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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"

7396 results found.

  1. GRB 260208A: Swift ToO observations
  2. GRB 260206A: Tiled Swift observations
  3. GRB 260204A: Swift-XRT observations
  4. GRB 260204A: SVOM/VT optical candidate
  5. Fermi GBM Sub-Threshold Detection of GRB 260204A
  6. GRB 260131A/B (AT2026bwg): J-band observations by SYSU 80cm infrared telescope
  7. GRB 260131A/B (AT2026bwg): COLIBRÍ further optical observations
  8. EP260131a: COLIBRÍ further observations
  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. EP260131a: COLIBRÍ observations of slow optical fading
  12. EP260131a: COLIBRÍ optical observations of the counterpart
  13. EP260128a / GRB 260128A: COLIBRÍ optical upper limit
  14. GRB 260127B: Swift-XRT observations
  15. EP260128a: NOT optical counterpart candidate
  16. IceCube-260125A: No Candidate Transients from the Zwicky Transient Facility
  17. GRB 260127A: COLIBRÍ optical observations
  18. GRB 260127B: Swift ToO observations
  19. GRB 260127A : MITSuME Akeno optical afterglow candidate detection
  20. GRB 260127B: GOTO candidate optical counterpart
  21. GRB 260127A: Swift detection of a burst
  22. GRB 260125A: NOT optical observations on GOTO26acv / AT 2026bjf
  23. GRB 260125A: Swift ToO observations
  24. GRB 260125A: GOTO candidate optical counterpart
  25. IceCube-260125A - IceCube observation of a high-energy neutrino candidate track-like event
  26. GRB 260114A: SVOM/VT optical upper limits
  27. IceCube-260115A: No Candidate Transients from the Zwicky Transient Facility
  28. GRB 260120B: COLIBRÍ optical upper limits
  29. GRB 260117A: Swift-XRT afterglow detection
  30. EP260119a: COLIBRÍ optical counterpart candidate
  31. GRB 260117A: SVOM/VT optical candidate
  32. GRB 260117A: SVOM/C-GFT upper limit
  33. GRB 260117A: Swift ToO observations
  34. GRB 260111A: COLIBRÍ fading of the optical counterpart candidate
  35. IceCube-260115A - IceCube observation of a high-energy neutrino candidate track-like event
  36. GRB 260114A: GMG Optical Observation
  37. GRB 260114A: Swift detection of a short burst
  38. Swift Trigger 1439093: is probably not GRB 260113A
  39. GRB 260111A: COLIBRÍ optical afterglow candidate
  40. GRB 260111A: Swift ToO observations
  41. IceCube-260111A - IceCube observation of a high-energy neutrino candidate track-like event
  42. Swift trigger 1436759 is not an astrophysical event
  43. EP260110a: SVOM/C-GFT upper limit
  44. Swift Trigger 1434591: possible GRB 260109C
  45. GRB 260104A: Swift detection of a burst
  46. GRB 260102A: Swift ToO observations
  47. GRB 260101A: Swift detection of a burst with an optical counterpart
  48. GRB 251230A: GRANDMA/TAROT Early Detection
  49. GRB 251230A/EP251230a: Optical upper limit with Kinder observations
  50. LIGO/Virgo/KAGRA S251112cm: Candidates from the NSF-DOE Vera C. Rubin Observatory
  51. GRB 251230A: Swift detection of a burst with a bright optical counterpart
  52. GRB 251129A: redshift correction and SN detection at z = 0.505 with GTC
  53. IceCube-251225A - IceCube observation of a high-energy neutrino candidate track-like event
  54. GRB 251222A/EP251222b: Optical detection with Kinder observations
  55. EP251222a: Optical upper limit with Kinder observations
  56. IceCube-251218A: No Candidate Transients from the Zwicky Transient Facility
  57. GRB 251222A: Swift ToO observations
  58. GRB 251222A: SVOM/VT optical candidate
  59. EP251220a: PRIME upper limit
  60. GRB 251221A: Swift detection of a burst
  61. IceCube-251218A - IceCube observation of a high-energy neutrino candidate track-like event
  62. EP251214a: Optical upper limit with Kinder observations
  63. GRB 251215A: Swift ToO observations
  64. GRB 251214B: Swift detection of a burst with an optical counterpart
  65. IceCube-251210A: No Candidate Transients from the Zwicky Transient Facility
  66. IceCube-251210A - IceCube observation of a high-energy neutrino candidate track-like event
  67. GRB 251208B: COLIBRÍ optical upper limits
  68. GRB 251208D: Swift-XRT observations
  69. GRB 251208B: Swift ToO observations
  70. GRB 251205A : MITSuME Akeno optical afterglow candidate detection
  71. GRB 251205A: Swift detection of a burst with an optical afterglow
  72. SVOM/sb25120502: SVOM detection of a faint X-ray transient candidate
  73. GRB 251203C: LCO optical afterglow confirmation
  74. GRB 251203B: Swift-XRT observations
  75. GRB 251203B: SVOM/VT optical observation
  76. GRB 251201B: Swift detection of a burst with an optical counterpart
  77. EP251130a: JinShan optical observations
  78. IceCube-251130A - IceCube observation of a high-energy neutrino candidate track-like event
  79. EP251130a: Swift-XRT counterpart detection
  80. EP251130a: COLIBRÍ optical counterpart candidate
  81. GRB 251129A: Swift ToO observations
  82. GRB 251129A: SVOM/COLIBRÍ (FM-GFT) optical counterpart candidate
  83. GRB 251126A : MITSuME Akeno optical afterglow candidate detection
  84. GRB 251125B: COLIBRÍ further observations and photometric redshift upper limit of z < 3
  85. GRB 251125B: COLIBRÍ observations of fading of the MASTER OT candidate
  86. EP251124a: Swift-XRT observations
  87. LIGO/Virgo/KAGRA S251112cm: AT 2025adht Kinder follow-up observations
  88. LIGO/Virgo/KAGRA S251105aj: EP-FXT follow-up observations and preliminary results on SVOM J2320.0-2901
  89. GRB 251122A/EP251122a: Additional, deeper LCO optical r band upper limit
  90. GRB 251122A / EP251122a: LCO optical upper limits
  91. EP251122a / GRB 251122A: optical counterpart candidate with Kinder observations
  92. GRB 251122A/EP251122a: SVOM/C-GFT upper limit
  93. EP251118a: Continued Optical Detection with Kinder observations
  94. LIGO/Virgo/KAGRA S251105aj: SVOM/ECLAIRs detection of a high-energy transient SVOM J2320.0-2901 through targeted search
  95. EP251118a: Optical detection with Kinder observations
  96. EP251118a: NOT candidate optical counterpart
  97. GRB 251118A: Swift ToO observations
  98. LIGO/Virgo/KAGRA S251112cm: Upper limits from Glowbug gamma-ray observations
  99. GRB 251117A: FTW Observations of Swift candidate X-ray sources
  100. LIGO/Virgo/KAGRA S251117dq: Updated Sky localization

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