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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 250601A: Fermi GBM Observation
  2. GRB 250602A: DDOTI Optical Follow-Up of the Fermi/LAT Localization
  3. GRB 250603A: Swift/UVOT Upper Limits
  4. GRB 250603A: Swift-XRT refined Analysis
  5. Fermi trigger No 770638414: Global MASTER-Net observations report
  6. GRB 250603A: Enhanced Swift-XRT position
  7. GRB 250603A: Swift-XRT position and confirmation of GRB nature
  8. Swift GRB250603.05: Global MASTER-Net observations report
  9. GRB 250603A: Swift detection of a burst or new Galactic transient Swift J0839.7-3916
  10. GRB 250602A: Fermi GBM Observation
  11. GRB 250602A: Fermi-LAT detection
  12. GRB 250602A: DDOTI Optical Upper Limit
  13. GRB 250530C: Swift-BAT refined analysis
  14. GRB 250521C: NOT spectroscopic observations exclude the afterglow candidate AT2025mgj
  15. GRB 250601A: EP-FXT follow-up observation and afterglow candidates
  16. GRB 250601A: Swift/XRT candidate afterglow
  17. GRB 250521C / AT2025mgj: Pan-STARRS multi-band and multi-epoch imaging and photometry
  18. GRB 250601A: Swift-XRT observations
  19. Fermi GRB 250601A: Global MASTER-Net observations report
  20. GRB 250602A: Fermi GBM Final Real-time Localization
  21. Fermi trigger No 770470765: Global MASTER-Net observations report
  22. GRB 250601A: Swift/BAT-GUANO arcminute localization of a likely short burst
  23. GRB 250601A: Swift ToO observations
  24. GRB 250530A: VLT/HAWK-I NIR counterpart fading
  25. GRB 250521C/AT2025mgj: FTW optical and NIR observations
  26. GRB 250601A: Fermi GBM Final Real-time Localization
  27. EP#01709177494: SVOM/VT optical observations
  28. Fermi GRB 250531A: Global MASTER-Net observations report
  29. GRB 250531A: Fermi GBM Final Real-time Localization
  30. EP#01709177494: Swift-XRT counterpart detection of known source
  31. GRB 250530C: BOOTES-7 optical upper limit
  32. GRB 250521C/ZTF25aarhkyn/AT2025mgj: COLIBRÍ optical observations
  33. GRB 250530C: Swift-XRT refined Analysis
  34. GRB 250530A: TNG detection of a NIR source inside the Swift/XRT error circle
  35. Swift GRB 250530C: Global MASTER-Net observations report
  36. GRB 250530C: Enhanced Swift-XRT position
  37. GRB 250530C: Swift detection of a burst
  38. GRB 250521C/AT2025mgj: NOT optical observations of the afterglow candidate
  39. GRB 250530A: EP-FXT counterpart detection
  40. GRB 250530A: SVOM/VT optical upper limit
  41. Fermi Gamma-ray Burst Monitor trigger 770296643/250530470 is not a GRB
  42. GRB 250530B: Fermi GBM Final Real-time Localization
  43. GRB 250530A: Swift-XRT counterpart detection
  44. GRB 250530A: SVOM/COLIBRÍ (FM-GFT) optical counterpart candidate retraction and detection limit
  45. GRB 250530A: SVOM/COLIBRÍ (FM-GFT) optical counterpart candidate
  46. GRB 250530A: SVOM detection of a burst
  47. GRB 250527D: CALET Gamma-Ray Burst Monitor detection
  48. GRB 250527C: Swift/UVOT Upper Limits
  49. GRB 250527D: Swift/BAT-GUANO localization skymap of a burst
  50. EP J1350.0-8622: EP-FXT follow-up observation
  51. GRB 250529B: Fermi GBM Final Real-time Localization
  52. GRB 250527B: Swift-XRT observations
  53. EP-WXT trigger 01709177124: confirmation of a stellar flare by BOOTES-6
  54. The EP-WXT trigger 01709177124 is likely a flaring star
  55. GRB 250529A: Fermi GBM Final Real-time Localization
  56. GRB 250521C (short): Zwicky Transient Facility identification of a possible fast optical transient counterpart
  57. GRB 250520A: Swift-BAT refined analysis
  58. GRB 250527C: Swift ToO observations
  59. GRB 250527C: Swift/BAT-GUANO arcminute localization of a burst
  60. EP250526a: SVOM/VT optical upper limit
  61. GRB 250521D: SVOM/GRM analysis suggests a possible “long” duration type I burst
  62. GRB 250527B: Tiled Swift observations
  63. GRB 250520A: Gemini-South optical afterglow detection
  64. Fermi trigger No 770058372: Global MASTER-Net observations report
  65. Fermi trigger No 770047117: Global MASTER-Net observations report
  66. GRB 250527B / MAXI J1450-527 : MAXI/GSC detection
  67. GRB 250527A: Fermi GBM Final Localization
  68. EP250526a: refined analysis of the EP-WXT and EP-FXT observations
  69. GRB 250314A: CIDER NB1008 upper limit
  70. EP250526a: COLIBRÍ optical upper limits
  71. EP250526a: Global MASTER-Net observations report
  72. EP250526a: Einstein Probe detection of a fast X-ray transient
  73. EP J1350.0-8622: BOOTES-6/DPRT optical upper limit
  74. EP J1350.0-8622: Einstein Probe detection of an X-ray transient candidate
  75. EP-WXT trigger 01709176712: SVOM/C-GFT observations of blue-to-red color variation
  76. GRB 250520A: 3 GHz MeerKAT Detection
  77. GRB 250520A: 10 GHz VLA Afterglow Confirmation
  78. Fermi GRB 250523A: Global MASTER-Net observations report
  79. Fermi trigger No 769611916: Global MASTER-Net observations report
  80. EP-WXT trigger 01709176712: GOTO observations confirm stellar counterpart variability
  81. GRB 250521A: GRBAlpha detection
  82. GRB 250520A: GRBAlpha detection
  83. GRB 250523A: BALROG localization (Fermi Trigger 769703188 / GRB 250523602)
  84. GRB 250523A: Fermi GBM Final Real-time Localization
  85. The EP-WXT trigger 01709176712 is likely a flaring star
  86. GRB 250521B: SVOM/VT optical upper limit
  87. The EP-WXT trigger 01709176612: SVOM/VT optical observations
  88. The EP-WXT trigger 01709176612: refined analysis of the EP-FXT observation
  89. Fermi GRB 250522B: Global MASTER-Net observations report
  90. GRB 250521B: EP-FXT follow-up observation and afterglow candidates
  91. GRB 250522B: Fermi GBM Final Localization
  92. GRB 250521D: SVOM/VT optical observations
  93. GRB 250522A: Fermi GBM Final Real-time Localization
  94. EP#01709176612: Swift-XRT counterpart detection of flaring star
  95. Fermi GRB 250521D: Global MASTER-Net observations report
  96. Fermi trigger No 769533898: Global MASTER-Net observations report
  97. Fermi trigger No 769499303: Global MASTER-Net observations report
  98. GRB 250521D: DDOTI Optical Upper Limit
  99. The EP-WXT trigger 01709176612 is likely a flaring star
  100. GRB 250521D: GOTO detects LAST counterpart candidate prior to the GRB

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