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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 260127A: INASAN-Kislovodsk, SAO RAS, and Terskol K-800 optical observations
  2. GRB 260128A / EP260128a: Fermi-GBM Sub-Threshold Detection
  3. EP260128a: NOT optical counterpart candidate
  4. EP260128a: refined analysis of the EP-WXT and autonomous EP-FXT observations
  5. EP260128a: Liverpool Telescope optical observations and possible counterpart
  6. EP260128a: LCO optical upper limits
  7. EP260126a: SVOM/VT optical upperlimit
  8. EP260128a: Global MASTER-Net observations report
  9. EP260128a: Einstein Probe detection of an X-ray transient
  10. Fermi GRB 260127A: Global MASTER-Net observations report
  11. IceCube-260125A: No Candidate Transients from the Zwicky Transient Facility
  12. GRB 260127A: Fermi GBM Observation
  13. IceCube-260125A: Upper limits from a search for additional neutrino events in IceCube
  14. GRB 260127A: COLIBRÍ optical observations
  15. GRB 260127A: NOT optical observations
  16. GRB 260127B: Swift ToO observations
  17. EP260126a: Seimei/TriCCS optical upper limit
  18. GRB 260127A : MITSuME Akeno optical afterglow candidate detection
  19. GRB 260127A: Swift-XRT refined Analysis
  20. GRB 260127B: GOTO candidate optical counterpart
  21. GRB 260127A: SVOM/C-GFT optical observations
  22. The EP-WXT trigger 01709253145 is likely a flaring star
  23. GRB 260127A: Enhanced Swift-XRT position
  24. Fermi GRB 260127B: Global MASTER-Net observations report
  25. GRB 260127B: Fermi GBM Final Real-time Localization
  26. GRB 260127A: Prompt enhanced Swift-XRT position
  27. Swift GRB 260127A: Global MASTER-Net observations report
  28. GRB 260127A: LCO optical afterglow discovery
  29. GRB 260127A: Swift detection of a burst
  30. GRB 260127A: Fermi GBM Final Real-time Localization
  31. GRB 260125A: Swift-XRT observations
  32. EP260126a: EP-FXT follow-up observation
  33. EP260126a: Optical upper limit with Kinder observations
  34. EP260126a: Liverpool Telescope optical upper limits
  35. EP260126a: Further NOT optical upper limits
  36. EP260126a: COLIBRÍ optical upper limits
  37. EP260126a: NOT optical observations
  38. EP260126a: Einstein Probe detection of a fast X-ray transient
  39. Fermi-LAT Gamma-ray Observations of IceCube-260125A
  40. GRB 260125A: NOT optical observations on GOTO26acv / AT 2026bjf
  41. Konus-Wind detection of GRB 260120B
  42. GRB 251222A: SVOM/ECLAIRs refined analysis
  43. GRB 260125A: Swift ToO observations
  44. GRB 260125A: GOTO candidate optical counterpart
  45. Fermi GRB 260125B: Global MASTER-Net observations report
  46. IceCube-260125A - IceCube observation of a high-energy neutrino candidate track-like event
  47. GRB 260125B: Fermi GBM Final Real-time Localization
  48. GRB 260125A: Fermi GBM Final Real-time Localization
  49. GRB 260114A: SVOM/VT optical upper limits
  50. GRB 260120A: AstroSat CZTI detection
  51. GRB 260122B: Swift-BAT refined analysis
  52. GRB 260120B: SVOM/GRM observation
  53. GRB 260120A: GECAM-B observation
  54. GRB 260120B: AstroSat CZTI detection
  55. GRB 260114A: Insight-HXMT/HE detection
  56. GRB 260122B: Swift detection of a burst
  57. Swift GRB260122.97: Global MASTER-Net observations report
  58. EP260119a: Assy AZT-20 optical observations
  59. EP260119a: Mondy and SAO RAS optical upper limits
  60. GRB 260122A: Fermi GBM Final Real-time Localization
  61. IceCube-260115A: No Candidate Transients from the Zwicky Transient Facility
  62. EP260119a: Xinglong optical upper limit
  63. The EP-WXT trigger 01709251871 is likely a flaring star
  64. Fermi GRB 260120C: Global MASTER-Net observations report
  65. GRB 260120B: Swift-BAT refined analysis
  66. GRB 260120B: Swift-XRT refined Analysis
  67. EP260116a: COLIBRÍ further observations
  68. GRB 251122A / EP251122a: VLT/X-shooter host redshift z = 1.765
  69. GRB 260120B: Fermi GBM Observation
  70. EP260105a: GTC/HiPERCAM optical observations
  71. GRB 260120B: Swift/UVOT Detection
  72. GRB 260120B: COLIBRÍ optical upper limits
  73. SVOM GRB260121.06: Global MASTER-Net observations report
  74. GRB 260120B: Enhanced Swift-XRT position
  75. GRB 260120B: SVOM/C-GFT optical counterpart detection
  76. GRB 260120C: Fermi GBM Final Real-time Localization
  77. GRB 260101A: 239Alferov CubeSat detection
  78. EP260116a: COLIBRÍ observations of a tentative optical rebrightening
  79. GRB 260120B: Swift detection of a burst
  80. Swift GRB260120B: Global MASTER-Net observations report
  81. GRB 260120B: Fermi GBM Final Real-time Localization
  82. EP260119A: Mondy I-Band Observations
  83. Fermi trigger No 790601190: Global MASTER-Net observations report
  84. Fermi trigger No 790570272: Global MASTER-Net observations report
  85. GRB 260114A: Swift/UVOT Upper Limits
  86. EP260119a: Liverpool Telescope optical follow-up observations
  87. GRB 251202A: further radio observations with the VLA
  88. Trigger 1442421: Swift detection of HMXB 1A 1118-61
  89. EP260119A: GTC/OSIRIS+ spectroscopic redshift z = 5.47
  90. EP260119a: KAIT optical observations
  91. GRB 260120A: Fermi GBM Final Real-time Localization
  92. EP260119a: SVOM/VT optical observation
  93. EP260119a: update of EP-FXT follow-up observation
  94. EP260119a: NOT optical observations
  95. EP260119a: SAO RAS optical observations
  96. SVOM GRB260119.92: Global MASTER-Net observations report
  97. SVOM GRB260119.92: Global MASTER-Net observations report
  98. SVOM GRB260119.90: Global MASTER-Net observations report
  99. EP260116a: COLIBRÍ detection of a fading optical source
  100. GRB 251208D: SVOM/ECLAIRs refined analysis

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