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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 250615A: COLIBRÍ optical upper limit
  2. GRB 250615A: DDOTI Optical Upper Limit
  3. GRB 250615A: Swift/UVOT Upper Limits
  4. Konus-Wind detection of GRB 250612C (short/hard with extended emission)
  5. GRB 250615A: Swift-XRT refined Analysis
  6. sb25061207/SVOM: T120 OHP optical upper limit
  7. EP250615a/GRB 250615A: EP-WXT detection of a fast X-ray transient
  8. Fermi trigger No 771752663: Global MASTER-Net observations report
  9. EP-WXT trigger 01709178875: confirmation of a stellar flare by BOOTES-6
  10. The EP-WXT trigger 01709178875 is likely a flaring star
  11. GRB 250615A: Enhanced Swift-XRT position
  12. Fermi Gamma-ray Burst Monitor trigger 771718064/250615922 is not a GRB
  13. GRB 250615A: Prompt enhanced Swift-XRT position
  14. GRB 250615A: Swift detection of a burst
  15. Swift GRB250615.93: Global MASTER-Net observations report
  16. Fermi trigger No 771718064: Global MASTER-Net observations report
  17. Fermi Gamma-ray Burst Monitor trigger 771704505/250615765 is not a GRB
  18. GRID detection of GRB 250612C
  19. sb25061207: Mephisto optical upper limits
  20. IceCube alert 141029_8144692 retraction
  21. Fermi Gamma-ray Burst Monitor trigger 771596290/250614513 is not a GRB
  22. GRB 250614A: Fermi GBM Final Real-time Localization
  23. EP250612a / GRB 250612B: NOT optical observations of the afterglow candidate
  24. Fermi Gamma-ray Burst Monitor trigger 771547945/250613953 is not a GRB
  25. Fermi Gamma-ray Burst Monitor trigger 771541927/250613883 is not a GRB
  26. sb25061218: SVOM/COLIBRÍ (FM-GFT) optical upper limits
  27. sb25061207: SVOM/COLIBRÍ (FM-GFT) optical upper limit
  28. Fermi trigger No 771494087: Global MASTER-Net observations report
  29. sb25061218: Swift-XRT observations
  30. EP250612a: refined analysis of the EP-WXT and EP-FXT observations
  31. GRB 250610B: J band upper limit by SYSU 80cm infrared telescope
  32. sb25061207: EP-FXT follow-up observation and afterglow candidate
  33. GRB 250612B: Fermi GBM Observation
  34. EP250612a: SVOM/VT optical candidate
  35. Fermi trigger No 771424081: Global MASTER-Net observations report
  36. EP250612a: Global MASTER-Net observations report
  37. GRB 250612C: Fermi GBM Observation
  38. sb25061218: SVOM detection of a X-ray transient
  39. sb25061207: Swift-XRT observations
  40. EP250612a/GRB 250612B: JinShan optical upper limit
  41. EP 250612a: AST3-3 Yaoan Optical Observation
  42. GRB 250612C: SVOM/GRM observation an intermedium duration burst
  43. sb25061207: SVOM/VT optical counterpart
  44. GRB 250612C: BALROG localization (Fermi Trigger 771432801 / GRB 250612620)
  45. GRB 250610B: Swift-XRT refined Analysis
  46. GRB 250612C: Fermi GBM Final Real-time Localization
  47. EP250610a: Upper limit from Fermi-GBM Observations
  48. GRB 250612B (250612519/771424081): Fermi GBM Final Localization
  49. GRB 250612B: BALROG localization (Fermi Trigger 771424081 / GRB 250612519)
  50. EP250612a: Einstein Probe detection of an X-ray transient
  51. GRB 250610B: Liverpool Telescope continued monitoring
  52. GRB 250610B: MISTRAL/T193 and T120 OHP further observations
  53. sb25061207: SVOM detection of a X-ray transient
  54. EP250610a: continuous follow-up observations with EP-FXT
  55. GRB 250610B - SVOM/ECLAIRs refined analysis
  56. GRB 250612A: Swift detection of a burst or new Galactic transient Swift J1643.6-3854
  57. Swift GRB250612.04: Global MASTER-Net observations report
  58. Fermi GBM Sub-Threshold Detection of GRB 250610B
  59. GRB 250610B: Swift/UVOT Detection
  60. EP250610A: Swift/UVOT Upper limits
  61. GRB 250610B: SVOM/COLIBRÍ (FM-GFT) optical observations
  62. EP250610a: TNG NIR upper limit
  63. GRB 250610B: REM optical/NIR observations
  64. EP250610a: Liverpool Telescope optical upper limits
  65. GRB 250610B: SVOM/VT optical shallow decay
  66. GRB 250610B: additional Liverpool Telescope optical observations
  67. GRB 250610B: SVOM/GRM analysis
  68. GRB 250610B: Fermi/GBM sub-threshold detection of a possibly hard burst
  69. GRB 250610B: EP-FXT follow-up observation and afterglow counterpart
  70. Fermi Gamma-ray Burst Monitor trigger 771286888/250610932 is not a GRB
  71. GRB 250610B: Swift-XRT counterpart detection
  72. GRB 250610B: SVOM/VT optical counterpart
  73. GRB 250610B: LT detection of the optical counterpart
  74. GRB 250610B: OHP/T120 optical counterpart candidate
  75. GRB 250610C: Fermi GBM Final Real-time Localization
  76. GRB 250610B: GOTO optical upper limit
  77. EP250610a: Global MASTER-Net observations report
  78. GRB 250610B : SVOM/GWAC-F60A and F50 observations
  79. GRB 250610B: SVOM detection of a long burst
  80. Fermi Gamma-ray Burst Monitor trigger 771256110/250610575 is not a GRB
  81. EP250610a: refined analysis of the EP-WXT and EP-FXT observations
  82. GRB 250610A: Fermi GBM Final Real-time Localization
  83. GRB 250605A: Swift-BAT refined analysis
  84. EP250610a: SVOM/VT optical upper limit
  85. EP250610a: REM optical/NIR observations
  86. GRB 250609A: Fermi GBM Observation
  87. GRBAlpha reentry on June 9, 2025
  88. EP250610a: Swift-XRT counterpart detection
  89. EP250610a: COLIBRÍ optical upper limit
  90. EP250610a: Einstein Probe detection of an X-ray transient
  91. Fermi trigger No 771072240: Global MASTER-Net observations report
  92. GRB 250609A: Swift/BAT-GUANO localization skymap of a likely short burst
  93. GRB 250605A: Swift/UVOT Upper Limits
  94. The EP-WXT trigger 01709178283 is likely a flaring star
  95. GRB 250608A: SVOM/GRM detection of a possible magnetar X-ray burst
  96. GRB 250529A: GOTO optical counterpart candidate (GOTO25dea/AT 2025ndt)
  97. GRB 250527C: CrAO Optical Upper Limit
  98. GRB 250609A: Fermi GBM Final Real-time Localization
  99. GRB 250607A: SVOM/GRM observation of a long burst
  100. EP-WXT trigger 01709178244: confirmation of a stellar flare by BOOTES-5 & BOOTES-7

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