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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 260131A/B (AT2026bwg): COLIBRÍ optical observations and confirmation of fading
  2. GRB 260131A/B: GOTO candidate optical counterpart consistent with the MAXI localisation
  3. GRB 260131A/B: Fermi GBM Observation
  4. EP260131a: COLIBRÍ observations of slow optical fading
  5. EP260131a: refined analysis of the EP-WXT and autonomous EP-FXT observations
  6. EP260131a: VLT/X-shooter spectroscopic redshift z = 0.937
  7. EP260131a: NOT early detection of the counterpart in "rapid response mode"
  8. GRB 260131B: MAXI/GSC detection
  9. GRB 260131A: Fermi GBM Final Real-time Localization
  10. EP260131a: COLIBRÍ optical observations of the counterpart
  11. EP260131a: Las Cumbres detection of an optical counterpart
  12. GRB 260127B: AstroSat CZTI detection
  13. GRB 260130A: Fermi GBM Detection
  14. EP260131a: Einstein Probe detection of an X-ray transient
  15. GRB 260127B: Fermi GBM Detection
  16. EP260128a / GRB 260128A: COLIBRÍ optical upper limit
  17. Fermi GRB 260130A: Global MASTER-Net observations report
  18. EP260128a / GRB 260128A: NOT and TNG optical and NIR upper limits
  19. GRB 260130A: Fermi GBM Final Real-time Localization
  20. Fermi GRB 260129A: Global MASTER-Net observations report
  21. GRB 260128B: LCO optical upper limits
  22. GRB 260128B: SVOM/COLIBRÍ (FM-GFT) optical upper limits
  23. EP260128a: J band upper limit by SYSU 80cm infrared telescope
  24. IPN triangulation of GRB 260121A
  25. GRB 260127A: Swift-BAT refined analysis
  26. GRB 260129B: Fermi GBM Final Localization
  27. GRB 260128B: SVOM detection of a burst through offline search
  28. GRB 260129A: Fermi GBM Final Localization
  29. IPN triangulation of GRB 260127B (short)
  30. GRB 260127B: Swift-XRT observations
  31. GRB 260127A: INASAN-Kislovodsk, SAO RAS, and Terskol K-800 optical observations
  32. GRB 260128A / EP260128a: Fermi-GBM Sub-Threshold Detection
  33. EP260128a: NOT optical counterpart candidate
  34. EP260128a: refined analysis of the EP-WXT and autonomous EP-FXT observations
  35. EP260128a: Liverpool Telescope optical observations and possible counterpart
  36. EP260128a: LCO optical upper limits
  37. EP260126a: SVOM/VT optical upperlimit
  38. EP260128a: Global MASTER-Net observations report
  39. EP260128a: Einstein Probe detection of an X-ray transient
  40. Fermi GRB 260127A: Global MASTER-Net observations report
  41. IceCube-260125A: No Candidate Transients from the Zwicky Transient Facility
  42. GRB 260127A: Fermi GBM Observation
  43. IceCube-260125A: Upper limits from a search for additional neutrino events in IceCube
  44. GRB 260127A: COLIBRÍ optical observations
  45. GRB 260127A: NOT optical observations
  46. GRB 260127B: Swift ToO observations
  47. EP260126a: Seimei/TriCCS optical upper limit
  48. GRB 260127A : MITSuME Akeno optical afterglow candidate detection
  49. GRB 260127A: Swift-XRT refined Analysis
  50. GRB 260127B: GOTO candidate optical counterpart
  51. GRB 260127A: SVOM/C-GFT optical observations
  52. The EP-WXT trigger 01709253145 is likely a flaring star
  53. GRB 260127A: Enhanced Swift-XRT position
  54. Fermi GRB 260127B: Global MASTER-Net observations report
  55. GRB 260127B: Fermi GBM Final Real-time Localization
  56. GRB 260127A: Prompt enhanced Swift-XRT position
  57. Swift GRB 260127A: Global MASTER-Net observations report
  58. GRB 260127A: LCO optical afterglow discovery
  59. GRB 260127A: Swift detection of a burst
  60. GRB 260127A: Fermi GBM Final Real-time Localization
  61. GRB 260125A: Swift-XRT observations
  62. EP260126a: EP-FXT follow-up observation
  63. EP260126a: Optical upper limit with Kinder observations
  64. EP260126a: Liverpool Telescope optical upper limits
  65. EP260126a: Further NOT optical upper limits
  66. EP260126a: COLIBRÍ optical upper limits
  67. EP260126a: NOT optical observations
  68. EP260126a: Einstein Probe detection of a fast X-ray transient
  69. Fermi-LAT Gamma-ray Observations of IceCube-260125A
  70. GRB 260125A: NOT optical observations on GOTO26acv / AT 2026bjf
  71. Konus-Wind detection of GRB 260120B
  72. GRB 251222A: SVOM/ECLAIRs refined analysis
  73. GRB 260125A: Swift ToO observations
  74. GRB 260125A: GOTO candidate optical counterpart
  75. Fermi GRB 260125B: Global MASTER-Net observations report
  76. IceCube-260125A - IceCube observation of a high-energy neutrino candidate track-like event
  77. GRB 260125B: Fermi GBM Final Real-time Localization
  78. GRB 260125A: Fermi GBM Final Real-time Localization
  79. GRB 260114A: SVOM/VT optical upper limits
  80. GRB 260120A: AstroSat CZTI detection
  81. GRB 260122B: Swift-BAT refined analysis
  82. GRB 260120B: SVOM/GRM observation
  83. GRB 260120A: GECAM-B observation
  84. GRB 260120B: AstroSat CZTI detection
  85. GRB 260114A: Insight-HXMT/HE detection
  86. GRB 260122B: Swift detection of a burst
  87. Swift GRB260122.97: Global MASTER-Net observations report
  88. EP260119a: Assy AZT-20 optical observations
  89. EP260119a: Mondy and SAO RAS optical upper limits
  90. GRB 260122A: Fermi GBM Final Real-time Localization
  91. IceCube-260115A: No Candidate Transients from the Zwicky Transient Facility
  92. EP260119a: Xinglong optical upper limit
  93. The EP-WXT trigger 01709251871 is likely a flaring star
  94. Fermi GRB 260120C: Global MASTER-Net observations report
  95. GRB 260120B: Swift-BAT refined analysis
  96. GRB 260120B: Swift-XRT refined Analysis
  97. EP260116a: COLIBRÍ further observations
  98. GRB 251122A / EP251122a: VLT/X-shooter host redshift z = 1.765
  99. GRB 260120B: Fermi GBM Observation
  100. EP260105a: GTC/HiPERCAM optical observations

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