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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. EP260104a: Global MASTER-Net observations report
  2. EP260104a: Einstein Probe detection of a fast X-ray transient
  3. GRB 260101A: COLIBRÍ optical upper limits
  4. EP260105a: Global MASTER-Net observations report
  5. EP260105a: Einstein Probe detection of an X-ray transient
  6. GRB 260103A: Insight-HXMT/HE detection
  7. GRB 260104A: COLIBRÍ optical upper limits
  8. GRB 260104C: Fermi GBM Final Real-time Localization
  9. Fermi GRB 260104B: Global MASTER-Net observations report
  10. Swift GRB 260104A: Global MASTER-Net observations report
  11. GRB 251230A/EP-WXT trigger 01709250693: Mephisto optical upper limits
  12. GRB 260104A: Swift-XRT refined Analysis
  13. GRB 260104A: Enhanced Swift-XRT position
  14. GRB 260101A: Swift/UVOT Detection
  15. GRB 260103A: GECAM-B observation of a burst
  16. GRB 260104B: Fermi GBM Final Localization
  17. GRB 260104A: Swift detection of a burst
  18. GRB 260103A: SVOM/GRM observation of a possible GRB
  19. Fermi-LAT Gamma-ray Observations of IceCube-251225A
  20. GRB 260101A: COLIBRÍ optical observations
  21. SVOM GRB260103.08: Global MASTER-Net observations report
  22. GRB 260102B: Fermi GBM Final Real-time Localization
  23. SVOM GRB260102A: Global MASTER-Net observations report
  24. Fermi GBM Sub-Threshold Detection of GRB 260102A
  25. GRB 260102A: EP-FXT follow-up observation
  26. EP260101a: Global MASTER-Net observations report
  27. GRB 260102A: LCO optical upper limits
  28. GRB 260102A: Swift-XRT observations
  29. GRB 260102A: SVOM/COLIBRÍ (FM-GFT) optical observations
  30. Fermi Gamma-ray Burst Monitor trigger 789047602/260102495 is not a GRB
  31. GRB 251230A / EP251230a: GECAM-B detection
  32. GRB 260102A: SVOM/VT optical counterpart
  33. GRB 251230A / EP251230a: Insight-HXMT/HE detection
  34. GRB 260102A: Swift ToO observations
  35. GRB 260101A: Fermi GBM Observation
  36. EP260101a: refined analysis of the EP-WXT and EP-FXT observations
  37. GRB 260102A: SVOM detection of a burst
  38. GRB 260101A: GECAM-B detection
  39. GRB 260101A: NOT spectroscopic observations
  40. GRB 260101A: SVOM/GRM observation
  41. GRB 260101A: Swift-XRT refined Analysis
  42. Swift GRB 260101A: Global MASTER-Net observations report
  43. GRB 260101A: Enhanced Swift-XRT position
  44. EP260101a: Einstein Probe detection of an X-ray transient
  45. GRB 260101A: OSIRIS+ redshift z = 2.623 for the new year burst
  46. GRB 260101A: LCO detection of the optical counterpart
  47. GRB 260101A: Swift detection of a burst with an optical counterpart
  48. GRB 260101A: Fermi GBM Final Real-time Localization
  49. SVOM GRB251231.57: Global MASTER-Net observations report
  50. GRB 251230A / EP251230a: SVOM/VT optical continued observations and upper limit
  51. GRB 251230A: GRANDMA/TAROT Early Detection
  52. GRB 251230A / EP251230a: further NOT optical observations revealing shallower decay or possible rebrightening
  53. GRB 251230A/EP251230a: Optical upper limit with Kinder observations
  54. EP251229a: Optical upper limit with Kinder observations
  55. GRB 251230A: 1.3m DFOT optical upper limit
  56. Fermi Gamma-ray Burst Monitor trigger 788833547/251231018 is not a GRB
  57. GRB 251230A: Swift-XRT refined Analysis
  58. GRB 251231A: Fermi GBM Final Real-time Localization
  59. GRB 251222A: Mondy Optical Observations
  60. EP251230a / GRB 251230A: refined analysis of the EP-WXT and EP-FXT observations
  61. GRB 251230A: Swift/UVOT detection
  62. GRB251230A: 7DT optical upper limits
  63. GRB 251230A / EP251230a: NOT observations and spectroscopic redshift upper limit z < 2.2
  64. EP251229a: BOOTES-2 early optical upper limit
  65. GRB 251230A: GOTO optical upper limit
  66. EP251229a: NOT optical upper limits
  67. GRB 251230A / EP251230a: SVOM/VT optical observation
  68. EP251229a: refined analysis of the EP-WXT and EP-FXT observations
  69. GRB 251230A: Enhanced Swift-XRT position
  70. GRB 251230A: Early optical counterpart detection by LCO.
  71. EP-WXT trigger 01709250662 Mephisto and 50cm telescope follow-up
  72. GRB 251230A: Optical Observations via Virtual Telescope Project, Italy
  73. EP251230a / GRB 251230A: Einstein Probe detection of an X-ray transient
  74. GRB 251230A/EP#01709250693 (likely EP251230a): FTW optical and NIR observations
  75. LIGO/Virgo/KAGRA S251112cm: Candidates from the NSF-DOE Vera C. Rubin Observatory
  76. Swift GRB 251230A: Global MASTER-Net observations report
  77. The EP-WXT trigger 01709250693/GRB 251230A: Las Cumbres detection of the optical counterpart
  78. EP251229a: Global MASTER-Net observations report
  79. EP251229a: Einstein Probe detection of an X-ray transient
  80. GRB 251230A: Swift detection of a burst with a bright optical counterpart
  81. GRB 251226A: Glowbug gamma-ray detection
  82. GRB 251222A/EP251222b: 1.6m Mephisto optical followup
  83. GRB 251129A: redshift correction and SN detection at z = 0.505 with GTC
  84. Fermi GRB 251228A: Global MASTER-Net observations report
  85. The EP-WXT trigger 01709250662 is likely a flaring star
  86. GRB 251228A: Fermi GBM Final Real-time Localization
  87. GRB 251226A: SVOM/GRM observation
  88. GRB 251226A: GECAM-B detection
  89. SVOM GRB251227.07: Global MASTER-Net observations report
  90. IceCube-251225A: Upper limits from a search for additional neutrino events in IceCube
  91. The EP-WXT trigger 01709250617 is likely a flaring star
  92. IceCube Alert 251225.84: Global MASTER-Net observations report
  93. IceCube-251225A - IceCube observation of a high-energy neutrino candidate track-like event
  94. Fermi Gamma-ray Burst Monitor trigger 788368008/251225630 is not a GRB
  95. GRB 251222A: NUTTelA-TAO Early Measurements
  96. GRB 251222A/EP251222b: Optical detection with Kinder observations
  97. EP251222a: Optical upper limit with Kinder observations
  98. GRB 251221A: Swift-BAT refined analysis
  99. GRB 251222A/EP251222b: FTW optical and NIR observations
  100. EP251222a: FTW optical and NIR observations

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