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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 260105A: Fermi GBM Final Real-time Localization
  2. FRB 20251229A: A potentially hyperactive repeating fast radio burst source
  3. EP260105a: refined analysis of the EP-WXT and EP-FXT observations
  4. EP260105a: LCO Optical Upper limit
  5. EP260104a: Global MASTER-Net observations report
  6. EP260104a: Einstein Probe detection of a fast X-ray transient
  7. GRB 260101A: COLIBRÍ optical upper limits
  8. EP260105a: Global MASTER-Net observations report
  9. EP260105a: Einstein Probe detection of an X-ray transient
  10. GRB 260103A: Insight-HXMT/HE detection
  11. GRB 260104A: COLIBRÍ optical upper limits
  12. GRB 260104C: Fermi GBM Final Real-time Localization
  13. Fermi GRB 260104B: Global MASTER-Net observations report
  14. Swift GRB 260104A: Global MASTER-Net observations report
  15. GRB 251230A/EP-WXT trigger 01709250693: Mephisto optical upper limits
  16. GRB 260104A: Swift-XRT refined Analysis
  17. GRB 260104A: Enhanced Swift-XRT position
  18. GRB 260101A: Swift/UVOT Detection
  19. GRB 260103A: GECAM-B observation of a burst
  20. GRB 260104B: Fermi GBM Final Localization
  21. GRB 260104A: Swift detection of a burst
  22. GRB 260103A: SVOM/GRM observation of a possible GRB
  23. Fermi-LAT Gamma-ray Observations of IceCube-251225A
  24. GRB 260101A: COLIBRÍ optical observations
  25. SVOM GRB260103.08: Global MASTER-Net observations report
  26. GRB 260102B: Fermi GBM Final Real-time Localization
  27. SVOM GRB260102A: Global MASTER-Net observations report
  28. Fermi GBM Sub-Threshold Detection of GRB 260102A
  29. GRB 260102A: EP-FXT follow-up observation
  30. EP260101a: Global MASTER-Net observations report
  31. GRB 260102A: LCO optical upper limits
  32. GRB 260102A: Swift-XRT observations
  33. GRB 260102A: SVOM/COLIBRÍ (FM-GFT) optical observations
  34. Fermi Gamma-ray Burst Monitor trigger 789047602/260102495 is not a GRB
  35. GRB 251230A / EP251230a: GECAM-B detection
  36. GRB 260102A: SVOM/VT optical counterpart
  37. GRB 251230A / EP251230a: Insight-HXMT/HE detection
  38. GRB 260102A: Swift ToO observations
  39. GRB 260101A: Fermi GBM Observation
  40. EP260101a: refined analysis of the EP-WXT and EP-FXT observations
  41. GRB 260102A: SVOM detection of a burst
  42. GRB 260101A: GECAM-B detection
  43. GRB 260101A: NOT spectroscopic observations
  44. GRB 260101A: SVOM/GRM observation
  45. GRB 260101A: Swift-XRT refined Analysis
  46. Swift GRB 260101A: Global MASTER-Net observations report
  47. GRB 260101A: Enhanced Swift-XRT position
  48. EP260101a: Einstein Probe detection of an X-ray transient
  49. GRB 260101A: OSIRIS+ redshift z = 2.623 for the new year burst
  50. GRB 260101A: LCO detection of the optical counterpart
  51. GRB 260101A: Swift detection of a burst with an optical counterpart
  52. GRB 260101A: Fermi GBM Final Real-time Localization
  53. SVOM GRB251231.57: Global MASTER-Net observations report
  54. GRB 251230A / EP251230a: SVOM/VT optical continued observations and upper limit
  55. GRB 251230A: GRANDMA/TAROT Early Detection
  56. GRB 251230A / EP251230a: further NOT optical observations revealing shallower decay or possible rebrightening
  57. GRB 251230A/EP251230a: Optical upper limit with Kinder observations
  58. EP251229a: Optical upper limit with Kinder observations
  59. GRB 251230A: 1.3m DFOT optical upper limit
  60. Fermi Gamma-ray Burst Monitor trigger 788833547/251231018 is not a GRB
  61. GRB 251230A: Swift-XRT refined Analysis
  62. GRB 251231A: Fermi GBM Final Real-time Localization
  63. GRB 251222A: Mondy Optical Observations
  64. EP251230a / GRB 251230A: refined analysis of the EP-WXT and EP-FXT observations
  65. GRB 251230A: Swift/UVOT detection
  66. GRB251230A: 7DT optical upper limits
  67. GRB 251230A / EP251230a: NOT observations and spectroscopic redshift upper limit z < 2.2
  68. EP251229a: BOOTES-2 early optical upper limit
  69. GRB 251230A: GOTO optical upper limit
  70. EP251229a: NOT optical upper limits
  71. GRB 251230A / EP251230a: SVOM/VT optical observation
  72. EP251229a: refined analysis of the EP-WXT and EP-FXT observations
  73. GRB 251230A: Enhanced Swift-XRT position
  74. GRB 251230A: Early optical counterpart detection by LCO.
  75. EP-WXT trigger 01709250662 Mephisto and 50cm telescope follow-up
  76. GRB 251230A: Optical Observations via Virtual Telescope Project, Italy
  77. EP251230a / GRB 251230A: Einstein Probe detection of an X-ray transient
  78. GRB 251230A/EP#01709250693 (likely EP251230a): FTW optical and NIR observations
  79. LIGO/Virgo/KAGRA S251112cm: Candidates from the NSF-DOE Vera C. Rubin Observatory
  80. Swift GRB 251230A: Global MASTER-Net observations report
  81. The EP-WXT trigger 01709250693/GRB 251230A: Las Cumbres detection of the optical counterpart
  82. EP251229a: Global MASTER-Net observations report
  83. EP251229a: Einstein Probe detection of an X-ray transient
  84. GRB 251230A: Swift detection of a burst with a bright optical counterpart
  85. GRB 251226A: Glowbug gamma-ray detection
  86. GRB 251222A/EP251222b: 1.6m Mephisto optical followup
  87. GRB 251129A: redshift correction and SN detection at z = 0.505 with GTC
  88. Fermi GRB 251228A: Global MASTER-Net observations report
  89. The EP-WXT trigger 01709250662 is likely a flaring star
  90. GRB 251228A: Fermi GBM Final Real-time Localization
  91. GRB 251226A: SVOM/GRM observation
  92. GRB 251226A: GECAM-B detection
  93. SVOM GRB251227.07: Global MASTER-Net observations report
  94. IceCube-251225A: Upper limits from a search for additional neutrino events in IceCube
  95. The EP-WXT trigger 01709250617 is likely a flaring star
  96. IceCube Alert 251225.84: Global MASTER-Net observations report
  97. IceCube-251225A - IceCube observation of a high-energy neutrino candidate track-like event
  98. Fermi Gamma-ray Burst Monitor trigger 788368008/251225630 is not a GRB
  99. GRB 251222A: NUTTelA-TAO Early Measurements
  100. GRB 251222A/EP251222b: Optical detection with Kinder observations

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