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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"

44328 results found.

  1. Fermi trigger No 771072240: Global MASTER-Net observations report
  2. GRB 250609A: Swift/BAT-GUANO localization skymap of a likely short burst
  3. GRB 250605A: Swift/UVOT Upper Limits
  4. The EP-WXT trigger 01709178283 is likely a flaring star
  5. GRB 250608A: SVOM/GRM detection of a possible magnetar X-ray burst
  6. GRB 250529A: GOTO optical counterpart candidate (GOTO25dea/AT 2025ndt)
  7. GRB 250527C: CrAO Optical Upper Limit
  8. GRB 250609A: Fermi GBM Final Real-time Localization
  9. GRB 250607A: SVOM/GRM observation of a long burst
  10. EP-WXT trigger 01709178244: confirmation of a stellar flare by BOOTES-5 & BOOTES-7
  11. The EP-WXT trigger 01709178244 is likely a flaring star
  12. GRB 250607A: Fermi GBM Final Localization
  13. EP-WXT trigger 01709178069: confirmation of a stellar flare by BOOTES-6 & BOOTES-7
  14. The EP-WXT trigger 01709178069 is likely a flaring star
  15. GRB 250605A: SVOM/VT optical upper limit
  16. GRB 250605A: Swift-XRT refined Analysis
  17. EP/WXT 01709177873: GOTO observations confirm stellar variability
  18. GRB 250605A: Enhanced Swift-XRT position
  19. Fermi GRB 250606A: Global MASTER-Net observations report
  20. GRB 250606A: Fermi GBM Final Real-time Localization
  21. Fermi Gamma-ray Burst Monitor trigger 770867684/250606080 is not a GRB
  22. Fermi Gamma-ray Burst Monitor trigger 770867684/250606080 is not a GRB
  23. GRB 250602A: GECAM detection
  24. Fermi trigger No 770867684: Global MASTER-Net observations report
  25. The EP-WXT trigger 01709177873 is likely a flaring star
  26. GRB 250605A: LT optical observations
  27. GRB 250605A: Swift detection of a burst
  28. Swift GRB250605.79: Global MASTER-Net observations report
  29. Konus-Wind detection of GRB 250601A
  30. IPN triangulation of GRB 250404B
  31. IPN triangulation of GRB 250529A
  32. The EP-WXT trigger 01709177837 is likely a flaring star
  33. Fermi Gamma-ray Burst Monitor trigger 770470765/250601486 is not a GRB
  34. GRB 250601A: PRIME H band upper limit.
  35. GRB 250530A: SVOM/GRM analysis
  36. GRB 250601A: PRIME J band upper limit.
  37. Fermi Gamma-ray Burst Monitor trigger 770675211/250603852 is not a GRB
  38. GRB 250601A: VLT/FORS2 Optical Observation
  39. GRB 250601A: Fermi GBM Observation
  40. GRB 250602A: DDOTI Optical Follow-Up of the Fermi/LAT Localization
  41. GRB 250603A: Swift/UVOT Upper Limits
  42. GRB 250603A: Swift-XRT refined Analysis
  43. Fermi trigger No 770638414: Global MASTER-Net observations report
  44. GRB 250603A: Enhanced Swift-XRT position
  45. GRB 250603A: Swift-XRT position and confirmation of GRB nature
  46. Swift GRB250603.05: Global MASTER-Net observations report
  47. GRB 250603A: Swift detection of a burst or new Galactic transient Swift J0839.7-3916
  48. GRB 250602A: Fermi GBM Observation
  49. GRB 250602A: Fermi-LAT detection
  50. GRB 250602A: DDOTI Optical Upper Limit
  51. GRB 250530C: Swift-BAT refined analysis
  52. GRB 250521C: NOT spectroscopic observations exclude the afterglow candidate AT2025mgj
  53. GRB 250601A: EP-FXT follow-up observation and afterglow candidates
  54. GRB 250601A: Swift/XRT candidate afterglow
  55. GRB 250521C / AT2025mgj: Pan-STARRS multi-band and multi-epoch imaging and photometry
  56. GRB 250601A: Swift-XRT observations
  57. Fermi GRB 250601A: Global MASTER-Net observations report
  58. GRB 250602A: Fermi GBM Final Real-time Localization
  59. Fermi trigger No 770470765: Global MASTER-Net observations report
  60. GRB 250601A: Swift/BAT-GUANO arcminute localization of a likely short burst
  61. GRB 250601A: Swift ToO observations
  62. GRB 250530A: VLT/HAWK-I NIR counterpart fading
  63. GRB 250521C/AT2025mgj: FTW optical and NIR observations
  64. GRB 250601A: Fermi GBM Final Real-time Localization
  65. EP#01709177494: SVOM/VT optical observations
  66. Fermi GRB 250531A: Global MASTER-Net observations report
  67. GRB 250531A: Fermi GBM Final Real-time Localization
  68. EP#01709177494: Swift-XRT counterpart detection of known source
  69. GRB 250530C: BOOTES-7 optical upper limit
  70. GRB 250521C/ZTF25aarhkyn/AT2025mgj: COLIBRÍ optical observations
  71. GRB 250530C: Swift-XRT refined Analysis
  72. GRB 250530A: TNG detection of a NIR source inside the Swift/XRT error circle
  73. Swift GRB 250530C: Global MASTER-Net observations report
  74. GRB 250530C: Enhanced Swift-XRT position
  75. GRB 250530C: Swift detection of a burst
  76. GRB 250521C/AT2025mgj: NOT optical observations of the afterglow candidate
  77. GRB 250530A: EP-FXT counterpart detection
  78. GRB 250530A: SVOM/VT optical upper limit
  79. Fermi Gamma-ray Burst Monitor trigger 770296643/250530470 is not a GRB
  80. GRB 250530B: Fermi GBM Final Real-time Localization
  81. GRB 250530A: Swift-XRT counterpart detection
  82. GRB 250530A: SVOM/COLIBRÍ (FM-GFT) optical counterpart candidate retraction and detection limit
  83. GRB 250530A: SVOM/COLIBRÍ (FM-GFT) optical counterpart candidate
  84. GRB 250530A: SVOM detection of a burst
  85. GRB 250527D: CALET Gamma-Ray Burst Monitor detection
  86. GRB 250527C: Swift/UVOT Upper Limits
  87. GRB 250527D: Swift/BAT-GUANO localization skymap of a burst
  88. EP J1350.0-8622: EP-FXT follow-up observation
  89. GRB 250529B: Fermi GBM Final Real-time Localization
  90. GRB 250527B: Swift-XRT observations
  91. EP-WXT trigger 01709177124: confirmation of a stellar flare by BOOTES-6
  92. The EP-WXT trigger 01709177124 is likely a flaring star
  93. GRB 250529A: Fermi GBM Final Real-time Localization
  94. GRB 250521C (short): Zwicky Transient Facility identification of a possible fast optical transient counterpart
  95. GRB 250520A: Swift-BAT refined analysis
  96. GRB 250527C: Swift ToO observations
  97. GRB 250527C: Swift/BAT-GUANO arcminute localization of a burst
  98. EP250526a: SVOM/VT optical upper limit
  99. GRB 250521D: SVOM/GRM analysis suggests a possible “long” duration type I burst
  100. GRB 250527B: Tiled Swift observations

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