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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"

11099 results found.

  1. Fermi Gamma-ray Burst Monitor trigger 770470765/250601486 is not a GRB
  2. GRB 250601A: PRIME H band upper limit.
  3. GRB 250601A: PRIME J band upper limit.
  4. Fermi Gamma-ray Burst Monitor trigger 770675211/250603852 is not a GRB
  5. GRB 250601A: VLT/FORS2 Optical Observation
  6. GRB 250601A: Fermi GBM Observation
  7. GRB 250602A: DDOTI Optical Follow-Up of the Fermi/LAT Localization
  8. Fermi trigger No 770638414: Global MASTER-Net observations report
  9. GRB 250603A: Swift detection of a burst or new Galactic transient Swift J0839.7-3916
  10. GRB 250602A: Fermi GBM Observation
  11. GRB 250602A: Fermi-LAT detection
  12. GRB 250602A: DDOTI Optical Upper Limit
  13. GRB 250521C: NOT spectroscopic observations exclude the afterglow candidate AT2025mgj
  14. GRB 250601A: EP-FXT follow-up observation and afterglow candidates
  15. GRB 250601A: Swift/XRT candidate afterglow
  16. GRB 250521C / AT2025mgj: Pan-STARRS multi-band and multi-epoch imaging and photometry
  17. Fermi GRB 250601A: Global MASTER-Net observations report
  18. GRB 250602A: Fermi GBM Final Real-time Localization
  19. Fermi trigger No 770470765: Global MASTER-Net observations report
  20. GRB 250601A: Swift/BAT-GUANO arcminute localization of a likely short burst
  21. GRB 250521C/AT2025mgj: FTW optical and NIR observations
  22. GRB 250601A: Fermi GBM Final Real-time Localization
  23. Fermi GRB 250531A: Global MASTER-Net observations report
  24. GRB 250531A: Fermi GBM Final Real-time Localization
  25. GRB 250521C/ZTF25aarhkyn/AT2025mgj: COLIBRÍ optical observations
  26. GRB 250521C/AT2025mgj: NOT optical observations of the afterglow candidate
  27. Fermi Gamma-ray Burst Monitor trigger 770296643/250530470 is not a GRB
  28. GRB 250530B: Fermi GBM Final Real-time Localization
  29. GRB 250529B: Fermi GBM Final Real-time Localization
  30. GRB 250529A: Fermi GBM Final Real-time Localization
  31. GRB 250521C (short): Zwicky Transient Facility identification of a possible fast optical transient counterpart
  32. GRB 250527C: Swift/BAT-GUANO arcminute localization of a burst
  33. GRB 250521D: SVOM/GRM analysis suggests a possible “long” duration type I burst
  34. Fermi trigger No 770058372: Global MASTER-Net observations report
  35. Fermi trigger No 770047117: Global MASTER-Net observations report
  36. GRB 250527A: Fermi GBM Final Localization
  37. Fermi GRB 250523A: Global MASTER-Net observations report
  38. Fermi trigger No 769611916: Global MASTER-Net observations report
  39. GRB 250521A: GRBAlpha detection
  40. GRB 250523A: BALROG localization (Fermi Trigger 769703188 / GRB 250523602)
  41. GRB 250523A: Fermi GBM Final Real-time Localization
  42. Fermi GRB 250522B: Global MASTER-Net observations report
  43. GRB 250522B: Fermi GBM Final Localization
  44. GRB 250521D: SVOM/VT optical observations
  45. GRB 250522A: Fermi GBM Final Real-time Localization
  46. Fermi GRB 250521D: Global MASTER-Net observations report
  47. Fermi trigger No 769533898: Global MASTER-Net observations report
  48. Fermi trigger No 769499303: Global MASTER-Net observations report
  49. GRB 250521D: DDOTI Optical Upper Limit
  50. GRB 250521D: GOTO detects LAST counterpart candidate prior to the GRB
  51. GRB 250521D: LAST tentative optical counterpart candidate
  52. GRB 250521D: Fermi GBM Final Real-time Localization
  53. GRB 250521C: Fermi GBM Final Localization
  54. GRB 250521A: DDOTI Optical Upper Limit
  55. GRB 250521A: Fermi GBM Final Real-time Localization
  56. GRB 250520B: Fermi GBM Final Real-time Localization
  57. GRB 250520A: DDOTI Optical Upper Limit
  58. GRB 250520A: AstroSat CZTI detection of a short burst
  59. GRB 250516A: COLIBRÍ optical upper limit
  60. Konus-Wind detection of GRB 250516A
  61. Fermi GRB 250516A: Global MASTER-Net observations report
  62. GRB 250515A: Swift-XRT observations
  63. GRB 250515A: NOT classification of GOTO25cqo as a type-Ia SN
  64. Fermi Gamma-ray Burst Monitor trigger 769160489/250517320 is not a GRB
  65. GRB 250515A:COLIBRÍ optical observations of the GOTO candidate
  66. GRB 250515A: 1.6m Mephisto optical detection
  67. GRB 250516A: AstroSat CZTI detection
  68. GRB 250515A/GOTO25cqo: SVOM/VT optical blue color
  69. GRB 250516A: Fermi GBM Observation
  70. GRB 250515A: Swift ToO observations
  71. GRB 250516A: Fermi GBM Final Real-time Localization
  72. GRB 250515A: GOTO candidate optical counterpart
  73. GRB 250515A: Fermi GBM Final Localization
  74. Fermi trigger No 768922089: Global MASTER-Net observations report
  75. Fermi GRB 250512A: Global MASTER-Net observations report
  76. Konus-Wind detection of GRB 250506A
  77. GRB 250506A: GRBAlpha detection
  78. GRB 250512A: Fermi GBM Final Real-time Localization
  79. GRB 250510B: Fermi GBM Observation
  80. Fermi GRB 250510C: Global MASTER-Net observations report
  81. Fermi GRB 250510B: Global MASTER-Net observations report
  82. GRB 250510C: Fermi GBM Final Real-time Localization
  83. GRB 250509A: Fermi GBM Observation
  84. GRB 250510B: Swift/BAT-GUANO localization skymap of a burst
  85. GRB 250510B: Fermi GBM Final Localization
  86. Fermi GRB 250509A: Global MASTER-Net observations report
  87. GRB 250509A: Fermi GBM Final Real-time Localization
  88. GRB 250506A: NOT optical upper limits
  89. GRB 250506A: GECAM detection
  90. GRB 250506A: SVOM/VT optical upper limit
  91. GRB 250506A: Swift/UVOT Upper Limits
  92. Fermi-LAT Gamma-ray Observations of IceCube-250506A
  93. GRB 250506A: Mephisto optical upper limits
  94. GRB 250504A: EIRSAT-1 GMOD Detection
  95. IceCube-250506A - IceCube observation of a high-energy neutrino candidate track-like event
  96. GRB 250506A: Xinglong 2.16m optical upper limit
  97. GRB 250506A: REM optical/NIR upper limits
  98. GRB 250506A: Fermi GBM Observation
  99. GRB 250506A: Swift XRT observations and possible counterpart detection
  100. GRB 250506A: TRT optical observations

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