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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"

28685 results found.

  1. EP250610a: refined analysis of the EP-WXT and EP-FXT observations
  2. GRB 250605A: Swift-BAT refined analysis
  3. EP250610a: SVOM/VT optical upper limit
  4. EP250610a: REM optical/NIR observations
  5. GRB 250609A: Fermi GBM Observation
  6. EP250610a: COLIBRÍ optical upper limit
  7. GRB 250609A: Swift/BAT-GUANO localization skymap of a likely short burst
  8. GRB 250605A: Swift/UVOT Upper Limits
  9. GRB 250529A: GOTO optical counterpart candidate (GOTO25dea/AT 2025ndt)
  10. GRB 250527C: CrAO Optical Upper Limit
  11. GRB 250607A: SVOM/GRM observation of a long burst
  12. EP-WXT trigger 01709178244: confirmation of a stellar flare by BOOTES-5 & BOOTES-7
  13. EP-WXT trigger 01709178069: confirmation of a stellar flare by BOOTES-6 & BOOTES-7
  14. GRB 250605A: SVOM/VT optical upper limit
  15. Fermi GRB 250606A: Global MASTER-Net observations report
  16. GRB 250602A: GECAM detection
  17. GRB 250605A: LT optical observations
  18. Konus-Wind detection of GRB 250601A
  19. IPN triangulation of GRB 250404B
  20. IPN triangulation of GRB 250529A
  21. GRB 250601A: PRIME H band upper limit.
  22. GRB 250530A: SVOM/GRM analysis
  23. GRB 250601A: PRIME J band upper limit.
  24. GRB 250601A: VLT/FORS2 Optical Observation
  25. GRB 250601A: Fermi GBM Observation
  26. GRB 250602A: DDOTI Optical Follow-Up of the Fermi/LAT Localization
  27. GRB 250603A: Swift/UVOT Upper Limits
  28. GRB 250603A: Swift-XRT position and confirmation of GRB nature
  29. GRB 250602A: Fermi GBM Observation
  30. GRB 250602A: Fermi-LAT detection
  31. GRB 250602A: DDOTI Optical Upper Limit
  32. GRB 250530C: Swift-BAT refined analysis
  33. GRB 250521C: NOT spectroscopic observations exclude the afterglow candidate AT2025mgj
  34. GRB 250601A: EP-FXT follow-up observation and afterglow candidates
  35. GRB 250601A: Swift/XRT candidate afterglow
  36. GRB 250521C / AT2025mgj: Pan-STARRS multi-band and multi-epoch imaging and photometry
  37. Fermi GRB 250601A: Global MASTER-Net observations report
  38. GRB 250601A: Swift/BAT-GUANO arcminute localization of a likely short burst
  39. GRB 250601A: Swift ToO observations
  40. GRB 250530A: VLT/HAWK-I NIR counterpart fading
  41. GRB 250521C/AT2025mgj: FTW optical and NIR observations
  42. EP#01709177494: SVOM/VT optical observations
  43. Fermi GRB 250531A: Global MASTER-Net observations report
  44. GRB 250530C: BOOTES-7 optical upper limit
  45. GRB 250521C/ZTF25aarhkyn/AT2025mgj: COLIBRÍ optical observations
  46. GRB 250530A: TNG detection of a NIR source inside the Swift/XRT error circle
  47. Swift GRB 250530C: Global MASTER-Net observations report
  48. GRB 250521C/AT2025mgj: NOT optical observations of the afterglow candidate
  49. GRB 250530A: EP-FXT counterpart detection
  50. GRB 250530A: SVOM/VT optical upper limit
  51. GRB 250530A: SVOM/COLIBRÍ (FM-GFT) optical counterpart candidate retraction and detection limit
  52. GRB 250530A: SVOM/COLIBRÍ (FM-GFT) optical counterpart candidate
  53. GRB 250527D: CALET Gamma-Ray Burst Monitor detection
  54. GRB 250527C: Swift/UVOT Upper Limits
  55. EP J1350.0-8622: EP-FXT follow-up observation
  56. EP-WXT trigger 01709177124: confirmation of a stellar flare by BOOTES-6
  57. GRB 250521C (short): Zwicky Transient Facility identification of a possible fast optical transient counterpart
  58. GRB 250520A: Swift-BAT refined analysis
  59. GRB 250527C: Swift ToO observations
  60. GRB 250527C: Swift/BAT-GUANO arcminute localization of a burst
  61. EP250526a: SVOM/VT optical upper limit
  62. GRB 250521D: SVOM/GRM analysis suggests a possible “long” duration type I burst
  63. GRB 250527B: Tiled Swift observations
  64. GRB 250520A: Gemini-South optical afterglow detection
  65. EP250526a: refined analysis of the EP-WXT and EP-FXT observations
  66. GRB 250314A: CIDER NB1008 upper limit
  67. EP250526a: COLIBRÍ optical upper limits
  68. EP250526a: Global MASTER-Net observations report
  69. EP J1350.0-8622: BOOTES-6/DPRT optical upper limit
  70. EP-WXT trigger 01709176712: SVOM/C-GFT observations of blue-to-red color variation
  71. GRB 250520A: 3 GHz MeerKAT Detection
  72. GRB 250520A: 10 GHz VLA Afterglow Confirmation
  73. Fermi GRB 250523A: Global MASTER-Net observations report
  74. EP-WXT trigger 01709176712: GOTO observations confirm stellar counterpart variability
  75. GRB 250521A: GRBAlpha detection
  76. GRB 250520A: GRBAlpha detection
  77. GRB 250521B: SVOM/VT optical upper limit
  78. The EP-WXT trigger 01709176612: SVOM/VT optical observations
  79. The EP-WXT trigger 01709176612: refined analysis of the EP-FXT observation
  80. Fermi GRB 250522B: Global MASTER-Net observations report
  81. GRB 250521B: EP-FXT follow-up observation and afterglow candidates
  82. GRB 250521D: SVOM/VT optical observations
  83. EP#01709176612: Swift-XRT counterpart detection of flaring star
  84. Fermi GRB 250521D: Global MASTER-Net observations report
  85. GRB 250521D: DDOTI Optical Upper Limit
  86. GRB 250521D: GOTO detects LAST counterpart candidate prior to the GRB
  87. GRB 250521B: SVOM/COLIBRÍ (FM-GFT) optical upper limit
  88. GRB 250521D: LAST tentative optical counterpart candidate
  89. GRB 250520A: CALET Gamma-Ray Burst Monitor detection
  90. GRB 250520A: 10 GHz VLA radio source
  91. GRB 250521B: Swift ToO observations
  92. GRB 250521A: DDOTI Optical Upper Limit
  93. Konus-Wind detection of GRB 250520A (short/hard)
  94. GRB 250520A: VLT/FORS2 Optical Observation
  95. GRB 250502A: Tautenburg observations
  96. GRB 250520A: Swift/UVOT Upper Limits
  97. Konus-Wind detection of GRB 250516B
  98. IPN triangulation of GRB 250516B
  99. GRB 250520A: J-band observations with WINTER
  100. GRB 250520A: Gemini-South optical observations

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