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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 260515A: SVOM/VT optical candidate from VHF data
  2. GRB 260515A: JinShan optical counterpart candidate
  3. IceCube-260504A: No Candidate Transients from the Zwicky Transient Facility
  4. GRB 260511B: NuSTAR detection of prompt emission
  5. GRB 260511A: NuSTAR detection of prompt emission
  6. GRB 260511B: SVOM/VT optical observation with VHF data
  7. GRB 260511B : MITSuME Akeno optical afterglow candidate detection
  8. GRB 260511A: SVOM/VT optical observation with VHF data
  9. GRB 260510C: SVOM/COLIBRÍ (FM-GFT) optical counterpart candidate
  10. Fermi GBM Sub-Threshold Detection of GRB 260510B
  11. GRB 260509A: LCO optical observations
  12. GRB 260509A: SVOM/VT optical candidate with VHF data
  13. GRB 260509A: LCO optical counterpart detection
  14. GRB 260509A: GOTO optical counterpart candidate
  15. EP260507a: COLIBRÍ optical observations
  16. EP260507a: Kinder optical counterpart candidate
  17. GRB 260504B: SVOM/MXT refined analysis and potential detection
  18. IceCube-260504A - IceCube observation of a high-energy neutrino candidate track-like event
  19. IceCube-260425A - IceCube observation of a high-energy neutrino candidate track-like event
  20. GRB 260421B: LCO optical afterglow confirmation
  21. GRB 260421B: SVOM/COLIBRÍ (FM-GFT) optical detection of a candidate counterpart
  22. EP260416a: Optical follow-up observations with Kinder
  23. EP260416a: COLIBRÍ confirmation of the optical rebrightening
  24. EP260416a: WFST optical observations and rebrightening
  25. EP260416a: SVOM/VT optical observation
  26. EP260416a: COLIBRÍ optical counterpart candidate
  27. COLIBRI optical observations of the transient GOTO26djh/AT2026jpw
  28. GOTO26djh/AT2026jpw: EP-FXT X-ray counterpart detection
  29. GOTO discovery of fast-fading transient GOTO26djh/AT2026jpw, a candidate orphan afterglow
  30. GRB 260411B: Fermi-LAT detection
  31. GRB 260411B: GOTO optical counterpart candidate
  32. EP260409a: Gemini/FLAMINGOS2 J-band counterpart
  33. GRB 260330B: SVOM/VT further optical observation
  34. EP260403a: COLIBRÍ optical counterpart candidate
  35. GRB 260330B: SVOM/VT optical candidate
  36. GRB 260330B: EP-FXT follow-up and identification of candidate afterglow
  37. EP260402a/GRB 260402A: SVOM/C-GFT upper limit
  38. GRB 260402A: SVOM/MXT candidate X-ray afterglow
  39. GRB 260310A / AT2026fgk: Luminance-band optical follow-up with a 28cm telescope in Daocheng
  40. EP260329b: GOTO detection of optical counterpart
  41. Fermi GBM Sub-Threshold Detection of GRB 260330B
  42. EP260329a: COLIBRÍ optical upper limit
  43. EP260329a: NOT optical counterpart candidate
  44. EP260329b: Optical follow-up with Kinder observations
  45. EP-WXT trigger 01709259209: TRT optical counterpart detection
  46. EP260327a: COLIBRÍ optical upper limits
  47. EP260321a: Continued brightening from Kinder follow-up of the emerging supernova candidate
  48. EP260321a: ZTF and Rubin detections of the candidate optical counterpart to EP260321a
  49. EP260321a: further Kinder optical observations
  50. EP260321a: refined analysis of the EP-WXT and EP-FXT observations, implying a possible supernova shock breakout candidate
  51. Fermi GBM Sub-Threshold Detection of GRB 260321A
  52. IceCube-260315A: No Candidate Transients from the Zwicky Transient Facility
  53. GRB 260316A / EP260316a: COLIBRÍ optical followup of counterpart candidate
  54. EP260316a / GRB 260316A: SVOM/VT optical upper limits
  55. EP260316a: COLIBRÍ faint optical counterpart candidate
  56. EP260316a: Xinglong optical upper limit
  57. IceCube-260315A: COLIBRÍ optical observations
  58. EP260314a: optical upper limit with Kinder observations
  59. IceCube Alert-260315A/AT2026fpm Automatic MASTER optical blue counterpart candidate
  60. EP260314a: COLIBRÍ optical upper limit
  61. IceCube-260315A - IceCube observation of a high-energy neutrino candidate track-like event
  62. EP260314a: refined analysis of the EP-WXT and EP-FXT observations
  63. EP260314a: SVOM/VT optical candidate
  64. GRB 260310A / AT2026fgk: SAO RAS optical observations
  65. GRB 260310A / AT2026fgk: further CAHA 1.23m telescope optical observations suggest shallow decay
  66. GRB 260310A/AT 2026fgk: Bok spectroscopic observation
  67. GRB 260310A / AT2026fgk: OSIRIS+/GTC spectroscopy confirms redshift z = 0.153
  68. GRB 260310A / AT2026fgk: CAHA 1.23m telescope optical observations
  69. GRB260310A / AT2026fgk: P200 Spectroscopy
  70. Fermi GBM Sub-Threshold Detection of GRB 260307B
  71. GRB 260307B: Mephisto optical upper limits
  72. GRB 260307B: possible NOT optical counterpart
  73. GRB 260307B: SVOM/VT upper limit with X band data analysis
  74. GRB 260307B: SVOM/VT optical candidate
  75. GRB 260307B: SVOM/C-GFT upper limit
  76. GRB 260211A: SVOM/VT optical rebrightening at 20 days after the burst, SN candidate
  77. IceCube-260217A: No Candidate Transients from the Zwicky Transient Facility
  78. GRB 260303A: SVOM/COLIBRÍ (FM-GFT) optical counterpart candidate
  79. EP/WXT trigger 01709258681 (EP260227a?): LCO candidate afterglow
  80. IceCube cascade alert 142200_1517143 retraction
  81. EP260214a: VLT/FORS2 optical observations
  82. EP260214a: VLA 6 GHz detection
  83. GRB 260225A: SVOM/COLIBRÍ (FM-GFT) Detection of an Optical Counterpart Candidate
  84. EP260213a: Mephisto optical upper limits
  85. sb26021801: SVOM/C-GFT upper limit
  86. EP260221a: Optical upper limit with Kinder observations
  87. GRB 260223A: DDOTI Optical Candidate
  88. EP260221a: Liverpool Telescope detection of COLIBRÍ counterpart candidate
  89. EP260221a: COLIBRÍ optical counterpart candidate
  90. ZTF26aaglqak/AT2026dbl: COLIBRÍ Optical Observations
  91. IceCube-260217A - IceCube observation of a high-energy neutrino candidate track-like event
  92. EP260213a: Mondy R-band optical upper limit
  93. EP260213a: SVOM/C-GFT upper limit
  94. GRB 260211A: EP-FXT follow-up observation
  95. EP260210a: SVOM/C-GFT upper limit
  96. GRB 260208B: COLIBRÍ optical observations
  97. GRB 260208B: EP-FXT observation
  98. GRB 260208B: SVOM/VT optical candidate
  99. GRB 260208A: Zwicky Transient Facility Follow-Up of a Fermi GRB (Trigger 792220053)
  100. GRB 260208B: Swift ToO observations

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