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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"

15554 results found.

  1. GRB 260208A: COLIBRÍ optical observations
  2. GRB 260208B: EP-FXT observation
  3. GRB 260208A: NOT spectroscopic redshift z = 2.36
  4. GRB 260208A: Liverpool Telescope optical detection
  5. GRB 260208B: SVOM/VT optical candidate
  6. GRB 260208A: Zwicky Transient Facility Follow-Up of a Fermi GRB (Trigger 792220053)
  7. GRB 260208A: SVOM/VT optical observation
  8. GRB 260208A: Swift-XRT observations
  9. GRB 260208B: SVOM/GRM observation of a bright burst
  10. GRB 260208A: Fermi GBM Classification Correction
  11. GRB 260208A: GOTO detection of a potential optical counterpart (GOTO26aob)
  12. GRB 260208A : MASTER bright optical transient inside retracted Fermi error-box
  13. GRB 260207A : MASTER optical counterpart discovery
  14. GRB 260131A/B: Mondy and Terskol optical observations
  15. GRB 260204A: SVOM/VT confirms fading of the optical afterglow
  16. GRB 260204A: Swift-XRT observations
  17. GRB 260204A: LCO optical afterglow detection
  18. GRB 260204A: SVOM/VT optical candidate
  19. GRB 260204A : MASTER Global robotic net optical observations
  20. GRB 260204A: GOTO optical upper limit
  21. GRB 260204A: LCO optical upper limits
  22. GRB 260131A/B: OHP/T193 optical observations
  23. GRB 260131A: KAIT optical observations
  24. GRB 251230A: MeerLICHT afterglow detection
  25. GRB 260131A: FTW optical and NIR observations
  26. GRB 260131A/AT2026bwg: Observations by the Zwicky Transient Facility
  27. GRB 260131A/B: GTC/OSIRIS+ redshift confimation
  28. GRB 260131A/B (AT2026bwg): J-band observations by SYSU 80cm infrared telescope
  29. GRB 260131A/B: EP/FXT X-ray afterglow detection
  30. GRB 260131A/B (AT2026bwg): COLIBRÍ further optical observations
  31. GRB 260131A: NOT spectroscopic redshift z = 1.434
  32. EP260131a: Liverpool Telescope optical upper limits
  33. EP260131a: COLIBRÍ further observations
  34. EP260131a: SVOM/VT optical observation
  35. EP260131a: Xinglong optical upper limit
  36. GRB 260131A/B (AT2026bwg): COLIBRÍ optical observations and confirmation of fading
  37. GRB 260131A/B: GOTO candidate optical counterpart consistent with the MAXI localisation
  38. EP260131a: COLIBRÍ observations of slow optical fading
  39. EP260131a: refined analysis of the EP-WXT and autonomous EP-FXT observations
  40. EP260131a: VLT/X-shooter spectroscopic redshift z = 0.937
  41. EP260131a: NOT early detection of the counterpart in "rapid response mode"
  42. EP260131a: COLIBRÍ optical observations of the counterpart
  43. EP260131a: Las Cumbres detection of an optical counterpart
  44. EP260128a / GRB 260128A: COLIBRÍ optical upper limit
  45. EP260128a / GRB 260128A: NOT and TNG optical and NIR upper limits
  46. GRB 260128B: LCO optical upper limits
  47. GRB 260128B: SVOM/COLIBRÍ (FM-GFT) optical upper limits
  48. EP260128a: J band upper limit by SYSU 80cm infrared telescope
  49. IPN triangulation of GRB 260127B (short)
  50. GRB 260127B: Swift-XRT observations
  51. GRB 260127A: INASAN-Kislovodsk, SAO RAS, and Terskol K-800 optical observations
  52. EP260128a: NOT optical counterpart candidate
  53. EP260128a: Liverpool Telescope optical observations and possible counterpart
  54. EP260128a: LCO optical upper limits
  55. EP260126a: SVOM/VT optical upperlimit
  56. IceCube-260125A: No Candidate Transients from the Zwicky Transient Facility
  57. GRB 260127A: COLIBRÍ optical observations
  58. GRB 260127A: NOT optical observations
  59. EP260126a: Seimei/TriCCS optical upper limit
  60. GRB 260127A : MITSuME Akeno optical afterglow candidate detection
  61. GRB 260127B: GOTO candidate optical counterpart
  62. GRB 260127A: SVOM/C-GFT optical observations
  63. GRB 260127A: LCO optical afterglow discovery
  64. EP260126a: Optical upper limit with Kinder observations
  65. EP260126a: Liverpool Telescope optical upper limits
  66. EP260126a: Further NOT optical upper limits
  67. EP260126a: COLIBRÍ optical upper limits
  68. EP260126a: NOT optical observations
  69. GRB 260125A: NOT optical observations on GOTO26acv / AT 2026bjf
  70. GRB 260125A: GOTO candidate optical counterpart
  71. GRB 260114A: SVOM/VT optical upper limits
  72. GRB 260120B: SVOM/GRM observation
  73. EP260119a: Assy AZT-20 optical observations
  74. EP260119a: Mondy and SAO RAS optical upper limits
  75. EP260119a: Xinglong optical upper limit
  76. GRB 251122A / EP251122a: VLT/X-shooter host redshift z = 1.765
  77. EP260105a: GTC/HiPERCAM optical observations
  78. GRB 260120B: Swift/UVOT Detection
  79. GRB 260120B: COLIBRÍ optical upper limits
  80. GRB 260120B: SVOM/C-GFT optical counterpart detection
  81. EP260116a: COLIBRÍ observations of a tentative optical rebrightening
  82. GRB 260114A: Swift/UVOT Upper Limits
  83. EP260119a: Liverpool Telescope optical follow-up observations
  84. EP260119A: GTC/OSIRIS+ spectroscopic redshift z = 5.47
  85. EP260119a: KAIT optical observations
  86. EP260119a: SVOM/VT optical observation
  87. EP260119a: update of EP-FXT follow-up observation
  88. EP260119a: NOT optical observations
  89. EP260119a: SAO RAS optical observations
  90. EP260116a: COLIBRÍ detection of a fading optical source
  91. GRB 260117A: Swift-XRT afterglow detection
  92. EP260119a: COLIBRÍ photometric redshift z ≈ 5.6
  93. EP260119a: LCO optical observations
  94. GRB 260117A: ZTSh optical upper limit
  95. EP260119a: COLIBRÍ optical counterpart candidate
  96. GRB 260117A: SVOM/COLIBRÍ (FM-GFT) optical observations
  97. GRB 260117A: SVOM/VT optical candidate
  98. GRB 260117A: SVOM detection of a long faint burst
  99. EP 260116a: COLIBRÍ optical upper limit
  100. EP260116a: Liverpool Telescope upper limits

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