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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"

7393 results found.

  1. GRB 260511B: NuSTAR detection of prompt emission
  2. GRB 260511A: NuSTAR detection of prompt emission
  3. GRB 260511B: SVOM/VT optical observation with VHF data
  4. GRB 260511B : MITSuME Akeno optical afterglow candidate detection
  5. GRB 260511A: SVOM/VT optical observation with VHF data
  6. GRB 260510C: SVOM/COLIBRÍ (FM-GFT) optical counterpart candidate
  7. Fermi GBM Sub-Threshold Detection of GRB 260510B
  8. GRB 260509A: LCO optical observations
  9. GRB 260509A: SVOM/VT optical candidate with VHF data
  10. GRB 260509A: LCO optical counterpart detection
  11. GRB 260509A: GOTO optical counterpart candidate
  12. EP260507a: COLIBRÍ optical observations
  13. EP260507a: Kinder optical counterpart candidate
  14. GRB 260504B: SVOM/MXT refined analysis and potential detection
  15. IceCube-260504A - IceCube observation of a high-energy neutrino candidate track-like event
  16. IceCube-260425A - IceCube observation of a high-energy neutrino candidate track-like event
  17. GRB 260421B: LCO optical afterglow confirmation
  18. GRB 260421B: SVOM/COLIBRÍ (FM-GFT) optical detection of a candidate counterpart
  19. EP260416a: Optical follow-up observations with Kinder
  20. EP260416a: COLIBRÍ confirmation of the optical rebrightening
  21. EP260416a: WFST optical observations and rebrightening
  22. EP260416a: SVOM/VT optical observation
  23. EP260416a: COLIBRÍ optical counterpart candidate
  24. COLIBRI optical observations of the transient GOTO26djh/AT2026jpw
  25. GOTO26djh/AT2026jpw: EP-FXT X-ray counterpart detection
  26. GOTO discovery of fast-fading transient GOTO26djh/AT2026jpw, a candidate orphan afterglow
  27. GRB 260411B: Fermi-LAT detection
  28. GRB 260411B: GOTO optical counterpart candidate
  29. EP260409a: Gemini/FLAMINGOS2 J-band counterpart
  30. GRB 260330B: SVOM/VT further optical observation
  31. EP260403a: COLIBRÍ optical counterpart candidate
  32. GRB 260330B: SVOM/VT optical candidate
  33. GRB 260330B: EP-FXT follow-up and identification of candidate afterglow
  34. EP260402a/GRB 260402A: SVOM/C-GFT upper limit
  35. GRB 260402A: SVOM/MXT candidate X-ray afterglow
  36. GRB 260310A / AT2026fgk: Luminance-band optical follow-up with a 28cm telescope in Daocheng
  37. EP260329b: GOTO detection of optical counterpart
  38. Fermi GBM Sub-Threshold Detection of GRB 260330B
  39. EP260329a: COLIBRÍ optical upper limit
  40. EP260329a: NOT optical counterpart candidate
  41. EP260329b: Optical follow-up with Kinder observations
  42. EP-WXT trigger 01709259209: TRT optical counterpart detection
  43. EP260327a: COLIBRÍ optical upper limits
  44. EP260321a: Continued brightening from Kinder follow-up of the emerging supernova candidate
  45. EP260321a: ZTF and Rubin detections of the candidate optical counterpart to EP260321a
  46. EP260321a: further Kinder optical observations
  47. EP260321a: refined analysis of the EP-WXT and EP-FXT observations, implying a possible supernova shock breakout candidate
  48. Fermi GBM Sub-Threshold Detection of GRB 260321A
  49. IceCube-260315A: No Candidate Transients from the Zwicky Transient Facility
  50. GRB 260316A / EP260316a: COLIBRÍ optical followup of counterpart candidate
  51. EP260316a / GRB 260316A: SVOM/VT optical upper limits
  52. EP260316a: COLIBRÍ faint optical counterpart candidate
  53. EP260316a: Xinglong optical upper limit
  54. IceCube-260315A: COLIBRÍ optical observations
  55. EP260314a: optical upper limit with Kinder observations
  56. IceCube Alert-260315A/AT2026fpm Automatic MASTER optical blue counterpart candidate
  57. EP260314a: COLIBRÍ optical upper limit
  58. IceCube-260315A - IceCube observation of a high-energy neutrino candidate track-like event
  59. EP260314a: refined analysis of the EP-WXT and EP-FXT observations
  60. EP260314a: SVOM/VT optical candidate
  61. GRB 260310A / AT2026fgk: SAO RAS optical observations
  62. GRB 260310A / AT2026fgk: further CAHA 1.23m telescope optical observations suggest shallow decay
  63. GRB 260310A/AT 2026fgk: Bok spectroscopic observation
  64. GRB 260310A / AT2026fgk: OSIRIS+/GTC spectroscopy confirms redshift z = 0.153
  65. GRB 260310A / AT2026fgk: CAHA 1.23m telescope optical observations
  66. GRB260310A / AT2026fgk: P200 Spectroscopy
  67. Fermi GBM Sub-Threshold Detection of GRB 260307B
  68. GRB 260307B: Mephisto optical upper limits
  69. GRB 260307B: possible NOT optical counterpart
  70. GRB 260307B: SVOM/VT upper limit with X band data analysis
  71. GRB 260307B: SVOM/VT optical candidate
  72. GRB 260307B: SVOM/C-GFT upper limit
  73. GRB 260211A: SVOM/VT optical rebrightening at 20 days after the burst, SN candidate
  74. IceCube-260217A: No Candidate Transients from the Zwicky Transient Facility
  75. GRB 260303A: SVOM/COLIBRÍ (FM-GFT) optical counterpart candidate
  76. EP/WXT trigger 01709258681 (EP260227a?): LCO candidate afterglow
  77. IceCube cascade alert 142200_1517143 retraction
  78. EP260214a: VLT/FORS2 optical observations
  79. EP260214a: VLA 6 GHz detection
  80. GRB 260225A: SVOM/COLIBRÍ (FM-GFT) Detection of an Optical Counterpart Candidate
  81. EP260213a: Mephisto optical upper limits
  82. sb26021801: SVOM/C-GFT upper limit
  83. EP260221a: Optical upper limit with Kinder observations
  84. GRB 260223A: DDOTI Optical Candidate
  85. EP260221a: Liverpool Telescope detection of COLIBRÍ counterpart candidate
  86. EP260221a: COLIBRÍ optical counterpart candidate
  87. ZTF26aaglqak/AT2026dbl: COLIBRÍ Optical Observations
  88. IceCube-260217A - IceCube observation of a high-energy neutrino candidate track-like event
  89. EP260213a: Mondy R-band optical upper limit
  90. EP260213a: SVOM/C-GFT upper limit
  91. GRB 260211A: EP-FXT follow-up observation
  92. EP260210a: SVOM/C-GFT upper limit
  93. GRB 260208B: COLIBRÍ optical observations
  94. GRB 260208B: EP-FXT observation
  95. GRB 260208B: SVOM/VT optical candidate
  96. GRB 260208A: Zwicky Transient Facility Follow-Up of a Fermi GRB (Trigger 792220053)
  97. GRB 260208B: Swift ToO observations
  98. GRB 260208A: Swift ToO observations
  99. GRB 260206A: Tiled Swift observations
  100. GRB 260204A: Swift-XRT observations

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