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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"

7407 results found.

  1. sb25061218: Swift-XRT observations
  2. EP250612a: refined analysis of the EP-WXT and EP-FXT observations
  3. sb25061207: EP-FXT follow-up observation and afterglow candidate
  4. EP250612a: SVOM/VT optical candidate
  5. sb25061207: Swift-XRT observations
  6. sb25061207: SVOM/VT optical counterpart
  7. EP250610a: TNG NIR upper limit
  8. GRB 250610B: OHP/T120 optical counterpart candidate
  9. GRB 250610B : SVOM/GWAC-F60A and F50 observations
  10. EP250610a: refined analysis of the EP-WXT and EP-FXT observations
  11. EP250610a: SVOM/VT optical upper limit
  12. EP250610a: REM optical/NIR observations
  13. EP250610a: Swift-XRT counterpart detection
  14. GRB 250529A: GOTO optical counterpart candidate (GOTO25dea/AT 2025ndt)
  15. GRB 250527C: CrAO Optical Upper Limit
  16. GRB 250605A: SVOM/VT optical upper limit
  17. EP/WXT 01709177873: GOTO observations confirm stellar variability
  18. GRB 250605A: Swift detection of a burst
  19. GRB 250521C: NOT spectroscopic observations exclude the afterglow candidate AT2025mgj
  20. GRB 250601A: Swift/XRT candidate afterglow
  21. GRB 250601A: Swift ToO observations
  22. GRB 250530A: VLT/HAWK-I NIR counterpart fading
  23. GRB 250521C/AT2025mgj: FTW optical and NIR observations
  24. EP#01709177494: Swift-XRT counterpart detection of known source
  25. GRB 250521C/ZTF25aarhkyn/AT2025mgj: COLIBRÍ optical observations
  26. GRB 250530C: Swift detection of a burst
  27. GRB 250521C/AT2025mgj: NOT optical observations of the afterglow candidate
  28. GRB 250530A: EP-FXT counterpart detection
  29. GRB 250530A: SVOM/VT optical upper limit
  30. GRB 250530A: Swift-XRT counterpart detection
  31. GRB 250530A: SVOM/COLIBRÍ (FM-GFT) optical counterpart candidate retraction and detection limit
  32. GRB 250530A: SVOM/COLIBRÍ (FM-GFT) optical counterpart candidate
  33. EP J1350.0-8622: EP-FXT follow-up observation
  34. GRB 250527C: Swift ToO observations
  35. GRB 250521D: SVOM/GRM analysis suggests a possible “long” duration type I burst
  36. GRB 250527B: Tiled Swift observations
  37. GRB 250520A: Gemini-South optical afterglow detection
  38. EP J1350.0-8622: BOOTES-6/DPRT optical upper limit
  39. EP J1350.0-8622: Einstein Probe detection of an X-ray transient candidate
  40. The EP-WXT trigger 01709176612: refined analysis of the EP-FXT observation
  41. GRB 250521D: SVOM/VT optical observations
  42. EP#01709176612: Swift-XRT counterpart detection of flaring star
  43. The EP-WXT trigger 01709176612 is likely a flaring star
  44. GRB 250521D: GOTO detects LAST counterpart candidate prior to the GRB
  45. GRB 250521D: LAST tentative optical counterpart candidate
  46. GRB 250521B: Swift ToO observations
  47. GRB 250520A: VLT/FORS2 Optical Observation
  48. GRB 250520A: Swift/UVOT Upper Limits
  49. GRB 250520A: J-band observations with WINTER
  50. GRB 250520A: Gemini-South optical observations
  51. GRB 250520A: REM optical/NIR early observations
  52. GRB 250520A:SVOM/VT optical candidate
  53. GRB 250520A: Swift detection of a burst
  54. EP-WXT trigger (ID: 01709176312): a new X-ray outburst of HMXB RX J0111.2-7317
  55. GRB 250515A: NOT classification of GOTO25cqo as a type-Ia SN
  56. GRB 250515A:COLIBRÍ optical observations of the GOTO candidate
  57. GRB 250515A: 1.6m Mephisto optical detection
  58. GRB 250515A/GOTO25cqo: SVOM/VT optical blue color
  59. GRB 250515A: Swift ToO observations
  60. GRB 250516A: Swift detection of a burst
  61. GRB 250515A: GOTO candidate optical counterpart
  62. LIGO/Virgo/KAGRA S250328ae: DECam DESGW Candidates (Final Epochs)
  63. EP250511a: Gemini optical counterpart observation
  64. EP250511a: REM optical/NIR observations
  65. EP250511a: SVOM/VT optical candidate comfirmation
  66. EP250511a: COLIBRÍ optical counterpart candidate
  67. IceCube-250506A: No Transient Candidates from the Zwicky Transient Facility
  68. EP250508a: SVOM/VT optical candidate fading
  69. GRB 250509A: Swift detection of a burst
  70. EP250508a: Liverpool Telescope optical upper limits
  71. EP250508a: SVOM/VT optical candidate
  72. EP250508a: KAIT optical upper limit
  73. GRB 250507A: KAIT optical upper limit
  74. EP-WXT trigger 01709175213: a new X-ray outburst of LMXB MAXI J1957+032
  75. GRB 250506A: Swift ToO observations
  76. IceCube-250506A - IceCube observation of a high-energy neutrino candidate track-like event
  77. GRB 250504A: MeerLICHT optical afterglow detection
  78. GRB 250504A: Swift detection of a burst
  79. GRB 250502A: Swift ToO observations
  80. GRB 250502A: SVOM/COLIBRÍ (FM-GFT) Detection of a Bright Optical Counterpart Candidate
  81. GRB 250430A: Swift detection of a burst with optical counterpart
  82. IceCube-250429A - IceCube observation of a high-energy neutrino candidate track-like event
  83. EP250427A: COLIBRÍ Optical Detection
  84. EP 250427a: BOOTES-7 optical afterglow candidate
  85. IceCube-250426A - IceCube observation of a high-energy neutrino candidate track-like event (duplicate submission)
  86. IceCube-250426A - IceCube observation of a high-energy neutrino candidate track-like event
  87. GRB 250424A: SVOM/VT optical observation
  88. Fermi-LAT gamma-ray observations of IceCube-250421A
  89. GRB 250424A: Swift detection of a burst with an optical counterpart
  90. EP250421a: Upper limits from Fermi-GBM Observations
  91. SVOM/sb25042207: SVOM detection of an X-ray transient
  92. IceCube-250421A: DDOTI Detection of the LAST Candidate
  93. IC-250421A: LAST optical observations of the IceCube neutrino candidate
  94. EP250421a: Mephisto optical counterpart confirmation
  95. IceCube-250421A - IceCube observation of a high-energy neutrino candidate track-like event
  96. The EP-WXT trigger 01709135179: Kinder optical counterpart candidate
  97. EP250416a: refined EP-WXT and EP-FXT analysis
  98. EP20250416a: Swift/XRT counterpart detection
  99. EP250225a: SVOM/VT optical brightening
  100. IceCube-250416A - IceCube observation of a high-energy neutrino candidate track-like event

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