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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. EP260105b/EP-WXT trigger 01709251028: Einstein Probe detection of an X-ray transient
  2. The EP-WXT trigger 01709251112 is likely a flaring star
  3. Fermi GRB 260105A: Global MASTER-Net observations report
  4. GRB 260105B: Fermi GBM Detection
  5. EP260105a: FTW optical observations
  6. EP260104a: FTW optical observations
  7. GRB 260105B: BALROG localization (Fermi Trigger 789348101 / GRB 260105973)
  8. GRB 260105A: SVOM/GRM observation
  9. GRB 260105B: SVOM/GRM observation
  10. The EP-WXT trigger 01709251028 is likely a flaring star
  11. FRB 20251229A: COLIBRÍ optical upper limits
  12. Fermi GRB 260105B: Global MASTER-Net observations report
  13. EP260105a: SVOM/VT optical upperlimit
  14. GRB 260105B: Fermi GBM Final Real-time Localization
  15. GRB 260105A: Fermi GBM Final Real-time Localization
  16. FRB 20251229A: A potentially hyperactive repeating fast radio burst source
  17. EP260105a: refined analysis of the EP-WXT and EP-FXT observations
  18. EP260105a: LCO Optical Upper limit
  19. EP260104a: Global MASTER-Net observations report
  20. EP260104a: Einstein Probe detection of a fast X-ray transient
  21. GRB 260101A: COLIBRÍ optical upper limits
  22. EP260105a: Global MASTER-Net observations report
  23. EP260105a: Einstein Probe detection of an X-ray transient
  24. GRB 260103A: Insight-HXMT/HE detection
  25. GRB 260104A: COLIBRÍ optical upper limits
  26. GRB 260104C: Fermi GBM Final Real-time Localization
  27. Fermi GRB 260104B: Global MASTER-Net observations report
  28. Swift GRB 260104A: Global MASTER-Net observations report
  29. GRB 251230A/EP-WXT trigger 01709250693: Mephisto optical upper limits
  30. GRB 260104A: Swift-XRT refined Analysis
  31. GRB 260104A: Enhanced Swift-XRT position
  32. GRB 260101A: Swift/UVOT Detection
  33. GRB 260103A: GECAM-B observation of a burst
  34. GRB 260104B: Fermi GBM Final Localization
  35. GRB 260104A: Swift detection of a burst
  36. GRB 260103A: SVOM/GRM observation of a possible GRB
  37. Fermi-LAT Gamma-ray Observations of IceCube-251225A
  38. GRB 260101A: COLIBRÍ optical observations
  39. SVOM GRB260103.08: Global MASTER-Net observations report
  40. GRB 260102B: Fermi GBM Final Real-time Localization
  41. SVOM GRB260102A: Global MASTER-Net observations report
  42. Fermi GBM Sub-Threshold Detection of GRB 260102A
  43. GRB 260102A: EP-FXT follow-up observation
  44. EP260101a: Global MASTER-Net observations report
  45. GRB 260102A: LCO optical upper limits
  46. GRB 260102A: Swift-XRT observations
  47. GRB 260102A: SVOM/COLIBRÍ (FM-GFT) optical observations
  48. Fermi Gamma-ray Burst Monitor trigger 789047602/260102495 is not a GRB
  49. GRB 251230A / EP251230a: GECAM-B detection
  50. GRB 260102A: SVOM/VT optical counterpart
  51. GRB 251230A / EP251230a: Insight-HXMT/HE detection
  52. GRB 260102A: Swift ToO observations
  53. GRB 260101A: Fermi GBM Observation
  54. EP260101a: refined analysis of the EP-WXT and EP-FXT observations
  55. GRB 260102A: SVOM detection of a burst
  56. GRB 260101A: GECAM-B detection
  57. GRB 260101A: NOT spectroscopic observations
  58. GRB 260101A: SVOM/GRM observation
  59. GRB 260101A: Swift-XRT refined Analysis
  60. Swift GRB 260101A: Global MASTER-Net observations report
  61. GRB 260101A: Enhanced Swift-XRT position
  62. EP260101a: Einstein Probe detection of an X-ray transient
  63. GRB 260101A: OSIRIS+ redshift z = 2.623 for the new year burst
  64. GRB 260101A: LCO detection of the optical counterpart
  65. GRB 260101A: Swift detection of a burst with an optical counterpart
  66. GRB 260101A: Fermi GBM Final Real-time Localization
  67. SVOM GRB251231.57: Global MASTER-Net observations report
  68. GRB 251230A / EP251230a: SVOM/VT optical continued observations and upper limit
  69. GRB 251230A: GRANDMA/TAROT Early Detection
  70. GRB 251230A / EP251230a: further NOT optical observations revealing shallower decay or possible rebrightening
  71. GRB 251230A/EP251230a: Optical upper limit with Kinder observations
  72. EP251229a: Optical upper limit with Kinder observations
  73. GRB 251230A: 1.3m DFOT optical upper limit
  74. Fermi Gamma-ray Burst Monitor trigger 788833547/251231018 is not a GRB
  75. GRB 251230A: Swift-XRT refined Analysis
  76. GRB 251231A: Fermi GBM Final Real-time Localization
  77. GRB 251222A: Mondy Optical Observations
  78. EP251230a / GRB 251230A: refined analysis of the EP-WXT and EP-FXT observations
  79. GRB 251230A: Swift/UVOT detection
  80. GRB251230A: 7DT optical upper limits
  81. GRB 251230A / EP251230a: NOT observations and spectroscopic redshift upper limit z < 2.2
  82. EP251229a: BOOTES-2 early optical upper limit
  83. GRB 251230A: GOTO optical upper limit
  84. EP251229a: NOT optical upper limits
  85. GRB 251230A / EP251230a: SVOM/VT optical observation
  86. EP251229a: refined analysis of the EP-WXT and EP-FXT observations
  87. GRB 251230A: Enhanced Swift-XRT position
  88. GRB 251230A: Early optical counterpart detection by LCO.
  89. EP-WXT trigger 01709250662 Mephisto and 50cm telescope follow-up
  90. GRB 251230A: Optical Observations via Virtual Telescope Project, Italy
  91. EP251230a / GRB 251230A: Einstein Probe detection of an X-ray transient
  92. GRB 251230A/EP#01709250693 (likely EP251230a): FTW optical and NIR observations
  93. LIGO/Virgo/KAGRA S251112cm: Candidates from the NSF-DOE Vera C. Rubin Observatory
  94. Swift GRB 251230A: Global MASTER-Net observations report
  95. The EP-WXT trigger 01709250693/GRB 251230A: Las Cumbres detection of the optical counterpart
  96. EP251229a: Global MASTER-Net observations report
  97. EP251229a: Einstein Probe detection of an X-ray transient
  98. GRB 251230A: Swift detection of a burst with a bright optical counterpart
  99. GRB 251226A: Glowbug gamma-ray detection
  100. GRB 251222A/EP251222b: 1.6m Mephisto optical followup

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