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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"

32419 results found.

  1. GRB 250606A: Fermi GBM Final Real-time Localization
  2. Fermi Gamma-ray Burst Monitor trigger 770867684/250606080 is not a GRB
  3. Fermi Gamma-ray Burst Monitor trigger 770867684/250606080 is not a GRB
  4. GRB 250602A: GECAM detection
  5. GRB 250605A: LT optical observations
  6. GRB 250605A: Swift detection of a burst
  7. Konus-Wind detection of GRB 250601A
  8. IPN triangulation of GRB 250404B
  9. IPN triangulation of GRB 250529A
  10. Fermi Gamma-ray Burst Monitor trigger 770470765/250601486 is not a GRB
  11. GRB 250601A: PRIME H band upper limit.
  12. GRB 250530A: SVOM/GRM analysis
  13. GRB 250601A: PRIME J band upper limit.
  14. Fermi Gamma-ray Burst Monitor trigger 770675211/250603852 is not a GRB
  15. GRB 250601A: VLT/FORS2 Optical Observation
  16. GRB 250601A: Fermi GBM Observation
  17. GRB 250602A: DDOTI Optical Follow-Up of the Fermi/LAT Localization
  18. GRB 250603A: Swift/UVOT Upper Limits
  19. GRB 250603A: Swift-XRT refined Analysis
  20. GRB 250603A: Enhanced Swift-XRT position
  21. GRB 250603A: Swift-XRT position and confirmation of GRB nature
  22. GRB 250603A: Swift detection of a burst or new Galactic transient Swift J0839.7-3916
  23. GRB 250602A: Fermi GBM Observation
  24. GRB 250602A: Fermi-LAT detection
  25. GRB 250602A: DDOTI Optical Upper Limit
  26. GRB 250530C: Swift-BAT refined analysis
  27. GRB 250521C: NOT spectroscopic observations exclude the afterglow candidate AT2025mgj
  28. GRB 250601A: EP-FXT follow-up observation and afterglow candidates
  29. GRB 250601A: Swift/XRT candidate afterglow
  30. GRB 250521C / AT2025mgj: Pan-STARRS multi-band and multi-epoch imaging and photometry
  31. GRB 250601A: Swift-XRT observations
  32. Fermi GRB 250601A: Global MASTER-Net observations report
  33. GRB 250602A: Fermi GBM Final Real-time Localization
  34. GRB 250601A: Swift/BAT-GUANO arcminute localization of a likely short burst
  35. GRB 250601A: Swift ToO observations
  36. GRB 250530A: VLT/HAWK-I NIR counterpart fading
  37. GRB 250521C/AT2025mgj: FTW optical and NIR observations
  38. GRB 250601A: Fermi GBM Final Real-time Localization
  39. Fermi GRB 250531A: Global MASTER-Net observations report
  40. GRB 250531A: Fermi GBM Final Real-time Localization
  41. GRB 250530C: BOOTES-7 optical upper limit
  42. GRB 250521C/ZTF25aarhkyn/AT2025mgj: COLIBRÍ optical observations
  43. GRB 250530C: Swift-XRT refined Analysis
  44. GRB 250530A: TNG detection of a NIR source inside the Swift/XRT error circle
  45. Swift GRB 250530C: Global MASTER-Net observations report
  46. GRB 250530C: Enhanced Swift-XRT position
  47. GRB 250530C: Swift detection of a burst
  48. GRB 250521C/AT2025mgj: NOT optical observations of the afterglow candidate
  49. GRB 250530A: EP-FXT counterpart detection
  50. GRB 250530A: SVOM/VT optical upper limit
  51. Fermi Gamma-ray Burst Monitor trigger 770296643/250530470 is not a GRB
  52. GRB 250530B: Fermi GBM Final Real-time Localization
  53. GRB 250530A: Swift-XRT counterpart detection
  54. GRB 250530A: SVOM/COLIBRÍ (FM-GFT) optical counterpart candidate retraction and detection limit
  55. GRB 250530A: SVOM/COLIBRÍ (FM-GFT) optical counterpart candidate
  56. GRB 250530A: SVOM detection of a burst
  57. GRB 250527D: CALET Gamma-Ray Burst Monitor detection
  58. GRB 250527C: Swift/UVOT Upper Limits
  59. GRB 250527D: Swift/BAT-GUANO localization skymap of a burst
  60. GRB 250529B: Fermi GBM Final Real-time Localization
  61. GRB 250527B: Swift-XRT observations
  62. GRB 250529A: Fermi GBM Final Real-time Localization
  63. GRB 250521C (short): Zwicky Transient Facility identification of a possible fast optical transient counterpart
  64. GRB 250520A: Swift-BAT refined analysis
  65. GRB 250527C: Swift ToO observations
  66. GRB 250527C: Swift/BAT-GUANO arcminute localization of a burst
  67. GRB 250521D: SVOM/GRM analysis suggests a possible “long” duration type I burst
  68. GRB 250527B: Tiled Swift observations
  69. GRB 250520A: Gemini-South optical afterglow detection
  70. GRB 250527B / MAXI J1450-527 : MAXI/GSC detection
  71. GRB 250527A: Fermi GBM Final Localization
  72. GRB 250314A: CIDER NB1008 upper limit
  73. GRB 250520A: 3 GHz MeerKAT Detection
  74. GRB 250520A: 10 GHz VLA Afterglow Confirmation
  75. Fermi GRB 250523A: Global MASTER-Net observations report
  76. GRB 250521A: GRBAlpha detection
  77. GRB 250520A: GRBAlpha detection
  78. GRB 250523A: BALROG localization (Fermi Trigger 769703188 / GRB 250523602)
  79. GRB 250523A: Fermi GBM Final Real-time Localization
  80. GRB 250521B: SVOM/VT optical upper limit
  81. Fermi GRB 250522B: Global MASTER-Net observations report
  82. GRB 250521B: EP-FXT follow-up observation and afterglow candidates
  83. GRB 250522B: Fermi GBM Final Localization
  84. GRB 250521D: SVOM/VT optical observations
  85. GRB 250522A: Fermi GBM Final Real-time Localization
  86. Fermi GRB 250521D: Global MASTER-Net observations report
  87. GRB 250521D: DDOTI Optical Upper Limit
  88. GRB 250521D: GOTO detects LAST counterpart candidate prior to the GRB
  89. GRB 250521B: SVOM/COLIBRÍ (FM-GFT) optical upper limit
  90. GRB 250521D: LAST tentative optical counterpart candidate
  91. GRB 250520A: CALET Gamma-Ray Burst Monitor detection
  92. GRB 250520A: 10 GHz VLA radio source
  93. GRB 250521B: Swift ToO observations
  94. GRB 250521D: Fermi GBM Final Real-time Localization
  95. GRB 250521C: Fermi GBM Final Localization
  96. GRB 250521A: DDOTI Optical Upper Limit
  97. GRB 250521B: SVOM detection of a burst through offline search
  98. Konus-Wind detection of GRB 250520A (short/hard)
  99. GRB 250520A: VLT/FORS2 Optical Observation
  100. GRB 250502A: Tautenburg observations

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