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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. Fermi GRB 260111A: Global MASTER-Net observations report
  2. GRB 260111A: Fermi GBM Final Real-time Localization
  3. Swift trigger 1436759 is not an astrophysical event
  4. EP260110a: KAIT optical upper limit
  5. EP260110a: refined analysis of the EP-WXT and EP-FXT observations
  6. EP 260110a: COLIBRÍ optical observations
  7. EP260110a: SVOM/C-GFT upper limit
  8. EP260110a: BOOTES-5/JGU optical upper limit
  9. EP260110a: Einstein Probe detection of an X-ray transient
  10. GRB 260109C: LCO optical upper limits
  11. GRB 260109C: Kilonova-Catcher optical upper limit
  12. EP260105b / GRB 260105C : Fermi-GBM Sub-Threshold Detection
  13. Swift Trigger 1434591: possible GRB 260109C
  14. GRB 260109B: Fermi GBM Final Real-time Localization
  15. GRB 260102A: Swift-XRT afterglow detection
  16. GRB 260109A: Fermi GBM Final Real-time Localization
  17. GRB 260104A: Swift-BAT refined analysis
  18. GRB 260101A: Swift-BAT refined analysis
  19. Swift GRB 251230A: Global MASTER-Net OT detection
  20. Fermi GRB 260107A: Global MASTER-Net observations report
  21. GRB 260102A: AbAO optical observations
  22. GRB 260107A: Fermi GBM Final Real-time Localization
  23. EP260105b/EP-WXT trigger 01709251028: Einstein Probe detection of an X-ray transient
  24. The EP-WXT trigger 01709251112 is likely a flaring star
  25. Fermi GRB 260105A: Global MASTER-Net observations report
  26. GRB 260105B: Fermi GBM Detection
  27. EP260105a: FTW optical observations
  28. EP260104a: FTW optical observations
  29. GRB 260105B: BALROG localization (Fermi Trigger 789348101 / GRB 260105973)
  30. GRB 260105A: SVOM/GRM observation
  31. GRB 260105B: SVOM/GRM observation
  32. The EP-WXT trigger 01709251028 is likely a flaring star
  33. FRB 20251229A: COLIBRÍ optical upper limits
  34. Fermi GRB 260105B: Global MASTER-Net observations report
  35. EP260105a: SVOM/VT optical upperlimit
  36. GRB 260105B: Fermi GBM Final Real-time Localization
  37. GRB 260105A: Fermi GBM Final Real-time Localization
  38. FRB 20251229A: A potentially hyperactive repeating fast radio burst source
  39. EP260105a: refined analysis of the EP-WXT and EP-FXT observations
  40. EP260105a: LCO Optical Upper limit
  41. EP260104a: Global MASTER-Net observations report
  42. EP260104a: Einstein Probe detection of a fast X-ray transient
  43. GRB 260101A: COLIBRÍ optical upper limits
  44. EP260105a: Global MASTER-Net observations report
  45. EP260105a: Einstein Probe detection of an X-ray transient
  46. GRB 260103A: Insight-HXMT/HE detection
  47. GRB 260104A: COLIBRÍ optical upper limits
  48. GRB 260104C: Fermi GBM Final Real-time Localization
  49. Fermi GRB 260104B: Global MASTER-Net observations report
  50. Swift GRB 260104A: Global MASTER-Net observations report
  51. GRB 251230A/EP-WXT trigger 01709250693: Mephisto optical upper limits
  52. GRB 260104A: Swift-XRT refined Analysis
  53. GRB 260104A: Enhanced Swift-XRT position
  54. GRB 260101A: Swift/UVOT Detection
  55. GRB 260103A: GECAM-B observation of a burst
  56. GRB 260104B: Fermi GBM Final Localization
  57. GRB 260104A: Swift detection of a burst
  58. GRB 260103A: SVOM/GRM observation of a possible GRB
  59. Fermi-LAT Gamma-ray Observations of IceCube-251225A
  60. GRB 260101A: COLIBRÍ optical observations
  61. SVOM GRB260103.08: Global MASTER-Net observations report
  62. GRB 260102B: Fermi GBM Final Real-time Localization
  63. SVOM GRB260102A: Global MASTER-Net observations report
  64. Fermi GBM Sub-Threshold Detection of GRB 260102A
  65. GRB 260102A: EP-FXT follow-up observation
  66. EP260101a: Global MASTER-Net observations report
  67. GRB 260102A: LCO optical upper limits
  68. GRB 260102A: Swift-XRT observations
  69. GRB 260102A: SVOM/COLIBRÍ (FM-GFT) optical observations
  70. Fermi Gamma-ray Burst Monitor trigger 789047602/260102495 is not a GRB
  71. GRB 251230A / EP251230a: GECAM-B detection
  72. GRB 260102A: SVOM/VT optical counterpart
  73. GRB 251230A / EP251230a: Insight-HXMT/HE detection
  74. GRB 260102A: Swift ToO observations
  75. GRB 260101A: Fermi GBM Observation
  76. EP260101a: refined analysis of the EP-WXT and EP-FXT observations
  77. GRB 260102A: SVOM detection of a burst
  78. GRB 260101A: GECAM-B detection
  79. GRB 260101A: NOT spectroscopic observations
  80. GRB 260101A: SVOM/GRM observation
  81. GRB 260101A: Swift-XRT refined Analysis
  82. Swift GRB 260101A: Global MASTER-Net observations report
  83. GRB 260101A: Enhanced Swift-XRT position
  84. EP260101a: Einstein Probe detection of an X-ray transient
  85. GRB 260101A: OSIRIS+ redshift z = 2.623 for the new year burst
  86. GRB 260101A: LCO detection of the optical counterpart
  87. GRB 260101A: Swift detection of a burst with an optical counterpart
  88. GRB 260101A: Fermi GBM Final Real-time Localization
  89. SVOM GRB251231.57: Global MASTER-Net observations report
  90. GRB 251230A / EP251230a: SVOM/VT optical continued observations and upper limit
  91. GRB 251230A: GRANDMA/TAROT Early Detection
  92. GRB 251230A / EP251230a: further NOT optical observations revealing shallower decay or possible rebrightening
  93. GRB 251230A/EP251230a: Optical upper limit with Kinder observations
  94. EP251229a: Optical upper limit with Kinder observations
  95. GRB 251230A: 1.3m DFOT optical upper limit
  96. Fermi Gamma-ray Burst Monitor trigger 788833547/251231018 is not a GRB
  97. GRB 251230A: Swift-XRT refined Analysis
  98. GRB 251231A: Fermi GBM Final Real-time Localization
  99. GRB 251222A: Mondy Optical Observations
  100. EP251230a / GRB 251230A: refined analysis of the EP-WXT and EP-FXT observations

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