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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"

28095 results found.

  1. EP260409a: Einstein Probe detection of an X-ray transient
  2. EP260321a: VLA radio detection
  3. GRB 260407A: Glowbug gamma-ray detection
  4. GRB 260402A: SVOM/ECLAIRs refined analysis
  5. GRB 260310A: Continued VLA Multi-frequency Radio Observations
  6. EP260402a / GRB 260402A: Mephisto optical upper limits
  7. EP-WXT01709259586: Xinglong optical upper limit
  8. EP260403a: Mephisto optical upper limits
  9. EP260402a/GRB 260402A: Xinglong optical upper limit
  10. EP260405a: GMOS-N optical upper limits
  11. EP260405a: Global MASTER-Net observations report
  12. EP260405a: Einstein Probe detection of a fast X-ray transient
  13. EP260405a / EP-WXT 11900672904: COLIBRÍ optical upper limits
  14. Fermi trigger No 797039833: Global MASTER-Net observations report
  15. EP260324A / AT 2026hir: COLIBRÍ further optical observations
  16. EP260403a: refined analysis of the EP-WXT and EP-FXT observations
  17. The EP-WXT trigger 01709259586 is likely a flaring star
  18. GRB 260330B: SVOM/VT further optical observation
  19. EP260403a: LCO optical observations of the counterpart
  20. GRB 260310A/AT2026fgk: Kilonova-Catcher long term optical monitoring
  21. EP260403a: LCO optical counterpart detection
  22. EP260403a: COLIBRÍ optical counterpart candidate
  23. GRB 260330B: SVOM/VT optical candidate
  24. EP260403a: Einstein Probe detection of an X-ray transient
  25. GRB 260330B: EP-FXT follow-up and identification of candidate afterglow
  26. EP260402a/GRB 260402A: refined analysis of the EP-WXT and EP-FXT observations
  27. EP260402a/GRB 260402A: Jinshan near-infrared upper limit
  28. GRB 260402C: NuSTAR detection of prompt emission
  29. GRB 260402C: AstroSat CZTI detection of a long burst
  30. EP260324A / AT 2026hir: COLIBRÍ optical observations
  31. GRB 260402A: WINTER J-band upper limit
  32. GRB260402A: GROWTH-India Telescope optical upper limit
  33. GRB 260402A / EP260402a: SVOM/VT optical upper limits
  34. EP260402a/GRB 260402A: SVOM/C-GFT upper limit
  35. GRB 260401A: SVOM/GRM observation
  36. EP260402a/GRB 260402A: Einstein Probe detection of an X-ray transient
  37. GRB 260402A: Kilonova-Catcher optical upper limit
  38. GRB 260402A: MASTER optical observations
  39. GRB 260402A: SVOM/COLIBRÍ (FM-GFT) optical upper limit
  40. GRB 260402A: SVOM/MXT candidate X-ray afterglow
  41. GRB 260402A: SVOM detection of a burst
  42. Fermi GRB 260401A: Global MASTER-Net observations report
  43. GRB 260401A: Fermi GBM Observation
  44. GRB 260401A: NuSTAR detection of prompt emission
  45. GRB 260401A: CALET Gamma-Ray Burst Monitor detection
  46. GRB 260401A: MAXI/GSC detection
  47. GRB 260401A: BALROG localization (Fermi Trigger 796733611 / GRB 260401454)
  48. GRB 260401A: Fermi GBM Final Real-time Localization
  49. EP260329b: Mondy and Assy-Turgen optical upper limits
  50. GRB 260310A / AT2026fgk: Luminance-band optical follow-up with a 28cm telescope in Daocheng
  51. EP260321a :Xinglong optical observations
  52. EP260327a: Xinglong optical upper limit
  53. GRB 260330B: SVOM/VT optical upper limits
  54. Konus-Wind detection of GRB 260320A
  55. GRB 260321A: SVOM/ECLAIRs refined analysis
  56. EP260329b: J-band upper limits with WINTER
  57. EP260329a: J-band upper limit with WINTER
  58. GRB 260330A: Glowbug gamma-ray detection
  59. Fermi GBM Sub-Threshold Detection of GRB 260330B
  60. GRB 260330B: LCO optical upper limits
  61. EP260324a / AT2026hir: g- and r-band optical follow-up with the PKU 60cm Telescope
  62. EP260329b: refined analysis of the EP-WXT and EP-FXT observations
  63. EP260329a: COLIBRÍ optical upper limit
  64. EP260329a: EP-FXT follow up observation
  65. EP260329a: NOT optical counterpart candidate
  66. EP260329b: Global MASTER-Net observations report
  67. Fermi trigger No 796485221: Global MASTER-Net observations report
  68. GRB 260327A: Insight-HXMT/HE detection
  69. EP260329b: Optical follow-up with Kinder observations
  70. EP 260329b: COLIBRÍ optical observations
  71. EP260329a: Optical upper limit with Kinder observations
  72. EP260329b: LCO optical observations of the counterpart
  73. GRB 260326A: Insight-HXMT/HE detection
  74. EP260329b: Einstein Probe detection of an X-ray transient
  75. EP260329a: Einstein Probe detection of an X-ray transient
  76. EP-WXT trigger 01709259209: TRT optical counterpart detection
  77. The EP-WXT trigger 01709259209 (EP260329b?): Las Cumbres discovery of the optical counterpart
  78. EP260327a: refined analysis of the EP-WXT and autonomous EP-FXT observations
  79. EP260327a: SVOM/VT optical upper limits
  80. EP260327a: WINTER J-band upper limit
  81. EP260327a: COLIBRÍ optical upper limits
  82. EP260327a: Gemini-North optical upper limits
  83. EP260324a: GROWTH-India Telescope optical observation
  84. EP260327a: Global MASTER-Net observations report
  85. EP260327a: Einstein Probe detection of an X-ray transient
  86. GRB 260310A / AT 2026fgk: COLIBRÍ photometric evidence of the emerging supernova
  87. GRB 260310A / AT2026fgk: Late-time infrared detection with MIRAGE on the MDM 1.3m telescope
  88. EP260324a: ZTF discovery of the optical counterpart ZTF26aapviim/AT2026hir
  89. GRB 260310A / AT2026fgk: R- and I-band observations with the PKU 60 cm optical telescope
  90. GRB 260326A: Fermi GBM Detection
  91. EP260321a: JinShan near-infrared observations
  92. EP260321a: Upper limits from a neutrino search with IceCube
  93. GRB 260310A/AT2026fgk: Kilonova-Catcher late optical afterglow detection at about 15 days post trigger time
  94. EP260321a: J-band observations by the SYSU 80 cm infrared telescope
  95. GRB 260321A: SVOM/COLIBRÍ (FM-GFT) optical upper limits at the FXT positions
  96. EP-WXT trigger 01709259112: confirmation of a stellar flare by BOOTES-5 & BOOTES-7
  97. Fermi GRB 260323A: Global MASTER-Net observations report
  98. GRB260310A: Palomar 60-inch photometry of an extremely bright late-time afterglow with a temporal break at 8 days
  99. GRB 260320A: Glowbug gamma-ray detection
  100. EP260321a: COLIBRÍ further optical observations and brightening

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