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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"

35987 results found.

  1. GRB 250612A: Swift detection of a burst or new Galactic transient Swift J1643.6-3854
  2. Fermi GBM Sub-Threshold Detection of GRB 250610B
  3. GRB 250610B: Swift/UVOT Detection
  4. GRB 250610B: SVOM/COLIBRÍ (FM-GFT) optical observations
  5. GRB 250610B: REM optical/NIR observations
  6. GRB 250610B: SVOM/VT optical shallow decay
  7. GRB 250610B: additional Liverpool Telescope optical observations
  8. GRB 250610B: SVOM/GRM analysis
  9. GRB 250610B: Fermi/GBM sub-threshold detection of a possibly hard burst
  10. GRB 250610B: EP-FXT follow-up observation and afterglow counterpart
  11. Fermi Gamma-ray Burst Monitor trigger 771286888/250610932 is not a GRB
  12. GRB 250610B: Swift-XRT counterpart detection
  13. GRB 250610B: SVOM/VT optical counterpart
  14. GRB 250610B: LT detection of the optical counterpart
  15. GRB 250610B: OHP/T120 optical counterpart candidate
  16. GRB 250610C: Fermi GBM Final Real-time Localization
  17. GRB 250610B: GOTO optical upper limit
  18. GRB 250610B : SVOM/GWAC-F60A and F50 observations
  19. GRB 250610B: SVOM detection of a long burst
  20. Fermi Gamma-ray Burst Monitor trigger 771256110/250610575 is not a GRB
  21. GRB 250610A: Fermi GBM Final Real-time Localization
  22. GRB 250605A: Swift-BAT refined analysis
  23. GRB 250609A: Fermi GBM Observation
  24. GRBAlpha reentry on June 9, 2025
  25. GRB 250609A: Swift/BAT-GUANO localization skymap of a likely short burst
  26. GRB 250605A: Swift/UVOT Upper Limits
  27. GRB 250608A: SVOM/GRM detection of a possible magnetar X-ray burst
  28. GRB 250529A: GOTO optical counterpart candidate (GOTO25dea/AT 2025ndt)
  29. GRB 250527C: CrAO Optical Upper Limit
  30. GRB 250609A: Fermi GBM Final Real-time Localization
  31. GRB 250607A: SVOM/GRM observation of a long burst
  32. GRB 250607A: Fermi GBM Final Localization
  33. GRB 250605A: SVOM/VT optical upper limit
  34. GRB 250605A: Swift-XRT refined Analysis
  35. GRB 250605A: Enhanced Swift-XRT position
  36. Fermi GRB 250606A: Global MASTER-Net observations report
  37. GRB 250606A: Fermi GBM Final Real-time Localization
  38. Fermi Gamma-ray Burst Monitor trigger 770867684/250606080 is not a GRB
  39. Fermi Gamma-ray Burst Monitor trigger 770867684/250606080 is not a GRB
  40. GRB 250602A: GECAM detection
  41. GRB 250605A: LT optical observations
  42. GRB 250605A: Swift detection of a burst
  43. Konus-Wind detection of GRB 250601A
  44. IPN triangulation of GRB 250404B
  45. IPN triangulation of GRB 250529A
  46. Fermi Gamma-ray Burst Monitor trigger 770470765/250601486 is not a GRB
  47. GRB 250601A: PRIME H band upper limit.
  48. GRB 250530A: SVOM/GRM analysis
  49. GRB 250601A: PRIME J band upper limit.
  50. Fermi Gamma-ray Burst Monitor trigger 770675211/250603852 is not a GRB
  51. GRB 250601A: VLT/FORS2 Optical Observation
  52. GRB 250601A: Fermi GBM Observation
  53. GRB 250602A: DDOTI Optical Follow-Up of the Fermi/LAT Localization
  54. GRB 250603A: Swift/UVOT Upper Limits
  55. GRB 250603A: Swift-XRT refined Analysis
  56. GRB 250603A: Enhanced Swift-XRT position
  57. GRB 250603A: Swift-XRT position and confirmation of GRB nature
  58. GRB 250603A: Swift detection of a burst or new Galactic transient Swift J0839.7-3916
  59. GRB 250602A: Fermi GBM Observation
  60. GRB 250602A: Fermi-LAT detection
  61. GRB 250602A: DDOTI Optical Upper Limit
  62. GRB 250530C: Swift-BAT refined analysis
  63. GRB 250521C: NOT spectroscopic observations exclude the afterglow candidate AT2025mgj
  64. GRB 250601A: EP-FXT follow-up observation and afterglow candidates
  65. GRB 250601A: Swift/XRT candidate afterglow
  66. GRB 250521C / AT2025mgj: Pan-STARRS multi-band and multi-epoch imaging and photometry
  67. GRB 250601A: Swift-XRT observations
  68. Fermi GRB 250601A: Global MASTER-Net observations report
  69. GRB 250602A: Fermi GBM Final Real-time Localization
  70. GRB 250601A: Swift/BAT-GUANO arcminute localization of a likely short burst
  71. GRB 250601A: Swift ToO observations
  72. GRB 250530A: VLT/HAWK-I NIR counterpart fading
  73. GRB 250521C/AT2025mgj: FTW optical and NIR observations
  74. GRB 250601A: Fermi GBM Final Real-time Localization
  75. Fermi GRB 250531A: Global MASTER-Net observations report
  76. GRB 250531A: Fermi GBM Final Real-time Localization
  77. GRB 250530C: BOOTES-7 optical upper limit
  78. GRB 250521C/ZTF25aarhkyn/AT2025mgj: COLIBRÍ optical observations
  79. GRB 250530C: Swift-XRT refined Analysis
  80. GRB 250530A: TNG detection of a NIR source inside the Swift/XRT error circle
  81. Swift GRB 250530C: Global MASTER-Net observations report
  82. GRB 250530C: Enhanced Swift-XRT position
  83. GRB 250530C: Swift detection of a burst
  84. GRB 250521C/AT2025mgj: NOT optical observations of the afterglow candidate
  85. GRB 250530A: EP-FXT counterpart detection
  86. GRB 250530A: SVOM/VT optical upper limit
  87. Fermi Gamma-ray Burst Monitor trigger 770296643/250530470 is not a GRB
  88. GRB 250530B: Fermi GBM Final Real-time Localization
  89. GRB 250530A: Swift-XRT counterpart detection
  90. GRB 250530A: SVOM/COLIBRÍ (FM-GFT) optical counterpart candidate retraction and detection limit
  91. GRB 250530A: SVOM/COLIBRÍ (FM-GFT) optical counterpart candidate
  92. GRB 250530A: SVOM detection of a burst
  93. GRB 250527D: CALET Gamma-Ray Burst Monitor detection
  94. GRB 250527C: Swift/UVOT Upper Limits
  95. GRB 250527D: Swift/BAT-GUANO localization skymap of a burst
  96. GRB 250529B: Fermi GBM Final Real-time Localization
  97. GRB 250527B: Swift-XRT observations
  98. GRB 250529A: Fermi GBM Final Real-time Localization
  99. GRB 250521C (short): Zwicky Transient Facility identification of a possible fast optical transient counterpart
  100. GRB 250520A: Swift-BAT refined analysis

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