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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"
  1. Swift Trigger 1434591: possible GRB 260109C
  2. GRB 260109B: Fermi GBM Final Real-time Localization
  3. GRB 260102A: Swift-XRT afterglow detection
  4. GRB 260109A: Fermi GBM Final Real-time Localization
  5. GRB 260104A: Swift-BAT refined analysis
  6. GRB 260101A: Swift-BAT refined analysis
  7. Swift GRB 251230A: Global MASTER-Net OT detection
  8. Fermi GRB 260107A: Global MASTER-Net observations report
  9. GRB 260102A: AbAO optical observations
  10. GRB 260107A: Fermi GBM Final Real-time Localization
  11. EP260105b/EP-WXT trigger 01709251028: Einstein Probe detection of an X-ray transient
  12. The EP-WXT trigger 01709251112 is likely a flaring star
  13. Fermi GRB 260105A: Global MASTER-Net observations report
  14. GRB 260105B: Fermi GBM Detection
  15. EP260105a: FTW optical observations
  16. EP260104a: FTW optical observations
  17. GRB 260105B: BALROG localization (Fermi Trigger 789348101 / GRB 260105973)
  18. GRB 260105A: SVOM/GRM observation
  19. GRB 260105B: SVOM/GRM observation
  20. The EP-WXT trigger 01709251028 is likely a flaring star
  21. FRB 20251229A: COLIBRÍ optical upper limits
  22. Fermi GRB 260105B: Global MASTER-Net observations report
  23. EP260105a: SVOM/VT optical upperlimit
  24. GRB 260105B: Fermi GBM Final Real-time Localization
  25. GRB 260105A: Fermi GBM Final Real-time Localization
  26. FRB 20251229A: A potentially hyperactive repeating fast radio burst source
  27. EP260105a: refined analysis of the EP-WXT and EP-FXT observations
  28. EP260105a: LCO Optical Upper limit
  29. EP260104a: Global MASTER-Net observations report
  30. EP260104a: Einstein Probe detection of a fast X-ray transient
  31. GRB 260101A: COLIBRÍ optical upper limits
  32. EP260105a: Global MASTER-Net observations report
  33. EP260105a: Einstein Probe detection of an X-ray transient
  34. GRB 260103A: Insight-HXMT/HE detection
  35. GRB 260104A: COLIBRÍ optical upper limits
  36. GRB 260104C: Fermi GBM Final Real-time Localization
  37. Fermi GRB 260104B: Global MASTER-Net observations report
  38. Swift GRB 260104A: Global MASTER-Net observations report
  39. GRB 251230A/EP-WXT trigger 01709250693: Mephisto optical upper limits
  40. GRB 260104A: Swift-XRT refined Analysis
  41. GRB 260104A: Enhanced Swift-XRT position
  42. GRB 260101A: Swift/UVOT Detection
  43. GRB 260103A: GECAM-B observation of a burst
  44. GRB 260104B: Fermi GBM Final Localization
  45. GRB 260104A: Swift detection of a burst
  46. GRB 260103A: SVOM/GRM observation of a possible GRB
  47. Fermi-LAT Gamma-ray Observations of IceCube-251225A
  48. GRB 260101A: COLIBRÍ optical observations
  49. SVOM GRB260103.08: Global MASTER-Net observations report
  50. GRB 260102B: Fermi GBM Final Real-time Localization
  51. SVOM GRB260102A: Global MASTER-Net observations report
  52. Fermi GBM Sub-Threshold Detection of GRB 260102A
  53. GRB 260102A: EP-FXT follow-up observation
  54. EP260101a: Global MASTER-Net observations report
  55. GRB 260102A: LCO optical upper limits
  56. GRB 260102A: Swift-XRT observations
  57. GRB 260102A: SVOM/COLIBRÍ (FM-GFT) optical observations
  58. Fermi Gamma-ray Burst Monitor trigger 789047602/260102495 is not a GRB
  59. GRB 251230A / EP251230a: GECAM-B detection
  60. GRB 260102A: SVOM/VT optical counterpart
  61. GRB 251230A / EP251230a: Insight-HXMT/HE detection
  62. GRB 260102A: Swift ToO observations
  63. GRB 260101A: Fermi GBM Observation
  64. EP260101a: refined analysis of the EP-WXT and EP-FXT observations
  65. GRB 260102A: SVOM detection of a burst
  66. GRB 260101A: GECAM-B detection
  67. GRB 260101A: NOT spectroscopic observations
  68. GRB 260101A: SVOM/GRM observation
  69. GRB 260101A: Swift-XRT refined Analysis
  70. Swift GRB 260101A: Global MASTER-Net observations report
  71. GRB 260101A: Enhanced Swift-XRT position
  72. EP260101a: Einstein Probe detection of an X-ray transient
  73. GRB 260101A: OSIRIS+ redshift z = 2.623 for the new year burst
  74. GRB 260101A: LCO detection of the optical counterpart
  75. GRB 260101A: Swift detection of a burst with an optical counterpart
  76. GRB 260101A: Fermi GBM Final Real-time Localization
  77. SVOM GRB251231.57: Global MASTER-Net observations report
  78. GRB 251230A / EP251230a: SVOM/VT optical continued observations and upper limit
  79. GRB 251230A: GRANDMA/TAROT Early Detection
  80. GRB 251230A / EP251230a: further NOT optical observations revealing shallower decay or possible rebrightening
  81. GRB 251230A/EP251230a: Optical upper limit with Kinder observations
  82. EP251229a: Optical upper limit with Kinder observations
  83. GRB 251230A: 1.3m DFOT optical upper limit
  84. Fermi Gamma-ray Burst Monitor trigger 788833547/251231018 is not a GRB
  85. GRB 251230A: Swift-XRT refined Analysis
  86. GRB 251231A: Fermi GBM Final Real-time Localization
  87. GRB 251222A: Mondy Optical Observations
  88. EP251230a / GRB 251230A: refined analysis of the EP-WXT and EP-FXT observations
  89. GRB 251230A: Swift/UVOT detection
  90. GRB251230A: 7DT optical upper limits
  91. GRB 251230A / EP251230a: NOT observations and spectroscopic redshift upper limit z < 2.2
  92. EP251229a: BOOTES-2 early optical upper limit
  93. GRB 251230A: GOTO optical upper limit
  94. EP251229a: NOT optical upper limits
  95. GRB 251230A / EP251230a: SVOM/VT optical observation
  96. EP251229a: refined analysis of the EP-WXT and EP-FXT observations
  97. GRB 251230A: Enhanced Swift-XRT position
  98. GRB 251230A: Early optical counterpart detection by LCO.
  99. EP-WXT trigger 01709250662 Mephisto and 50cm telescope follow-up
  100. GRB 251230A: Optical Observations via Virtual Telescope Project, Italy

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