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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"

32541 results found.

  1. GRB 250521C/ZTF25aarhkyn/AT2025mgj: COLIBRÍ optical observations
  2. GRB 250530A: TNG detection of a NIR source inside the Swift/XRT error circle
  3. Swift GRB 250530C: Global MASTER-Net observations report
  4. GRB 250521C/AT2025mgj: NOT optical observations of the afterglow candidate
  5. GRB 250530A: EP-FXT counterpart detection
  6. GRB 250530A: SVOM/VT optical upper limit
  7. GRB 250530A: SVOM/COLIBRÍ (FM-GFT) optical counterpart candidate retraction and detection limit
  8. GRB 250530A: SVOM/COLIBRÍ (FM-GFT) optical counterpart candidate
  9. GRB 250527D: CALET Gamma-Ray Burst Monitor detection
  10. GRB 250527C: Swift/UVOT Upper Limits
  11. EP J1350.0-8622: EP-FXT follow-up observation
  12. EP-WXT trigger 01709177124: confirmation of a stellar flare by BOOTES-6
  13. GRB 250521C (short): Zwicky Transient Facility identification of a possible fast optical transient counterpart
  14. GRB 250520A: Swift-BAT refined analysis
  15. GRB 250527C: Swift ToO observations
  16. GRB 250527C: Swift/BAT-GUANO arcminute localization of a burst
  17. EP250526a: SVOM/VT optical upper limit
  18. GRB 250521D: SVOM/GRM analysis suggests a possible “long” duration type I burst
  19. GRB 250527B: Tiled Swift observations
  20. GRB 250520A: Gemini-South optical afterglow detection
  21. EP250526a: refined analysis of the EP-WXT and EP-FXT observations
  22. GRB 250314A: CIDER NB1008 upper limit
  23. EP250526a: COLIBRÍ optical upper limits
  24. EP250526a: Global MASTER-Net observations report
  25. EP J1350.0-8622: BOOTES-6/DPRT optical upper limit
  26. EP-WXT trigger 01709176712: SVOM/C-GFT observations of blue-to-red color variation
  27. GRB 250520A: 3 GHz MeerKAT Detection
  28. GRB 250520A: 10 GHz VLA Afterglow Confirmation
  29. Fermi GRB 250523A: Global MASTER-Net observations report
  30. EP-WXT trigger 01709176712: GOTO observations confirm stellar counterpart variability
  31. GRB 250521A: GRBAlpha detection
  32. GRB 250520A: GRBAlpha detection
  33. GRB 250521B: SVOM/VT optical upper limit
  34. The EP-WXT trigger 01709176612: SVOM/VT optical observations
  35. The EP-WXT trigger 01709176612: refined analysis of the EP-FXT observation
  36. Fermi GRB 250522B: Global MASTER-Net observations report
  37. GRB 250521B: EP-FXT follow-up observation and afterglow candidates
  38. GRB 250521D: SVOM/VT optical observations
  39. EP#01709176612: Swift-XRT counterpart detection of flaring star
  40. Fermi GRB 250521D: Global MASTER-Net observations report
  41. GRB 250521D: DDOTI Optical Upper Limit
  42. GRB 250521D: GOTO detects LAST counterpart candidate prior to the GRB
  43. GRB 250521B: SVOM/COLIBRÍ (FM-GFT) optical upper limit
  44. GRB 250521D: LAST tentative optical counterpart candidate
  45. GRB 250520A: CALET Gamma-Ray Burst Monitor detection
  46. GRB 250520A: 10 GHz VLA radio source
  47. GRB 250521B: Swift ToO observations
  48. GRB 250521A: DDOTI Optical Upper Limit
  49. Konus-Wind detection of GRB 250520A (short/hard)
  50. GRB 250520A: VLT/FORS2 Optical Observation
  51. GRB 250502A: Tautenburg observations
  52. GRB 250520A: Swift/UVOT Upper Limits
  53. Konus-Wind detection of GRB 250516B
  54. IPN triangulation of GRB 250516B
  55. GRB 250520A: J-band observations with WINTER
  56. GRB 250520A: Gemini-South optical observations
  57. GRB 250520A: REM optical/NIR early observations
  58. GRB 250520A:SVOM/VT optical candidate
  59. GRB 250520A: COLIBRÍ optical upper limit
  60. GRB 250520A: DDOTI Optical Upper Limit
  61. GRB 250520A: AstroSat CZTI detection of a short burst
  62. GRB 250516B: GRBAlpha detection
  63. GRB 250520A: SVOM/GRM observation
  64. GRB 250520A: GOTO optical upper limit
  65. GRB 250516B: Insight-HXMT detection
  66. EP250427a/GRB250427A: VLA Detection of Radio Counterpart
  67. GRB 250516A: Swift-BAT refined analysis
  68. GRB 250516A: COLIBRÍ optical upper limit
  69. Konus-Wind detection of GRB 250516A
  70. GRB 250516B: NuSTAR Detection of the Prompt Emission
  71. Fermi GRB 250516A: Global MASTER-Net observations report
  72. GRB 250515A: Swift-XRT observations
  73. GRB 250515A: NOT classification of GOTO25cqo as a type-Ia SN
  74. GRB 250515A:COLIBRÍ optical observations of the GOTO candidate
  75. Swift GRB 250516A: Global MASTER-Net observations report
  76. GRB 250515A: 1.6m Mephisto optical detection
  77. GRB 250516A: AstroSat CZTI detection
  78. GRB 250515A/GOTO25cqo: SVOM/VT optical blue color
  79. GRB 250516A: Fermi GBM Observation
  80. GRB 250516A: Swift/UVOT Detection
  81. GRB 250515A: Swift ToO observations
  82. GRB 250512B / EP250512a: SVOM/GRM analysis
  83. GRB 250515A: GOTO candidate optical counterpart
  84. GRB 250424A: COLIBRÍ detection of the associated supernova
  85. Konus-Wind detection of GRB 250512B / EP250512a
  86. GRB 250502A: TESS observations
  87. GRB 250509A: Swift-BAT refined analysis
  88. LIGO/Virgo/KAGRA S250328ae: DECam DESGW Candidates (Final Epochs)
  89. Fermi GRB 250512A: Global MASTER-Net observations report
  90. Konus-Wind detection of GRB 250506A
  91. EP250512a/GRB 250512B: REM optical/NIR observations
  92. EP250511a: Koshka Zeiss-1000 Optical Upper Limit
  93. GRB 250507B: AstroSat CZTI detection
  94. EP250511a: Gemini optical counterpart observation
  95. EP250512a/GRB 250512B refined analysis of the EP-WXT and EP-FXT observations
  96. EP250512a/GRB 250512B: FTW optical and NIR observations of the counterpart
  97. EP250512a: Global MASTER-Net observations report
  98. EP250511a: FTW optical and NIR observations
  99. GRB 250512B/EP250512a: SVOM/VT optical fading
  100. GRB 250512B/EP250512a:SVOM/VT bright optical counterpart

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