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

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