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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. Fermi Gamma-ray Burst Monitor trigger 770867684/250606080 is not a GRB
  2. GRB 250602A: GECAM detection
  3. Fermi trigger No 770867684: Global MASTER-Net observations report
  4. The EP-WXT trigger 01709177873 is likely a flaring star
  5. GRB 250605A: LT optical observations
  6. GRB 250605A: Swift detection of a burst
  7. Swift GRB250605.79: Global MASTER-Net observations report
  8. Konus-Wind detection of GRB 250601A
  9. IPN triangulation of GRB 250404B
  10. IPN triangulation of GRB 250529A
  11. The EP-WXT trigger 01709177837 is likely a flaring star
  12. Fermi Gamma-ray Burst Monitor trigger 770470765/250601486 is not a GRB
  13. GRB 250601A: PRIME H band upper limit.
  14. GRB 250530A: SVOM/GRM analysis
  15. GRB 250601A: PRIME J band upper limit.
  16. Fermi Gamma-ray Burst Monitor trigger 770675211/250603852 is not a GRB
  17. GRB 250601A: VLT/FORS2 Optical Observation
  18. GRB 250601A: Fermi GBM Observation
  19. GRB 250602A: DDOTI Optical Follow-Up of the Fermi/LAT Localization
  20. GRB 250603A: Swift/UVOT Upper Limits
  21. GRB 250603A: Swift-XRT refined Analysis
  22. Fermi trigger No 770638414: Global MASTER-Net observations report
  23. GRB 250603A: Enhanced Swift-XRT position
  24. GRB 250603A: Swift-XRT position and confirmation of GRB nature
  25. Swift GRB250603.05: Global MASTER-Net observations report
  26. GRB 250603A: Swift detection of a burst or new Galactic transient Swift J0839.7-3916
  27. GRB 250602A: Fermi GBM Observation
  28. GRB 250602A: Fermi-LAT detection
  29. GRB 250602A: DDOTI Optical Upper Limit
  30. GRB 250530C: Swift-BAT refined analysis
  31. GRB 250521C: NOT spectroscopic observations exclude the afterglow candidate AT2025mgj
  32. GRB 250601A: EP-FXT follow-up observation and afterglow candidates
  33. GRB 250601A: Swift/XRT candidate afterglow
  34. GRB 250521C / AT2025mgj: Pan-STARRS multi-band and multi-epoch imaging and photometry
  35. GRB 250601A: Swift-XRT observations
  36. Fermi GRB 250601A: Global MASTER-Net observations report
  37. GRB 250602A: Fermi GBM Final Real-time Localization
  38. Fermi trigger No 770470765: Global MASTER-Net observations report
  39. GRB 250601A: Swift/BAT-GUANO arcminute localization of a likely short burst
  40. GRB 250601A: Swift ToO observations
  41. GRB 250530A: VLT/HAWK-I NIR counterpart fading
  42. GRB 250521C/AT2025mgj: FTW optical and NIR observations
  43. GRB 250601A: Fermi GBM Final Real-time Localization
  44. EP#01709177494: SVOM/VT optical observations
  45. Fermi GRB 250531A: Global MASTER-Net observations report
  46. GRB 250531A: Fermi GBM Final Real-time Localization
  47. EP#01709177494: Swift-XRT counterpart detection of known source
  48. GRB 250530C: BOOTES-7 optical upper limit
  49. GRB 250521C/ZTF25aarhkyn/AT2025mgj: COLIBRÍ optical observations
  50. GRB 250530C: Swift-XRT refined Analysis
  51. GRB 250530A: TNG detection of a NIR source inside the Swift/XRT error circle
  52. Swift GRB 250530C: Global MASTER-Net observations report
  53. GRB 250530C: Enhanced Swift-XRT position
  54. GRB 250530C: Swift detection of a burst
  55. GRB 250521C/AT2025mgj: NOT optical observations of the afterglow candidate
  56. GRB 250530A: EP-FXT counterpart detection
  57. GRB 250530A: SVOM/VT optical upper limit
  58. Fermi Gamma-ray Burst Monitor trigger 770296643/250530470 is not a GRB
  59. GRB 250530B: Fermi GBM Final Real-time Localization
  60. GRB 250530A: Swift-XRT counterpart detection
  61. GRB 250530A: SVOM/COLIBRÍ (FM-GFT) optical counterpart candidate retraction and detection limit
  62. GRB 250530A: SVOM/COLIBRÍ (FM-GFT) optical counterpart candidate
  63. GRB 250530A: SVOM detection of a burst
  64. GRB 250527D: CALET Gamma-Ray Burst Monitor detection
  65. GRB 250527C: Swift/UVOT Upper Limits
  66. GRB 250527D: Swift/BAT-GUANO localization skymap of a burst
  67. EP J1350.0-8622: EP-FXT follow-up observation
  68. GRB 250529B: Fermi GBM Final Real-time Localization
  69. GRB 250527B: Swift-XRT observations
  70. EP-WXT trigger 01709177124: confirmation of a stellar flare by BOOTES-6
  71. The EP-WXT trigger 01709177124 is likely a flaring star
  72. GRB 250529A: Fermi GBM Final Real-time Localization
  73. GRB 250521C (short): Zwicky Transient Facility identification of a possible fast optical transient counterpart
  74. GRB 250520A: Swift-BAT refined analysis
  75. GRB 250527C: Swift ToO observations
  76. GRB 250527C: Swift/BAT-GUANO arcminute localization of a burst
  77. EP250526a: SVOM/VT optical upper limit
  78. GRB 250521D: SVOM/GRM analysis suggests a possible “long” duration type I burst
  79. GRB 250527B: Tiled Swift observations
  80. GRB 250520A: Gemini-South optical afterglow detection
  81. Fermi trigger No 770058372: Global MASTER-Net observations report
  82. Fermi trigger No 770047117: Global MASTER-Net observations report
  83. GRB 250527B / MAXI J1450-527 : MAXI/GSC detection
  84. GRB 250527A: Fermi GBM Final Localization
  85. EP250526a: refined analysis of the EP-WXT and EP-FXT observations
  86. GRB 250314A: CIDER NB1008 upper limit
  87. EP250526a: COLIBRÍ optical upper limits
  88. EP250526a: Global MASTER-Net observations report
  89. EP250526a: Einstein Probe detection of a fast X-ray transient
  90. EP J1350.0-8622: BOOTES-6/DPRT optical upper limit
  91. EP J1350.0-8622: Einstein Probe detection of an X-ray transient candidate
  92. EP-WXT trigger 01709176712: SVOM/C-GFT observations of blue-to-red color variation
  93. GRB 250520A: 3 GHz MeerKAT Detection
  94. GRB 250520A: 10 GHz VLA Afterglow Confirmation
  95. Fermi GRB 250523A: Global MASTER-Net observations report
  96. Fermi trigger No 769611916: Global MASTER-Net observations report
  97. EP-WXT trigger 01709176712: GOTO observations confirm stellar counterpart variability
  98. GRB 250521A: GRBAlpha detection
  99. GRB 250520A: GRBAlpha detection
  100. GRB 250523A: BALROG localization (Fermi Trigger 769703188 / GRB 250523602)

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