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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"

8474 results found.

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

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