Yaoan Optical Observation
  24. GRB 250612C: SVOM/GRM observation an intermedium duration burst
  25. sb25061207: SVOM/VT optical counterpart
  26. GRB 250612C: BALROG localization (Fermi Trigger 771432801 / GRB 250612620)
  27. GRB 250610B: Swift-XRT refined Analysis
  28. GRB 250612C: Fermi GBM Final Real-time Localization
  29. EP250610a: Upper limit from Fermi-GBM Observations
  30. GRB 250612B (250612519/771424081): Fermi GBM Final Localization
  31. GRB 250612B: BALROG localization (Fermi Trigger 771424081 / GRB 250612519)
  32. EP250612a: Einstein Probe detection of an X-ray transient
  33. GRB 250610B: Liverpool Telescope continued monitoring
  34. GRB 250610B: MISTRAL/T193 and T120 OHP further observations
  35. sb25061207: SVOM detection of a X-ray transient
  36. EP250610a: continuous follow-up observations with EP-FXT
  37. GRB 250610B - SVOM/ECLAIRs refined analysis
  38. GRB 250612A: Swift detection of a burst or new Galactic transient Swift J1643.6-3854
  39. Swift GRB250612.04: Global MASTER-Net observations report
  40. Fermi GBM Sub-Threshold Detection of GRB 250610B
  41. GRB 250610B: Swift/UVOT Detection
  42. EP250610A: Swift/UVOT Upper limits
  43. GRB 250610B: SVOM/COLIBRÍ (FM-GFT) optical observations
  44. EP250610a: TNG NIR upper limit
  45. GRB 250610B: REM optical/NIR observations
  46. EP250610a: Liverpool Telescope optical upper limits
  47. GRB 250610B: SVOM/VT optical shallow decay
  48. GRB 250610B: additional Liverpool Telescope optical observations
  49. GRB 250610B: SVOM/GRM analysis
  50. GRB 250610B: Fermi/GBM sub-threshold detection of a possibly hard burst
  51. GRB 250610B: EP-FXT follow-up observation and afterglow counterpart
  52. Fermi Gamma-ray Burst Monitor trigger 771286888/250610932 is not a GRB
  53. GRB 250610B: Swift-XRT counterpart detection
  54. GRB 250610B: SVOM/VT optical counterpart
  55. GRB 250610B: LT detection of the optical counterpart
  56. GRB 250610B: OHP/T120 optical counterpart candidate
  57. GRB 250610C: Fermi GBM Final Real-time Localization
  58. GRB 250610B: GOTO optical upper limit
  59. EP250610a: Global MASTER-Net observations report
  60. GRB 250610B : SVOM/GWAC-F60A and F50 observations
  61. GRB 250610B: SVOM detection of a long burst
  62. Fermi Gamma-ray Burst Monitor trigger 771256110/250610575 is not a GRB
  63. EP250610a: refined analysis of the EP-WXT and EP-FXT observations
  64. GRB 250610A: Fermi GBM Final Real-time Localization
  65. GRB 250605A: Swift-BAT refined analysis
  66. EP250610a: SVOM/VT optical upper limit
  67. EP250610a: REM optical/NIR observations
  68. GRB 250609A: Fermi GBM Observation
  69. GRBAlpha reentry on June 9, 2025
  70. EP250610a: Swift-XRT counterpart detection
  71. EP250610a: COLIBRÍ optical upper limit
  72. EP250610a: Einstein Probe detection of an X-ray transient
  73. Fermi trigger No 771072240: Global MASTER-Net observations report
  74. GRB 250609A: Swift/BAT-GUANO localization skymap of a likely short burst
  75. GRB 250605A: Swift/UVOT Upper Limits
  76. The EP-WXT trigger 01709178283 is likely a flaring star
  77. GRB 250608A: SVOM/GRM detection of a possible magnetar X-ray burst
  78. GRB 250529A: GOTO optical counterpart candidate (GOTO25dea/AT 2025ndt)
  79. GRB 250527C: CrAO Optical Upper Limit
  80. GRB 250609A: Fermi GBM Final Real-time Localization
  81. GRB 250607A: SVOM/GRM observation of a long burst
  82. EP-WXT trigger 01709178244: confirmation of a stellar flare by BOOTES-5 & BOOTES-7
  83. The EP-WXT trigger 01709178244 is likely a flaring star
  84. GRB 250607A: Fermi GBM Final Localization
  85. EP-WXT trigger 01709178069: confirmation of a stellar flare by BOOTES-6 & BOOTES-7
  86. The EP-WXT trigger 01709178069 is likely a flaring star
  87. GRB 250605A: SVOM/VT optical upper limit
  88. GRB 250605A: Swift-XRT refined Analysis
  89. EP/WXT 01709177873: GOTO observations confirm stellar variability
  90. GRB 250605A: Enhanced Swift-XRT position
  91. Fermi GRB 250606A: Global MASTER-Net observations report
  92. GRB 250606A: Fermi GBM Final Real-time Localization
  93. Fermi Gamma-ray Burst Monitor trigger 770867684/250606080 is not a GRB
  94. Fermi Gamma-ray Burst Monitor trigger 770867684/250606080 is not a GRB
  95. GRB 250602A: GECAM detection
  96. Fermi trigger No 770867684: Global MASTER-Net observations report
  97. The EP-WXT trigger 01709177873 is likely a flaring star
  98. GRB 250605A: LT optical observations
  99. GRB 250605A: Swift detection of a burst
  100. Swift GRB250605.79: Global MASTER-Net observations report

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