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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"

8477 results found.

  1. GRB 250527C: Swift ToO observations
  2. GRB 250527B: Tiled Swift observations
  3. GRB 250520A: Gemini-South optical afterglow detection
  4. EP J1350.0-8622: BOOTES-6/DPRT optical upper limit
  5. EP J1350.0-8622: Einstein Probe detection of an X-ray transient candidate
  6. The EP-WXT trigger 01709176612: refined analysis of the EP-FXT observation
  7. GRB 250521D: SVOM/VT optical observations
  8. EP#01709176612: Swift-XRT counterpart detection of flaring star
  9. The EP-WXT trigger 01709176612 is likely a flaring star
  10. GRB 250521D: GOTO detects LAST counterpart candidate prior to the GRB
  11. GRB 250521D: LAST tentative optical counterpart candidate
  12. GRB 250521B: Swift ToO observations
  13. GRB 250520A: VLT/FORS2 Optical Observation
  14. GRB 250520A: Swift/UVOT Upper Limits
  15. GRB 250520A: J-band observations with WINTER
  16. GRB 250520A: Gemini-South optical observations
  17. GRB 250520A: REM optical/NIR early observations
  18. GRB 250520A：SVOM/VT optical candidate
  19. GRB 250520A: Swift detection of a burst
  20. EP250427a/GRB250427A: VLA Detection of Radio Counterpart
  21. GRB 250515A: NOT classification of GOTO25cqo as a type-Ia SN
  22. GRB 250515A:COLIBRÍ optical observations of the GOTO candidate
  23. GRB 250515A: 1.6m Mephisto optical detection
  24. GRB 250515A/GOTO25cqo: SVOM/VT optical blue color
  25. GRB 250515A: Swift ToO observations
  26. GRB 250516A: Swift detection of a burst
  27. GRB 250515A: GOTO candidate optical counterpart
  28. LIGO/Virgo/KAGRA S250328ae: DECam DESGW Candidates (Final Epochs)
  29. EP250511a: Gemini optical counterpart observation
  30. EP250511a: REM optical/NIR observations
  31. EP250511a: SVOM/VT optical candidate comfirmation
  32. EP250511a: COLIBRÍ optical counterpart candidate
  33. EP250511a: BOOTES-5 optical upper limit
  34. IceCube-250506A: No Transient Candidates from the Zwicky Transient Facility
  35. EP250508a: SVOM/VT optical candidate fading
  36. GRB 250509A: Swift detection of a burst
  37. EP250508a: Liverpool Telescope optical upper limits
  38. EP250508a: SVOM/VT optical candidate
  39. EP250508a: KAIT optical upper limit
  40. GRB 250507A: KAIT optical upper limit
  41. IceCube-250506A: Upper limits from a search for additional neutrino events in IceCube
  42. GRB 250506A: Swift ToO observations
  43. IceCube-250506A - IceCube observation of a high-energy neutrino candidate track-like event
  44. GRB 250504A: MeerLICHT optical afterglow detection
  45. GRB 250504A: Swift detection of a burst
  46. GRB 250502A: Swift ToO observations
  47. GRB 250502A: SVOM/COLIBRÍ (FM-GFT) Detection of a Bright Optical Counterpart Candidate
  48. EP250428b: Pan-STARRS follow-up, upper limit on the optical counterpart, and possible host galaxy.
  49. IceCube-250429A: Upper limits from a search for additional neutrino events in IceCube
  50. IceCube-250426A: Upper limits from a search for additional neutrino events in IceCube
  51. GRB 250430A: Swift detection of a burst with optical counterpart
  52. IceCube-250429A - IceCube observation of a high-energy neutrino candidate track-like event
  53. GRB 250427A/ EP250427a: Fermi-GBM Sub-Threshold Detection
  54. EP250427A: COLIBRÍ Optical Detection
  55. EP 250427a: BOOTES-7 optical afterglow candidate
  56. IceCube-250426A - IceCube observation of a high-energy neutrino candidate track-like event (duplicate submission)
  57. IceCube-250426A - IceCube observation of a high-energy neutrino candidate track-like event
  58. IceCube-250416A: Upper limits from a search for additional neutrino events in IceCube
  59. IceCube-250421A: Upper limits from a search for additional neutrino events in IceCube
  60. GRB 250424A: SVOM/VT optical observation
  61. Fermi-LAT gamma-ray observations of IceCube-250421A
  62. GRB 250424A: Swift detection of a burst with an optical counterpart
  63. EP250421a: Upper limits from Fermi-GBM Observations
  64. SVOM/sb25042207: BOOTES-2 early optical upper limit
  65. SVOM/sb25042207: SVOM detection of an X-ray transient
  66. IceCube-250421A: DDOTI Detection of the LAST Candidate
  67. IC-250421A: LAST optical observations of the IceCube neutrino candidate
  68. EP250421a: Mephisto optical counterpart confirmation
  69. IceCube-250421A - IceCube observation of a high-energy neutrino candidate track-like event
  70. IceCube-Cascade 250414A: Upper limits from a search for additional neutrino events in IceCube
  71. The EP-WXT trigger 01709135179: Kinder optical counterpart candidate
  72. EP250416a: refined EP-WXT and EP-FXT analysis
  73. EP20250416a: Swift/XRT counterpart detection
  74. EP250225a: SVOM/VT optical brightening
  75. IceCube-250416A - IceCube observation of a high-energy neutrino candidate track-like event
  76. SVOM/sb25041603: SVOM detection of an X-ray transient
  77. EP250227a: Further NOT optical observations
  78. IceCube-250406A: Swift-XRT observations
  79. EP250407a: Swift-XRT observations
  80. IceCube-250406A: Upper limits from a search for additional neutrino events in IceCube
  81. GRB 250407A: KAIT Optical Afterglow Candidate
  82. IceCube-250406A: No candidates from the Zwicky Transient Facility
  83. GRB 250407A: Swift ToO observations
  84. LIGO/Virgo/KAGRA S250331o: Upper limits from Swift/BAT-GUANO
  85. IceCube-250406A - IceCube observation of a high-energy neutrino candidate track-like event
  86. EP250402a: Optical upper limit with Kinder observations
  87. GRB 250403A: LCO optical counterpart detection
  88. GRB 250403A: GOTO detection of the optical afterglow
  89. GRB 250402A: REM optical/NIR upper limits
  90. GRB 250402A: refined SVOM/MXT data analysis
  91. GRB 250219A: NOT candidate host galaxy detection
  92. LIGO/Virgo/KAGRA S250328ae: DECam DESGW Candidates (Epoch 2)
  93. LIGO/Virgo/KAGRA S250331o: Updated Sky localization
  94. GRB 250331D: Swift ToO observations
  95. IceCube-250330A: Upper limits from a search for additional neutrino events in IceCube
  96. LIGO/Virgo/KAGRA S250331o: NED Galaxies in the 3-Initial Localization Volume
  97. GRB 250328A: Swift-XRT refined Analysis
  98. GRB 250331C: Swift detection of a burst
  99. GRB 250331B: Swift detection of a burst
  100. LIGO/Virgo/KAGRA S250331o: Identification of a GW compact binary merger candidate

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