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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"
  1. The EP-WXT trigger 01709259615 is likely a flaring star
  2. Fermi trigger No 797039833: Global MASTER-Net observations report
  3. GRB 260403A: GECAM-B observation of a long burst
  4. EP260324A / AT 2026hir: COLIBRÍ further optical observations
  5. Fermi Gamma-ray Burst Monitor trigger 796972356/260404217 is not a GRB
  6. EP260403a: refined analysis of the EP-WXT and EP-FXT observations
  7. The EP-WXT trigger 01709259586 is likely a flaring star
  8. GRB 260330B: SVOM/VT further optical observation
  9. Fermi Gamma-ray Burst Monitor trigger 796931884/260403749 is not a GRB
  10. GRB 260330B: SVOM/ECLAIRs refined analysis
  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. GRB 260402B: GECAM-B observation
  21. EP260402a/GRB 260402A: Jinshan near-infrared upper limit
  22. GRB 260402C: NuSTAR detection of prompt emission
  23. GRB 260402C: AstroSat CZTI detection of a long burst
  24. EP260324A / AT 2026hir: COLIBRÍ optical observations
  25. GRB 260403A: Fermi GBM Final Real-time Localization
  26. EP260324A / AT 2026hir: Spectroscopic Observations with the Next Generation Palomar Spectrograph
  27. GRB 260402B: Fermi GBM Final Real-time Localization
  28. GRB 260402A: WINTER J-band upper limit
  29. GRB260402A: GROWTH-India Telescope optical upper limit
  30. GRB 260402A / EP260402a: SVOM/VT optical upper limits
  31. EP260402a/GRB 260402A: SVOM/C-GFT upper limit
  32. GRB 260401A: SVOM/GRM observation
  33. GRB 260401A: GECAM-B observation
  34. EP260402a/GRB 260402A: Einstein Probe detection of an X-ray transient
  35. GRB 260402A: Kilonova-Catcher optical upper limit
  36. GRB 260402A: MASTER optical observations
  37. GRB 260402A: SVOM/COLIBRÍ (FM-GFT) optical upper limit
  38. GRB 260402A: SVOM/MXT candidate X-ray afterglow
  39. GRB 260402A: SVOM detection of a burst
  40. Fermi GRB 260401A: Global MASTER-Net observations report
  41. GRB 260401A: Fermi GBM Observation
  42. GRB 260401A: NuSTAR detection of prompt emission
  43. GRB 260401A: CALET Gamma-Ray Burst Monitor detection
  44. GRB 260401A: MAXI/GSC detection
  45. GRB 260401A: BALROG localization (Fermi Trigger 796733611 / GRB 260401454)
  46. GRB 260401A: Fermi GBM Final Real-time Localization
  47. EP260329b: Mondy and Assy-Turgen optical upper limits
  48. GRB 260310A / AT2026fgk: Luminance-band optical follow-up with a 28cm telescope in Daocheng
  49. EP260321a :Xinglong optical observations
  50. EP260327a: Xinglong optical upper limit
  51. EP260329b: GOTO detection of optical counterpart
  52. GRB 260330B: SVOM/VT optical upper limits
  53. Konus-Wind detection of GRB 260320A
  54. Konus-Wind detection of GRB 260316B (duplicate submission)
  55. Konus-Wind detection of GRB 260316B
  56. GRB 260321A: SVOM/ECLAIRs refined analysis
  57. EP260329b: J-band upper limits with WINTER
  58. EP260329a: J-band upper limit with WINTER
  59. GRB 260330A: Glowbug gamma-ray detection
  60. GRB 260310A: VLA Multi-frequency Radio Observations
  61. Fermi GBM Sub-Threshold Detection of GRB 260330B
  62. GRB 260330B: LCO optical upper limits
  63. GRB 260330B: SVOM detection of a burst
  64. EP260324a / AT2026hir: g- and r-band optical follow-up with the PKU 60cm Telescope
  65. EP260329b: refined analysis of the EP-WXT and EP-FXT observations
  66. EP260329a: COLIBRÍ optical upper limit
  67. EP260329a: EP-FXT follow up observation
  68. EP260329a: NOT optical counterpart candidate
  69. GRB 260330A: Fermi GBM Final Real-time Localization
  70. EP260329b: Global MASTER-Net observations report
  71. Fermi trigger No 796485221: Global MASTER-Net observations report
  72. GRB 260327A: Insight-HXMT/HE detection
  73. EP260329b: Optical follow-up with Kinder observations
  74. EP 260329b: COLIBRÍ optical observations
  75. EP260329a: Optical upper limit with Kinder observations
  76. EP260329b: LCO optical observations of the counterpart
  77. GRB 260326A: Insight-HXMT/HE detection
  78. EP260329b: Einstein Probe detection of an X-ray transient
  79. EP260329a: Einstein Probe detection of an X-ray transient
  80. EP-WXT trigger 01709259209: TRT optical counterpart detection
  81. The EP-WXT trigger 01709259209 (EP260329b?): Las Cumbres discovery of the optical counterpart
  82. GRID detection of GRB 260326A
  83. GRB 260310A: Gemini-North Spectral Confirmation of Supernova Features
  84. EP260327a: refined analysis of the EP-WXT and autonomous EP-FXT observations
  85. EP260327a: SVOM/VT optical upper limits
  86. SMA Detection of GRB 260310A / AT 2026fgk
  87. GRB 260307B: ATCA Radio Upper Limits
  88. EP260327a: WINTER J-band upper limit
  89. EP260327a: COLIBRÍ optical upper limits
  90. GRB 260327A: AstroSat CZTI detection of a long burst
  91. EP260327a: Gemini-North optical upper limits
  92. EP260324a: GROWTH-India Telescope optical observation
  93. EP260327a: Global MASTER-Net observations report
  94. EP260327a: Einstein Probe detection of an X-ray transient
  95. GRB 260310A / AT 2026fgk: COLIBRÍ photometric evidence of the emerging supernova
  96. GRB 260310A: OSIRIS+/GTC spectroscopic detection of the associated BL-Ic, SN 2026fgk
  97. The EP-WXT trigger 01709259173 is likely a flaring star
  98. GRB 260310A / AT2026fgk: Late-time infrared detection with MIRAGE on the MDM 1.3m telescope
  99. IPN triangulation of GRB 260320A
  100. EP260324a: ZTF discovery of the optical counterpart ZTF26aapviim/AT2026hir

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