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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. Fermi GBM Sub-Threshold Detection of GRB 260330B
  2. GRB 260330B: LCO optical upper limits
  3. GRB 260330B: SVOM detection of a burst
  4. EP260324a / AT2026hir: g- and r-band optical follow-up with the PKU 60cm Telescope
  5. EP260329b: refined analysis of the EP-WXT and EP-FXT observations
  6. EP260329a: COLIBRÍ optical upper limit
  7. EP260329a: EP-FXT follow up observation
  8. EP260329a: NOT optical counterpart candidate
  9. GRB 260330A: Fermi GBM Final Real-time Localization
  10. EP260329b: Global MASTER-Net observations report
  11. Fermi trigger No 796485221: Global MASTER-Net observations report
  12. GRB 260327A: Insight-HXMT/HE detection
  13. EP260329b: Optical follow-up with Kinder observations
  14. EP 260329b: COLIBRÍ optical observations
  15. EP260329a: Optical upper limit with Kinder observations
  16. EP260329b: LCO optical observations of the counterpart
  17. GRB 260326A: Insight-HXMT/HE detection
  18. EP260329b: Einstein Probe detection of an X-ray transient
  19. EP260329a: Einstein Probe detection of an X-ray transient
  20. EP-WXT trigger 01709259209: TRT optical counterpart detection
  21. The EP-WXT trigger 01709259209 (EP260329b?): Las Cumbres discovery of the optical counterpart
  22. GRID detection of GRB 260326A
  23. GRB 260310A: Gemini-North Spectral Confirmation of Supernova Features
  24. EP260327a: refined analysis of the EP-WXT and autonomous EP-FXT observations
  25. EP260327a: SVOM/VT optical upper limits
  26. SMA Detection of GRB 260310A / AT 2026fgk
  27. GRB 260307B: ATCA Radio Upper Limits
  28. EP260327a: WINTER J-band upper limit
  29. EP260327a: COLIBRÍ optical upper limits
  30. GRB 260327A: AstroSat CZTI detection of a long burst
  31. EP260327a: Gemini-North optical upper limits
  32. EP260324a: GROWTH-India Telescope optical observation
  33. EP260327a: Global MASTER-Net observations report
  34. EP260327a: Einstein Probe detection of an X-ray transient
  35. GRB 260310A / AT 2026fgk: COLIBRÍ photometric evidence of the emerging supernova
  36. GRB 260310A: OSIRIS+/GTC spectroscopic detection of the associated BL-Ic, SN 2026fgk
  37. The EP-WXT trigger 01709259173 is likely a flaring star
  38. GRB 260310A / AT2026fgk: Late-time infrared detection with MIRAGE on the MDM 1.3m telescope
  39. IPN triangulation of GRB 260320A
  40. EP260324a: ZTF discovery of the optical counterpart ZTF26aapviim/AT2026hir
  41. GRB 260310A / AT2026fgk: R- and I-band observations with the PKU 60 cm optical telescope
  42. GRB 260326A: Fermi GBM Detection
  43. EP260321a: JinShan near-infrared observations
  44. GRB 260325A: Fermi GBM Final Localization
  45. GRB 260326A: Fermi GBM Final Real-time Localization
  46. EP260321a: Upper limits from a neutrino search with IceCube
  47. Fermi Gamma-ray Burst Monitor trigger 796145512/260325647 is not a GRB
  48. GRB 260310A/AT2026fgk: Kilonova-Catcher late optical afterglow detection at about 15 days post trigger time
  49. IPN triangulation of GRB 260316B
  50. EP260321a: J-band observations by the SYSU 80 cm infrared telescope
  51. GRID detection of GRB 260320A
  52. EP260321a: Gemini-South confirmation of a supernova (duplicate submission)
  53. EP260321a: Gemini-South confirmation of a supernova
  54. Fermi Gamma-ray Burst Monitor trigger 796060650/260324665 is not a GRB
  55. EP260321a: VLT/FORS2 spectroscopy confirmation of an associated type Ic-BL supernova SN 2026gzf
  56. GRB 260310A: LBT optical observations
  57. EP260321A: Mondy optical observations
  58. GRB 260321A: SVOM/COLIBRÍ (FM-GFT) optical upper limits at the FXT positions
  59. EP-WXT trigger 01709259112: confirmation of a stellar flare by BOOTES-5 & BOOTES-7
  60. GRB 260316B: CALET Gamma-Ray Burst Monitor detection
  61. The EP-WXT trigger 01709259112 is likely a flaring star
  62. Fermi GRB 260323A: Global MASTER-Net observations report
  63. GRB 260323A: Fermi GBM Final Real-time Localization
  64. GRB260310A: Palomar 60-inch photometry of an extremely bright late-time afterglow with a temporal break at 8 days
  65. GRB 260310A/AT2026fgk: Detection of temporal steepening in Einstein Probe X-ray data
  66. GRB 260322A: Fermi GBM Final Localization
  67. GRB 260320A: Glowbug gamma-ray detection
  68. EP260321a / AT2026gzf: VLT/X-shooter detection of supernova-like spectral features at z = 0.0344
  69. EP260321a: COLIBRÍ further optical observations and brightening
  70. Fermi Gamma-ray Burst Monitor trigger 795918973/260323025 is not a GRB
  71. EP260321a: Continued brightening from Kinder follow-up of the emerging supernova candidate
  72. EP260214b: ATCA 6 GHz detection
  73. EP260321a: Early TRT rising followed by JinShan decaying and then re-rising
  74. GRB 260321A: EP-FXT follow-up observation
  75. The EP-WXT trigger 01709259045 is likely a flaring star
  76. EP260321a: ZTF and Rubin detections of the candidate optical counterpart to EP260321a
  77. EP260321a: GOTO detection of blue variable source
  78. EP260321a: VLT imaging and spectroscopy show the variable source to be at z = 0.0343
  79. EP260321a: further Kinder optical observations
  80. GRB 260321A: SVOM/VT optical upper limits
  81. EP260321a: Las Cumbres upper limit
  82. GRB 260321A: SVOM/COLIBRÍ (FM-GFT) optical upper limit
  83. GRB 260320A: Insight-HXMT/HE detection
  84. EP260321a: COLIBRÍ optical upper limit on any supernova shock breakout emission
  85. EP260321a: refined analysis of the EP-WXT and EP-FXT observations, implying a possible supernova shock breakout candidate
  86. EP260321a: SVOM/VT optical upper limit
  87. GRB 260310A: continued optical observation at Mondy
  88. Fermi GBM Sub-Threshold Detection of GRB 260321A
  89. GRB 260321A: SVOM detection of a burst
  90. EP260321a: Kinder observations detect a blue variable star and set limits on a source from the z =0.034 galaxy within the error circle
  91. EP260321a: Global MASTER-Net observations report
  92. EP260321a: Einstein Probe detection of an X-ray transient
  93. GRB 260310A / AT2026fgk: ABObservatory and NOCTIS new optical observations
  94. GRB 260318A: Glowbug gamma-ray detection
  95. GRB 260310A / AT 2026fgk: KAIT optical observations
  96. GRB 260320A: NuSTAR detection of prompt emission
  97. GRB 260310A / AT2026fgk: NuSTAR follow-up detection
  98. EP-WXT trigger 01709258989: KAIT confirmation of a stellar flare
  99. GRB 260310A / AT 2026fgk: FTW optical and NIR observations show no rebrightening
  100. GRB 260310A: no evidence of re-brightening up to 9.6 days in optical observation at Mondy

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