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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. EP/WXT 01709177873: GOTO observations confirm stellar variability
  2. GRB 250605A: Enhanced Swift-XRT position
  3. Fermi GRB 250606A: Global MASTER-Net observations report
  4. GRB 250606A: Fermi GBM Final Real-time Localization
  5. Fermi Gamma-ray Burst Monitor trigger 770867684/250606080 is not a GRB
  6. Fermi Gamma-ray Burst Monitor trigger 770867684/250606080 is not a GRB
  7. GRB 250602A: GECAM detection
  8. Fermi trigger No 770867684: Global MASTER-Net observations report
  9. The EP-WXT trigger 01709177873 is likely a flaring star
  10. GRB 250605A: LT optical observations
  11. GRB 250605A: Swift detection of a burst
  12. Swift GRB250605.79: Global MASTER-Net observations report
  13. Konus-Wind detection of GRB 250601A
  14. IPN triangulation of GRB 250404B
  15. IPN triangulation of GRB 250529A
  16. The EP-WXT trigger 01709177837 is likely a flaring star
  17. Fermi Gamma-ray Burst Monitor trigger 770470765/250601486 is not a GRB
  18. GRB 250601A: PRIME H band upper limit.
  19. GRB 250530A: SVOM/GRM analysis
  20. GRB 250601A: PRIME J band upper limit.
  21. Fermi Gamma-ray Burst Monitor trigger 770675211/250603852 is not a GRB
  22. GRB 250601A: VLT/FORS2 Optical Observation
  23. GRB 250601A: Fermi GBM Observation
  24. GRB 250602A: DDOTI Optical Follow-Up of the Fermi/LAT Localization
  25. GRB 250603A: Swift/UVOT Upper Limits
  26. GRB 250603A: Swift-XRT refined Analysis
  27. Fermi trigger No 770638414: Global MASTER-Net observations report
  28. GRB 250603A: Enhanced Swift-XRT position
  29. GRB 250603A: Swift-XRT position and confirmation of GRB nature
  30. Swift GRB250603.05: Global MASTER-Net observations report
  31. GRB 250603A: Swift detection of a burst or new Galactic transient Swift J0839.7-3916
  32. GRB 250602A: Fermi GBM Observation
  33. GRB 250602A: Fermi-LAT detection
  34. GRB 250602A: DDOTI Optical Upper Limit
  35. GRB 250530C: Swift-BAT refined analysis
  36. GRB 250521C: NOT spectroscopic observations exclude the afterglow candidate AT2025mgj
  37. GRB 250601A: EP-FXT follow-up observation and afterglow candidates
  38. GRB 250601A: Swift/XRT candidate afterglow
  39. GRB 250521C / AT2025mgj: Pan-STARRS multi-band and multi-epoch imaging and photometry
  40. GRB 250601A: Swift-XRT observations
  41. Fermi GRB 250601A: Global MASTER-Net observations report
  42. GRB 250602A: Fermi GBM Final Real-time Localization
  43. Fermi trigger No 770470765: Global MASTER-Net observations report
  44. GRB 250601A: Swift/BAT-GUANO arcminute localization of a likely short burst
  45. GRB 250601A: Swift ToO observations
  46. GRB 250530A: VLT/HAWK-I NIR counterpart fading
  47. GRB 250521C/AT2025mgj: FTW optical and NIR observations
  48. GRB 250601A: Fermi GBM Final Real-time Localization
  49. EP#01709177494: SVOM/VT optical observations
  50. Fermi GRB 250531A: Global MASTER-Net observations report
  51. GRB 250531A: Fermi GBM Final Real-time Localization
  52. EP#01709177494: Swift-XRT counterpart detection of known source
  53. GRB 250530C: BOOTES-7 optical upper limit
  54. GRB 250521C/ZTF25aarhkyn/AT2025mgj: COLIBRÍ optical observations
  55. GRB 250530C: Swift-XRT refined Analysis
  56. GRB 250530A: TNG detection of a NIR source inside the Swift/XRT error circle
  57. Swift GRB 250530C: Global MASTER-Net observations report
  58. GRB 250530C: Enhanced Swift-XRT position
  59. GRB 250530C: Swift detection of a burst
  60. GRB 250521C/AT2025mgj: NOT optical observations of the afterglow candidate
  61. GRB 250530A: EP-FXT counterpart detection
  62. GRB 250530A: SVOM/VT optical upper limit
  63. Fermi Gamma-ray Burst Monitor trigger 770296643/250530470 is not a GRB
  64. GRB 250530B: Fermi GBM Final Real-time Localization
  65. GRB 250530A: Swift-XRT counterpart detection
  66. GRB 250530A: SVOM/COLIBRÍ (FM-GFT) optical counterpart candidate retraction and detection limit
  67. GRB 250530A: SVOM/COLIBRÍ (FM-GFT) optical counterpart candidate
  68. GRB 250530A: SVOM detection of a burst
  69. GRB 250527D: CALET Gamma-Ray Burst Monitor detection
  70. GRB 250527C: Swift/UVOT Upper Limits
  71. GRB 250527D: Swift/BAT-GUANO localization skymap of a burst
  72. EP J1350.0-8622: EP-FXT follow-up observation
  73. GRB 250529B: Fermi GBM Final Real-time Localization
  74. GRB 250527B: Swift-XRT observations
  75. EP-WXT trigger 01709177124: confirmation of a stellar flare by BOOTES-6
  76. The EP-WXT trigger 01709177124 is likely a flaring star
  77. GRB 250529A: Fermi GBM Final Real-time Localization
  78. GRB 250521C (short): Zwicky Transient Facility identification of a possible fast optical transient counterpart
  79. GRB 250520A: Swift-BAT refined analysis
  80. GRB 250527C: Swift ToO observations
  81. GRB 250527C: Swift/BAT-GUANO arcminute localization of a burst
  82. EP250526a: SVOM/VT optical upper limit
  83. GRB 250521D: SVOM/GRM analysis suggests a possible “long” duration type I burst
  84. GRB 250527B: Tiled Swift observations
  85. GRB 250520A: Gemini-South optical afterglow detection
  86. Fermi trigger No 770058372: Global MASTER-Net observations report
  87. Fermi trigger No 770047117: Global MASTER-Net observations report
  88. GRB 250527B / MAXI J1450-527 : MAXI/GSC detection
  89. GRB 250527A: Fermi GBM Final Localization
  90. EP250526a: refined analysis of the EP-WXT and EP-FXT observations
  91. GRB 250314A: CIDER NB1008 upper limit
  92. EP250526a: COLIBRÍ optical upper limits
  93. EP250526a: Global MASTER-Net observations report
  94. EP250526a: Einstein Probe detection of a fast X-ray transient
  95. EP J1350.0-8622: BOOTES-6/DPRT optical upper limit
  96. EP J1350.0-8622: Einstein Probe detection of an X-ray transient candidate
  97. EP-WXT trigger 01709176712: SVOM/C-GFT observations of blue-to-red color variation
  98. GRB 250520A: 3 GHz MeerKAT Detection
  99. GRB 250520A: 10 GHz VLA Afterglow Confirmation
  100. Fermi GRB 250523A: Global MASTER-Net observations report

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