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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. EP250612a / GRB 250612B: NOT optical observations of the afterglow candidate
  2. Fermi Gamma-ray Burst Monitor trigger 771547945/250613953 is not a GRB
  3. Fermi Gamma-ray Burst Monitor trigger 771541927/250613883 is not a GRB
  4. sb25061218: SVOM/COLIBRÍ (FM-GFT) optical upper limits
  5. sb25061207: SVOM/COLIBRÍ (FM-GFT) optical upper limit
  6. Fermi trigger No 771494087: Global MASTER-Net observations report
  7. sb25061218: Swift-XRT observations
  8. EP250612a: refined analysis of the EP-WXT and EP-FXT observations
  9. GRB 250610B: J band upper limit by SYSU 80cm infrared telescope
  10. sb25061207: EP-FXT follow-up observation and afterglow candidate
  11. GRB 250612B: Fermi GBM Observation
  12. EP250612a: SVOM/VT optical candidate
  13. Fermi trigger No 771424081: Global MASTER-Net observations report
  14. EP250612a: Global MASTER-Net observations report
  15. GRB 250612C: Fermi GBM Observation
  16. sb25061218: SVOM detection of a X-ray transient
  17. sb25061207: Swift-XRT observations
  18. EP250612a/GRB 250612B: JinShan optical upper limit
  19. EP 250612a: AST3-3 Yaoan Optical Observation
  20. GRB 250612C: SVOM/GRM observation an intermedium duration burst
  21. sb25061207: SVOM/VT optical counterpart
  22. GRB 250612C: BALROG localization (Fermi Trigger 771432801 / GRB 250612620)
  23. GRB 250610B: Swift-XRT refined Analysis
  24. GRB 250612C: Fermi GBM Final Real-time Localization
  25. EP250610a: Upper limit from Fermi-GBM Observations
  26. GRB 250612B (250612519/771424081): Fermi GBM Final Localization
  27. GRB 250612B: BALROG localization (Fermi Trigger 771424081 / GRB 250612519)
  28. EP250612a: Einstein Probe detection of an X-ray transient
  29. GRB 250610B: Liverpool Telescope continued monitoring
  30. GRB 250610B: MISTRAL/T193 and T120 OHP further observations
  31. sb25061207: SVOM detection of a X-ray transient
  32. EP250610a: continuous follow-up observations with EP-FXT
  33. GRB 250610B - SVOM/ECLAIRs refined analysis
  34. GRB 250612A: Swift detection of a burst or new Galactic transient Swift J1643.6-3854
  35. Swift GRB250612.04: Global MASTER-Net observations report
  36. Fermi GBM Sub-Threshold Detection of GRB 250610B
  37. GRB 250610B: Swift/UVOT Detection
  38. EP250610A: Swift/UVOT Upper limits
  39. GRB 250610B: SVOM/COLIBRÍ (FM-GFT) optical observations
  40. EP250610a: TNG NIR upper limit
  41. GRB 250610B: REM optical/NIR observations
  42. EP250610a: Liverpool Telescope optical upper limits
  43. GRB 250610B: SVOM/VT optical shallow decay
  44. GRB 250610B: additional Liverpool Telescope optical observations
  45. GRB 250610B: SVOM/GRM analysis
  46. GRB 250610B: Fermi/GBM sub-threshold detection of a possibly hard burst
  47. GRB 250610B: EP-FXT follow-up observation and afterglow counterpart
  48. Fermi Gamma-ray Burst Monitor trigger 771286888/250610932 is not a GRB
  49. GRB 250610B: Swift-XRT counterpart detection
  50. GRB 250610B: SVOM/VT optical counterpart
  51. GRB 250610B: LT detection of the optical counterpart
  52. GRB 250610B: OHP/T120 optical counterpart candidate
  53. GRB 250610C: Fermi GBM Final Real-time Localization
  54. GRB 250610B: GOTO optical upper limit
  55. EP250610a: Global MASTER-Net observations report
  56. GRB 250610B : SVOM/GWAC-F60A and F50 observations
  57. GRB 250610B: SVOM detection of a long burst
  58. Fermi Gamma-ray Burst Monitor trigger 771256110/250610575 is not a GRB
  59. EP250610a: refined analysis of the EP-WXT and EP-FXT observations
  60. GRB 250610A: Fermi GBM Final Real-time Localization
  61. GRB 250605A: Swift-BAT refined analysis
  62. EP250610a: SVOM/VT optical upper limit
  63. EP250610a: REM optical/NIR observations
  64. GRB 250609A: Fermi GBM Observation
  65. GRBAlpha reentry on June 9, 2025
  66. EP250610a: Swift-XRT counterpart detection
  67. EP250610a: COLIBRÍ optical upper limit
  68. EP250610a: Einstein Probe detection of an X-ray transient
  69. Fermi trigger No 771072240: Global MASTER-Net observations report
  70. GRB 250609A: Swift/BAT-GUANO localization skymap of a likely short burst
  71. GRB 250605A: Swift/UVOT Upper Limits
  72. The EP-WXT trigger 01709178283 is likely a flaring star
  73. GRB 250608A: SVOM/GRM detection of a possible magnetar X-ray burst
  74. GRB 250529A: GOTO optical counterpart candidate (GOTO25dea/AT 2025ndt)
  75. GRB 250527C: CrAO Optical Upper Limit
  76. GRB 250609A: Fermi GBM Final Real-time Localization
  77. GRB 250607A: SVOM/GRM observation of a long burst
  78. EP-WXT trigger 01709178244: confirmation of a stellar flare by BOOTES-5 & BOOTES-7
  79. The EP-WXT trigger 01709178244 is likely a flaring star
  80. GRB 250607A: Fermi GBM Final Localization
  81. EP-WXT trigger 01709178069: confirmation of a stellar flare by BOOTES-6 & BOOTES-7
  82. The EP-WXT trigger 01709178069 is likely a flaring star
  83. GRB 250605A: SVOM/VT optical upper limit
  84. GRB 250605A: Swift-XRT refined Analysis
  85. EP/WXT 01709177873: GOTO observations confirm stellar variability
  86. GRB 250605A: Enhanced Swift-XRT position
  87. Fermi GRB 250606A: Global MASTER-Net observations report
  88. GRB 250606A: Fermi GBM Final Real-time Localization
  89. Fermi Gamma-ray Burst Monitor trigger 770867684/250606080 is not a GRB
  90. Fermi Gamma-ray Burst Monitor trigger 770867684/250606080 is not a GRB
  91. GRB 250602A: GECAM detection
  92. Fermi trigger No 770867684: Global MASTER-Net observations report
  93. The EP-WXT trigger 01709177873 is likely a flaring star
  94. GRB 250605A: LT optical observations
  95. GRB 250605A: Swift detection of a burst
  96. Swift GRB250605.79: Global MASTER-Net observations report
  97. Konus-Wind detection of GRB 250601A
  98. IPN triangulation of GRB 250404B
  99. IPN triangulation of GRB 250529A
  100. The EP-WXT trigger 01709177837 is likely a flaring star

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