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

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