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

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