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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"

39166 results found.

  1. GRB 250602A: DDOTI Optical Follow-Up of the Fermi/LAT Localization
  2. GRB 250603A: Swift/UVOT Upper Limits
  3. GRB 250603A: Swift-XRT refined Analysis
  4. Fermi trigger No 770638414: Global MASTER-Net observations report
  5. GRB 250603A: Enhanced Swift-XRT position
  6. GRB 250603A: Swift-XRT position and confirmation of GRB nature
  7. Swift GRB250603.05: Global MASTER-Net observations report
  8. GRB 250603A: Swift detection of a burst or new Galactic transient Swift J0839.7-3916
  9. GRB 250602A: Fermi GBM Observation
  10. GRB 250602A: Fermi-LAT detection
  11. GRB 250602A: DDOTI Optical Upper Limit
  12. GRB 250530C: Swift-BAT refined analysis
  13. GRB 250521C: NOT spectroscopic observations exclude the afterglow candidate AT2025mgj
  14. GRB 250601A: EP-FXT follow-up observation and afterglow candidates
  15. GRB 250601A: Swift/XRT candidate afterglow
  16. GRB 250521C / AT2025mgj: Pan-STARRS multi-band and multi-epoch imaging and photometry
  17. GRB 250601A: Swift-XRT observations
  18. Fermi GRB 250601A: Global MASTER-Net observations report
  19. GRB 250602A: Fermi GBM Final Real-time Localization
  20. Fermi trigger No 770470765: Global MASTER-Net observations report
  21. GRB 250601A: Swift/BAT-GUANO arcminute localization of a likely short burst
  22. GRB 250601A: Swift ToO observations
  23. GRB 250530A: VLT/HAWK-I NIR counterpart fading
  24. GRB 250521C/AT2025mgj: FTW optical and NIR observations
  25. GRB 250601A: Fermi GBM Final Real-time Localization
  26. Fermi GRB 250531A: Global MASTER-Net observations report
  27. GRB 250531A: Fermi GBM Final Real-time Localization
  28. GRB 250530C: BOOTES-7 optical upper limit
  29. GRB 250521C/ZTF25aarhkyn/AT2025mgj: COLIBRÍ optical observations
  30. GRB 250530C: Swift-XRT refined Analysis
  31. GRB 250530A: TNG detection of a NIR source inside the Swift/XRT error circle
  32. Swift GRB 250530C: Global MASTER-Net observations report
  33. GRB 250530C: Enhanced Swift-XRT position
  34. GRB 250530C: Swift detection of a burst
  35. GRB 250521C/AT2025mgj: NOT optical observations of the afterglow candidate
  36. GRB 250530A: EP-FXT counterpart detection
  37. GRB 250530A: SVOM/VT optical upper limit
  38. Fermi Gamma-ray Burst Monitor trigger 770296643/250530470 is not a GRB
  39. GRB 250530B: Fermi GBM Final Real-time Localization
  40. GRB 250530A: Swift-XRT counterpart detection
  41. GRB 250530A: SVOM/COLIBRÍ (FM-GFT) optical counterpart candidate retraction and detection limit
  42. GRB 250530A: SVOM/COLIBRÍ (FM-GFT) optical counterpart candidate
  43. GRB 250530A: SVOM detection of a burst
  44. GRB 250527D: CALET Gamma-Ray Burst Monitor detection
  45. GRB 250527C: Swift/UVOT Upper Limits
  46. GRB 250527D: Swift/BAT-GUANO localization skymap of a burst
  47. GRB 250529B: Fermi GBM Final Real-time Localization
  48. GRB 250527B: Swift-XRT observations
  49. GRB 250529A: Fermi GBM Final Real-time Localization
  50. GRB 250521C (short): Zwicky Transient Facility identification of a possible fast optical transient counterpart
  51. GRB 250520A: Swift-BAT refined analysis
  52. GRB 250527C: Swift ToO observations
  53. GRB 250527C: Swift/BAT-GUANO arcminute localization of a burst
  54. GRB 250521D: SVOM/GRM analysis suggests a possible “long” duration type I burst
  55. GRB 250527B: Tiled Swift observations
  56. GRB 250520A: Gemini-South optical afterglow detection
  57. Fermi trigger No 770058372: Global MASTER-Net observations report
  58. Fermi trigger No 770047117: Global MASTER-Net observations report
  59. GRB 250527B / MAXI J1450-527 : MAXI/GSC detection
  60. GRB 250527A: Fermi GBM Final Localization
  61. GRB 250314A: CIDER NB1008 upper limit
  62. EP250526a: COLIBRÍ optical upper limits
  63. EP250526a: Global MASTER-Net observations report
  64. EP-WXT trigger 01709176712: SVOM/C-GFT observations of blue-to-red color variation
  65. GRB 250520A: 3 GHz MeerKAT Detection
  66. GRB 250520A: 10 GHz VLA Afterglow Confirmation
  67. Fermi GRB 250523A: Global MASTER-Net observations report
  68. Fermi trigger No 769611916: Global MASTER-Net observations report
  69. GRB 250521A: GRBAlpha detection
  70. GRB 250520A: GRBAlpha detection
  71. GRB 250523A: BALROG localization (Fermi Trigger 769703188 / GRB 250523602)
  72. GRB 250523A: Fermi GBM Final Real-time Localization
  73. GRB 250521B: SVOM/VT optical upper limit
  74. Fermi GRB 250522B: Global MASTER-Net observations report
  75. GRB 250521B: EP-FXT follow-up observation and afterglow candidates
  76. GRB 250522B: Fermi GBM Final Localization
  77. GRB 250521D: SVOM/VT optical observations
  78. GRB 250522A: Fermi GBM Final Real-time Localization
  79. Fermi GRB 250521D: Global MASTER-Net observations report
  80. Fermi trigger No 769533898: Global MASTER-Net observations report
  81. Fermi trigger No 769499303: Global MASTER-Net observations report
  82. GRB 250521D: DDOTI Optical Upper Limit
  83. GRB 250521D: GOTO detects LAST counterpart candidate prior to the GRB
  84. GRB 250521B: SVOM/COLIBRÍ (FM-GFT) optical upper limit
  85. GRB 250521D: LAST tentative optical counterpart candidate
  86. GRB 250520A: CALET Gamma-Ray Burst Monitor detection
  87. GRB 250520A: 10 GHz VLA radio source
  88. GRB 250521B: Swift ToO observations
  89. GRB 250521D: Fermi GBM Final Real-time Localization
  90. GRB 250521C: Fermi GBM Final Localization
  91. GRB 250521A: DDOTI Optical Upper Limit
  92. GRB 250521B: SVOM detection of a burst through offline search
  93. Konus-Wind detection of GRB 250520A (short/hard)
  94. GRB 250520A: VLT/FORS2 Optical Observation
  95. GRB 250502A: Tautenburg observations
  96. GRB 250520A: Swift/UVOT Upper Limits
  97. GRB 250521A: Fermi GBM Final Real-time Localization
  98. Konus-Wind detection of GRB 250516B
  99. IPN triangulation of GRB 250516B
  100. GRB 250520A: J-band observations with WINTER

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