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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"

22856 results found.

  1. EP260403a: Mephisto optical upper limits
  2. EP260402a/GRB 260402A: Xinglong optical upper limit
  3. EP260321a: Upper limits from VLA radio observations
  4. EP260405a: GMOS-N optical upper limits
  5. EP260405a: SVOM/VT optical upper limits
  6. EP260405a: Einstein Probe detection of a fast X-ray transient
  7. EP260405a / EP-WXT 11900672904: COLIBRÍ optical upper limits
  8. EP260324A / AT 2026hir: COLIBRÍ further optical observations
  9. EP260403a: refined analysis of the EP-WXT and EP-FXT observations
  10. GRB 260330B: SVOM/VT further optical observation
  11. EP260403a: LCO optical observations of the counterpart
  12. GRB 260310A/AT2026fgk: Kilonova-Catcher long term optical monitoring
  13. EP260403a: LCO optical counterpart detection
  14. EP260403a: COLIBRÍ optical counterpart candidate
  15. GRB 260330B: SVOM/VT optical candidate
  16. EP260403a: Einstein Probe detection of an X-ray transient
  17. GRB 260330B: EP-FXT follow-up and identification of candidate afterglow
  18. GRB 260403A: AstroSat CZTI detection
  19. EP260402a/GRB 260402A: refined analysis of the EP-WXT and EP-FXT observations
  20. EP260402a/GRB 260402A: Jinshan near-infrared upper limit
  21. GRB 260402C: AstroSat CZTI detection of a long burst
  22. EP260324A / AT 2026hir: COLIBRÍ optical observations
  23. GRB 260403A: Fermi GBM Final Real-time Localization
  24. EP260324A / AT 2026hir: Spectroscopic Observations with the Next Generation Palomar Spectrograph
  25. GRB 260402A: WINTER J-band upper limit
  26. GRB260402A: GROWTH-India Telescope optical upper limit
  27. GRB 260402A / EP260402a: SVOM/VT optical upper limits
  28. EP260402a/GRB 260402A: SVOM/C-GFT upper limit
  29. GRB 260401A: SVOM/GRM observation
  30. EP260402a/GRB 260402A: Einstein Probe detection of an X-ray transient
  31. GRB 260402A: Kilonova-Catcher optical upper limit
  32. GRB 260402A: MASTER optical observations
  33. GRB 260402A: SVOM/COLIBRÍ (FM-GFT) optical upper limit
  34. GRB 260402A: SVOM/MXT candidate X-ray afterglow
  35. GRB 260402A: SVOM detection of a burst
  36. EP260329b: Mondy and Assy-Turgen optical upper limits
  37. GRB 260310A / AT2026fgk: Luminance-band optical follow-up with a 28cm telescope in Daocheng
  38. EP260321a :Xinglong optical observations
  39. EP260327a: Xinglong optical upper limit
  40. EP260329b: GOTO detection of optical counterpart
  41. GRB 260330B: SVOM/VT optical upper limits
  42. GRB 260321A: SVOM/ECLAIRs refined analysis
  43. EP260329b: J-band upper limits with WINTER
  44. EP260329a: J-band upper limit with WINTER
  45. GRB 260330A: Glowbug gamma-ray detection
  46. GRB 260310A: VLA Multi-frequency Radio Observations
  47. GRB 260330B: LCO optical upper limits
  48. EP260324a / AT2026hir: g- and r-band optical follow-up with the PKU 60cm Telescope
  49. EP260329b: refined analysis of the EP-WXT and EP-FXT observations
  50. EP260329a: COLIBRÍ optical upper limit
  51. EP260329a: EP-FXT follow up observation
  52. EP260329a: NOT optical counterpart candidate
  53. EP260329b: Optical follow-up with Kinder observations
  54. EP 260329b: COLIBRÍ optical observations
  55. EP260329a: Optical upper limit with Kinder observations
  56. EP260329b: LCO optical observations of the counterpart
  57. EP260329b: Einstein Probe detection of an X-ray transient
  58. EP260329a: Einstein Probe detection of an X-ray transient
  59. EP-WXT trigger 01709259209: TRT optical counterpart detection
  60. The EP-WXT trigger 01709259209 (EP260329b?): Las Cumbres discovery of the optical counterpart
  61. EP260327a: refined analysis of the EP-WXT and autonomous EP-FXT observations
  62. EP260327a: SVOM/VT optical upper limits
  63. GRB 260307B: ATCA Radio Upper Limits
  64. EP260327a: WINTER J-band upper limit
  65. EP260327a: COLIBRÍ optical upper limits
  66. GRB 260327A: AstroSat CZTI detection of a long burst
  67. EP260327a: Gemini-North optical upper limits
  68. EP260324a: GROWTH-India Telescope optical observation
  69. EP260327a: Einstein Probe detection of an X-ray transient
  70. GRB 260310A / AT 2026fgk: COLIBRÍ photometric evidence of the emerging supernova
  71. GRB 260310A: OSIRIS+/GTC spectroscopic detection of the associated BL-Ic, SN 2026fgk
  72. GRB 260310A / AT2026fgk: Late-time infrared detection with MIRAGE on the MDM 1.3m telescope
  73. IPN triangulation of GRB 260320A
  74. EP260324a: ZTF discovery of the optical counterpart ZTF26aapviim/AT2026hir
  75. GRB 260310A / AT2026fgk: R- and I-band observations with the PKU 60 cm optical telescope
  76. EP260321a: JinShan near-infrared observations
  77. EP260321a: Upper limits from a neutrino search with IceCube
  78. GRB 260310A/AT2026fgk: Kilonova-Catcher late optical afterglow detection at about 15 days post trigger time
  79. IPN triangulation of GRB 260316B
  80. EP260321a: J-band observations by the SYSU 80 cm infrared telescope
  81. GRB 260321A: SVOM/COLIBRÍ (FM-GFT) optical upper limits at the FXT positions
  82. GRB 260310A/AT2026fgk: Detection of temporal steepening in Einstein Probe X-ray data
  83. GRB 260320A: Glowbug gamma-ray detection
  84. EP260321a: COLIBRÍ further optical observations and brightening
  85. EP260321a: Continued brightening from Kinder follow-up of the emerging supernova candidate
  86. EP260321a: Early TRT rising followed by JinShan decaying and then re-rising
  87. EP260321a: GOTO detection of blue variable source
  88. EP260321a: VLT imaging and spectroscopy show the variable source to be at z = 0.0343
  89. EP260321a: further Kinder optical observations
  90. GRB 260321A: SVOM/VT optical upper limits
  91. EP260321a: Las Cumbres upper limit
  92. GRB 260321A: SVOM/COLIBRÍ (FM-GFT) optical upper limit
  93. EP260321a: COLIBRÍ optical upper limit on any supernova shock breakout emission
  94. EP260321a: refined analysis of the EP-WXT and EP-FXT observations, implying a possible supernova shock breakout candidate
  95. EP260321a: SVOM/VT optical upper limit
  96. EP260321a: Kinder observations detect a blue variable star and set limits on a source from the z =0.034 galaxy within the error circle
  97. EP260321a: Einstein Probe detection of an X-ray transient
  98. GRB 260318A: Glowbug gamma-ray detection
  99. GRB 260310A / AT 2026fgk: KAIT optical observations
  100. GRB 260310A / AT2026fgk: NuSTAR follow-up detection

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