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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"

20966 results found.

  1. GRB 250521C/AT2025mgj: NOT optical observations of the afterglow candidate
  2. GRB 250530A: SVOM/VT optical upper limit
  3. GRB 250530A: Swift-XRT counterpart detection
  4. GRB 250530A: SVOM/COLIBRÍ (FM-GFT) optical counterpart candidate
  5. GRB 250527C: Swift/UVOT Upper Limits
  6. GRB 250527B: Swift-XRT observations
  7. GRB 250521C (short): Zwicky Transient Facility identification of a possible fast optical transient counterpart
  8. GRB 250527C: Swift ToO observations
  9. GRB 250527C: Swift/BAT-GUANO arcminute localization of a burst
  10. EP250526a: SVOM/VT optical upper limit
  11. GRB 250521D: SVOM/GRM analysis suggests a possible “long” duration type I burst
  12. GRB 250527B: Tiled Swift observations
  13. GRB 250520A: Gemini-South optical afterglow detection
  14. Fermi trigger No 770058372: Global MASTER-Net observations report
  15. Fermi trigger No 770047117: Global MASTER-Net observations report
  16. EP250526a: refined analysis of the EP-WXT and EP-FXT observations
  17. EP250526a: Global MASTER-Net observations report
  18. EP-WXT trigger 01709176712: SVOM/C-GFT observations of blue-to-red color variation
  19. GRB 250520A: 3 GHz MeerKAT Detection
  20. GRB 250520A: 10 GHz VLA Afterglow Confirmation
  21. Fermi GRB 250523A: Global MASTER-Net observations report
  22. Fermi trigger No 769611916: Global MASTER-Net observations report
  23. EP-WXT trigger 01709176712: GOTO observations confirm stellar counterpart variability
  24. GRB 250521B: SVOM/VT optical upper limit
  25. The EP-WXT trigger 01709176612: SVOM/VT optical observations
  26. The EP-WXT trigger 01709176612: refined analysis of the EP-FXT observation
  27. Fermi GRB 250522B: Global MASTER-Net observations report
  28. GRB 250521D: SVOM/VT optical observations
  29. EP#01709176612: Swift-XRT counterpart detection of flaring star
  30. Fermi GRB 250521D: Global MASTER-Net observations report
  31. Fermi trigger No 769533898: Global MASTER-Net observations report
  32. Fermi trigger No 769499303: Global MASTER-Net observations report
  33. GRB 250521D: DDOTI Optical Upper Limit
  34. GRB 250521D: GOTO detects LAST counterpart candidate prior to the GRB
  35. GRB 250521B: SVOM/COLIBRÍ (FM-GFT) optical upper limit
  36. GRB 250521D: LAST tentative optical counterpart candidate
  37. GRB 250520A: 10 GHz VLA radio source
  38. GRB 250521B: Swift ToO observations
  39. GRB 250521A: DDOTI Optical Upper Limit
  40. GRB 250520A: VLT/FORS2 Optical Observation
  41. GRB 250502A: Tautenburg observations
  42. GRB 250520A: Swift/UVOT Upper Limits
  43. GRB 250520A: J-band observations with WINTER
  44. GRB 250520A: Gemini-South optical observations
  45. GRB 250520A: REM optical/NIR early observations
  46. GRB 250520A: COLIBRÍ optical upper limit
  47. GRB 250520A: DDOTI Optical Upper Limit
  48. GRB 250520A: GOTO optical upper limit
  49. Swift GRB 250520A: Global MASTER-Net observations report
  50. EP250427a/GRB250427A: VLA Detection of Radio Counterpart
  51. EP-WXT trigger (ID: 01709176312): a new X-ray outburst of HMXB RX J0111.2-7317
  52. Fermi GRB 250516A: Global MASTER-Net observations report
  53. GRB 250515A: Swift-XRT observations
  54. GRB 250515A: NOT classification of GOTO25cqo as a type-Ia SN
  55. GRB 250515A:COLIBRÍ optical observations of the GOTO candidate
  56. Swift GRB 250516A: Global MASTER-Net observations report
  57. GRB 250515A: 1.6m Mephisto optical detection
  58. GRB 250515A/GOTO25cqo: SVOM/VT optical blue color
  59. GRB 250516A: Swift/UVOT Detection
  60. GRB 250515A: Swift ToO observations
  61. GRB 250515A: GOTO candidate optical counterpart
  62. MAXI GRB250515.65: Global MASTER-Net observations report
  63. GRB 250424A: COLIBRÍ detection of the associated supernova
  64. GRB 250502A: TESS observations
  65. Fermi trigger No 768922089: Global MASTER-Net observations report
  66. LIGO/Virgo/KAGRA S250328ae: DECam DESGW Candidates (Final Epochs)
  67. Fermi GRB 250512A: Global MASTER-Net observations report
  68. EP250512a/GRB 250512B: REM optical/NIR observations
  69. EP250511a: Koshka Zeiss-1000 Optical Upper Limit
  70. EP250511a: Gemini optical counterpart observation
  71. EP250512a/GRB 250512B refined analysis of the EP-WXT and EP-FXT observations
  72. EP250512a/GRB 250512B: FTW optical and NIR observations of the counterpart
  73. EP250512a: Global MASTER-Net observations report
  74. EP250511a: FTW optical and NIR observations
  75. GRB 250512B/EP250512a：SVOM/VT bright optical counterpart
  76. EP250511a: Mephisto optical upper limits
  77. EP250511a: REM optical/NIR observations
  78. EP250511a: SVOM/VT optical candidate comfirmation
  79. EP250511a: Global MASTER-Net observations report
  80. EP250508a: Gemini NIR upper limits
  81. Fermi GRB 250510C: Global MASTER-Net observations report
  82. Fermi GRB 250510B: Global MASTER-Net observations report
  83. GRB 250510A: Swift-XRT observations
  84. IceCube-250506A: No Transient Candidates from the Zwicky Transient Facility
  85. GRB 250510A: follow-up observation with EP-FXT
  86. GRB 250510A: SVOM/COLIBRÍ (FM-GFT) optical upper limit
  87. GRB 250507A: J-band observations with WINTER (duplicate submission)
  88. GRB 250507A: J-band observations with WINTER
  89. Fermi GRB 250509A: Global MASTER-Net observations report
  90. Swift GRB 250509A: Global MASTER-Net observations report
  91. EP250508a: follow-up observation with EP-FXT
  92. GRB 250507A: KAIT optical upper limit
  93. EP250508a: refined analysis of the EP-WXT and EP-FXT observations
  94. GRB 250502A: Calapai Observatory, Massa S. Giorgio (Messina), optical observation.
  95. EP250508a: REM optical/NIR observations
  96. GRB 250506A: Swift-XRT afterglow detection
  97. EP250508a: Global MASTER-Net observations report
  98. GRB 250506A: SVOM/VT optical upper limit
  99. EP250508a: COLIBRÍ Optical Limit
  100. GRB 250506A: Swift/UVOT Upper Limits

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