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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"

7307 results found.

  1. ZTF26aaglqak/AT2026dbl: COLIBRÍ Optical Observations
  2. IceCube-260217A - IceCube observation of a high-energy neutrino candidate track-like event
  3. EP260213a: Mondy R-band optical upper limit
  4. EP260213a: SVOM/C-GFT upper limit
  5. GRB 260211A: EP-FXT follow-up observation
  6. EP260210a: SVOM/C-GFT upper limit
  7. GRB 260208B: COLIBRÍ optical observations
  8. GRB 260208B: EP-FXT observation
  9. GRB 260208B: SVOM/VT optical candidate
  10. GRB 260208A: Zwicky Transient Facility Follow-Up of a Fermi GRB (Trigger 792220053)
  11. GRB 260208B: Swift ToO observations
  12. GRB 260208A: Swift ToO observations
  13. GRB 260206A: Tiled Swift observations
  14. GRB 260204A: Swift-XRT observations
  15. GRB 260204A: SVOM/VT optical candidate
  16. Fermi GBM Sub-Threshold Detection of GRB 260204A
  17. GRB 260131A/B (AT2026bwg): J-band observations by SYSU 80cm infrared telescope
  18. GRB 260131A/B (AT2026bwg): COLIBRÍ further optical observations
  19. EP260131a: COLIBRÍ further observations
  20. GRB 260131A/B (AT2026bwg): COLIBRÍ optical observations and confirmation of fading
  21. GRB 260131A/B: GOTO candidate optical counterpart consistent with the MAXI localisation
  22. EP260131a: COLIBRÍ observations of slow optical fading
  23. EP260131a: COLIBRÍ optical observations of the counterpart
  24. EP260128a / GRB 260128A: COLIBRÍ optical upper limit
  25. GRB 260127B: Swift-XRT observations
  26. EP260128a: NOT optical counterpart candidate
  27. IceCube-260125A: No Candidate Transients from the Zwicky Transient Facility
  28. GRB 260127A: COLIBRÍ optical observations
  29. GRB 260127B: Swift ToO observations
  30. GRB 260127A : MITSuME Akeno optical afterglow candidate detection
  31. GRB 260127B: GOTO candidate optical counterpart
  32. GRB 260127A: Swift detection of a burst
  33. GRB 260125A: NOT optical observations on GOTO26acv / AT 2026bjf
  34. GRB 260125A: Swift ToO observations
  35. GRB 260125A: GOTO candidate optical counterpart
  36. IceCube-260125A - IceCube observation of a high-energy neutrino candidate track-like event
  37. GRB 260114A: SVOM/VT optical upper limits
  38. IceCube-260115A: No Candidate Transients from the Zwicky Transient Facility
  39. GRB 260120B: COLIBRÍ optical upper limits
  40. GRB 260117A: Swift-XRT afterglow detection
  41. EP260119a: COLIBRÍ optical counterpart candidate
  42. GRB 260117A: SVOM/VT optical candidate
  43. GRB 260117A: SVOM/C-GFT upper limit
  44. GRB 260117A: Swift ToO observations
  45. GRB 260111A: COLIBRÍ fading of the optical counterpart candidate
  46. IceCube-260115A - IceCube observation of a high-energy neutrino candidate track-like event
  47. GRB 260114A: GMG Optical Observation
  48. GRB 260114A: Swift detection of a short burst
  49. Swift Trigger 1439093: is probably not GRB 260113A
  50. GRB 260111A: COLIBRÍ optical afterglow candidate
  51. GRB 260111A: Swift ToO observations
  52. IceCube-260111A - IceCube observation of a high-energy neutrino candidate track-like event
  53. Swift trigger 1436759 is not an astrophysical event
  54. EP260110a: SVOM/C-GFT upper limit
  55. Swift Trigger 1434591: possible GRB 260109C
  56. GRB 260104A: Swift detection of a burst
  57. GRB 260102A: Swift ToO observations
  58. GRB 260101A: Swift detection of a burst with an optical counterpart
  59. GRB 251230A: GRANDMA/TAROT Early Detection
  60. GRB 251230A/EP251230a: Optical upper limit with Kinder observations
  61. LIGO/Virgo/KAGRA S251112cm: Candidates from the NSF-DOE Vera C. Rubin Observatory
  62. GRB 251230A: Swift detection of a burst with a bright optical counterpart
  63. GRB 251129A: redshift correction and SN detection at z = 0.505 with GTC
  64. IceCube-251225A - IceCube observation of a high-energy neutrino candidate track-like event
  65. GRB 251222A/EP251222b: Optical detection with Kinder observations
  66. EP251222a: Optical upper limit with Kinder observations
  67. IceCube-251218A: No Candidate Transients from the Zwicky Transient Facility
  68. GRB 251222A: Swift ToO observations
  69. GRB 251222A: SVOM/VT optical candidate
  70. EP251220a: PRIME upper limit
  71. GRB 251221A: Swift detection of a burst
  72. IceCube-251218A - IceCube observation of a high-energy neutrino candidate track-like event
  73. EP251214a: Optical upper limit with Kinder observations
  74. GRB 251215A: Swift ToO observations
  75. GRB 251214B: Swift detection of a burst with an optical counterpart
  76. IceCube-251210A: No Candidate Transients from the Zwicky Transient Facility
  77. IceCube-251210A - IceCube observation of a high-energy neutrino candidate track-like event
  78. GRB 251208B: COLIBRÍ optical upper limits
  79. GRB 251208D: Swift-XRT observations
  80. GRB 251208B: Swift ToO observations
  81. GRB 251205A : MITSuME Akeno optical afterglow candidate detection
  82. GRB 251205A: Swift detection of a burst with an optical afterglow
  83. SVOM/sb25120502: SVOM detection of a faint X-ray transient candidate
  84. GRB 251203C: LCO optical afterglow confirmation
  85. GRB 251203B: Swift-XRT observations
  86. GRB 251203B: SVOM/VT optical observation
  87. GRB 251201B: Swift detection of a burst with an optical counterpart
  88. EP251130a: JinShan optical observations
  89. IceCube-251130A - IceCube observation of a high-energy neutrino candidate track-like event
  90. EP251130a: Swift-XRT counterpart detection
  91. EP251130a: COLIBRÍ optical counterpart candidate
  92. GRB 251129A: Swift ToO observations
  93. GRB 251129A: SVOM/COLIBRÍ (FM-GFT) optical counterpart candidate
  94. GRB 251126A : MITSuME Akeno optical afterglow candidate detection
  95. GRB 251125B: COLIBRÍ further observations and photometric redshift upper limit of z < 3
  96. GRB 251125B: COLIBRÍ observations of fading of the MASTER OT candidate
  97. EP251124a: Swift-XRT observations
  98. LIGO/Virgo/KAGRA S251112cm: AT 2025adht Kinder follow-up observations
  99. LIGO/Virgo/KAGRA S251105aj: EP-FXT follow-up observations and preliminary results on SVOM J2320.0-2901
  100. GRB 251122A/EP251122a: Additional, deeper LCO optical r band upper limit

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