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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"

7296 results found.

  1. EP250610a: REM optical/NIR observations
  2. EP250610a: Swift-XRT counterpart detection
  3. GRB 250529A: GOTO optical counterpart candidate (GOTO25dea/AT 2025ndt)
  4. GRB 250527C: CrAO Optical Upper Limit
  5. GRB 250605A: SVOM/VT optical upper limit
  6. EP/WXT 01709177873: GOTO observations confirm stellar variability
  7. GRB 250605A: Swift detection of a burst
  8. GRB 250521C: NOT spectroscopic observations exclude the afterglow candidate AT2025mgj
  9. GRB 250601A: Swift/XRT candidate afterglow
  10. GRB 250601A: Swift ToO observations
  11. GRB 250530A: VLT/HAWK-I NIR counterpart fading
  12. GRB 250521C/AT2025mgj: FTW optical and NIR observations
  13. EP#01709177494: Swift-XRT counterpart detection of known source
  14. GRB 250521C/ZTF25aarhkyn/AT2025mgj: COLIBRÍ optical observations
  15. GRB 250530C: Swift detection of a burst
  16. GRB 250521C/AT2025mgj: NOT optical observations of the afterglow candidate
  17. GRB 250530A: EP-FXT counterpart detection
  18. GRB 250530A: SVOM/VT optical upper limit
  19. GRB 250530A: Swift-XRT counterpart detection
  20. GRB 250530A: SVOM/COLIBRÍ (FM-GFT) optical counterpart candidate retraction and detection limit
  21. GRB 250530A: SVOM/COLIBRÍ (FM-GFT) optical counterpart candidate
  22. EP J1350.0-8622: EP-FXT follow-up observation
  23. GRB 250527C: Swift ToO observations
  24. GRB 250521D: SVOM/GRM analysis suggests a possible “long” duration type I burst
  25. GRB 250527B: Tiled Swift observations
  26. GRB 250520A: Gemini-South optical afterglow detection
  27. EP J1350.0-8622: BOOTES-6/DPRT optical upper limit
  28. EP J1350.0-8622: Einstein Probe detection of an X-ray transient candidate
  29. The EP-WXT trigger 01709176612: refined analysis of the EP-FXT observation
  30. GRB 250521D: SVOM/VT optical observations
  31. EP#01709176612: Swift-XRT counterpart detection of flaring star
  32. The EP-WXT trigger 01709176612 is likely a flaring star
  33. GRB 250521D: GOTO detects LAST counterpart candidate prior to the GRB
  34. GRB 250521D: LAST tentative optical counterpart candidate
  35. GRB 250521B: Swift ToO observations
  36. GRB 250520A: VLT/FORS2 Optical Observation
  37. GRB 250520A: Swift/UVOT Upper Limits
  38. GRB 250520A: J-band observations with WINTER
  39. GRB 250520A: Gemini-South optical observations
  40. GRB 250520A: REM optical/NIR early observations
  41. GRB 250520A：SVOM/VT optical candidate
  42. GRB 250520A: Swift detection of a burst
  43. EP-WXT trigger (ID: 01709176312): a new X-ray outburst of HMXB RX J0111.2-7317
  44. GRB 250515A: NOT classification of GOTO25cqo as a type-Ia SN
  45. GRB 250515A:COLIBRÍ optical observations of the GOTO candidate
  46. GRB 250515A: 1.6m Mephisto optical detection
  47. GRB 250515A/GOTO25cqo: SVOM/VT optical blue color
  48. GRB 250515A: Swift ToO observations
  49. GRB 250516A: Swift detection of a burst
  50. GRB 250515A: GOTO candidate optical counterpart
  51. LIGO/Virgo/KAGRA S250328ae: DECam DESGW Candidates (Final Epochs)
  52. EP250511a: Gemini optical counterpart observation
  53. EP250511a: REM optical/NIR observations
  54. EP250511a: SVOM/VT optical candidate comfirmation
  55. EP250511a: COLIBRÍ optical counterpart candidate
  56. IceCube-250506A: No Transient Candidates from the Zwicky Transient Facility
  57. EP250508a: SVOM/VT optical candidate fading
  58. GRB 250509A: Swift detection of a burst
  59. EP250508a: Liverpool Telescope optical upper limits
  60. EP250508a: SVOM/VT optical candidate
  61. EP250508a: KAIT optical upper limit
  62. GRB 250507A: KAIT optical upper limit
  63. EP-WXT trigger 01709175213: a new X-ray outburst of LMXB MAXI J1957+032
  64. GRB 250506A: Swift ToO observations
  65. IceCube-250506A - IceCube observation of a high-energy neutrino candidate track-like event
  66. GRB 250504A: MeerLICHT optical afterglow detection
  67. GRB 250504A: Swift detection of a burst
  68. GRB 250502A: Swift ToO observations
  69. GRB 250502A: SVOM/COLIBRÍ (FM-GFT) Detection of a Bright Optical Counterpart Candidate
  70. GRB 250430A: Swift detection of a burst with optical counterpart
  71. IceCube-250429A - IceCube observation of a high-energy neutrino candidate track-like event
  72. EP250427A: COLIBRÍ Optical Detection
  73. EP 250427a: BOOTES-7 optical afterglow candidate
  74. IceCube-250426A - IceCube observation of a high-energy neutrino candidate track-like event (duplicate submission)
  75. IceCube-250426A - IceCube observation of a high-energy neutrino candidate track-like event
  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: SVOM detection of an X-ray transient
  81. IceCube-250421A: DDOTI Detection of the LAST Candidate
  82. IC-250421A: LAST optical observations of the IceCube neutrino candidate
  83. EP250421a: Mephisto optical counterpart confirmation
  84. IceCube-250421A - IceCube observation of a high-energy neutrino candidate track-like event
  85. The EP-WXT trigger 01709135179: Kinder optical counterpart candidate
  86. EP250416a: refined EP-WXT and EP-FXT analysis
  87. EP20250416a: Swift/XRT counterpart detection
  88. EP250225a: SVOM/VT optical brightening
  89. IceCube-250416A - IceCube observation of a high-energy neutrino candidate track-like event
  90. SVOM/sb25041603: SVOM detection of an X-ray transient
  91. EP250227a: Further NOT optical observations
  92. GRB 250407A: KAIT Optical Afterglow Candidate
  93. IceCube-250406A: No candidates from the Zwicky Transient Facility
  94. GRB 250407A: Swift ToO observations
  95. LIGO/Virgo/KAGRA S250331o: Upper limits from Swift/BAT-GUANO
  96. IceCube-250406A - IceCube observation of a high-energy neutrino candidate track-like event
  97. EP250402a: Optical upper limit with Kinder observations
  98. GRB 250402A: REM optical/NIR upper limits
  99. GRB 250402A: refined SVOM/MXT data analysis
  100. GRB 250219A: NOT candidate host galaxy detection

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