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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"

28082 results found.

  1. EP260405a / EP-WXT 11900672904: COLIBRÍ optical upper limits
  2. Fermi trigger No 797039833: Global MASTER-Net observations report
  3. EP260324A / AT 2026hir: COLIBRÍ further optical observations
  4. EP260403a: refined analysis of the EP-WXT and EP-FXT observations
  5. The EP-WXT trigger 01709259586 is likely a flaring star
  6. GRB 260330B: SVOM/VT further optical observation
  7. EP260403a: LCO optical observations of the counterpart
  8. GRB 260310A/AT2026fgk: Kilonova-Catcher long term optical monitoring
  9. EP260403a: LCO optical counterpart detection
  10. EP260403a: COLIBRÍ optical counterpart candidate
  11. GRB 260330B: SVOM/VT optical candidate
  12. EP260403a: Einstein Probe detection of an X-ray transient
  13. GRB 260330B: EP-FXT follow-up and identification of candidate afterglow
  14. EP260402a/GRB 260402A: refined analysis of the EP-WXT and EP-FXT observations
  15. EP260402a/GRB 260402A: Jinshan near-infrared upper limit
  16. GRB 260402C: NuSTAR detection of prompt emission
  17. GRB 260402C: AstroSat CZTI detection of a long burst
  18. EP260324A / AT 2026hir: COLIBRÍ optical observations
  19. GRB 260402A: WINTER J-band upper limit
  20. GRB260402A: GROWTH-India Telescope optical upper limit
  21. GRB 260402A / EP260402a: SVOM/VT optical upper limits
  22. EP260402a/GRB 260402A: SVOM/C-GFT upper limit
  23. GRB 260401A: SVOM/GRM observation
  24. EP260402a/GRB 260402A: Einstein Probe detection of an X-ray transient
  25. GRB 260402A: Kilonova-Catcher optical upper limit
  26. GRB 260402A: MASTER optical observations
  27. GRB 260402A: SVOM/COLIBRÍ (FM-GFT) optical upper limit
  28. GRB 260402A: SVOM/MXT candidate X-ray afterglow
  29. GRB 260402A: SVOM detection of a burst
  30. Fermi GRB 260401A: Global MASTER-Net observations report
  31. GRB 260401A: Fermi GBM Observation
  32. GRB 260401A: NuSTAR detection of prompt emission
  33. GRB 260401A: CALET Gamma-Ray Burst Monitor detection
  34. GRB 260401A: MAXI/GSC detection
  35. GRB 260401A: BALROG localization (Fermi Trigger 796733611 / GRB 260401454)
  36. GRB 260401A: Fermi GBM Final Real-time Localization
  37. EP260329b: Mondy and Assy-Turgen optical upper limits
  38. GRB 260310A / AT2026fgk: Luminance-band optical follow-up with a 28cm telescope in Daocheng
  39. EP260321a :Xinglong optical observations
  40. EP260327a: Xinglong optical upper limit
  41. GRB 260330B: SVOM/VT optical upper limits
  42. Konus-Wind detection of GRB 260320A
  43. GRB 260321A: SVOM/ECLAIRs refined analysis
  44. EP260329b: J-band upper limits with WINTER
  45. EP260329a: J-band upper limit with WINTER
  46. GRB 260330A: Glowbug gamma-ray detection
  47. Fermi GBM Sub-Threshold Detection of GRB 260330B
  48. GRB 260330B: LCO optical upper limits
  49. EP260324a / AT2026hir: g- and r-band optical follow-up with the PKU 60cm Telescope
  50. EP260329b: refined analysis of the EP-WXT and EP-FXT observations
  51. EP260329a: COLIBRÍ optical upper limit
  52. EP260329a: EP-FXT follow up observation
  53. EP260329a: NOT optical counterpart candidate
  54. EP260329b: Global MASTER-Net observations report
  55. Fermi trigger No 796485221: Global MASTER-Net observations report
  56. GRB 260327A: Insight-HXMT/HE detection
  57. EP260329b: Optical follow-up with Kinder observations
  58. EP 260329b: COLIBRÍ optical observations
  59. EP260329a: Optical upper limit with Kinder observations
  60. EP260329b: LCO optical observations of the counterpart
  61. GRB 260326A: Insight-HXMT/HE detection
  62. EP260329b: Einstein Probe detection of an X-ray transient
  63. EP260329a: Einstein Probe detection of an X-ray transient
  64. EP-WXT trigger 01709259209: TRT optical counterpart detection
  65. The EP-WXT trigger 01709259209 (EP260329b?): Las Cumbres discovery of the optical counterpart
  66. EP260327a: refined analysis of the EP-WXT and autonomous EP-FXT observations
  67. EP260327a: SVOM/VT optical upper limits
  68. EP260327a: WINTER J-band upper limit
  69. EP260327a: COLIBRÍ optical upper limits
  70. EP260327a: Gemini-North optical upper limits
  71. EP260324a: GROWTH-India Telescope optical observation
  72. EP260327a: Global MASTER-Net observations report
  73. EP260327a: Einstein Probe detection of an X-ray transient
  74. GRB 260310A / AT 2026fgk: COLIBRÍ photometric evidence of the emerging supernova
  75. GRB 260310A / AT2026fgk: Late-time infrared detection with MIRAGE on the MDM 1.3m telescope
  76. EP260324a: ZTF discovery of the optical counterpart ZTF26aapviim/AT2026hir
  77. GRB 260310A / AT2026fgk: R- and I-band observations with the PKU 60 cm optical telescope
  78. GRB 260326A: Fermi GBM Detection
  79. EP260321a: JinShan near-infrared observations
  80. EP260321a: Upper limits from a neutrino search with IceCube
  81. GRB 260310A/AT2026fgk: Kilonova-Catcher late optical afterglow detection at about 15 days post trigger time
  82. EP260321a: J-band observations by the SYSU 80 cm infrared telescope
  83. GRB 260321A: SVOM/COLIBRÍ (FM-GFT) optical upper limits at the FXT positions
  84. EP-WXT trigger 01709259112: confirmation of a stellar flare by BOOTES-5 & BOOTES-7
  85. Fermi GRB 260323A: Global MASTER-Net observations report
  86. GRB260310A: Palomar 60-inch photometry of an extremely bright late-time afterglow with a temporal break at 8 days
  87. GRB 260320A: Glowbug gamma-ray detection
  88. EP260321a: COLIBRÍ further optical observations and brightening
  89. EP260321a: Continued brightening from Kinder follow-up of the emerging supernova candidate
  90. EP260321a: Early TRT rising followed by JinShan decaying and then re-rising
  91. GRB 260321A: EP-FXT follow-up observation
  92. EP260321a: GOTO detection of blue variable source
  93. EP260321a: VLT imaging and spectroscopy show the variable source to be at z = 0.0343
  94. EP260321a: further Kinder optical observations
  95. GRB 260321A: SVOM/VT optical upper limits
  96. EP260321a: Las Cumbres upper limit
  97. GRB 260321A: SVOM/COLIBRÍ (FM-GFT) optical upper limit
  98. EP260321a: COLIBRÍ optical upper limit on any supernova shock breakout emission
  99. EP260321a: refined analysis of the EP-WXT and EP-FXT observations, implying a possible supernova shock breakout candidate
  100. EP260321a: SVOM/VT optical upper limit

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