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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 260127B: Fermi GBM Final Real-time Localization
  2. GRB 260127A: Prompt enhanced Swift-XRT position
  3. Swift GRB 260127A: Global MASTER-Net observations report
  4. GRB 260127A: LCO optical afterglow discovery
  5. GRB 260127A: Swift detection of a burst
  6. GRB 260127A: Fermi GBM Final Real-time Localization
  7. GRB 260125A: Swift-XRT observations
  8. EP260126a: EP-FXT follow-up observation
  9. EP260126a: Optical upper limit with Kinder observations
  10. EP260126a: Liverpool Telescope optical upper limits
  11. EP260126a: Further NOT optical upper limits
  12. EP260126a: COLIBRÍ optical upper limits
  13. EP260126a: NOT optical observations
  14. EP260126a: Einstein Probe detection of a fast X-ray transient
  15. Fermi-LAT Gamma-ray Observations of IceCube-260125A
  16. GRB 260125A: NOT optical observations on GOTO26acv / AT 2026bjf
  17. Konus-Wind detection of GRB 260120B
  18. GRB 251222A: SVOM/ECLAIRs refined analysis
  19. GRB 260125A: Swift ToO observations
  20. GRB 260125A: GOTO candidate optical counterpart
  21. Fermi GRB 260125B: Global MASTER-Net observations report
  22. IceCube-260125A - IceCube observation of a high-energy neutrino candidate track-like event
  23. GRB 260125B: Fermi GBM Final Real-time Localization
  24. GRB 260125A: Fermi GBM Final Real-time Localization
  25. GRB 260114A: SVOM/VT optical upper limits
  26. GRB 260120A: AstroSat CZTI detection
  27. GRB 260122B: Swift-BAT refined analysis
  28. GRB 260120B: SVOM/GRM observation
  29. GRB 260120A: GECAM-B observation
  30. GRB 260120B: AstroSat CZTI detection
  31. GRB 260114A: Insight-HXMT/HE detection
  32. GRB 260122B: Swift detection of a burst
  33. Swift GRB260122.97: Global MASTER-Net observations report
  34. EP260119a: Assy AZT-20 optical observations
  35. EP260119a: Mondy and SAO RAS optical upper limits
  36. GRB 260122A: Fermi GBM Final Real-time Localization
  37. IceCube-260115A: No Candidate Transients from the Zwicky Transient Facility
  38. EP260119a: Xinglong optical upper limit
  39. The EP-WXT trigger 01709251871 is likely a flaring star
  40. Fermi GRB 260120C: Global MASTER-Net observations report
  41. GRB 260120B: Swift-BAT refined analysis
  42. GRB 260120B: Swift-XRT refined Analysis
  43. EP260116a: COLIBRÍ further observations
  44. GRB 251122A / EP251122a: VLT/X-shooter host redshift z = 1.765
  45. GRB 260120B: Fermi GBM Observation
  46. EP260105a: GTC/HiPERCAM optical observations
  47. GRB 260120B: Swift/UVOT Detection
  48. GRB 260120B: COLIBRÍ optical upper limits
  49. SVOM GRB260121.06: Global MASTER-Net observations report
  50. GRB 260120B: Enhanced Swift-XRT position
  51. GRB 260120B: SVOM/C-GFT optical counterpart detection
  52. GRB 260120C: Fermi GBM Final Real-time Localization
  53. GRB 260101A: 239Alferov CubeSat detection
  54. EP260116a: COLIBRÍ observations of a tentative optical rebrightening
  55. GRB 260120B: Swift detection of a burst
  56. Swift GRB260120B: Global MASTER-Net observations report
  57. GRB 260120B: Fermi GBM Final Real-time Localization
  58. EP260119A: Mondy I-Band Observations
  59. Fermi trigger No 790601190: Global MASTER-Net observations report
  60. Fermi trigger No 790570272: Global MASTER-Net observations report
  61. GRB 260114A: Swift/UVOT Upper Limits
  62. EP260119a: Liverpool Telescope optical follow-up observations
  63. GRB 251202A: further radio observations with the VLA
  64. Trigger 1442421: Swift detection of HMXB 1A 1118-61
  65. EP260119A: GTC/OSIRIS+ spectroscopic redshift z = 5.47
  66. EP260119a: KAIT optical observations
  67. GRB 260120A: Fermi GBM Final Real-time Localization
  68. EP260119a: SVOM/VT optical observation
  69. EP260119a: update of EP-FXT follow-up observation
  70. EP260119a: NOT optical observations
  71. EP260119a: SAO RAS optical observations
  72. SVOM GRB260119.92: Global MASTER-Net observations report
  73. SVOM GRB260119.92: Global MASTER-Net observations report
  74. SVOM GRB260119.90: Global MASTER-Net observations report
  75. EP260116a: COLIBRÍ detection of a fading optical source
  76. GRB 251208D: SVOM/ECLAIRs refined analysis
  77. GRB 251208D: SVOM/ECLAIRs refined analysis
  78. GRB 260117A: Swift-XRT afterglow detection
  79. EP260119a: COLIBRÍ photometric redshift z ≈ 5.6
  80. EP260119a: Global MASTER-Net observations report
  81. GRB 260115A: AstroSat CZTI detection
  82. EP260119a: LCO optical observations
  83. GRB 260117A: ZTSh optical upper limit
  84. EP260119a: COLIBRÍ optical counterpart candidate
  85. EP260119a: preliminary result from the EP-FXT observation
  86. GRB 260110A: SVOM detection of a burst through offline search
  87. EP260119a: EP-WXT detection of a fast X-ray transient
  88. Swift GRB260118.48: Global MASTER-Net observations report
  89. GRB 260117A: SVOM/COLIBRÍ (FM-GFT) optical observations
  90. SVOM GRB260117.82: Global MASTER-Net observations report
  91. Fermi-LAT Gamma-ray Observations of IceCube-260115A
  92. Swift trigger on the HMXB 1A 1118-61
  93. GRB 260117A: SVOM/VT optical candidate
  94. GRB 260117A: SVOM/C-GFT upper limit
  95. GRB 260117A: Swift-XRT observations
  96. GRB 260117A: Swift ToO observations
  97. GRB 260117A: SVOM detection of a long faint burst
  98. EP 260116a: COLIBRÍ optical upper limit
  99. Swift triggered on the HMXB 1A 1118-61
  100. GRB 260115A: GECAM-B observation

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