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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 250610B: Swift-XRT counterpart detection
  2. GRB 250610B: SVOM/VT optical counterpart
  3. GRB 250610B: LT detection of the optical counterpart
  4. GRB 250610B: OHP/T120 optical counterpart candidate
  5. GRB 250610C: Fermi GBM Final Real-time Localization
  6. GRB 250610B: GOTO optical upper limit
  7. EP250610a: Global MASTER-Net observations report
  8. GRB 250610B : SVOM/GWAC-F60A and F50 observations
  9. GRB 250610B: SVOM detection of a long burst
  10. Fermi Gamma-ray Burst Monitor trigger 771256110/250610575 is not a GRB
  11. EP250610a: refined analysis of the EP-WXT and EP-FXT observations
  12. GRB 250610A: Fermi GBM Final Real-time Localization
  13. GRB 250605A: Swift-BAT refined analysis
  14. EP250610a: SVOM/VT optical upper limit
  15. EP250610a: REM optical/NIR observations
  16. GRB 250609A: Fermi GBM Observation
  17. GRBAlpha reentry on June 9, 2025
  18. EP250610a: Swift-XRT counterpart detection
  19. EP250610a: COLIBRÍ optical upper limit
  20. EP250610a: Einstein Probe detection of an X-ray transient
  21. Fermi trigger No 771072240: Global MASTER-Net observations report
  22. GRB 250609A: Swift/BAT-GUANO localization skymap of a likely short burst
  23. GRB 250605A: Swift/UVOT Upper Limits
  24. The EP-WXT trigger 01709178283 is likely a flaring star
  25. GRB 250608A: SVOM/GRM detection of a possible magnetar X-ray burst
  26. GRB 250529A: GOTO optical counterpart candidate (GOTO25dea/AT 2025ndt)
  27. GRB 250527C: CrAO Optical Upper Limit
  28. GRB 250609A: Fermi GBM Final Real-time Localization
  29. GRB 250607A: SVOM/GRM observation of a long burst
  30. EP-WXT trigger 01709178244: confirmation of a stellar flare by BOOTES-5 & BOOTES-7
  31. The EP-WXT trigger 01709178244 is likely a flaring star
  32. GRB 250607A: Fermi GBM Final Localization
  33. EP-WXT trigger 01709178069: confirmation of a stellar flare by BOOTES-6 & BOOTES-7
  34. The EP-WXT trigger 01709178069 is likely a flaring star
  35. GRB 250605A: SVOM/VT optical upper limit
  36. GRB 250605A: Swift-XRT refined Analysis
  37. EP/WXT 01709177873: GOTO observations confirm stellar variability
  38. GRB 250605A: Enhanced Swift-XRT position
  39. Fermi GRB 250606A: Global MASTER-Net observations report
  40. GRB 250606A: Fermi GBM Final Real-time Localization
  41. Fermi Gamma-ray Burst Monitor trigger 770867684/250606080 is not a GRB
  42. Fermi Gamma-ray Burst Monitor trigger 770867684/250606080 is not a GRB
  43. GRB 250602A: GECAM detection
  44. Fermi trigger No 770867684: Global MASTER-Net observations report
  45. The EP-WXT trigger 01709177873 is likely a flaring star
  46. GRB 250605A: LT optical observations
  47. GRB 250605A: Swift detection of a burst
  48. Swift GRB250605.79: Global MASTER-Net observations report
  49. Konus-Wind detection of GRB 250601A
  50. IPN triangulation of GRB 250404B
  51. IPN triangulation of GRB 250529A
  52. The EP-WXT trigger 01709177837 is likely a flaring star
  53. Fermi Gamma-ray Burst Monitor trigger 770470765/250601486 is not a GRB
  54. GRB 250601A: PRIME H band upper limit.
  55. GRB 250530A: SVOM/GRM analysis
  56. GRB 250601A: PRIME J band upper limit.
  57. Fermi Gamma-ray Burst Monitor trigger 770675211/250603852 is not a GRB
  58. GRB 250601A: VLT/FORS2 Optical Observation
  59. GRB 250601A: Fermi GBM Observation
  60. GRB 250602A: DDOTI Optical Follow-Up of the Fermi/LAT Localization
  61. GRB 250603A: Swift/UVOT Upper Limits
  62. GRB 250603A: Swift-XRT refined Analysis
  63. Fermi trigger No 770638414: Global MASTER-Net observations report
  64. GRB 250603A: Enhanced Swift-XRT position
  65. GRB 250603A: Swift-XRT position and confirmation of GRB nature
  66. Swift GRB250603.05: Global MASTER-Net observations report
  67. GRB 250603A: Swift detection of a burst or new Galactic transient Swift J0839.7-3916
  68. GRB 250602A: Fermi GBM Observation
  69. GRB 250602A: Fermi-LAT detection
  70. GRB 250602A: DDOTI Optical Upper Limit
  71. GRB 250530C: Swift-BAT refined analysis
  72. GRB 250521C: NOT spectroscopic observations exclude the afterglow candidate AT2025mgj
  73. GRB 250601A: EP-FXT follow-up observation and afterglow candidates
  74. GRB 250601A: Swift/XRT candidate afterglow
  75. GRB 250521C / AT2025mgj: Pan-STARRS multi-band and multi-epoch imaging and photometry
  76. GRB 250601A: Swift-XRT observations
  77. Fermi GRB 250601A: Global MASTER-Net observations report
  78. GRB 250602A: Fermi GBM Final Real-time Localization
  79. Fermi trigger No 770470765: Global MASTER-Net observations report
  80. GRB 250601A: Swift/BAT-GUANO arcminute localization of a likely short burst
  81. GRB 250601A: Swift ToO observations
  82. GRB 250530A: VLT/HAWK-I NIR counterpart fading
  83. GRB 250521C/AT2025mgj: FTW optical and NIR observations
  84. GRB 250601A: Fermi GBM Final Real-time Localization
  85. EP#01709177494: SVOM/VT optical observations
  86. Fermi GRB 250531A: Global MASTER-Net observations report
  87. GRB 250531A: Fermi GBM Final Real-time Localization
  88. EP#01709177494: Swift-XRT counterpart detection of known source
  89. GRB 250530C: BOOTES-7 optical upper limit
  90. GRB 250521C/ZTF25aarhkyn/AT2025mgj: COLIBRÍ optical observations
  91. GRB 250530C: Swift-XRT refined Analysis
  92. GRB 250530A: TNG detection of a NIR source inside the Swift/XRT error circle
  93. Swift GRB 250530C: Global MASTER-Net observations report
  94. GRB 250530C: Enhanced Swift-XRT position
  95. GRB 250530C: Swift detection of a burst
  96. GRB 250521C/AT2025mgj: NOT optical observations of the afterglow candidate
  97. GRB 250530A: EP-FXT counterpart detection
  98. GRB 250530A: SVOM/VT optical upper limit
  99. Fermi Gamma-ray Burst Monitor trigger 770296643/250530470 is not a GRB
  100. GRB 250530B: Fermi GBM Final Real-time Localization

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