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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"

23404 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. GRB 250603A: Enhanced Swift-XRT position
  5. GRB 250603A: Swift-XRT position and confirmation of GRB nature
  6. GRB 250603A: Swift detection of a burst or new Galactic transient Swift J0839.7-3916
  7. GRB 250602A: DDOTI Optical Upper Limit
  8. GRB 250601A: EP-FXT follow-up observation and afterglow candidates
  9. GRB 250601A: Swift/XRT candidate afterglow
  10. GRB 250521C / AT2025mgj: Pan-STARRS multi-band and multi-epoch imaging and photometry
  11. GRB 250601A: Swift-XRT observations
  12. GRB 250601A: Swift/BAT-GUANO arcminute localization of a likely short burst
  13. EP#01709177494: SVOM/VT optical observations
  14. EP#01709177494: Swift-XRT counterpart detection of known source
  15. GRB 250521C/ZTF25aarhkyn/AT2025mgj: COLIBRÍ optical observations
  16. GRB 250530A: TNG detection of a NIR source inside the Swift/XRT error circle
  17. GRB 250530C: Enhanced Swift-XRT position
  18. GRB 250530C: Swift detection of a burst
  19. GRB 250530A: EP-FXT counterpart detection
  20. GRB 250530A: SVOM/VT optical upper limit
  21. GRB 250530A: Swift-XRT counterpart detection
  22. GRB 250530A: SVOM/COLIBRÍ (FM-GFT) optical counterpart candidate retraction and detection limit
  23. GRB 250530A: SVOM/COLIBRÍ (FM-GFT) optical counterpart candidate
  24. GRB 250530A: SVOM detection of a burst
  25. GRB 250527C: Swift/UVOT Upper Limits
  26. GRB 250527D: Swift/BAT-GUANO localization skymap of a burst
  27. GRB 250527B: Swift-XRT observations
  28. EP-WXT trigger 01709177124: confirmation of a stellar flare by BOOTES-6
  29. EP250526a: SVOM/VT optical upper limit
  30. GRB 250520A: Gemini-South optical afterglow detection
  31. EP250526a: refined analysis of the EP-WXT and EP-FXT observations
  32. GRB 250314A: CIDER NB1008 upper limit
  33. EP250526a: COLIBRÍ optical upper limits
  34. EP250526a: Einstein Probe detection of a fast X-ray transient
  35. EP J1350.0-8622: Einstein Probe detection of an X-ray transient candidate
  36. EP-WXT trigger 01709176712: SVOM/C-GFT observations of blue-to-red color variation
  37. GRB 250520A: 3 GHz MeerKAT Detection
  38. GRB 250520A: 10 GHz VLA Afterglow Confirmation
  39. GRB 250521B: SVOM/VT optical upper limit
  40. The EP-WXT trigger 01709176612: SVOM/VT optical observations
  41. GRB 250521B: EP-FXT follow-up observation and afterglow candidates
  42. EP#01709176612: Swift-XRT counterpart detection of flaring star
  43. GRB 250521D: DDOTI Optical Upper Limit
  44. GRB 250521B: SVOM/COLIBRÍ (FM-GFT) optical upper limit
  45. GRB 250521D: LAST tentative optical counterpart candidate
  46. GRB 250521A: DDOTI Optical Upper Limit
  47. GRB 250520A: VLT/FORS2 Optical Observation
  48. GRB 250502A: Tautenburg observations
  49. GRB 250520A: Swift/UVOT Upper Limits
  50. IPN triangulation of GRB 250516B
  51. GRB 250520A: J-band observations with WINTER
  52. GRB 250520A: Gemini-South optical observations
  53. GRB 250520A: REM optical/NIR early observations
  54. GRB 250520A:SVOM/VT optical candidate
  55. GRB 250520A: COLIBRÍ optical upper limit
  56. GRB 250520A: DDOTI Optical Upper Limit
  57. GRB 250520A: Enhanced Swift-XRT position
  58. GRB 250520A: GOTO optical upper limit
  59. GRB 250520A: Swift detection of a burst
  60. GRB 250516A: COLIBRÍ optical upper limit
  61. EP-WXT trigger (ID: 01709176312): a new X-ray outburst of HMXB RX J0111.2-7317
  62. GRB 250515A: Swift-XRT observations
  63. GRB 250515A:COLIBRÍ optical observations of the GOTO candidate
  64. GRB 250515A: 1.6m Mephisto optical detection
  65. GRB 250516A: Swift-XRT refined Analysis
  66. GRB 250516A: Swift/UVOT Detection
  67. GRB 250516A: Enhanced Swift-XRT position
  68. GRB 250516A: Swift detection of a burst
  69. GRB 250512B / EP250512a: SVOM/GRM analysis
  70. GRB 250515A: GOTO candidate optical counterpart
  71. GRB 250424A: COLIBRÍ detection of the associated supernova
  72. GRB 250502A: TESS observations
  73. LIGO/Virgo/KAGRA S250328ae: DECam DESGW Candidates (Final Epochs)
  74. EP250512a/GRB 250512B: REM optical/NIR observations
  75. EP250511a: Koshka Zeiss-1000 Optical Upper Limit
  76. EP250511a: Gemini optical counterpart observation
  77. EP250512a/GRB 250512B refined analysis of the EP-WXT and EP-FXT observations
  78. EP250512a/GRB 250512B: FTW optical and NIR observations of the counterpart
  79. EP250511a: FTW optical and NIR observations
  80. EP250511a: Mephisto optical upper limits
  81. GRB 250512B: SVOM detection of a burst
  82. EP250512a: Einstein Probe detection of an X-ray transient
  83. EP250511a: REM optical/NIR observations
  84. EP250511a: Einstein Probe follow-up obsevation and refined analysis
  85. EP250511a: COLIBRÍ optical counterpart candidate
  86. EP250511a: Einstein Probe detection of an X-ray transient
  87. EP250508a: Gemini NIR upper limits
  88. GRB 250510A: Swift-XRT observations
  89. IceCube-250506A: No Transient Candidates from the Zwicky Transient Facility
  90. GRB 250510B: Swift/BAT-GUANO localization skymap of a burst
  91. GRB 250510A: SVOM/COLIBRÍ (FM-GFT) optical upper limit
  92. GRB 250509A: Swift-XRT refined Analysis
  93. GRB 250507A: J-band observations with WINTER
  94. GRB 250509A: Enhanced Swift-XRT position
  95. GRB 250509A: Swift detection of a burst
  96. GRB 250506A: NOT optical upper limits
  97. EP250508a: Liverpool Telescope optical upper limits
  98. EP250508a: KAIT optical upper limit
  99. GRB 250507A: KAIT optical upper limit
  100. EP250508a: refined analysis of the EP-WXT and EP-FXT observations

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