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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"

28688 results found.

  1. GRB 250610B: GOTO optical upper limit
  2. EP250610a: Global MASTER-Net observations report
  3. GRB 250610B : SVOM/GWAC-F60A and F50 observations
  4. EP250610a: refined analysis of the EP-WXT and EP-FXT observations
  5. GRB 250605A: Swift-BAT refined analysis
  6. EP250610a: SVOM/VT optical upper limit
  7. EP250610a: REM optical/NIR observations
  8. GRB 250609A: Fermi GBM Observation
  9. EP250610a: COLIBRÍ optical upper limit
  10. GRB 250609A: Swift/BAT-GUANO localization skymap of a likely short burst
  11. GRB 250605A: Swift/UVOT Upper Limits
  12. GRB 250529A: GOTO optical counterpart candidate (GOTO25dea/AT 2025ndt)
  13. GRB 250527C: CrAO Optical Upper Limit
  14. GRB 250607A: SVOM/GRM observation of a long burst
  15. EP-WXT trigger 01709178244: confirmation of a stellar flare by BOOTES-5 & BOOTES-7
  16. EP-WXT trigger 01709178069: confirmation of a stellar flare by BOOTES-6 & BOOTES-7
  17. GRB 250605A: SVOM/VT optical upper limit
  18. Fermi GRB 250606A: Global MASTER-Net observations report
  19. GRB 250602A: GECAM detection
  20. GRB 250605A: LT optical observations
  21. Konus-Wind detection of GRB 250601A
  22. IPN triangulation of GRB 250404B
  23. IPN triangulation of GRB 250529A
  24. GRB 250601A: PRIME H band upper limit.
  25. GRB 250530A: SVOM/GRM analysis
  26. GRB 250601A: PRIME J band upper limit.
  27. GRB 250601A: VLT/FORS2 Optical Observation
  28. GRB 250601A: Fermi GBM Observation
  29. GRB 250602A: DDOTI Optical Follow-Up of the Fermi/LAT Localization
  30. GRB 250603A: Swift/UVOT Upper Limits
  31. GRB 250603A: Swift-XRT position and confirmation of GRB nature
  32. GRB 250602A: Fermi GBM Observation
  33. GRB 250602A: Fermi-LAT detection
  34. GRB 250602A: DDOTI Optical Upper Limit
  35. GRB 250530C: Swift-BAT refined analysis
  36. GRB 250521C: NOT spectroscopic observations exclude the afterglow candidate AT2025mgj
  37. GRB 250601A: EP-FXT follow-up observation and afterglow candidates
  38. GRB 250601A: Swift/XRT candidate afterglow
  39. GRB 250521C / AT2025mgj: Pan-STARRS multi-band and multi-epoch imaging and photometry
  40. Fermi GRB 250601A: Global MASTER-Net observations report
  41. GRB 250601A: Swift/BAT-GUANO arcminute localization of a likely short burst
  42. GRB 250601A: Swift ToO observations
  43. GRB 250530A: VLT/HAWK-I NIR counterpart fading
  44. GRB 250521C/AT2025mgj: FTW optical and NIR observations
  45. EP#01709177494: SVOM/VT optical observations
  46. Fermi GRB 250531A: Global MASTER-Net observations report
  47. GRB 250530C: BOOTES-7 optical upper limit
  48. GRB 250521C/ZTF25aarhkyn/AT2025mgj: COLIBRÍ optical observations
  49. GRB 250530A: TNG detection of a NIR source inside the Swift/XRT error circle
  50. Swift GRB 250530C: Global MASTER-Net observations report
  51. GRB 250521C/AT2025mgj: NOT optical observations of the afterglow candidate
  52. GRB 250530A: EP-FXT counterpart detection
  53. GRB 250530A: SVOM/VT optical upper limit
  54. GRB 250530A: SVOM/COLIBRÍ (FM-GFT) optical counterpart candidate retraction and detection limit
  55. GRB 250530A: SVOM/COLIBRÍ (FM-GFT) optical counterpart candidate
  56. GRB 250527D: CALET Gamma-Ray Burst Monitor detection
  57. GRB 250527C: Swift/UVOT Upper Limits
  58. EP J1350.0-8622: EP-FXT follow-up observation
  59. EP-WXT trigger 01709177124: confirmation of a stellar flare by BOOTES-6
  60. GRB 250521C (short): Zwicky Transient Facility identification of a possible fast optical transient counterpart
  61. GRB 250520A: Swift-BAT refined analysis
  62. GRB 250527C: Swift ToO observations
  63. GRB 250527C: Swift/BAT-GUANO arcminute localization of a burst
  64. EP250526a: SVOM/VT optical upper limit
  65. GRB 250521D: SVOM/GRM analysis suggests a possible “long” duration type I burst
  66. GRB 250527B: Tiled Swift observations
  67. GRB 250520A: Gemini-South optical afterglow detection
  68. EP250526a: refined analysis of the EP-WXT and EP-FXT observations
  69. GRB 250314A: CIDER NB1008 upper limit
  70. EP250526a: COLIBRÍ optical upper limits
  71. EP250526a: Global MASTER-Net observations report
  72. EP J1350.0-8622: BOOTES-6/DPRT optical upper limit
  73. EP-WXT trigger 01709176712: SVOM/C-GFT observations of blue-to-red color variation
  74. GRB 250520A: 3 GHz MeerKAT Detection
  75. GRB 250520A: 10 GHz VLA Afterglow Confirmation
  76. Fermi GRB 250523A: Global MASTER-Net observations report
  77. EP-WXT trigger 01709176712: GOTO observations confirm stellar counterpart variability
  78. GRB 250521A: GRBAlpha detection
  79. GRB 250520A: GRBAlpha detection
  80. GRB 250521B: SVOM/VT optical upper limit
  81. The EP-WXT trigger 01709176612: SVOM/VT optical observations
  82. The EP-WXT trigger 01709176612: refined analysis of the EP-FXT observation
  83. Fermi GRB 250522B: Global MASTER-Net observations report
  84. GRB 250521B: EP-FXT follow-up observation and afterglow candidates
  85. GRB 250521D: SVOM/VT optical observations
  86. EP#01709176612: Swift-XRT counterpart detection of flaring star
  87. Fermi GRB 250521D: Global MASTER-Net observations report
  88. GRB 250521D: DDOTI Optical Upper Limit
  89. GRB 250521D: GOTO detects LAST counterpart candidate prior to the GRB
  90. GRB 250521B: SVOM/COLIBRÍ (FM-GFT) optical upper limit
  91. GRB 250521D: LAST tentative optical counterpart candidate
  92. GRB 250520A: CALET Gamma-Ray Burst Monitor detection
  93. GRB 250520A: 10 GHz VLA radio source
  94. GRB 250521B: Swift ToO observations
  95. GRB 250521A: DDOTI Optical Upper Limit
  96. Konus-Wind detection of GRB 250520A (short/hard)
  97. GRB 250520A: VLT/FORS2 Optical Observation
  98. GRB 250502A: Tautenburg observations
  99. GRB 250520A: Swift/UVOT Upper Limits
  100. Konus-Wind detection of GRB 250516B

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