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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"

38926 results found.

  1. GRB 250612A: Swift detection of a burst or new Galactic transient Swift J1643.6-3854
  2. Swift GRB250612.04: Global MASTER-Net observations report
  3. Fermi GBM Sub-Threshold Detection of GRB 250610B
  4. GRB 250610B: Swift/UVOT Detection
  5. GRB 250610B: SVOM/COLIBRÍ (FM-GFT) optical observations
  6. EP250610a: TNG NIR upper limit
  7. GRB 250610B: REM optical/NIR observations
  8. GRB 250610B: SVOM/VT optical shallow decay
  9. GRB 250610B: additional Liverpool Telescope optical observations
  10. GRB 250610B: SVOM/GRM analysis
  11. GRB 250610B: Fermi/GBM sub-threshold detection of a possibly hard burst
  12. GRB 250610B: EP-FXT follow-up observation and afterglow counterpart
  13. Fermi Gamma-ray Burst Monitor trigger 771286888/250610932 is not a GRB
  14. GRB 250610B: Swift-XRT counterpart detection
  15. GRB 250610B: SVOM/VT optical counterpart
  16. GRB 250610B: LT detection of the optical counterpart
  17. GRB 250610B: OHP/T120 optical counterpart candidate
  18. GRB 250610C: Fermi GBM Final Real-time Localization
  19. GRB 250610B: GOTO optical upper limit
  20. EP250610a: Global MASTER-Net observations report
  21. GRB 250610B : SVOM/GWAC-F60A and F50 observations
  22. GRB 250610B: SVOM detection of a long burst
  23. Fermi Gamma-ray Burst Monitor trigger 771256110/250610575 is not a GRB
  24. GRB 250610A: Fermi GBM Final Real-time Localization
  25. GRB 250605A: Swift-BAT refined analysis
  26. EP250610a: REM optical/NIR observations
  27. GRB 250609A: Fermi GBM Observation
  28. GRBAlpha reentry on June 9, 2025
  29. EP250610a: COLIBRÍ optical upper limit
  30. Fermi trigger No 771072240: Global MASTER-Net observations report
  31. GRB 250609A: Swift/BAT-GUANO localization skymap of a likely short burst
  32. GRB 250605A: Swift/UVOT Upper Limits
  33. GRB 250608A: SVOM/GRM detection of a possible magnetar X-ray burst
  34. GRB 250529A: GOTO optical counterpart candidate (GOTO25dea/AT 2025ndt)
  35. GRB 250527C: CrAO Optical Upper Limit
  36. GRB 250609A: Fermi GBM Final Real-time Localization
  37. GRB 250607A: SVOM/GRM observation of a long burst
  38. GRB 250607A: Fermi GBM Final Localization
  39. GRB 250605A: SVOM/VT optical upper limit
  40. GRB 250605A: Swift-XRT refined Analysis
  41. GRB 250605A: Enhanced Swift-XRT position
  42. Fermi GRB 250606A: Global MASTER-Net observations report
  43. GRB 250606A: Fermi GBM Final Real-time Localization
  44. Fermi Gamma-ray Burst Monitor trigger 770867684/250606080 is not a GRB
  45. Fermi Gamma-ray Burst Monitor trigger 770867684/250606080 is not a GRB
  46. GRB 250602A: GECAM detection
  47. Fermi trigger No 770867684: Global MASTER-Net observations report
  48. GRB 250605A: LT optical observations
  49. GRB 250605A: Swift detection of a burst
  50. Swift GRB250605.79: Global MASTER-Net observations report
  51. Konus-Wind detection of GRB 250601A
  52. IPN triangulation of GRB 250404B
  53. IPN triangulation of GRB 250529A
  54. Fermi Gamma-ray Burst Monitor trigger 770470765/250601486 is not a GRB
  55. GRB 250601A: PRIME H band upper limit.
  56. GRB 250530A: SVOM/GRM analysis
  57. GRB 250601A: PRIME J band upper limit.
  58. Fermi Gamma-ray Burst Monitor trigger 770675211/250603852 is not a GRB
  59. GRB 250601A: VLT/FORS2 Optical Observation
  60. GRB 250601A: Fermi GBM Observation
  61. GRB 250602A: DDOTI Optical Follow-Up of the Fermi/LAT Localization
  62. GRB 250603A: Swift/UVOT Upper Limits
  63. GRB 250603A: Swift-XRT refined Analysis
  64. Fermi trigger No 770638414: Global MASTER-Net observations report
  65. GRB 250603A: Enhanced Swift-XRT position
  66. GRB 250603A: Swift-XRT position and confirmation of GRB nature
  67. Swift GRB250603.05: Global MASTER-Net observations report
  68. GRB 250603A: Swift detection of a burst or new Galactic transient Swift J0839.7-3916
  69. GRB 250602A: Fermi GBM Observation
  70. GRB 250602A: Fermi-LAT detection
  71. GRB 250602A: DDOTI Optical Upper Limit
  72. GRB 250530C: Swift-BAT refined analysis
  73. GRB 250521C: NOT spectroscopic observations exclude the afterglow candidate AT2025mgj
  74. GRB 250601A: EP-FXT follow-up observation and afterglow candidates
  75. GRB 250601A: Swift/XRT candidate afterglow
  76. GRB 250521C / AT2025mgj: Pan-STARRS multi-band and multi-epoch imaging and photometry
  77. GRB 250601A: Swift-XRT observations
  78. Fermi GRB 250601A: Global MASTER-Net observations report
  79. GRB 250602A: Fermi GBM Final Real-time Localization
  80. Fermi trigger No 770470765: Global MASTER-Net observations report
  81. GRB 250601A: Swift/BAT-GUANO arcminute localization of a likely short burst
  82. GRB 250601A: Swift ToO observations
  83. GRB 250530A: VLT/HAWK-I NIR counterpart fading
  84. GRB 250521C/AT2025mgj: FTW optical and NIR observations
  85. GRB 250601A: Fermi GBM Final Real-time Localization
  86. Fermi GRB 250531A: Global MASTER-Net observations report
  87. GRB 250531A: Fermi GBM Final Real-time Localization
  88. GRB 250530C: BOOTES-7 optical upper limit
  89. GRB 250521C/ZTF25aarhkyn/AT2025mgj: COLIBRÍ optical observations
  90. GRB 250530C: Swift-XRT refined Analysis
  91. GRB 250530A: TNG detection of a NIR source inside the Swift/XRT error circle
  92. Swift GRB 250530C: Global MASTER-Net observations report
  93. GRB 250530C: Enhanced Swift-XRT position
  94. GRB 250530C: Swift detection of a burst
  95. GRB 250521C/AT2025mgj: NOT optical observations of the afterglow candidate
  96. GRB 250530A: EP-FXT counterpart detection
  97. GRB 250530A: SVOM/VT optical upper limit
  98. Fermi Gamma-ray Burst Monitor trigger 770296643/250530470 is not a GRB
  99. GRB 250530B: Fermi GBM Final Real-time Localization
  100. GRB 250530A: Swift-XRT counterpart detection

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