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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. EP260329b: Global MASTER-Net observations report
  2. Fermi trigger No 796485221: Global MASTER-Net observations report
  3. GRB 260327A: Insight-HXMT/HE detection
  4. EP260329b: Optical follow-up with Kinder observations
  5. EP 260329b: COLIBRÍ optical observations
  6. EP260329a: Optical upper limit with Kinder observations
  7. EP260329b: LCO optical observations of the counterpart
  8. GRB 260326A: Insight-HXMT/HE detection
  9. EP260329b: Einstein Probe detection of an X-ray transient
  10. EP260329a: Einstein Probe detection of an X-ray transient
  11. EP-WXT trigger 01709259209: TRT optical counterpart detection
  12. The EP-WXT trigger 01709259209 (EP260329b?): Las Cumbres discovery of the optical counterpart
  13. GRID detection of GRB 260326A
  14. GRB 260310A: Gemini-North Spectral Confirmation of Supernova Features
  15. EP260327a: refined analysis of the EP-WXT and autonomous EP-FXT observations
  16. EP260327a: SVOM/VT optical upper limits
  17. SMA Detection of GRB 260310A / AT 2026fgk
  18. GRB 260307B: ATCA Radio Upper Limits
  19. EP260327a: WINTER J-band upper limit
  20. EP260327a: COLIBRÍ optical upper limits
  21. GRB 260327A: AstroSat CZTI detection of a long burst
  22. EP260327a: Gemini-North optical upper limits
  23. EP260324a: GROWTH-India Telescope optical observation
  24. EP260327a: Global MASTER-Net observations report
  25. EP260327a: Einstein Probe detection of an X-ray transient
  26. GRB 260310A / AT 2026fgk: COLIBRÍ photometric evidence of the emerging supernova
  27. GRB 260310A: OSIRIS+/GTC spectroscopic detection of the associated BL-Ic, SN 2026fgk
  28. The EP-WXT trigger 01709259173 is likely a flaring star
  29. GRB 260310A / AT2026fgk: Late-time infrared detection with MIRAGE on the MDM 1.3m telescope
  30. IPN triangulation of GRB 260320A
  31. EP260324a: ZTF discovery of the optical counterpart ZTF26aapviim/AT2026hir
  32. GRB 260310A / AT2026fgk: R- and I-band observations with the PKU 60 cm optical telescope
  33. GRB 260326A: Fermi GBM Detection
  34. EP260321a: JinShan near-infrared observations
  35. GRB 260325A: Fermi GBM Final Localization
  36. GRB 260326A: Fermi GBM Final Real-time Localization
  37. EP260321a: Upper limits from a neutrino search with IceCube
  38. Fermi Gamma-ray Burst Monitor trigger 796145512/260325647 is not a GRB
  39. GRB 260310A/AT2026fgk: Kilonova-Catcher late optical afterglow detection at about 15 days post trigger time
  40. IPN triangulation of GRB 260316B
  41. EP260321a: J-band observations by the SYSU 80 cm infrared telescope
  42. GRID detection of GRB 260320A
  43. EP260321a: Gemini-South confirmation of a supernova (duplicate submission)
  44. EP260321a: Gemini-South confirmation of a supernova
  45. Fermi Gamma-ray Burst Monitor trigger 796060650/260324665 is not a GRB
  46. EP260321a: VLT/FORS2 spectroscopy confirmation of an associated type Ic-BL supernova SN 2026gzf
  47. GRB 260310A: LBT optical observations
  48. EP260321A: Mondy optical observations
  49. GRB 260321A: SVOM/COLIBRÍ (FM-GFT) optical upper limits at the FXT positions
  50. EP-WXT trigger 01709259112: confirmation of a stellar flare by BOOTES-5 & BOOTES-7
  51. GRB 260316B: CALET Gamma-Ray Burst Monitor detection
  52. The EP-WXT trigger 01709259112 is likely a flaring star
  53. Fermi GRB 260323A: Global MASTER-Net observations report
  54. GRB 260323A: Fermi GBM Final Real-time Localization
  55. GRB260310A: Palomar 60-inch photometry of an extremely bright late-time afterglow with a temporal break at 8 days
  56. GRB 260310A/AT2026fgk: Detection of temporal steepening in Einstein Probe X-ray data
  57. GRB 260322A: Fermi GBM Final Localization
  58. GRB 260320A: Glowbug gamma-ray detection
  59. EP260321a / AT2026gzf: VLT/X-shooter detection of supernova-like spectral features at z = 0.0344
  60. EP260321a: COLIBRÍ further optical observations and brightening
  61. Fermi Gamma-ray Burst Monitor trigger 795918973/260323025 is not a GRB
  62. EP260321a: Continued brightening from Kinder follow-up of the emerging supernova candidate
  63. EP260214b: ATCA 6 GHz detection
  64. EP260321a: Early TRT rising followed by JinShan decaying and then re-rising
  65. GRB 260321A: EP-FXT follow-up observation
  66. The EP-WXT trigger 01709259045 is likely a flaring star
  67. EP260321a: ZTF and Rubin detections of the candidate optical counterpart to EP260321a
  68. EP260321a: GOTO detection of blue variable source
  69. EP260321a: VLT imaging and spectroscopy show the variable source to be at z = 0.0343
  70. EP260321a: further Kinder optical observations
  71. GRB 260321A: SVOM/VT optical upper limits
  72. EP260321a: Las Cumbres upper limit
  73. GRB 260321A: SVOM/COLIBRÍ (FM-GFT) optical upper limit
  74. GRB 260320A: Insight-HXMT/HE detection
  75. EP260321a: COLIBRÍ optical upper limit on any supernova shock breakout emission
  76. EP260321a: refined analysis of the EP-WXT and EP-FXT observations, implying a possible supernova shock breakout candidate
  77. EP260321a: SVOM/VT optical upper limit
  78. GRB 260310A: continued optical observation at Mondy
  79. Fermi GBM Sub-Threshold Detection of GRB 260321A
  80. GRB 260321A: SVOM detection of a burst
  81. EP260321a: Kinder observations detect a blue variable star and set limits on a source from the z =0.034 galaxy within the error circle
  82. EP260321a: Global MASTER-Net observations report
  83. EP260321a: Einstein Probe detection of an X-ray transient
  84. GRB 260310A / AT2026fgk: ABObservatory and NOCTIS new optical observations
  85. GRB 260318A: Glowbug gamma-ray detection
  86. GRB 260310A / AT 2026fgk: KAIT optical observations
  87. GRB 260320A: NuSTAR detection of prompt emission
  88. GRB 260310A / AT2026fgk: NuSTAR follow-up detection
  89. EP-WXT trigger 01709258989: KAIT confirmation of a stellar flare
  90. GRB 260310A / AT 2026fgk: FTW optical and NIR observations show no rebrightening
  91. GRB 260310A: no evidence of re-brightening up to 9.6 days in optical observation at Mondy
  92. GRB 260310A / AT 2026fgk: COLIBRÍ evidence of a late rebrightening
  93. GRB 260310A/AT2026fgk: LBT near-infrared observations
  94. NOEMA Detection of GRB 260310A / AT 2026fgk
  95. EP-WXT trigger 01709258989: confirmation of a stellar flare by BOOTES-7
  96. GRB 260318A: SVOM/GRM observation
  97. The EP-WXT trigger 01709258989 is likely a flaring star
  98. GRB 260310A: classification as long GRB based on Eiso, Ep, and T_90
  99. GRB 260318A: GECAM-B observation
  100. GRB260310A/AT2026fgk: Further optical observation from 1.3m DFOT

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