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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"

7260 results found.

  1. EP260402a/GRB 260402A: SVOM/C-GFT upper limit
  2. GRB 260402A: SVOM/MXT candidate X-ray afterglow
  3. GRB 260310A / AT2026fgk: Luminance-band optical follow-up with a 28cm telescope in Daocheng
  4. EP260329b: GOTO detection of optical counterpart
  5. Fermi GBM Sub-Threshold Detection of GRB 260330B
  6. EP260329a: COLIBRÍ optical upper limit
  7. EP260329a: NOT optical counterpart candidate
  8. EP260329b: Optical follow-up with Kinder observations
  9. EP-WXT trigger 01709259209: TRT optical counterpart detection
  10. EP260327a: COLIBRÍ optical upper limits
  11. EP260321a: Continued brightening from Kinder follow-up of the emerging supernova candidate
  12. EP260321a: ZTF and Rubin detections of the candidate optical counterpart to EP260321a
  13. EP260321a: further Kinder optical observations
  14. EP260321a: refined analysis of the EP-WXT and EP-FXT observations, implying a possible supernova shock breakout candidate
  15. Fermi GBM Sub-Threshold Detection of GRB 260321A
  16. IceCube-260315A: No Candidate Transients from the Zwicky Transient Facility
  17. GRB 260316A / EP260316a: COLIBRÍ optical followup of counterpart candidate
  18. EP260316a / GRB 260316A: SVOM/VT optical upper limits
  19. EP260316a: COLIBRÍ faint optical counterpart candidate
  20. EP260316a: Xinglong optical upper limit
  21. IceCube-260315A: COLIBRÍ optical observations
  22. EP260314a: optical upper limit with Kinder observations
  23. IceCube Alert-260315A/AT2026fpm Automatic MASTER optical blue counterpart candidate
  24. EP260314a: COLIBRÍ optical upper limit
  25. IceCube-260315A - IceCube observation of a high-energy neutrino candidate track-like event
  26. EP260314a: refined analysis of the EP-WXT and EP-FXT observations
  27. EP260314a: SVOM/VT optical candidate
  28. GRB 260310A / AT2026fgk: SAO RAS optical observations
  29. GRB 260310A / AT2026fgk: further CAHA 1.23m telescope optical observations suggest shallow decay
  30. GRB 260310A/AT 2026fgk: Bok spectroscopic observation
  31. GRB 260310A / AT2026fgk: OSIRIS+/GTC spectroscopy confirms redshift z = 0.153
  32. GRB 260310A / AT2026fgk: CAHA 1.23m telescope optical observations
  33. GRB260310A / AT2026fgk: P200 Spectroscopy
  34. Fermi GBM Sub-Threshold Detection of GRB 260307B
  35. GRB 260307B: Mephisto optical upper limits
  36. GRB 260307B: possible NOT optical counterpart
  37. GRB 260307B: SVOM/VT upper limit with X band data analysis
  38. GRB 260307B: SVOM/VT optical candidate
  39. GRB 260307B: SVOM/C-GFT upper limit
  40. GRB 260211A: SVOM/VT optical rebrightening at 20 days after the burst, SN candidate
  41. IceCube-260217A: No Candidate Transients from the Zwicky Transient Facility
  42. GRB 260303A: SVOM/COLIBRÍ (FM-GFT) optical counterpart candidate
  43. EP/WXT trigger 01709258681 (EP260227a?): LCO candidate afterglow
  44. IceCube cascade alert 142200_1517143 retraction
  45. EP260214a: VLT/FORS2 optical observations
  46. EP260214a: VLA 6 GHz detection
  47. GRB 260225A: SVOM/COLIBRÍ (FM-GFT) Detection of an Optical Counterpart Candidate
  48. EP260213a: Mephisto optical upper limits
  49. sb26021801: SVOM/C-GFT upper limit
  50. EP260221a: Optical upper limit with Kinder observations
  51. GRB 260223A: DDOTI Optical Candidate
  52. EP260221a: Liverpool Telescope detection of COLIBRÍ counterpart candidate
  53. EP260221a: COLIBRÍ optical counterpart candidate
  54. ZTF26aaglqak/AT2026dbl: COLIBRÍ Optical Observations
  55. IceCube-260217A - IceCube observation of a high-energy neutrino candidate track-like event
  56. EP260213a: Mondy R-band optical upper limit
  57. EP260213a: SVOM/C-GFT upper limit
  58. GRB 260211A: EP-FXT follow-up observation
  59. EP260210a: SVOM/C-GFT upper limit
  60. GRB 260208B: COLIBRÍ optical observations
  61. GRB 260208B: EP-FXT observation
  62. GRB 260208B: SVOM/VT optical candidate
  63. GRB 260208A: Zwicky Transient Facility Follow-Up of a Fermi GRB (Trigger 792220053)
  64. GRB 260208B: Swift ToO observations
  65. GRB 260208A: Swift ToO observations
  66. GRB 260206A: Tiled Swift observations
  67. GRB 260204A: Swift-XRT observations
  68. GRB 260204A: SVOM/VT optical candidate
  69. Fermi GBM Sub-Threshold Detection of GRB 260204A
  70. GRB 260131A/B (AT2026bwg): J-band observations by SYSU 80cm infrared telescope
  71. GRB 260131A/B (AT2026bwg): COLIBRÍ further optical observations
  72. EP260131a: COLIBRÍ further observations
  73. GRB 260131A/B (AT2026bwg): COLIBRÍ optical observations and confirmation of fading
  74. GRB 260131A/B: GOTO candidate optical counterpart consistent with the MAXI localisation
  75. EP260131a: COLIBRÍ observations of slow optical fading
  76. EP260131a: COLIBRÍ optical observations of the counterpart
  77. EP260128a / GRB 260128A: COLIBRÍ optical upper limit
  78. GRB 260127B: Swift-XRT observations
  79. EP260128a: NOT optical counterpart candidate
  80. IceCube-260125A: No Candidate Transients from the Zwicky Transient Facility
  81. GRB 260127A: COLIBRÍ optical observations
  82. GRB 260127B: Swift ToO observations
  83. GRB 260127A : MITSuME Akeno optical afterglow candidate detection
  84. GRB 260127B: GOTO candidate optical counterpart
  85. GRB 260127A: Swift detection of a burst
  86. GRB 260125A: NOT optical observations on GOTO26acv / AT 2026bjf
  87. GRB 260125A: Swift ToO observations
  88. GRB 260125A: GOTO candidate optical counterpart
  89. IceCube-260125A - IceCube observation of a high-energy neutrino candidate track-like event
  90. GRB 260114A: SVOM/VT optical upper limits
  91. IceCube-260115A: No Candidate Transients from the Zwicky Transient Facility
  92. GRB 260120B: COLIBRÍ optical upper limits
  93. GRB 260117A: Swift-XRT afterglow detection
  94. EP260119a: COLIBRÍ optical counterpart candidate
  95. GRB 260117A: SVOM/VT optical candidate
  96. GRB 260117A: SVOM/C-GFT upper limit
  97. GRB 260117A: Swift ToO observations
  98. GRB 260111A: COLIBRÍ fading of the optical counterpart candidate
  99. IceCube-260115A - IceCube observation of a high-energy neutrino candidate track-like event
  100. GRB 260114A: GMG Optical Observation

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