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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. EP260128a: Einstein Probe detection of an X-ray transient
  2. Fermi GRB 260127A: Global MASTER-Net observations report
  3. IceCube-260125A: No Candidate Transients from the Zwicky Transient Facility
  4. GRB 260127A: Fermi GBM Observation
  5. IceCube-260125A: Upper limits from a search for additional neutrino events in IceCube
  6. GRB 260127A: COLIBRÍ optical observations
  7. GRB 260127A: NOT optical observations
  8. GRB 260127B: Swift ToO observations
  9. EP260126a: Seimei/TriCCS optical upper limit
  10. GRB 260127A : MITSuME Akeno optical afterglow candidate detection
  11. GRB 260127A: Swift-XRT refined Analysis
  12. GRB 260127B: GOTO candidate optical counterpart
  13. GRB 260127A: SVOM/C-GFT optical observations
  14. The EP-WXT trigger 01709253145 is likely a flaring star
  15. GRB 260127A: Enhanced Swift-XRT position
  16. Fermi GRB 260127B: Global MASTER-Net observations report
  17. GRB 260127B: Fermi GBM Final Real-time Localization
  18. GRB 260127A: Prompt enhanced Swift-XRT position
  19. Swift GRB 260127A: Global MASTER-Net observations report
  20. GRB 260127A: LCO optical afterglow discovery
  21. GRB 260127A: Swift detection of a burst
  22. GRB 260127A: Fermi GBM Final Real-time Localization
  23. GRB 260125A: Swift-XRT observations
  24. EP260126a: EP-FXT follow-up observation
  25. EP260126a: Optical upper limit with Kinder observations
  26. EP260126a: Liverpool Telescope optical upper limits
  27. EP260126a: Further NOT optical upper limits
  28. EP260126a: COLIBRÍ optical upper limits
  29. EP260126a: NOT optical observations
  30. EP260126a: Einstein Probe detection of a fast X-ray transient
  31. Fermi-LAT Gamma-ray Observations of IceCube-260125A
  32. GRB 260125A: NOT optical observations on GOTO26acv / AT 2026bjf
  33. Konus-Wind detection of GRB 260120B
  34. GRB 251222A: SVOM/ECLAIRs refined analysis
  35. GRB 260125A: Swift ToO observations
  36. GRB 260125A: GOTO candidate optical counterpart
  37. Fermi GRB 260125B: Global MASTER-Net observations report
  38. IceCube-260125A - IceCube observation of a high-energy neutrino candidate track-like event
  39. GRB 260125B: Fermi GBM Final Real-time Localization
  40. GRB 260125A: Fermi GBM Final Real-time Localization
  41. GRB 260114A: SVOM/VT optical upper limits
  42. GRB 260120A: AstroSat CZTI detection
  43. GRB 260122B: Swift-BAT refined analysis
  44. GRB 260120B: SVOM/GRM observation
  45. GRB 260120A: GECAM-B observation
  46. GRB 260120B: AstroSat CZTI detection
  47. GRB 260114A: Insight-HXMT/HE detection
  48. GRB 260122B: Swift detection of a burst
  49. Swift GRB260122.97: Global MASTER-Net observations report
  50. EP260119a: Assy AZT-20 optical observations
  51. EP260119a: Mondy and SAO RAS optical upper limits
  52. GRB 260122A: Fermi GBM Final Real-time Localization
  53. IceCube-260115A: No Candidate Transients from the Zwicky Transient Facility
  54. EP260119a: Xinglong optical upper limit
  55. The EP-WXT trigger 01709251871 is likely a flaring star
  56. Fermi GRB 260120C: Global MASTER-Net observations report
  57. GRB 260120B: Swift-BAT refined analysis
  58. GRB 260120B: Swift-XRT refined Analysis
  59. EP260116a: COLIBRÍ further observations
  60. GRB 251122A / EP251122a: VLT/X-shooter host redshift z = 1.765
  61. GRB 260120B: Fermi GBM Observation
  62. EP260105a: GTC/HiPERCAM optical observations
  63. GRB 260120B: Swift/UVOT Detection
  64. GRB 260120B: COLIBRÍ optical upper limits
  65. SVOM GRB260121.06: Global MASTER-Net observations report
  66. GRB 260120B: Enhanced Swift-XRT position
  67. GRB 260120B: SVOM/C-GFT optical counterpart detection
  68. GRB 260120C: Fermi GBM Final Real-time Localization
  69. GRB 260101A: 239Alferov CubeSat detection
  70. EP260116a: COLIBRÍ observations of a tentative optical rebrightening
  71. GRB 260120B: Swift detection of a burst
  72. Swift GRB260120B: Global MASTER-Net observations report
  73. GRB 260120B: Fermi GBM Final Real-time Localization
  74. EP260119A: Mondy I-Band Observations
  75. Fermi trigger No 790601190: Global MASTER-Net observations report
  76. Fermi trigger No 790570272: Global MASTER-Net observations report
  77. GRB 260114A: Swift/UVOT Upper Limits
  78. EP260119a: Liverpool Telescope optical follow-up observations
  79. GRB 251202A: further radio observations with the VLA
  80. Trigger 1442421: Swift detection of HMXB 1A 1118-61
  81. EP260119A: GTC/OSIRIS+ spectroscopic redshift z = 5.47
  82. EP260119a: KAIT optical observations
  83. GRB 260120A: Fermi GBM Final Real-time Localization
  84. EP260119a: SVOM/VT optical observation
  85. EP260119a: update of EP-FXT follow-up observation
  86. EP260119a: NOT optical observations
  87. EP260119a: SAO RAS optical observations
  88. SVOM GRB260119.92: Global MASTER-Net observations report
  89. SVOM GRB260119.92: Global MASTER-Net observations report
  90. SVOM GRB260119.90: Global MASTER-Net observations report
  91. EP260116a: COLIBRÍ detection of a fading optical source
  92. GRB 251208D: SVOM/ECLAIRs refined analysis
  93. GRB 251208D: SVOM/ECLAIRs refined analysis
  94. GRB 260117A: Swift-XRT afterglow detection
  95. EP260119a: COLIBRÍ photometric redshift z ≈ 5.6
  96. EP260119a: Global MASTER-Net observations report
  97. GRB 260115A: AstroSat CZTI detection
  98. EP260119a: LCO optical observations
  99. GRB 260117A: ZTSh optical upper limit
  100. EP260119a: COLIBRÍ optical counterpart candidate

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