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

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