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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. SVOM GRB260103.08: Global MASTER-Net observations report
  2. GRB 260102B: Fermi GBM Final Real-time Localization
  3. SVOM GRB260102A: Global MASTER-Net observations report
  4. Fermi GBM Sub-Threshold Detection of GRB 260102A
  5. GRB 260102A: EP-FXT follow-up observation
  6. EP260101a: Global MASTER-Net observations report
  7. GRB 260102A: LCO optical upper limits
  8. GRB 260102A: Swift-XRT observations
  9. GRB 260102A: SVOM/COLIBRÍ (FM-GFT) optical observations
  10. Fermi Gamma-ray Burst Monitor trigger 789047602/260102495 is not a GRB
  11. GRB 251230A / EP251230a: GECAM-B detection
  12. GRB 260102A: SVOM/VT optical counterpart
  13. GRB 251230A / EP251230a: Insight-HXMT/HE detection
  14. GRB 260102A: Swift ToO observations
  15. GRB 260101A: Fermi GBM Observation
  16. EP260101a: refined analysis of the EP-WXT and EP-FXT observations
  17. GRB 260102A: SVOM detection of a burst
  18. GRB 260101A: GECAM-B detection
  19. GRB 260101A: NOT spectroscopic observations
  20. GRB 260101A: SVOM/GRM observation
  21. GRB 260101A: Swift-XRT refined Analysis
  22. Swift GRB 260101A: Global MASTER-Net observations report
  23. GRB 260101A: Enhanced Swift-XRT position
  24. EP260101a: Einstein Probe detection of an X-ray transient
  25. GRB 260101A: OSIRIS+ redshift z = 2.623 for the new year burst
  26. GRB 260101A: LCO detection of the optical counterpart
  27. GRB 260101A: Swift detection of a burst with an optical counterpart
  28. GRB 260101A: Fermi GBM Final Real-time Localization
  29. SVOM GRB251231.57: Global MASTER-Net observations report
  30. GRB 251230A / EP251230a: SVOM/VT optical continued observations and upper limit
  31. GRB 251230A: GRANDMA/TAROT Early Detection
  32. GRB 251230A / EP251230a: further NOT optical observations revealing shallower decay or possible rebrightening
  33. GRB 251230A/EP251230a: Optical upper limit with Kinder observations
  34. EP251229a: Optical upper limit with Kinder observations
  35. GRB 251230A: 1.3m DFOT optical upper limit
  36. Fermi Gamma-ray Burst Monitor trigger 788833547/251231018 is not a GRB
  37. GRB 251230A: Swift-XRT refined Analysis
  38. GRB 251231A: Fermi GBM Final Real-time Localization
  39. GRB 251222A: Mondy Optical Observations
  40. EP251230a / GRB 251230A: refined analysis of the EP-WXT and EP-FXT observations
  41. GRB 251230A: Swift/UVOT detection
  42. GRB251230A: 7DT optical upper limits
  43. GRB 251230A / EP251230a: NOT observations and spectroscopic redshift upper limit z < 2.2
  44. EP251229a: BOOTES-2 early optical upper limit
  45. GRB 251230A: GOTO optical upper limit
  46. EP251229a: NOT optical upper limits
  47. GRB 251230A / EP251230a: SVOM/VT optical observation
  48. EP251229a: refined analysis of the EP-WXT and EP-FXT observations
  49. GRB 251230A: Enhanced Swift-XRT position
  50. GRB 251230A: Early optical counterpart detection by LCO.
  51. EP-WXT trigger 01709250662 Mephisto and 50cm telescope follow-up
  52. GRB 251230A: Optical Observations via Virtual Telescope Project, Italy
  53. EP251230a / GRB 251230A: Einstein Probe detection of an X-ray transient
  54. GRB 251230A/EP#01709250693 (likely EP251230a): FTW optical and NIR observations
  55. LIGO/Virgo/KAGRA S251112cm: Candidates from the NSF-DOE Vera C. Rubin Observatory
  56. Swift GRB 251230A: Global MASTER-Net observations report
  57. The EP-WXT trigger 01709250693/GRB 251230A: Las Cumbres detection of the optical counterpart
  58. EP251229a: Global MASTER-Net observations report
  59. EP251229a: Einstein Probe detection of an X-ray transient
  60. GRB 251230A: Swift detection of a burst with a bright optical counterpart
  61. GRB 251226A: Glowbug gamma-ray detection
  62. GRB 251222A/EP251222b: 1.6m Mephisto optical followup
  63. GRB 251129A: redshift correction and SN detection at z = 0.505 with GTC
  64. Fermi GRB 251228A: Global MASTER-Net observations report
  65. The EP-WXT trigger 01709250662 is likely a flaring star
  66. GRB 251228A: Fermi GBM Final Real-time Localization
  67. GRB 251226A: SVOM/GRM observation
  68. GRB 251226A: GECAM-B detection
  69. SVOM GRB251227.07: Global MASTER-Net observations report
  70. IceCube-251225A: Upper limits from a search for additional neutrino events in IceCube
  71. The EP-WXT trigger 01709250617 is likely a flaring star
  72. IceCube Alert 251225.84: Global MASTER-Net observations report
  73. IceCube-251225A - IceCube observation of a high-energy neutrino candidate track-like event
  74. Fermi Gamma-ray Burst Monitor trigger 788368008/251225630 is not a GRB
  75. GRB 251222A: NUTTelA-TAO Early Measurements
  76. GRB 251222A/EP251222b: Optical detection with Kinder observations
  77. EP251222a: Optical upper limit with Kinder observations
  78. GRB 251221A: Swift-BAT refined analysis
  79. GRB 251222A/EP251222b: FTW optical and NIR observations
  80. EP251222a: FTW optical and NIR observations
  81. GRB 251205A: Kilonova-Catcher optical afterglow detection
  82. GRB 251222A: AbAO optical observations
  83. GRB 251222A / EP251222b: Kilonova-Catcher optical afterglow detection
  84. GRB 251129A / EP251129a: VLA detection of a radio counterpart
  85. EP251222a: VLT/FORS2 spectroscopic redshift z = 0.505
  86. GRB 251222A: ZTSH BVRI optical observations
  87. GRB 251222A: SVOM/COLIBRÍ (FM-GFT) optical observations
  88. GRB 251222A: Continued 1.3m DFOT optical observation
  89. EP251220a: 3.6m DOT optical afterglow detection
  90. GRB 251222A: Fermi GBM Observation
  91. EP251220a: CrAO ZTSh optical observations
  92. EP251221a: PRIME upper limit
  93. EP251222a: Global MASTER-Net observations report
  94. GRB 251222A / EP251222b: GECAM-B observation
  95. EP251221a: Liverpool Telescope upper limits
  96. EP251222a: refined analysis of the EP-WXT and EP-FXT observations
  97. EP251222b/GRB 251222A: refined analysis of the EP-WXT and EP-FXT observations
  98. Konus-Wind detection of GRB 251222A / EP251222b
  99. GRB 251222A: Swift-XRT afterglow detection
  100. GRB 251222A / EP251222b: LCO detection of the optical counterpart

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