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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"

19609 results found.

  1. GRB 250916A: Swift ToO observations
  2. GRB 250917B: Fermi GBM Observation
  3. GRB 250917B: Swift-XRT observations
  4. GRB 250917B: Swift detection of a short burst
  5. GRB 250912A: Swift/BAT-GUANO localization skymap of a possibly short burst
  6. GRB 250912A: Swift-XRT observations
  7. GRB 250911A: Insight-HXMT detection
  8. GRB 250911A: GECAM-B detection
  9. GRB 250911A: Swift-BAT refined analysis
  10. EP250911a: refined analysis of the EP-WXT and EP-FXT observations
  11. EP250911a: SVOM/VT optical observation
  12. GRB 250911A: MASTER optical counterpart observations
  13. GRB 250911A: Swift-XRT refined Analysis
  14. EP250911a: Swift-XRT observations
  15. GRB 250911A: Swift/UVOT Detection
  16. GRB 250910A / EP250910a: Swift-XRT afterglow detection
  17. GRB 250910A / EP250910a: SVOM/VT afterglow confirmation
  18. GRB 250910A / EP250910a : VLT/HAWK-I NIR counterpart discovery
  19. GRB 250911A: Enhanced Swift-XRT position
  20. GRB 250911A: Swift-XRT observations
  21. GRB 250911A: COLIBRÍ optical counterpart candidate
  22. GRB 250911A: Swift detection of a burst
  23. GRB 250702B: Late time Chandra observations
  24. EP250908b/EP#01709240653: Swift/UVOT Detection
  25. EP#01709240653: Swift-XRT observations
  26. GRB 250905A: Swift-BAT refined analysis
  27. GRB 250903A: Swift-XRT afterglow detection
  28. GRB 250905A: Swift-XRT refined Analysis
  29. GRB 250904A: Swift-BAT refined analysis
  30. GRB 250905A: Swift/UVOT Upper Limits
  31. GRB 250905A: Enhanced Swift-XRT position
  32. GRB 250904A: Swift/UVOT Detection
  33. GRB 250903A: Swift/UVOT detection
  34. GRB 250904A: Swift-XRT refined Analysis
  35. GRB 250905A: KAIT optical upper limit
  36. GRB 250905A: Swift detection of a burst
  37. Swift GRB250905.09: Global MASTER-Net observations report
  38. Swift GRB 250904A: Global MASTER-Net observations report
  39. GRB 250904A: Enhanced Swift-XRT position
  40. GRB 250904A: TRT optical counterpart detection
  41. GRB 250904A: Prompt enhanced Swift-XRT position
  42. GRB 250904A: Swift detection of a burst
  43. GRB 250903A: Swift-XRT observations
  44. EP250903a: Swift-XRT observations
  45. EP#01709201209: Swift-XRT observations
  46. EP250903a: retraction of the LCO candidate, and discovery of the likely counterpart
  47. EP250901a: Mondy, Assy and SAO RAS optical limits
  48. GRB 250901A: Swift/UVOT Upper Limit
  49. GRB 250830B: Swift-XRT afterglow detection
  50. GRB 250901A: EP-FXT follow-up observation
  51. GRB 250901A: SVOM/VT optical afterglow with VHF data
  52. GRB 250901A: Swift-XRT afterglow detection
  53. EP250901a: Swift-XRT observations
  54. GRB 250901A: LCO optical upper limit
  55. EP250827b: Swift observations of AT 2025wkm
  56. GRB 250901A: SVOM detection of a burst
  57. EP250831a: EP-FXT follow-up observation
  58. EP250831a: Swift-XRT observations
  59. GRB 250831A: Swift-XRT counterpart detection
  60. GRB 250830B: Swift-XRT observations
  61. EP250830a/GRB 250830B: Einstein Probe detection of an X-ray transient and Swift/XRT follow-up
  62. GRB 250830B: Swift ToO observations
  63. GRB 250830B: MAXI/GSC detection
  64. GRB 250828B: Swift-BAT refined analysis
  65. EP250827a: very early ATLAS detections, starting 43 sec after the EP trigger
  66. Swift GRB 250828B: Global MASTER-Net observations report
  67. EP250827a: Swift/UVOT Detection
  68. GRB 250828B: Swift detection of a burst
  69. EP250827a: confirmation of optical rebrightening with LCO
  70. EP250827a: Swift-XRT counterpart detection
  71. GRB 250823A: Swift-BAT refined analysis
  72. GRB 250823A: Swift-XRT refined Analysis
  73. LIGO/Virgo/KAGRA S250818k: Swift Observations of AT 2025ulz - Second Epoch
  74. GRB 250823A: COLIBRÍ optical observations
  75. GRB 250823A: SVOM/VT optical observation
  76. GRB 250823A: Swift/UVOT Detection
  77. GRB 250823A: NOT optical observations
  78. GRB 250823A: Fermi GBM Observation
  79. GRB 250818B: MeerKAT Detection
  80. GRB 250823A: Enhanced Swift-XRT position
  81. GRB 250823A: LCOGT Optical Detection
  82. GRB 250823A: BOOTES6/DPRT early optical detection
  83. GRB 250823A: Liverpool Telescope optical detection
  84. GRB 250823A: Swift detection of a burst
  85. Swift GRB250823.84: Global MASTER-Net observations report
  86. GRB 250821A: Kilonova-Catcher optical upper limits
  87. EP250821a: Swift/XRT counterpart fading
  88. GRB 250821A: Swift-BAT refined analysis
  89. EP250821a: Swift/UVOT further observations.
  90. GRB 250821A: VLT/FORS2 Optical Observation
  91. GRB 250821A: GECAM-B detection
  92. EP250821a: SVOM/VT optical observation
  93. GRB 250821A: NOT z-band upper limit
  94. GRB 250821A: Swift-XRT refined Analysis
  95. Swift GRB 250821A: Global MASTER-Net observations report
  96. GRB 250821A: Enhanced Swift-XRT position
  97. GRB 250821A: Swift/UVOT Upper Limits
  98. EP250821a: Rapidly fading optical source detected in Las Cumbres followup
  99. EP250821a: Swift XRT and UVOT counterpart detection
  100. GRB 250821A: LCOGT Optical Upper Limits

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