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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. Fermi GRB 260129A: Global MASTER-Net observations report
  2. GRB 260128B: LCO optical upper limits
  3. GRB 260128B: SVOM/COLIBRÍ (FM-GFT) optical upper limits
  4. EP260128a: J band upper limit by SYSU 80cm infrared telescope
  5. IPN triangulation of GRB 260121A
  6. GRB 260127A: Swift-BAT refined analysis
  7. GRB 260129B: Fermi GBM Final Localization
  8. GRB 260128B: SVOM detection of a burst through offline search
  9. GRB 260129A: Fermi GBM Final Localization
  10. IPN triangulation of GRB 260127B (short)
  11. GRB 260127B: Swift-XRT observations
  12. GRB 260127A: INASAN-Kislovodsk, SAO RAS, and Terskol K-800 optical observations
  13. GRB 260128A / EP260128a: Fermi-GBM Sub-Threshold Detection
  14. EP260128a: NOT optical counterpart candidate
  15. EP260128a: refined analysis of the EP-WXT and autonomous EP-FXT observations
  16. EP260128a: Liverpool Telescope optical observations and possible counterpart
  17. EP260128a: LCO optical upper limits
  18. EP260126a: SVOM/VT optical upperlimit
  19. EP260128a: Global MASTER-Net observations report
  20. EP260128a: Einstein Probe detection of an X-ray transient
  21. Fermi GRB 260127A: Global MASTER-Net observations report
  22. IceCube-260125A: No Candidate Transients from the Zwicky Transient Facility
  23. GRB 260127A: Fermi GBM Observation
  24. IceCube-260125A: Upper limits from a search for additional neutrino events in IceCube
  25. GRB 260127A: COLIBRÍ optical observations
  26. GRB 260127A: NOT optical observations
  27. GRB 260127B: Swift ToO observations
  28. EP260126a: Seimei/TriCCS optical upper limit
  29. GRB 260127A : MITSuME Akeno optical afterglow candidate detection
  30. GRB 260127A: Swift-XRT refined Analysis
  31. GRB 260127B: GOTO candidate optical counterpart
  32. GRB 260127A: SVOM/C-GFT optical observations
  33. The EP-WXT trigger 01709253145 is likely a flaring star
  34. GRB 260127A: Enhanced Swift-XRT position
  35. Fermi GRB 260127B: Global MASTER-Net observations report
  36. GRB 260127B: Fermi GBM Final Real-time Localization
  37. GRB 260127A: Prompt enhanced Swift-XRT position
  38. Swift GRB 260127A: Global MASTER-Net observations report
  39. GRB 260127A: LCO optical afterglow discovery
  40. GRB 260127A: Swift detection of a burst
  41. GRB 260127A: Fermi GBM Final Real-time Localization
  42. GRB 260125A: Swift-XRT observations
  43. EP260126a: EP-FXT follow-up observation
  44. EP260126a: Optical upper limit with Kinder observations
  45. EP260126a: Liverpool Telescope optical upper limits
  46. EP260126a: Further NOT optical upper limits
  47. EP260126a: COLIBRÍ optical upper limits
  48. EP260126a: NOT optical observations
  49. EP260126a: Einstein Probe detection of a fast X-ray transient
  50. Fermi-LAT Gamma-ray Observations of IceCube-260125A
  51. GRB 260125A: NOT optical observations on GOTO26acv / AT 2026bjf
  52. Konus-Wind detection of GRB 260120B
  53. GRB 251222A: SVOM/ECLAIRs refined analysis
  54. GRB 260125A: Swift ToO observations
  55. GRB 260125A: GOTO candidate optical counterpart
  56. Fermi GRB 260125B: Global MASTER-Net observations report
  57. IceCube-260125A - IceCube observation of a high-energy neutrino candidate track-like event
  58. GRB 260125B: Fermi GBM Final Real-time Localization
  59. GRB 260125A: Fermi GBM Final Real-time Localization
  60. GRB 260114A: SVOM/VT optical upper limits
  61. GRB 260120A: AstroSat CZTI detection
  62. GRB 260122B: Swift-BAT refined analysis
  63. GRB 260120B: SVOM/GRM observation
  64. GRB 260120A: GECAM-B observation
  65. GRB 260120B: AstroSat CZTI detection
  66. GRB 260114A: Insight-HXMT/HE detection
  67. GRB 260122B: Swift detection of a burst
  68. Swift GRB260122.97: Global MASTER-Net observations report
  69. EP260119a: Assy AZT-20 optical observations
  70. EP260119a: Mondy and SAO RAS optical upper limits
  71. GRB 260122A: Fermi GBM Final Real-time Localization
  72. IceCube-260115A: No Candidate Transients from the Zwicky Transient Facility
  73. EP260119a: Xinglong optical upper limit
  74. The EP-WXT trigger 01709251871 is likely a flaring star
  75. Fermi GRB 260120C: Global MASTER-Net observations report
  76. GRB 260120B: Swift-BAT refined analysis
  77. GRB 260120B: Swift-XRT refined Analysis
  78. EP260116a: COLIBRÍ further observations
  79. GRB 251122A / EP251122a: VLT/X-shooter host redshift z = 1.765
  80. GRB 260120B: Fermi GBM Observation
  81. EP260105a: GTC/HiPERCAM optical observations
  82. GRB 260120B: Swift/UVOT Detection
  83. GRB 260120B: COLIBRÍ optical upper limits
  84. SVOM GRB260121.06: Global MASTER-Net observations report
  85. GRB 260120B: Enhanced Swift-XRT position
  86. GRB 260120B: SVOM/C-GFT optical counterpart detection
  87. GRB 260120C: Fermi GBM Final Real-time Localization
  88. GRB 260101A: 239Alferov CubeSat detection
  89. EP260116a: COLIBRÍ observations of a tentative optical rebrightening
  90. GRB 260120B: Swift detection of a burst
  91. Swift GRB260120B: Global MASTER-Net observations report
  92. GRB 260120B: Fermi GBM Final Real-time Localization
  93. EP260119A: Mondy I-Band Observations
  94. Fermi trigger No 790601190: Global MASTER-Net observations report
  95. Fermi trigger No 790570272: Global MASTER-Net observations report
  96. GRB 260114A: Swift/UVOT Upper Limits
  97. EP260119a: Liverpool Telescope optical follow-up observations
  98. GRB 251202A: further radio observations with the VLA
  99. Trigger 1442421: Swift detection of HMXB 1A 1118-61
  100. EP260119A: GTC/OSIRIS+ spectroscopic redshift z = 5.47

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