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

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