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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"

21467 results found.

  1. GRB 250920C: GOTO optical counterpart candidate
  2. GRB 250920C: Swift detection of a burst
  3. Swift GRB 250920B: Global MASTER-Net observations report
  4. GRB 250920B: Swift detection of a burst with a bright optical counterpart.
  5. GRB 250919A / EP250919a: MASTER bright afterglow detection 24h after GRB time
  6. GRB 250916A: Mondy R-band optical observations
  7. GRB 250919A: Fermi GBM Observation
  8. GRB 250919A/EP250919A: Swift/UVOT afterglow detection
  9. GRB 250919A: Swift-XRT afterglow detection
  10. GRB 250917B: Swift-BAT refined analysis
  11. GRB 250917B: Swift/UVOT Upper Limits
  12. GRB 250916A: Swift-XRT observations
  13. GRB250917B: WFST optical observations
  14. GRB 250916A: Swift ToO observations
  15. GRB 250917B: Fermi GBM Observation
  16. GRB 250917B: Swift-XRT observations
  17. GRB 250917B: Swift detection of a short burst
  18. GRB 250912A: Swift/BAT-GUANO localization skymap of a possibly short burst
  19. GRB 250912A: Swift-XRT observations
  20. GRB 250911A: Insight-HXMT detection
  21. GRB 250911A: GECAM-B detection
  22. GRB 250911A: Swift-BAT refined analysis
  23. EP250911a: refined analysis of the EP-WXT and EP-FXT observations
  24. EP250911a: SVOM/VT optical observation
  25. GRB 250911A: MASTER optical counterpart observations
  26. GRB 250911A: Swift-XRT refined Analysis
  27. EP250911a: Swift-XRT observations
  28. GRB 250911A: Swift/UVOT Detection
  29. GRB 250910A / EP250910a: Swift-XRT afterglow detection
  30. GRB 250910A / EP250910a: SVOM/VT afterglow confirmation
  31. GRB 250910A / EP250910a : VLT/HAWK-I NIR counterpart discovery
  32. GRB 250911A: Enhanced Swift-XRT position
  33. GRB 250911A: Swift-XRT observations
  34. GRB 250911A: COLIBRÍ optical counterpart candidate
  35. GRB 250911A: Swift detection of a burst
  36. GRB 250702B: Late time Chandra observations
  37. EP250908b/EP#01709240653: Swift/UVOT Detection
  38. EP#01709240653: Swift-XRT observations
  39. GRB 250905A: Swift-BAT refined analysis
  40. GRB 250903A: Swift-XRT afterglow detection
  41. GRB 250905A: Swift-XRT refined Analysis
  42. GRB 250904A: Swift-BAT refined analysis
  43. GRB 250905A: Swift/UVOT Upper Limits
  44. GRB250904A: Liverpool Telescope upper limits
  45. GRB 250905A: Enhanced Swift-XRT position
  46. GRB 250904A: Swift/UVOT Detection
  47. GRB 250903A: Swift/UVOT detection
  48. GRB 250904A: Swift-XRT refined Analysis
  49. GRB 250905A: KAIT optical upper limit
  50. GRB 250905A: Swift detection of a burst
  51. Swift GRB250905.09: Global MASTER-Net observations report
  52. Swift GRB 250904A: Global MASTER-Net observations report
  53. GRB 250904A: Enhanced Swift-XRT position
  54. GRB 250904A: TRT optical counterpart detection
  55. GRB 250904A: Prompt enhanced Swift-XRT position
  56. GRB 250904A: Swift detection of a burst
  57. GRB 250903A: Swift-XRT observations
  58. EP250903a: Swift-XRT observations
  59. EP#01709201209: Swift-XRT observations
  60. EP250903a: retraction of the LCO candidate, and discovery of the likely counterpart
  61. EP250901a: Mondy, Assy and SAO RAS optical limits
  62. GRB 250901A: Swift/UVOT Upper Limit
  63. GRB 250830B: Swift-XRT afterglow detection
  64. GRB 250831A (SVOM trigger sb25083102): confirmation of a stellar flare by SVOM/VT
  65. GRB 250901A: EP-FXT follow-up observation
  66. GRB 250901A: SVOM/VT optical afterglow with VHF data
  67. GRB 250901A: Swift-XRT afterglow detection
  68. EP250901a: Swift-XRT observations
  69. GRB 250901A: LCO optical upper limit
  70. EP250827b: Swift observations of AT 2025wkm
  71. GRB 250901A: SVOM detection of a burst
  72. EP250831a: EP-FXT follow-up observation
  73. EP250831a: Swift-XRT observations
  74. GRB 250831A (SVOM trigger sb25083102) is likely an outburst from star G 272-61
  75. GRB 250831A: Swift-XRT counterpart detection
  76. GRB 250830B: Swift-XRT observations
  77. EP250830a/GRB 250830B: Einstein Probe detection of an X-ray transient and Swift/XRT follow-up
  78. GRB 250830B: Swift ToO observations
  79. GRB 250830B: MAXI/GSC detection
  80. GRB 250828B: Swift-BAT refined analysis
  81. EP250827a: very early ATLAS detections, starting 43 sec after the EP trigger
  82. Swift GRB 250828B: Global MASTER-Net observations report
  83. EP250827a: Swift/UVOT Detection
  84. GRB 250828B: Swift detection of a burst
  85. EP250827a: confirmation of optical rebrightening with LCO
  86. EP250827a: Swift-XRT counterpart detection
  87. GRB 250806A: HiPERCAM/GTC limits on a possible supernova
  88. GRB 250823A: Swift-BAT refined analysis
  89. GRB 250823A: Swift-XRT refined Analysis
  90. LIGO/Virgo/KAGRA S250818k: Swift Observations of AT 2025ulz - Second Epoch
  91. GRB 250823A: COLIBRÍ optical observations
  92. GRB 250823A: SVOM/VT optical observation
  93. GRB 250823A: Swift/UVOT Detection
  94. GRB 250823A: NOT optical observations
  95. GRB 250823A: Fermi GBM Observation
  96. GRB 250818B: MeerKAT Detection
  97. GRB 250823A: Enhanced Swift-XRT position
  98. GRB 250823A: LCOGT Optical Detection
  99. GRB 250823A: BOOTES6/DPRT early optical detection
  100. GRB 250823A: Liverpool Telescope optical detection

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