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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"

26166 results found.

  1. EP260403a: refined analysis of the EP-WXT and EP-FXT observations
  2. The EP-WXT trigger 01709259586 is likely a flaring star
  3. GRB 260330B: SVOM/VT further optical observation
  4. Fermi Gamma-ray Burst Monitor trigger 796931884/260403749 is not a GRB
  5. GRB 260330B: SVOM/ECLAIRs refined analysis
  6. EP260403a: LCO optical observations of the counterpart
  7. GRB 260310A/AT2026fgk: Kilonova-Catcher long term optical monitoring
  8. EP260403a: LCO optical counterpart detection
  9. EP260403a: COLIBRÍ optical counterpart candidate
  10. GRB 260330B: SVOM/VT optical candidate
  11. EP260403a: Einstein Probe detection of an X-ray transient
  12. GRB 260330B: EP-FXT follow-up and identification of candidate afterglow
  13. EP260402a/GRB 260402A: refined analysis of the EP-WXT and EP-FXT observations
  14. GRB 260402B: GECAM-B observation
  15. EP260324A / AT 2026hir: COLIBRÍ optical observations
  16. GRB 260403A: Fermi GBM Final Real-time Localization
  17. EP260324A / AT 2026hir: Spectroscopic Observations with the Next Generation Palomar Spectrograph
  18. GRB 260402B: Fermi GBM Final Real-time Localization
  19. GRB 260402A: WINTER J-band upper limit
  20. GRB260402A: GROWTH-India Telescope optical upper limit
  21. GRB 260402A / EP260402a: SVOM/VT optical upper limits
  22. EP260402a/GRB 260402A: SVOM/C-GFT upper limit
  23. GRB 260401A: SVOM/GRM observation
  24. GRB 260401A: GECAM-B observation
  25. EP260402a/GRB 260402A: Einstein Probe detection of an X-ray transient
  26. GRB 260402A: Kilonova-Catcher optical upper limit
  27. GRB 260402A: MASTER optical observations
  28. GRB 260402A: SVOM/COLIBRÍ (FM-GFT) optical upper limit
  29. GRB 260402A: SVOM/MXT candidate X-ray afterglow
  30. GRB 260402A: SVOM detection of a burst
  31. Fermi GRB 260401A: Global MASTER-Net observations report
  32. GRB 260401A: Fermi GBM Observation
  33. GRB 260401A: CALET Gamma-Ray Burst Monitor detection
  34. GRB 260401A: BALROG localization (Fermi Trigger 796733611 / GRB 260401454)
  35. GRB 260401A: Fermi GBM Final Real-time Localization
  36. GRB 260310A / AT2026fgk: Luminance-band optical follow-up with a 28cm telescope in Daocheng
  37. EP260321a :Xinglong optical observations
  38. EP260327a: Xinglong optical upper limit
  39. EP260329b: GOTO detection of optical counterpart
  40. GRB 260330B: SVOM/VT optical upper limits
  41. GRB 260321A: SVOM/ECLAIRs refined analysis
  42. EP260329b: J-band upper limits with WINTER
  43. EP260329a: J-band upper limit with WINTER
  44. Fermi GBM Sub-Threshold Detection of GRB 260330B
  45. GRB 260330B: LCO optical upper limits
  46. GRB 260330B: SVOM detection of a burst
  47. EP260329b: refined analysis of the EP-WXT and EP-FXT observations
  48. EP260329a: COLIBRÍ optical upper limit
  49. EP260329a: EP-FXT follow up observation
  50. EP260329a: NOT optical counterpart candidate
  51. GRB 260330A: Fermi GBM Final Real-time Localization
  52. EP260329b: Global MASTER-Net observations report
  53. Fermi trigger No 796485221: Global MASTER-Net observations report
  54. EP 260329b: COLIBRÍ optical observations
  55. EP260329b: LCO optical observations of the counterpart
  56. EP260329b: Einstein Probe detection of an X-ray transient
  57. EP260329a: Einstein Probe detection of an X-ray transient
  58. EP-WXT trigger 01709259209: TRT optical counterpart detection
  59. The EP-WXT trigger 01709259209 (EP260329b?): Las Cumbres discovery of the optical counterpart
  60. GRID detection of GRB 260326A
  61. GRB 260310A: Gemini-North Spectral Confirmation of Supernova Features
  62. EP260327a: refined analysis of the EP-WXT and autonomous EP-FXT observations
  63. EP260327a: SVOM/VT optical upper limits
  64. EP260327a: WINTER J-band upper limit
  65. EP260327a: COLIBRÍ optical upper limits
  66. EP260327a: Gemini-North optical upper limits
  67. EP260324a: GROWTH-India Telescope optical observation
  68. EP260327a: Global MASTER-Net observations report
  69. EP260327a: Einstein Probe detection of an X-ray transient
  70. GRB 260310A / AT 2026fgk: COLIBRÍ photometric evidence of the emerging supernova
  71. GRB 260310A: OSIRIS+/GTC spectroscopic detection of the associated BL-Ic, SN 2026fgk
  72. The EP-WXT trigger 01709259173 is likely a flaring star
  73. GRB 260310A / AT2026fgk: Late-time infrared detection with MIRAGE on the MDM 1.3m telescope
  74. GRB 260310A / AT2026fgk: R- and I-band observations with the PKU 60 cm optical telescope
  75. GRB 260326A: Fermi GBM Detection
  76. GRB 260325A: Fermi GBM Final Localization
  77. GRB 260326A: Fermi GBM Final Real-time Localization
  78. Fermi Gamma-ray Burst Monitor trigger 796145512/260325647 is not a GRB
  79. GRB 260310A/AT2026fgk: Kilonova-Catcher late optical afterglow detection at about 15 days post trigger time
  80. IPN triangulation of GRB 260316B
  81. EP260321a: J-band observations by the SYSU 80 cm infrared telescope
  82. GRID detection of GRB 260320A
  83. Fermi Gamma-ray Burst Monitor trigger 796060650/260324665 is not a GRB
  84. EP260321a: VLT/FORS2 spectroscopy confirmation of an associated type Ic-BL supernova SN 2026gzf
  85. GRB 260310A: LBT optical observations
  86. GRB 260321A: SVOM/COLIBRÍ (FM-GFT) optical upper limits at the FXT positions
  87. EP-WXT trigger 01709259112: confirmation of a stellar flare by BOOTES-5 & BOOTES-7
  88. GRB 260316B: CALET Gamma-Ray Burst Monitor detection
  89. The EP-WXT trigger 01709259112 is likely a flaring star
  90. Fermi GRB 260323A: Global MASTER-Net observations report
  91. GRB 260323A: Fermi GBM Final Real-time Localization
  92. GRB 260310A/AT2026fgk: Detection of temporal steepening in Einstein Probe X-ray data
  93. GRB 260322A: Fermi GBM Final Localization
  94. EP260321a / AT2026gzf: VLT/X-shooter detection of supernova-like spectral features at z = 0.0344
  95. EP260321a: COLIBRÍ further optical observations and brightening
  96. Fermi Gamma-ray Burst Monitor trigger 795918973/260323025 is not a GRB
  97. EP260321a: Continued brightening from Kinder follow-up of the emerging supernova candidate
  98. EP260214b: ATCA 6 GHz detection
  99. EP260321a: Early TRT rising followed by JinShan decaying and then re-rising
  100. GRB 260321A: EP-FXT follow-up observation

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