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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: NOT spectroscopic redshift z = 1.434
  2. EP260131a: Liverpool Telescope optical upper limits
  3. EP260131a: COLIBRÍ further observations
  4. Konus-Wind detection of GRB 260128A / EP260128a
  5. GRB 260131A: Insight-HXMT/HE detection
  6. Konus-Wind detection of GRB 260131A/B
  7. EP260131a: SVOM/VT optical observation
  8. EP260131a: Xinglong optical upper limit
  9. GRB 260131A/B (AT2026bwg): COLIBRÍ optical observations and confirmation of fading
  10. GRB 260131A/B: GOTO candidate optical counterpart consistent with the MAXI localisation
  11. GRB 260131A/B: Fermi GBM Observation
  12. EP260131a: COLIBRÍ observations of slow optical fading
  13. EP260131a: refined analysis of the EP-WXT and autonomous EP-FXT observations
  14. EP260131a: VLT/X-shooter spectroscopic redshift z = 0.937
  15. EP260131a: NOT early detection of the counterpart in "rapid response mode"
  16. GRB 260131B: MAXI/GSC detection
  17. GRB 260131A: Fermi GBM Final Real-time Localization
  18. EP260131a: COLIBRÍ optical observations of the counterpart
  19. EP260131a: Las Cumbres detection of an optical counterpart
  20. GRB 260127B: AstroSat CZTI detection
  21. GRB 260130A: Fermi GBM Detection
  22. EP260131a: Einstein Probe detection of an X-ray transient
  23. GRB 260127B: Fermi GBM Detection
  24. EP260128a / GRB 260128A: COLIBRÍ optical upper limit
  25. Fermi GRB 260130A: Global MASTER-Net observations report
  26. EP260128a / GRB 260128A: NOT and TNG optical and NIR upper limits
  27. GRB 260130A: Fermi GBM Final Real-time Localization
  28. Fermi GRB 260129A: Global MASTER-Net observations report
  29. GRB 260128B: LCO optical upper limits
  30. GRB 260128B: SVOM/COLIBRÍ (FM-GFT) optical upper limits
  31. EP260128a: J band upper limit by SYSU 80cm infrared telescope
  32. IPN triangulation of GRB 260121A
  33. GRB 260127A: Swift-BAT refined analysis
  34. GRB 260129B: Fermi GBM Final Localization
  35. GRB 260128B: SVOM detection of a burst through offline search
  36. GRB 260129A: Fermi GBM Final Localization
  37. IPN triangulation of GRB 260127B (short)
  38. GRB 260127B: Swift-XRT observations
  39. GRB 260127A: INASAN-Kislovodsk, SAO RAS, and Terskol K-800 optical observations
  40. GRB 260128A / EP260128a: Fermi-GBM Sub-Threshold Detection
  41. EP260128a: NOT optical counterpart candidate
  42. EP260128a: refined analysis of the EP-WXT and autonomous EP-FXT observations
  43. EP260128a: Liverpool Telescope optical observations and possible counterpart
  44. EP260128a: LCO optical upper limits
  45. EP260126a: SVOM/VT optical upperlimit
  46. EP260128a: Global MASTER-Net observations report
  47. EP260128a: Einstein Probe detection of an X-ray transient
  48. Fermi GRB 260127A: Global MASTER-Net observations report
  49. IceCube-260125A: No Candidate Transients from the Zwicky Transient Facility
  50. GRB 260127A: Fermi GBM Observation
  51. IceCube-260125A: Upper limits from a search for additional neutrino events in IceCube
  52. GRB 260127A: COLIBRÍ optical observations
  53. GRB 260127A: NOT optical observations
  54. GRB 260127B: Swift ToO observations
  55. EP260126a: Seimei/TriCCS optical upper limit
  56. GRB 260127A : MITSuME Akeno optical afterglow candidate detection
  57. GRB 260127A: Swift-XRT refined Analysis
  58. GRB 260127B: GOTO candidate optical counterpart
  59. GRB 260127A: SVOM/C-GFT optical observations
  60. The EP-WXT trigger 01709253145 is likely a flaring star
  61. GRB 260127A: Enhanced Swift-XRT position
  62. Fermi GRB 260127B: Global MASTER-Net observations report
  63. GRB 260127B: Fermi GBM Final Real-time Localization
  64. GRB 260127A: Prompt enhanced Swift-XRT position
  65. Swift GRB 260127A: Global MASTER-Net observations report
  66. GRB 260127A: LCO optical afterglow discovery
  67. GRB 260127A: Swift detection of a burst
  68. GRB 260127A: Fermi GBM Final Real-time Localization
  69. GRB 260125A: Swift-XRT observations
  70. EP260126a: EP-FXT follow-up observation
  71. EP260126a: Optical upper limit with Kinder observations
  72. EP260126a: Liverpool Telescope optical upper limits
  73. EP260126a: Further NOT optical upper limits
  74. EP260126a: COLIBRÍ optical upper limits
  75. EP260126a: NOT optical observations
  76. EP260126a: Einstein Probe detection of a fast X-ray transient
  77. Fermi-LAT Gamma-ray Observations of IceCube-260125A
  78. GRB 260125A: NOT optical observations on GOTO26acv / AT 2026bjf
  79. Konus-Wind detection of GRB 260120B
  80. GRB 251222A: SVOM/ECLAIRs refined analysis
  81. GRB 260125A: Swift ToO observations
  82. GRB 260125A: GOTO candidate optical counterpart
  83. Fermi GRB 260125B: Global MASTER-Net observations report
  84. IceCube-260125A - IceCube observation of a high-energy neutrino candidate track-like event
  85. GRB 260125B: Fermi GBM Final Real-time Localization
  86. GRB 260125A: Fermi GBM Final Real-time Localization
  87. GRB 260114A: SVOM/VT optical upper limits
  88. GRB 260120A: AstroSat CZTI detection
  89. GRB 260122B: Swift-BAT refined analysis
  90. GRB 260120B: SVOM/GRM observation
  91. GRB 260120A: GECAM-B observation
  92. GRB 260120B: AstroSat CZTI detection
  93. GRB 260114A: Insight-HXMT/HE detection
  94. GRB 260122B: Swift detection of a burst
  95. Swift GRB260122.97: Global MASTER-Net observations report
  96. EP260119a: Assy AZT-20 optical observations
  97. EP260119a: Mondy and SAO RAS optical upper limits
  98. GRB 260122A: Fermi GBM Final Real-time Localization
  99. IceCube-260115A: No Candidate Transients from the Zwicky Transient Facility
  100. EP260119a: Xinglong optical upper limit

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