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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"

8293 results found.

  1. GRB 250601A: Swift/XRT candidate afterglow
  2. GRB 250521C / AT2025mgj: Pan-STARRS multi-band and multi-epoch imaging and photometry
  3. GRB 250601A: Swift ToO observations
  4. GRB 250530A: VLT/HAWK-I NIR counterpart fading
  5. GRB 250521C/AT2025mgj: FTW optical and NIR observations
  6. EP#01709177494: Swift-XRT counterpart detection of known source
  7. GRB 250530C: BOOTES-7 optical upper limit
  8. GRB 250521C/ZTF25aarhkyn/AT2025mgj: COLIBRÍ optical observations
  9. GRB 250530C: Swift detection of a burst
  10. GRB 250521C/AT2025mgj: NOT optical observations of the afterglow candidate
  11. GRB 250530A: EP-FXT counterpart detection
  12. GRB 250530A: SVOM/VT optical upper limit
  13. GRB 250530A: Swift-XRT counterpart detection
  14. GRB 250530A: SVOM/COLIBRÍ (FM-GFT) optical counterpart candidate retraction and detection limit
  15. GRB 250530A: SVOM/COLIBRÍ (FM-GFT) optical counterpart candidate
  16. EP J1350.0-8622: EP-FXT follow-up observation
  17. GRB 250527C: Swift ToO observations
  18. GRB 250527B: Tiled Swift observations
  19. GRB 250520A: Gemini-South optical afterglow detection
  20. EP J1350.0-8622: BOOTES-6/DPRT optical upper limit
  21. EP J1350.0-8622: Einstein Probe detection of an X-ray transient candidate
  22. The EP-WXT trigger 01709176612: refined analysis of the EP-FXT observation
  23. GRB 250521D: SVOM/VT optical observations
  24. EP#01709176612: Swift-XRT counterpart detection of flaring star
  25. The EP-WXT trigger 01709176612 is likely a flaring star
  26. GRB 250521D: GOTO detects LAST counterpart candidate prior to the GRB
  27. GRB 250521D: LAST tentative optical counterpart candidate
  28. GRB 250521B: Swift ToO observations
  29. GRB 250520A: VLT/FORS2 Optical Observation
  30. GRB 250520A: Swift/UVOT Upper Limits
  31. GRB 250520A: J-band observations with WINTER
  32. GRB 250520A: Gemini-South optical observations
  33. GRB 250520A: REM optical/NIR early observations
  34. GRB 250520A：SVOM/VT optical candidate
  35. GRB 250520A: Swift detection of a burst
  36. EP250427a/GRB250427A: VLA Detection of Radio Counterpart
  37. GRB 250515A: NOT classification of GOTO25cqo as a type-Ia SN
  38. GRB 250515A:COLIBRÍ optical observations of the GOTO candidate
  39. GRB 250515A: 1.6m Mephisto optical detection
  40. GRB 250515A/GOTO25cqo: SVOM/VT optical blue color
  41. GRB 250515A: Swift ToO observations
  42. GRB 250516A: Swift detection of a burst
  43. GRB 250515A: GOTO candidate optical counterpart
  44. LIGO/Virgo/KAGRA S250328ae: DECam DESGW Candidates (Final Epochs)
  45. EP250511a: Gemini optical counterpart observation
  46. EP250511a: REM optical/NIR observations
  47. EP250511a: SVOM/VT optical candidate comfirmation
  48. EP250511a: COLIBRÍ optical counterpart candidate
  49. EP250511a: BOOTES-5 optical upper limit
  50. IceCube-250506A: No Transient Candidates from the Zwicky Transient Facility
  51. EP250508a: SVOM/VT optical candidate fading
  52. GRB 250509A: Swift detection of a burst
  53. EP250508a: Liverpool Telescope optical upper limits
  54. EP250508a: SVOM/VT optical candidate
  55. EP250508a: KAIT optical upper limit
  56. GRB 250507A: KAIT optical upper limit
  57. IceCube-250506A: Upper limits from a search for additional neutrino events in IceCube
  58. GRB 250506A: Swift ToO observations
  59. IceCube-250506A - IceCube observation of a high-energy neutrino candidate track-like event
  60. GRB 250504A: MeerLICHT optical afterglow detection
  61. GRB 250504A: Swift detection of a burst
  62. GRB 250502A: Swift ToO observations
  63. GRB 250502A: SVOM/COLIBRÍ (FM-GFT) Detection of a Bright Optical Counterpart Candidate
  64. EP250428b: Pan-STARRS follow-up, upper limit on the optical counterpart, and possible host galaxy.
  65. IceCube-250429A: Upper limits from a search for additional neutrino events in IceCube
  66. IceCube-250426A: Upper limits from a search for additional neutrino events in IceCube
  67. GRB 250430A: Swift detection of a burst with optical counterpart
  68. IceCube-250429A - IceCube observation of a high-energy neutrino candidate track-like event
  69. GRB 250427A/ EP250427a: Fermi-GBM Sub-Threshold Detection
  70. EP250427A: COLIBRÍ Optical Detection
  71. EP 250427a: BOOTES-7 optical afterglow candidate
  72. IceCube-250426A - IceCube observation of a high-energy neutrino candidate track-like event (duplicate submission)
  73. IceCube-250426A - IceCube observation of a high-energy neutrino candidate track-like event
  74. IceCube-250416A: Upper limits from a search for additional neutrino events in IceCube
  75. IceCube-250421A: Upper limits from a search for additional neutrino events in IceCube
  76. GRB 250424A: SVOM/VT optical observation
  77. Fermi-LAT gamma-ray observations of IceCube-250421A
  78. GRB 250424A: Swift detection of a burst with an optical counterpart
  79. EP250421a: Upper limits from Fermi-GBM Observations
  80. SVOM/sb25042207: BOOTES-2 early optical upper limit
  81. SVOM/sb25042207: SVOM detection of an X-ray transient
  82. IceCube-250421A: DDOTI Detection of the LAST Candidate
  83. IC-250421A: LAST optical observations of the IceCube neutrino candidate
  84. EP250421a: Mephisto optical counterpart confirmation
  85. IceCube-250421A - IceCube observation of a high-energy neutrino candidate track-like event
  86. IceCube-Cascade 250414A: Upper limits from a search for additional neutrino events in IceCube
  87. The EP-WXT trigger 01709135179: Kinder optical counterpart candidate
  88. EP250416a: refined EP-WXT and EP-FXT analysis
  89. EP20250416a: Swift/XRT counterpart detection
  90. EP250225a: SVOM/VT optical brightening
  91. IceCube-250416A - IceCube observation of a high-energy neutrino candidate track-like event
  92. SVOM/sb25041603: SVOM detection of an X-ray transient
  93. EP250227a: Further NOT optical observations
  94. IceCube-250406A: Swift-XRT observations
  95. EP250407a: Swift-XRT observations
  96. IceCube-250406A: Upper limits from a search for additional neutrino events in IceCube
  97. GRB 250407A: KAIT Optical Afterglow Candidate
  98. IceCube-250406A: No candidates from the Zwicky Transient Facility
  99. GRB 250407A: Swift ToO observations
  100. LIGO/Virgo/KAGRA S250331o: Upper limits from Swift/BAT-GUANO

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