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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: SVOM/C-GFT optical observations
  2. The EP-WXT trigger 01709253145 is likely a flaring star
  3. GRB 260127A: Enhanced Swift-XRT position
  4. Fermi GRB 260127B: Global MASTER-Net observations report
  5. GRB 260127B: Fermi GBM Final Real-time Localization
  6. GRB 260127A: Prompt enhanced Swift-XRT position
  7. Swift GRB 260127A: Global MASTER-Net observations report
  8. GRB 260127A: LCO optical afterglow discovery
  9. GRB 260127A: Swift detection of a burst
  10. GRB 260127A: Fermi GBM Final Real-time Localization
  11. GRB 260125A: Swift-XRT observations
  12. EP260126a: EP-FXT follow-up observation
  13. EP260126a: Optical upper limit with Kinder observations
  14. EP260126a: Liverpool Telescope optical upper limits
  15. EP260126a: Further NOT optical upper limits
  16. EP260126a: COLIBRÍ optical upper limits
  17. EP260126a: NOT optical observations
  18. EP260126a: Einstein Probe detection of a fast X-ray transient
  19. Fermi-LAT Gamma-ray Observations of IceCube-260125A
  20. GRB 260125A: NOT optical observations on GOTO26acv / AT 2026bjf
  21. Konus-Wind detection of GRB 260120B
  22. GRB 251222A: SVOM/ECLAIRs refined analysis
  23. GRB 260125A: Swift ToO observations
  24. GRB 260125A: GOTO candidate optical counterpart
  25. Fermi GRB 260125B: Global MASTER-Net observations report
  26. IceCube-260125A - IceCube observation of a high-energy neutrino candidate track-like event
  27. GRB 260125B: Fermi GBM Final Real-time Localization
  28. GRB 260125A: Fermi GBM Final Real-time Localization
  29. GRB 260114A: SVOM/VT optical upper limits
  30. GRB 260120A: AstroSat CZTI detection
  31. GRB 260122B: Swift-BAT refined analysis
  32. GRB 260120B: SVOM/GRM observation
  33. GRB 260120A: GECAM-B observation
  34. GRB 260120B: AstroSat CZTI detection
  35. GRB 260114A: Insight-HXMT/HE detection
  36. GRB 260122B: Swift detection of a burst
  37. Swift GRB260122.97: Global MASTER-Net observations report
  38. EP260119a: Assy AZT-20 optical observations
  39. EP260119a: Mondy and SAO RAS optical upper limits
  40. GRB 260122A: Fermi GBM Final Real-time Localization
  41. IceCube-260115A: No Candidate Transients from the Zwicky Transient Facility
  42. EP260119a: Xinglong optical upper limit
  43. The EP-WXT trigger 01709251871 is likely a flaring star
  44. Fermi GRB 260120C: Global MASTER-Net observations report
  45. GRB 260120B: Swift-BAT refined analysis
  46. GRB 260120B: Swift-XRT refined Analysis
  47. EP260116a: COLIBRÍ further observations
  48. GRB 251122A / EP251122a: VLT/X-shooter host redshift z = 1.765
  49. GRB 260120B: Fermi GBM Observation
  50. EP260105a: GTC/HiPERCAM optical observations
  51. GRB 260120B: Swift/UVOT Detection
  52. GRB 260120B: COLIBRÍ optical upper limits
  53. SVOM GRB260121.06: Global MASTER-Net observations report
  54. GRB 260120B: Enhanced Swift-XRT position
  55. GRB 260120B: SVOM/C-GFT optical counterpart detection
  56. GRB 260120C: Fermi GBM Final Real-time Localization
  57. GRB 260101A: 239Alferov CubeSat detection
  58. EP260116a: COLIBRÍ observations of a tentative optical rebrightening
  59. GRB 260120B: Swift detection of a burst
  60. Swift GRB260120B: Global MASTER-Net observations report
  61. GRB 260120B: Fermi GBM Final Real-time Localization
  62. EP260119A: Mondy I-Band Observations
  63. Fermi trigger No 790601190: Global MASTER-Net observations report
  64. Fermi trigger No 790570272: Global MASTER-Net observations report
  65. GRB 260114A: Swift/UVOT Upper Limits
  66. EP260119a: Liverpool Telescope optical follow-up observations
  67. GRB 251202A: further radio observations with the VLA
  68. Trigger 1442421: Swift detection of HMXB 1A 1118-61
  69. EP260119A: GTC/OSIRIS+ spectroscopic redshift z = 5.47
  70. EP260119a: KAIT optical observations
  71. GRB 260120A: Fermi GBM Final Real-time Localization
  72. EP260119a: SVOM/VT optical observation
  73. EP260119a: update of EP-FXT follow-up observation
  74. EP260119a: NOT optical observations
  75. EP260119a: SAO RAS optical observations
  76. SVOM GRB260119.92: Global MASTER-Net observations report
  77. SVOM GRB260119.92: Global MASTER-Net observations report
  78. SVOM GRB260119.90: Global MASTER-Net observations report
  79. EP260116a: COLIBRÍ detection of a fading optical source
  80. GRB 251208D: SVOM/ECLAIRs refined analysis
  81. GRB 251208D: SVOM/ECLAIRs refined analysis
  82. GRB 260117A: Swift-XRT afterglow detection
  83. EP260119a: COLIBRÍ photometric redshift z ≈ 5.6
  84. EP260119a: Global MASTER-Net observations report
  85. GRB 260115A: AstroSat CZTI detection
  86. EP260119a: LCO optical observations
  87. GRB 260117A: ZTSh optical upper limit
  88. EP260119a: COLIBRÍ optical counterpart candidate
  89. EP260119a: preliminary result from the EP-FXT observation
  90. GRB 260110A: SVOM detection of a burst through offline search
  91. EP260119a: EP-WXT detection of a fast X-ray transient
  92. Swift GRB260118.48: Global MASTER-Net observations report
  93. GRB 260117A: SVOM/COLIBRÍ (FM-GFT) optical observations
  94. SVOM GRB260117.82: Global MASTER-Net observations report
  95. Fermi-LAT Gamma-ray Observations of IceCube-260115A
  96. Swift trigger on the HMXB 1A 1118-61
  97. GRB 260117A: SVOM/VT optical candidate
  98. GRB 260117A: SVOM/C-GFT upper limit
  99. GRB 260117A: Swift-XRT observations
  100. GRB 260117A: Swift ToO observations

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