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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. EP260110a: SVOM/C-GFT upper limit
  2. EP260110a: BOOTES-5/JGU optical upper limit
  3. EP260110a: Einstein Probe detection of an X-ray transient
  4. GRB 260109C: LCO optical upper limits
  5. GRB 260109C: Kilonova-Catcher optical upper limit
  6. EP260105b / GRB 260105C : Fermi-GBM Sub-Threshold Detection
  7. Swift Trigger 1434591: possible GRB 260109C
  8. GRB 260109B: Fermi GBM Final Real-time Localization
  9. GRB 260102A: Swift-XRT afterglow detection
  10. GRB 260109A: Fermi GBM Final Real-time Localization
  11. GRB 260104A: Swift-BAT refined analysis
  12. GRB 260101A: Swift-BAT refined analysis
  13. Swift GRB 251230A: Global MASTER-Net OT detection
  14. Fermi GRB 260107A: Global MASTER-Net observations report
  15. GRB 260102A: AbAO optical observations
  16. GRB 260107A: Fermi GBM Final Real-time Localization
  17. EP260105b/EP-WXT trigger 01709251028: Einstein Probe detection of an X-ray transient
  18. The EP-WXT trigger 01709251112 is likely a flaring star
  19. Fermi GRB 260105A: Global MASTER-Net observations report
  20. GRB 260105B: Fermi GBM Detection
  21. EP260105a: FTW optical observations
  22. EP260104a: FTW optical observations
  23. GRB 260105B: BALROG localization (Fermi Trigger 789348101 / GRB 260105973)
  24. GRB 260105A: SVOM/GRM observation
  25. GRB 260105B: SVOM/GRM observation
  26. The EP-WXT trigger 01709251028 is likely a flaring star
  27. FRB 20251229A: COLIBRÍ optical upper limits
  28. Fermi GRB 260105B: Global MASTER-Net observations report
  29. EP260105a: SVOM/VT optical upperlimit
  30. GRB 260105B: Fermi GBM Final Real-time Localization
  31. GRB 260105A: Fermi GBM Final Real-time Localization
  32. FRB 20251229A: A potentially hyperactive repeating fast radio burst source
  33. EP260105a: refined analysis of the EP-WXT and EP-FXT observations
  34. EP260105a: LCO Optical Upper limit
  35. EP260104a: Global MASTER-Net observations report
  36. EP260104a: Einstein Probe detection of a fast X-ray transient
  37. GRB 260101A: COLIBRÍ optical upper limits
  38. EP260105a: Global MASTER-Net observations report
  39. EP260105a: Einstein Probe detection of an X-ray transient
  40. GRB 260103A: Insight-HXMT/HE detection
  41. GRB 260104A: COLIBRÍ optical upper limits
  42. GRB 260104C: Fermi GBM Final Real-time Localization
  43. Fermi GRB 260104B: Global MASTER-Net observations report
  44. Swift GRB 260104A: Global MASTER-Net observations report
  45. GRB 251230A/EP-WXT trigger 01709250693: Mephisto optical upper limits
  46. GRB 260104A: Swift-XRT refined Analysis
  47. GRB 260104A: Enhanced Swift-XRT position
  48. GRB 260101A: Swift/UVOT Detection
  49. GRB 260103A: GECAM-B observation of a burst
  50. GRB 260104B: Fermi GBM Final Localization
  51. GRB 260104A: Swift detection of a burst
  52. GRB 260103A: SVOM/GRM observation of a possible GRB
  53. Fermi-LAT Gamma-ray Observations of IceCube-251225A
  54. GRB 260101A: COLIBRÍ optical observations
  55. SVOM GRB260103.08: Global MASTER-Net observations report
  56. GRB 260102B: Fermi GBM Final Real-time Localization
  57. SVOM GRB260102A: Global MASTER-Net observations report
  58. Fermi GBM Sub-Threshold Detection of GRB 260102A
  59. GRB 260102A: EP-FXT follow-up observation
  60. EP260101a: Global MASTER-Net observations report
  61. GRB 260102A: LCO optical upper limits
  62. GRB 260102A: Swift-XRT observations
  63. GRB 260102A: SVOM/COLIBRÍ (FM-GFT) optical observations
  64. Fermi Gamma-ray Burst Monitor trigger 789047602/260102495 is not a GRB
  65. GRB 251230A / EP251230a: GECAM-B detection
  66. GRB 260102A: SVOM/VT optical counterpart
  67. GRB 251230A / EP251230a: Insight-HXMT/HE detection
  68. GRB 260102A: Swift ToO observations
  69. GRB 260101A: Fermi GBM Observation
  70. EP260101a: refined analysis of the EP-WXT and EP-FXT observations
  71. GRB 260102A: SVOM detection of a burst
  72. GRB 260101A: GECAM-B detection
  73. GRB 260101A: NOT spectroscopic observations
  74. GRB 260101A: SVOM/GRM observation
  75. GRB 260101A: Swift-XRT refined Analysis
  76. Swift GRB 260101A: Global MASTER-Net observations report
  77. GRB 260101A: Enhanced Swift-XRT position
  78. EP260101a: Einstein Probe detection of an X-ray transient
  79. GRB 260101A: OSIRIS+ redshift z = 2.623 for the new year burst
  80. GRB 260101A: LCO detection of the optical counterpart
  81. GRB 260101A: Swift detection of a burst with an optical counterpart
  82. GRB 260101A: Fermi GBM Final Real-time Localization
  83. SVOM GRB251231.57: Global MASTER-Net observations report
  84. GRB 251230A / EP251230a: SVOM/VT optical continued observations and upper limit
  85. GRB 251230A: GRANDMA/TAROT Early Detection
  86. GRB 251230A / EP251230a: further NOT optical observations revealing shallower decay or possible rebrightening
  87. GRB 251230A/EP251230a: Optical upper limit with Kinder observations
  88. EP251229a: Optical upper limit with Kinder observations
  89. GRB 251230A: 1.3m DFOT optical upper limit
  90. Fermi Gamma-ray Burst Monitor trigger 788833547/251231018 is not a GRB
  91. GRB 251230A: Swift-XRT refined Analysis
  92. GRB 251231A: Fermi GBM Final Real-time Localization
  93. GRB 251222A: Mondy Optical Observations
  94. EP251230a / GRB 251230A: refined analysis of the EP-WXT and EP-FXT observations
  95. GRB 251230A: Swift/UVOT detection
  96. GRB251230A: 7DT optical upper limits
  97. GRB 251230A / EP251230a: NOT observations and spectroscopic redshift upper limit z < 2.2
  98. EP251229a: BOOTES-2 early optical upper limit
  99. GRB 251230A: GOTO optical upper limit
  100. EP251229a: NOT optical upper limits

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