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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"

19593 results found.

  1. GRB 250911A: MASTER optical counterpart observations
  2. GRB 250911A: Swift-XRT refined Analysis
  3. EP250911a: Swift-XRT observations
  4. GRB 250911A: Swift/UVOT Detection
  5. GRB 250910A / EP250910a: Swift-XRT afterglow detection
  6. GRB 250910A / EP250910a: SVOM/VT afterglow confirmation
  7. GRB 250910A / EP250910a : VLT/HAWK-I NIR counterpart discovery
  8. GRB 250911A: Enhanced Swift-XRT position
  9. GRB 250911A: Swift-XRT observations
  10. GRB 250911A: COLIBRÍ optical counterpart candidate
  11. GRB 250911A: Swift detection of a burst
  12. GRB 250702B: Late time Chandra observations
  13. EP250908b/EP#01709240653: Swift/UVOT Detection
  14. EP#01709240653: Swift-XRT observations
  15. GRB 250905A: Swift-BAT refined analysis
  16. GRB 250903A: Swift-XRT afterglow detection
  17. GRB 250905A: Swift-XRT refined Analysis
  18. GRB 250904A: Swift-BAT refined analysis
  19. GRB 250905A: Swift/UVOT Upper Limits
  20. GRB 250905A: Enhanced Swift-XRT position
  21. GRB 250904A: Swift/UVOT Detection
  22. GRB 250903A: Swift/UVOT detection
  23. GRB 250904A: Swift-XRT refined Analysis
  24. GRB 250905A: KAIT optical upper limit
  25. GRB 250905A: Swift detection of a burst
  26. Swift GRB250905.09: Global MASTER-Net observations report
  27. Swift GRB 250904A: Global MASTER-Net observations report
  28. GRB 250904A: Enhanced Swift-XRT position
  29. GRB 250904A: TRT optical counterpart detection
  30. GRB 250904A: Prompt enhanced Swift-XRT position
  31. GRB 250904A: Swift detection of a burst
  32. GRB 250903A: Swift-XRT observations
  33. EP250903a: Swift-XRT observations
  34. EP#01709201209: Swift-XRT observations
  35. EP250903a: retraction of the LCO candidate, and discovery of the likely counterpart
  36. EP250901a: Mondy, Assy and SAO RAS optical limits
  37. GRB 250901A: Swift/UVOT Upper Limit
  38. GRB 250830B: Swift-XRT afterglow detection
  39. GRB 250901A: EP-FXT follow-up observation
  40. GRB 250901A: SVOM/VT optical afterglow with VHF data
  41. GRB 250901A: Swift-XRT afterglow detection
  42. EP250901a: Swift-XRT observations
  43. GRB 250901A: LCO optical upper limit
  44. EP250827b: Swift observations of AT 2025wkm
  45. GRB 250901A: SVOM detection of a burst
  46. EP250831a: EP-FXT follow-up observation
  47. EP250831a: Swift-XRT observations
  48. GRB 250831A: Swift-XRT counterpart detection
  49. GRB 250830B: Swift-XRT observations
  50. EP250830a/GRB 250830B: Einstein Probe detection of an X-ray transient and Swift/XRT follow-up
  51. GRB 250830B: Swift ToO observations
  52. GRB 250830B: MAXI/GSC detection
  53. GRB 250828B: Swift-BAT refined analysis
  54. EP250827a: very early ATLAS detections, starting 43 sec after the EP trigger
  55. Swift GRB 250828B: Global MASTER-Net observations report
  56. EP250827a: Swift/UVOT Detection
  57. GRB 250828B: Swift detection of a burst
  58. EP250827a: confirmation of optical rebrightening with LCO
  59. EP250827a: Swift-XRT counterpart detection
  60. GRB 250823A: Swift-BAT refined analysis
  61. GRB 250823A: Swift-XRT refined Analysis
  62. LIGO/Virgo/KAGRA S250818k: Swift Observations of AT 2025ulz - Second Epoch
  63. GRB 250823A: COLIBRÍ optical observations
  64. GRB 250823A: SVOM/VT optical observation
  65. GRB 250823A: Swift/UVOT Detection
  66. GRB 250823A: NOT optical observations
  67. GRB 250823A: Fermi GBM Observation
  68. GRB 250818B: MeerKAT Detection
  69. GRB 250823A: Enhanced Swift-XRT position
  70. GRB 250823A: LCOGT Optical Detection
  71. GRB 250823A: BOOTES6/DPRT early optical detection
  72. GRB 250823A: Liverpool Telescope optical detection
  73. GRB 250823A: Swift detection of a burst
  74. Swift GRB250823.84: Global MASTER-Net observations report
  75. GRB 250821A: Kilonova-Catcher optical upper limits
  76. EP250821a: Swift/XRT counterpart fading
  77. GRB 250821A: Swift-BAT refined analysis
  78. EP250821a: Swift/UVOT further observations.
  79. GRB 250821A: VLT/FORS2 Optical Observation
  80. GRB 250821A: GECAM-B detection
  81. EP250821a: SVOM/VT optical observation
  82. GRB 250821A: NOT z-band upper limit
  83. GRB 250821A: Swift-XRT refined Analysis
  84. Swift GRB 250821A: Global MASTER-Net observations report
  85. GRB 250821A: Enhanced Swift-XRT position
  86. GRB 250821A: Swift/UVOT Upper Limits
  87. EP250821a: Rapidly fading optical source detected in Las Cumbres followup
  88. EP250821a: Swift XRT and UVOT counterpart detection
  89. GRB 250821A: LCOGT Optical Upper Limits
  90. GRB 250814A: CMO SAI and SAO RAS izJ observations.
  91. GRB 250821A: Prompt enhanced Swift-XRT position
  92. GRB 250821A: Swift detection of a burst
  93. LIGO/Virgo/KAGRA S250818k: Swift observations of AT 2025ulz
  94. GRB 250814A: Swift/UVOT Upper Limits
  95. GRB 250813B: Swift/UVOT Upper Limit
  96. IPN triangulation of GRB 250814C (short)
  97. IPN triangulation of GRB 250804B (short)
  98. GRB 250818B: Kilonova-Catcher optical afterglow detection
  99. GRB 250818A: AstroSat CZTI detection
  100. GRB 250818B: Swift/UVOT Detection

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