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

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