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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 260103A: Insight-HXMT/HE detection
  2. GRB 260104A: COLIBRÍ optical upper limits
  3. GRB 260104C: Fermi GBM Final Real-time Localization
  4. Fermi GRB 260104B: Global MASTER-Net observations report
  5. Swift GRB 260104A: Global MASTER-Net observations report
  6. GRB 251230A/EP-WXT trigger 01709250693: Mephisto optical upper limits
  7. GRB 260104A: Swift-XRT refined Analysis
  8. GRB 260104A: Enhanced Swift-XRT position
  9. GRB 260101A: Swift/UVOT Detection
  10. GRB 260103A: GECAM-B observation of a burst
  11. GRB 260104B: Fermi GBM Final Localization
  12. GRB 260104A: Swift detection of a burst
  13. GRB 260103A: SVOM/GRM observation of a possible GRB
  14. Fermi-LAT Gamma-ray Observations of IceCube-251225A
  15. GRB 260101A: COLIBRÍ optical observations
  16. SVOM GRB260103.08: Global MASTER-Net observations report
  17. GRB 260102B: Fermi GBM Final Real-time Localization
  18. SVOM GRB260102A: Global MASTER-Net observations report
  19. Fermi GBM Sub-Threshold Detection of GRB 260102A
  20. GRB 260102A: EP-FXT follow-up observation
  21. EP260101a: Global MASTER-Net observations report
  22. GRB 260102A: LCO optical upper limits
  23. GRB 260102A: Swift-XRT observations
  24. GRB 260102A: SVOM/COLIBRÍ (FM-GFT) optical observations
  25. Fermi Gamma-ray Burst Monitor trigger 789047602/260102495 is not a GRB
  26. GRB 251230A / EP251230a: GECAM-B detection
  27. GRB 260102A: SVOM/VT optical counterpart
  28. GRB 251230A / EP251230a: Insight-HXMT/HE detection
  29. GRB 260102A: Swift ToO observations
  30. GRB 260101A: Fermi GBM Observation
  31. EP260101a: refined analysis of the EP-WXT and EP-FXT observations
  32. GRB 260102A: SVOM detection of a burst
  33. GRB 260101A: GECAM-B detection
  34. GRB 260101A: NOT spectroscopic observations
  35. GRB 260101A: SVOM/GRM observation
  36. GRB 260101A: Swift-XRT refined Analysis
  37. Swift GRB 260101A: Global MASTER-Net observations report
  38. GRB 260101A: Enhanced Swift-XRT position
  39. EP260101a: Einstein Probe detection of an X-ray transient
  40. GRB 260101A: OSIRIS+ redshift z = 2.623 for the new year burst
  41. GRB 260101A: LCO detection of the optical counterpart
  42. GRB 260101A: Swift detection of a burst with an optical counterpart
  43. GRB 260101A: Fermi GBM Final Real-time Localization
  44. SVOM GRB251231.57: Global MASTER-Net observations report
  45. GRB 251230A / EP251230a: SVOM/VT optical continued observations and upper limit
  46. GRB 251230A: GRANDMA/TAROT Early Detection
  47. GRB 251230A / EP251230a: further NOT optical observations revealing shallower decay or possible rebrightening
  48. GRB 251230A/EP251230a: Optical upper limit with Kinder observations
  49. EP251229a: Optical upper limit with Kinder observations
  50. GRB 251230A: 1.3m DFOT optical upper limit
  51. Fermi Gamma-ray Burst Monitor trigger 788833547/251231018 is not a GRB
  52. GRB 251230A: Swift-XRT refined Analysis
  53. GRB 251231A: Fermi GBM Final Real-time Localization
  54. GRB 251222A: Mondy Optical Observations
  55. EP251230a / GRB 251230A: refined analysis of the EP-WXT and EP-FXT observations
  56. GRB 251230A: Swift/UVOT detection
  57. GRB251230A: 7DT optical upper limits
  58. GRB 251230A / EP251230a: NOT observations and spectroscopic redshift upper limit z < 2.2
  59. EP251229a: BOOTES-2 early optical upper limit
  60. GRB 251230A: GOTO optical upper limit
  61. EP251229a: NOT optical upper limits
  62. GRB 251230A / EP251230a: SVOM/VT optical observation
  63. EP251229a: refined analysis of the EP-WXT and EP-FXT observations
  64. GRB 251230A: Enhanced Swift-XRT position
  65. GRB 251230A: Early optical counterpart detection by LCO.
  66. EP-WXT trigger 01709250662 Mephisto and 50cm telescope follow-up
  67. GRB 251230A: Optical Observations via Virtual Telescope Project, Italy
  68. EP251230a / GRB 251230A: Einstein Probe detection of an X-ray transient
  69. GRB 251230A/EP#01709250693 (likely EP251230a): FTW optical and NIR observations
  70. LIGO/Virgo/KAGRA S251112cm: Candidates from the NSF-DOE Vera C. Rubin Observatory
  71. Swift GRB 251230A: Global MASTER-Net observations report
  72. The EP-WXT trigger 01709250693/GRB 251230A: Las Cumbres detection of the optical counterpart
  73. EP251229a: Global MASTER-Net observations report
  74. EP251229a: Einstein Probe detection of an X-ray transient
  75. GRB 251230A: Swift detection of a burst with a bright optical counterpart
  76. GRB 251226A: Glowbug gamma-ray detection
  77. GRB 251222A/EP251222b: 1.6m Mephisto optical followup
  78. GRB 251129A: redshift correction and SN detection at z = 0.505 with GTC
  79. Fermi GRB 251228A: Global MASTER-Net observations report
  80. The EP-WXT trigger 01709250662 is likely a flaring star
  81. GRB 251228A: Fermi GBM Final Real-time Localization
  82. GRB 251226A: SVOM/GRM observation
  83. GRB 251226A: GECAM-B detection
  84. SVOM GRB251227.07: Global MASTER-Net observations report
  85. IceCube-251225A: Upper limits from a search for additional neutrino events in IceCube
  86. The EP-WXT trigger 01709250617 is likely a flaring star
  87. IceCube Alert 251225.84: Global MASTER-Net observations report
  88. IceCube-251225A - IceCube observation of a high-energy neutrino candidate track-like event
  89. Fermi Gamma-ray Burst Monitor trigger 788368008/251225630 is not a GRB
  90. GRB 251222A: NUTTelA-TAO Early Measurements
  91. GRB 251222A/EP251222b: Optical detection with Kinder observations
  92. EP251222a: Optical upper limit with Kinder observations
  93. GRB 251221A: Swift-BAT refined analysis
  94. GRB 251222A/EP251222b: FTW optical and NIR observations
  95. EP251222a: FTW optical and NIR observations
  96. GRB 251205A: Kilonova-Catcher optical afterglow detection
  97. GRB 251222A: AbAO optical observations
  98. GRB 251222A / EP251222b: Kilonova-Catcher optical afterglow detection
  99. GRB 251129A / EP251129a: VLA detection of a radio counterpart
  100. EP251222a: VLT/FORS2 spectroscopic redshift z = 0.505

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