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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"

28083 results found.

  1. Fermi trigger No 797039833: Global MASTER-Net observations report
  2. EP260324A / AT 2026hir: COLIBRÍ further optical observations
  3. EP260403a: refined analysis of the EP-WXT and EP-FXT observations
  4. The EP-WXT trigger 01709259586 is likely a flaring star
  5. GRB 260330B: SVOM/VT further optical observation
  6. EP260403a: LCO optical observations of the counterpart
  7. GRB 260310A/AT2026fgk: Kilonova-Catcher long term optical monitoring
  8. EP260403a: LCO optical counterpart detection
  9. EP260403a: COLIBRÍ optical counterpart candidate
  10. GRB 260330B: SVOM/VT optical candidate
  11. EP260403a: Einstein Probe detection of an X-ray transient
  12. GRB 260330B: EP-FXT follow-up and identification of candidate afterglow
  13. EP260402a/GRB 260402A: refined analysis of the EP-WXT and EP-FXT observations
  14. EP260402a/GRB 260402A: Jinshan near-infrared upper limit
  15. GRB 260402C: NuSTAR detection of prompt emission
  16. GRB 260402C: AstroSat CZTI detection of a long burst
  17. EP260324A / AT 2026hir: COLIBRÍ optical observations
  18. GRB 260402A: WINTER J-band upper limit
  19. GRB260402A: GROWTH-India Telescope optical upper limit
  20. GRB 260402A / EP260402a: SVOM/VT optical upper limits
  21. EP260402a/GRB 260402A: SVOM/C-GFT upper limit
  22. GRB 260401A: SVOM/GRM observation
  23. EP260402a/GRB 260402A: Einstein Probe detection of an X-ray transient
  24. GRB 260402A: Kilonova-Catcher optical upper limit
  25. GRB 260402A: MASTER optical observations
  26. GRB 260402A: SVOM/COLIBRÍ (FM-GFT) optical upper limit
  27. GRB 260402A: SVOM/MXT candidate X-ray afterglow
  28. GRB 260402A: SVOM detection of a burst
  29. Fermi GRB 260401A: Global MASTER-Net observations report
  30. GRB 260401A: Fermi GBM Observation
  31. GRB 260401A: NuSTAR detection of prompt emission
  32. GRB 260401A: CALET Gamma-Ray Burst Monitor detection
  33. GRB 260401A: MAXI/GSC detection
  34. GRB 260401A: BALROG localization (Fermi Trigger 796733611 / GRB 260401454)
  35. GRB 260401A: Fermi GBM Final Real-time Localization
  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. GRB 260330B: SVOM/VT optical upper limits
  41. Konus-Wind detection of GRB 260320A
  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. Fermi GBM Sub-Threshold Detection of GRB 260330B
  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: Global MASTER-Net observations report
  54. Fermi trigger No 796485221: Global MASTER-Net observations report
  55. GRB 260327A: Insight-HXMT/HE detection
  56. EP260329b: Optical follow-up with Kinder observations
  57. EP 260329b: COLIBRÍ optical observations
  58. EP260329a: Optical upper limit with Kinder observations
  59. EP260329b: LCO optical observations of the counterpart
  60. GRB 260326A: Insight-HXMT/HE detection
  61. EP260329b: Einstein Probe detection of an X-ray transient
  62. EP260329a: Einstein Probe detection of an X-ray transient
  63. EP-WXT trigger 01709259209: TRT optical counterpart detection
  64. The EP-WXT trigger 01709259209 (EP260329b?): Las Cumbres discovery of the optical counterpart
  65. EP260327a: refined analysis of the EP-WXT and autonomous EP-FXT observations
  66. EP260327a: SVOM/VT optical upper limits
  67. EP260327a: WINTER J-band upper limit
  68. EP260327a: COLIBRÍ optical upper limits
  69. EP260327a: Gemini-North optical upper limits
  70. EP260324a: GROWTH-India Telescope optical observation
  71. EP260327a: Global MASTER-Net observations report
  72. EP260327a: Einstein Probe detection of an X-ray transient
  73. GRB 260310A / AT 2026fgk: COLIBRÍ photometric evidence of the emerging supernova
  74. GRB 260310A / AT2026fgk: Late-time infrared detection with MIRAGE on the MDM 1.3m telescope
  75. EP260324a: ZTF discovery of the optical counterpart ZTF26aapviim/AT2026hir
  76. GRB 260310A / AT2026fgk: R- and I-band observations with the PKU 60 cm optical telescope
  77. GRB 260326A: Fermi GBM Detection
  78. EP260321a: JinShan near-infrared observations
  79. EP260321a: Upper limits from a neutrino search with IceCube
  80. GRB 260310A/AT2026fgk: Kilonova-Catcher late optical afterglow detection at about 15 days post trigger time
  81. EP260321a: J-band observations by the SYSU 80 cm infrared telescope
  82. GRB 260321A: SVOM/COLIBRÍ (FM-GFT) optical upper limits at the FXT positions
  83. EP-WXT trigger 01709259112: confirmation of a stellar flare by BOOTES-5 & BOOTES-7
  84. Fermi GRB 260323A: Global MASTER-Net observations report
  85. GRB260310A: Palomar 60-inch photometry of an extremely bright late-time afterglow with a temporal break at 8 days
  86. GRB 260320A: Glowbug gamma-ray detection
  87. EP260321a: COLIBRÍ further optical observations and brightening
  88. EP260321a: Continued brightening from Kinder follow-up of the emerging supernova candidate
  89. EP260321a: Early TRT rising followed by JinShan decaying and then re-rising
  90. GRB 260321A: EP-FXT follow-up observation
  91. EP260321a: GOTO detection of blue variable source
  92. EP260321a: VLT imaging and spectroscopy show the variable source to be at z = 0.0343
  93. EP260321a: further Kinder optical observations
  94. GRB 260321A: SVOM/VT optical upper limits
  95. EP260321a: Las Cumbres upper limit
  96. GRB 260321A: SVOM/COLIBRÍ (FM-GFT) optical upper limit
  97. EP260321a: COLIBRÍ optical upper limit on any supernova shock breakout emission
  98. EP260321a: refined analysis of the EP-WXT and EP-FXT observations, implying a possible supernova shock breakout candidate
  99. EP260321a: SVOM/VT optical upper limit
  100. Fermi GBM Sub-Threshold Detection of GRB 260321A

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