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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 250602A: Fermi-LAT detection
  2. GRB 250602A: DDOTI Optical Upper Limit
  3. GRB 250530C: Swift-BAT refined analysis
  4. GRB 250521C: NOT spectroscopic observations exclude the afterglow candidate AT2025mgj
  5. GRB 250601A: EP-FXT follow-up observation and afterglow candidates
  6. GRB 250601A: Swift/XRT candidate afterglow
  7. GRB 250521C / AT2025mgj: Pan-STARRS multi-band and multi-epoch imaging and photometry
  8. GRB 250601A: Swift-XRT observations
  9. Fermi GRB 250601A: Global MASTER-Net observations report
  10. GRB 250602A: Fermi GBM Final Real-time Localization
  11. Fermi trigger No 770470765: Global MASTER-Net observations report
  12. GRB 250601A: Swift/BAT-GUANO arcminute localization of a likely short burst
  13. GRB 250601A: Swift ToO observations
  14. GRB 250530A: VLT/HAWK-I NIR counterpart fading
  15. GRB 250521C/AT2025mgj: FTW optical and NIR observations
  16. GRB 250601A: Fermi GBM Final Real-time Localization
  17. EP#01709177494: SVOM/VT optical observations
  18. Fermi GRB 250531A: Global MASTER-Net observations report
  19. GRB 250531A: Fermi GBM Final Real-time Localization
  20. EP#01709177494: Swift-XRT counterpart detection of known source
  21. GRB 250530C: BOOTES-7 optical upper limit
  22. GRB 250521C/ZTF25aarhkyn/AT2025mgj: COLIBRÍ optical observations
  23. GRB 250530C: Swift-XRT refined Analysis
  24. GRB 250530A: TNG detection of a NIR source inside the Swift/XRT error circle
  25. Swift GRB 250530C: Global MASTER-Net observations report
  26. GRB 250530C: Enhanced Swift-XRT position
  27. GRB 250530C: Swift detection of a burst
  28. GRB 250521C/AT2025mgj: NOT optical observations of the afterglow candidate
  29. GRB 250530A: EP-FXT counterpart detection
  30. GRB 250530A: SVOM/VT optical upper limit
  31. Fermi Gamma-ray Burst Monitor trigger 770296643/250530470 is not a GRB
  32. GRB 250530B: Fermi GBM Final Real-time Localization
  33. GRB 250530A: Swift-XRT counterpart detection
  34. GRB 250530A: SVOM/COLIBRÍ (FM-GFT) optical counterpart candidate retraction and detection limit
  35. GRB 250530A: SVOM/COLIBRÍ (FM-GFT) optical counterpart candidate
  36. GRB 250530A: SVOM detection of a burst
  37. GRB 250527D: CALET Gamma-Ray Burst Monitor detection
  38. GRB 250527C: Swift/UVOT Upper Limits
  39. GRB 250527D: Swift/BAT-GUANO localization skymap of a burst
  40. EP J1350.0-8622: EP-FXT follow-up observation
  41. GRB 250529B: Fermi GBM Final Real-time Localization
  42. GRB 250527B: Swift-XRT observations
  43. EP-WXT trigger 01709177124: confirmation of a stellar flare by BOOTES-6
  44. The EP-WXT trigger 01709177124 is likely a flaring star
  45. GRB 250529A: Fermi GBM Final Real-time Localization
  46. GRB 250521C (short): Zwicky Transient Facility identification of a possible fast optical transient counterpart
  47. GRB 250520A: Swift-BAT refined analysis
  48. GRB 250527C: Swift ToO observations
  49. GRB 250527C: Swift/BAT-GUANO arcminute localization of a burst
  50. EP250526a: SVOM/VT optical upper limit
  51. GRB 250521D: SVOM/GRM analysis suggests a possible “long” duration type I burst
  52. GRB 250527B: Tiled Swift observations
  53. GRB 250520A: Gemini-South optical afterglow detection
  54. Fermi trigger No 770058372: Global MASTER-Net observations report
  55. Fermi trigger No 770047117: Global MASTER-Net observations report
  56. GRB 250527B / MAXI J1450-527 : MAXI/GSC detection
  57. GRB 250527A: Fermi GBM Final Localization
  58. EP250526a: refined analysis of the EP-WXT and EP-FXT observations
  59. GRB 250314A: CIDER NB1008 upper limit
  60. EP250526a: COLIBRÍ optical upper limits
  61. EP250526a: Global MASTER-Net observations report
  62. EP250526a: Einstein Probe detection of a fast X-ray transient
  63. EP J1350.0-8622: BOOTES-6/DPRT optical upper limit
  64. EP J1350.0-8622: Einstein Probe detection of an X-ray transient candidate
  65. EP-WXT trigger 01709176712: SVOM/C-GFT observations of blue-to-red color variation
  66. GRB 250520A: 3 GHz MeerKAT Detection
  67. GRB 250520A: 10 GHz VLA Afterglow Confirmation
  68. Fermi GRB 250523A: Global MASTER-Net observations report
  69. Fermi trigger No 769611916: Global MASTER-Net observations report
  70. EP-WXT trigger 01709176712: GOTO observations confirm stellar counterpart variability
  71. GRB 250521A: GRBAlpha detection
  72. GRB 250520A: GRBAlpha detection
  73. GRB 250523A: BALROG localization (Fermi Trigger 769703188 / GRB 250523602)
  74. GRB 250523A: Fermi GBM Final Real-time Localization
  75. The EP-WXT trigger 01709176712 is likely a flaring star
  76. GRB 250521B: SVOM/VT optical upper limit
  77. The EP-WXT trigger 01709176612: SVOM/VT optical observations
  78. The EP-WXT trigger 01709176612: refined analysis of the EP-FXT observation
  79. Fermi GRB 250522B: Global MASTER-Net observations report
  80. GRB 250521B: EP-FXT follow-up observation and afterglow candidates
  81. GRB 250522B: Fermi GBM Final Localization
  82. GRB 250521D: SVOM/VT optical observations
  83. GRB 250522A: Fermi GBM Final Real-time Localization
  84. EP#01709176612: Swift-XRT counterpart detection of flaring star
  85. Fermi GRB 250521D: Global MASTER-Net observations report
  86. Fermi trigger No 769533898: Global MASTER-Net observations report
  87. Fermi trigger No 769499303: Global MASTER-Net observations report
  88. GRB 250521D: DDOTI Optical Upper Limit
  89. The EP-WXT trigger 01709176612 is likely a flaring star
  90. GRB 250521D: GOTO detects LAST counterpart candidate prior to the GRB
  91. GRB 250521B: SVOM/COLIBRÍ (FM-GFT) optical upper limit
  92. GRB 250521D: LAST tentative optical counterpart candidate
  93. GRB 250520A: CALET Gamma-Ray Burst Monitor detection
  94. GRB 250520A: 10 GHz VLA radio source
  95. GRB 250521B: Swift ToO observations
  96. GRB 250521D: Fermi GBM Final Real-time Localization
  97. GRB 250521C: Fermi GBM Final Localization
  98. GRB 250521A: DDOTI Optical Upper Limit
  99. GRB 250521B: SVOM detection of a burst through offline search
  100. Konus-Wind detection of GRB 250520A (short/hard)

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