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

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