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

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