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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: GTC/OSIRIS+ redshift confimation
  2. GRB 260130A: Insight-HXMT/HE detection
  3. GRB 260130A: GECAM-B observation of a short burst
  4. GRB 260131A/B (AT2026bwg): J-band observations by SYSU 80cm infrared telescope
  5. GRB 260131A/B: EP/FXT X-ray afterglow detection
  6. GRB 260131A/B (AT2026bwg): COLIBRÍ further optical observations
  7. GRB 260127B: Insight-HXMT/HE detection
  8. GRB 260127B: GECAM-B observation of a short burst
  9. GRB 260127A: GECAM-B observation
  10. GRB 260131A: NOT spectroscopic redshift z = 1.434
  11. EP260131a: Liverpool Telescope optical upper limits
  12. EP260131a: COLIBRÍ further observations
  13. Konus-Wind detection of GRB 260128A / EP260128a
  14. GRB 260131A: Insight-HXMT/HE detection
  15. Konus-Wind detection of GRB 260131A/B
  16. EP260131a: SVOM/VT optical observation
  17. EP260131a: Xinglong optical upper limit
  18. GRB 260131A/B (AT2026bwg): COLIBRÍ optical observations and confirmation of fading
  19. GRB 260131A/B: GOTO candidate optical counterpart consistent with the MAXI localisation
  20. GRB 260131A/B: Fermi GBM Observation
  21. EP260131a: COLIBRÍ observations of slow optical fading
  22. EP260131a: refined analysis of the EP-WXT and autonomous EP-FXT observations
  23. EP260131a: VLT/X-shooter spectroscopic redshift z = 0.937
  24. EP260131a: NOT early detection of the counterpart in "rapid response mode"
  25. GRB 260131B: MAXI/GSC detection
  26. GRB 260131A: Fermi GBM Final Real-time Localization
  27. EP260131a: COLIBRÍ optical observations of the counterpart
  28. EP260131a: Las Cumbres detection of an optical counterpart
  29. GRB 260127B: AstroSat CZTI detection
  30. GRB 260130A: Fermi GBM Detection
  31. EP260131a: Einstein Probe detection of an X-ray transient
  32. GRB 260127B: Fermi GBM Detection
  33. EP260128a / GRB 260128A: COLIBRÍ optical upper limit
  34. Fermi GRB 260130A: Global MASTER-Net observations report
  35. EP260128a / GRB 260128A: NOT and TNG optical and NIR upper limits
  36. GRB 260130A: Fermi GBM Final Real-time Localization
  37. Fermi GRB 260129A: Global MASTER-Net observations report
  38. GRB 260128B: LCO optical upper limits
  39. GRB 260128B: SVOM/COLIBRÍ (FM-GFT) optical upper limits
  40. EP260128a: J band upper limit by SYSU 80cm infrared telescope
  41. IPN triangulation of GRB 260121A
  42. GRB 260127A: Swift-BAT refined analysis
  43. GRB 260129B: Fermi GBM Final Localization
  44. GRB 260128B: SVOM detection of a burst through offline search
  45. GRB 260129A: Fermi GBM Final Localization
  46. IPN triangulation of GRB 260127B (short)
  47. GRB 260127B: Swift-XRT observations
  48. GRB 260127A: INASAN-Kislovodsk, SAO RAS, and Terskol K-800 optical observations
  49. GRB 260128A / EP260128a: Fermi-GBM Sub-Threshold Detection
  50. EP260128a: NOT optical counterpart candidate
  51. EP260128a: refined analysis of the EP-WXT and autonomous EP-FXT observations
  52. EP260128a: Liverpool Telescope optical observations and possible counterpart
  53. EP260128a: LCO optical upper limits
  54. EP260126a: SVOM/VT optical upperlimit
  55. EP260128a: Global MASTER-Net observations report
  56. EP260128a: Einstein Probe detection of an X-ray transient
  57. Fermi GRB 260127A: Global MASTER-Net observations report
  58. IceCube-260125A: No Candidate Transients from the Zwicky Transient Facility
  59. GRB 260127A: Fermi GBM Observation
  60. IceCube-260125A: Upper limits from a search for additional neutrino events in IceCube
  61. GRB 260127A: COLIBRÍ optical observations
  62. GRB 260127A: NOT optical observations
  63. GRB 260127B: Swift ToO observations
  64. EP260126a: Seimei/TriCCS optical upper limit
  65. GRB 260127A : MITSuME Akeno optical afterglow candidate detection
  66. GRB 260127A: Swift-XRT refined Analysis
  67. GRB 260127B: GOTO candidate optical counterpart
  68. GRB 260127A: SVOM/C-GFT optical observations
  69. The EP-WXT trigger 01709253145 is likely a flaring star
  70. GRB 260127A: Enhanced Swift-XRT position
  71. Fermi GRB 260127B: Global MASTER-Net observations report
  72. GRB 260127B: Fermi GBM Final Real-time Localization
  73. GRB 260127A: Prompt enhanced Swift-XRT position
  74. Swift GRB 260127A: Global MASTER-Net observations report
  75. GRB 260127A: LCO optical afterglow discovery
  76. GRB 260127A: Swift detection of a burst
  77. GRB 260127A: Fermi GBM Final Real-time Localization
  78. GRB 260125A: Swift-XRT observations
  79. EP260126a: EP-FXT follow-up observation
  80. EP260126a: Optical upper limit with Kinder observations
  81. EP260126a: Liverpool Telescope optical upper limits
  82. EP260126a: Further NOT optical upper limits
  83. EP260126a: COLIBRÍ optical upper limits
  84. EP260126a: NOT optical observations
  85. EP260126a: Einstein Probe detection of a fast X-ray transient
  86. Fermi-LAT Gamma-ray Observations of IceCube-260125A
  87. GRB 260125A: NOT optical observations on GOTO26acv / AT 2026bjf
  88. Konus-Wind detection of GRB 260120B
  89. GRB 251222A: SVOM/ECLAIRs refined analysis
  90. GRB 260125A: Swift ToO observations
  91. GRB 260125A: GOTO candidate optical counterpart
  92. Fermi GRB 260125B: Global MASTER-Net observations report
  93. IceCube-260125A - IceCube observation of a high-energy neutrino candidate track-like event
  94. GRB 260125B: Fermi GBM Final Real-time Localization
  95. GRB 260125A: Fermi GBM Final Real-time Localization
  96. GRB 260114A: SVOM/VT optical upper limits
  97. GRB 260120A: AstroSat CZTI detection
  98. GRB 260122B: Swift-BAT refined analysis
  99. GRB 260120B: SVOM/GRM observation
  100. GRB 260120A: GECAM-B observation

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