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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. GRB 260401A: MAXI/GSC detection
  2. GRB 260401A: BALROG localization (Fermi Trigger 796733611 / GRB 260401454)
  3. GRB 260401A: Fermi GBM Final Real-time Localization
  4. EP260329b: Mondy and Assy-Turgen optical upper limits
  5. GRB 260310A / AT2026fgk: Luminance-band optical follow-up with a 28cm telescope in Daocheng
  6. EP260321a :Xinglong optical observations
  7. EP260327a: Xinglong optical upper limit
  8. EP260329b: GOTO detection of optical counterpart
  9. GRB 260330B: SVOM/VT optical upper limits
  10. Konus-Wind detection of GRB 260320A
  11. Konus-Wind detection of GRB 260316B (duplicate submission)
  12. Konus-Wind detection of GRB 260316B
  13. GRB 260321A: SVOM/ECLAIRs refined analysis
  14. EP260329b: J-band upper limits with WINTER
  15. EP260329a: J-band upper limit with WINTER
  16. GRB 260330A: Glowbug gamma-ray detection
  17. GRB 260310A: VLA Multi-frequency Radio Observations
  18. Fermi GBM Sub-Threshold Detection of GRB 260330B
  19. GRB 260330B: LCO optical upper limits
  20. GRB 260330B: SVOM detection of a burst
  21. EP260324a / AT2026hir: g- and r-band optical follow-up with the PKU 60cm Telescope
  22. EP260329b: refined analysis of the EP-WXT and EP-FXT observations
  23. EP260329a: COLIBRÍ optical upper limit
  24. EP260329a: EP-FXT follow up observation
  25. EP260329a: NOT optical counterpart candidate
  26. GRB 260330A: Fermi GBM Final Real-time Localization
  27. EP260329b: Global MASTER-Net observations report
  28. Fermi trigger No 796485221: Global MASTER-Net observations report
  29. GRB 260327A: Insight-HXMT/HE detection
  30. EP260329b: Optical follow-up with Kinder observations
  31. EP 260329b: COLIBRÍ optical observations
  32. EP260329a: Optical upper limit with Kinder observations
  33. EP260329b: LCO optical observations of the counterpart
  34. GRB 260326A: Insight-HXMT/HE detection
  35. EP260329b: Einstein Probe detection of an X-ray transient
  36. EP260329a: Einstein Probe detection of an X-ray transient
  37. EP-WXT trigger 01709259209: TRT optical counterpart detection
  38. The EP-WXT trigger 01709259209 (EP260329b?): Las Cumbres discovery of the optical counterpart
  39. GRID detection of GRB 260326A
  40. GRB 260310A: Gemini-North Spectral Confirmation of Supernova Features
  41. EP260327a: refined analysis of the EP-WXT and autonomous EP-FXT observations
  42. EP260327a: SVOM/VT optical upper limits
  43. SMA Detection of GRB 260310A / AT 2026fgk
  44. GRB 260307B: ATCA Radio Upper Limits
  45. EP260327a: WINTER J-band upper limit
  46. EP260327a: COLIBRÍ optical upper limits
  47. GRB 260327A: AstroSat CZTI detection of a long burst
  48. EP260327a: Gemini-North optical upper limits
  49. EP260324a: GROWTH-India Telescope optical observation
  50. EP260327a: Global MASTER-Net observations report
  51. EP260327a: Einstein Probe detection of an X-ray transient
  52. GRB 260310A / AT 2026fgk: COLIBRÍ photometric evidence of the emerging supernova
  53. GRB 260310A: OSIRIS+/GTC spectroscopic detection of the associated BL-Ic, SN 2026fgk
  54. The EP-WXT trigger 01709259173 is likely a flaring star
  55. GRB 260310A / AT2026fgk: Late-time infrared detection with MIRAGE on the MDM 1.3m telescope
  56. IPN triangulation of GRB 260320A
  57. EP260324a: ZTF discovery of the optical counterpart ZTF26aapviim/AT2026hir
  58. GRB 260310A / AT2026fgk: R- and I-band observations with the PKU 60 cm optical telescope
  59. GRB 260326A: Fermi GBM Detection
  60. EP260321a: JinShan near-infrared observations
  61. GRB 260325A: Fermi GBM Final Localization
  62. GRB 260326A: Fermi GBM Final Real-time Localization
  63. EP260321a: Upper limits from a neutrino search with IceCube
  64. Fermi Gamma-ray Burst Monitor trigger 796145512/260325647 is not a GRB
  65. GRB 260310A/AT2026fgk: Kilonova-Catcher late optical afterglow detection at about 15 days post trigger time
  66. IPN triangulation of GRB 260316B
  67. EP260321a: J-band observations by the SYSU 80 cm infrared telescope
  68. GRID detection of GRB 260320A
  69. EP260321a: Gemini-South confirmation of a supernova (duplicate submission)
  70. EP260321a: Gemini-South confirmation of a supernova
  71. Fermi Gamma-ray Burst Monitor trigger 796060650/260324665 is not a GRB
  72. EP260321a: VLT/FORS2 spectroscopy confirmation of an associated type Ic-BL supernova SN 2026gzf
  73. GRB 260310A: LBT optical observations
  74. EP260321A: Mondy optical observations
  75. GRB 260321A: SVOM/COLIBRÍ (FM-GFT) optical upper limits at the FXT positions
  76. EP-WXT trigger 01709259112: confirmation of a stellar flare by BOOTES-5 & BOOTES-7
  77. GRB 260316B: CALET Gamma-Ray Burst Monitor detection
  78. The EP-WXT trigger 01709259112 is likely a flaring star
  79. Fermi GRB 260323A: Global MASTER-Net observations report
  80. GRB 260323A: Fermi GBM Final Real-time Localization
  81. GRB260310A: Palomar 60-inch photometry of an extremely bright late-time afterglow with a temporal break at 8 days
  82. GRB 260310A/AT2026fgk: Detection of temporal steepening in Einstein Probe X-ray data
  83. GRB 260322A: Fermi GBM Final Localization
  84. GRB 260320A: Glowbug gamma-ray detection
  85. EP260321a / AT2026gzf: VLT/X-shooter detection of supernova-like spectral features at z = 0.0344
  86. EP260321a: COLIBRÍ further optical observations and brightening
  87. Fermi Gamma-ray Burst Monitor trigger 795918973/260323025 is not a GRB
  88. EP260321a: Continued brightening from Kinder follow-up of the emerging supernova candidate
  89. EP260214b: ATCA 6 GHz detection
  90. EP260321a: Early TRT rising followed by JinShan decaying and then re-rising
  91. GRB 260321A: EP-FXT follow-up observation
  92. The EP-WXT trigger 01709259045 is likely a flaring star
  93. EP260321a: ZTF and Rubin detections of the candidate optical counterpart to EP260321a
  94. EP260321a: GOTO detection of blue variable source
  95. EP260321a: VLT imaging and spectroscopy show the variable source to be at z = 0.0343
  96. EP260321a: further Kinder optical observations
  97. GRB 260321A: SVOM/VT optical upper limits
  98. EP260321a: Las Cumbres upper limit
  99. GRB 260321A: SVOM/COLIBRÍ (FM-GFT) optical upper limit
  100. GRB 260320A: Insight-HXMT/HE detection

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