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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"

44339 results found.

  1. GRB 260330A: Glowbug gamma-ray detection
  2. GRB 260310A: VLA Multi-frequency Radio Observations
  3. Fermi GBM Sub-Threshold Detection of GRB 260330B
  4. GRB 260330B: LCO optical upper limits
  5. GRB 260330B: SVOM detection of a burst
  6. EP260324a / AT2026hir: g- and r-band optical follow-up with the PKU 60cm Telescope
  7. EP260329b: refined analysis of the EP-WXT and EP-FXT observations
  8. EP260329a: COLIBRÍ optical upper limit
  9. EP260329a: EP-FXT follow up observation
  10. EP260329a: NOT optical counterpart candidate
  11. GRB 260330A: Fermi GBM Final Real-time Localization
  12. EP260329b: Global MASTER-Net observations report
  13. Fermi trigger No 796485221: Global MASTER-Net observations report
  14. GRB 260327A: Insight-HXMT/HE detection
  15. EP260329b: Optical follow-up with Kinder observations
  16. EP 260329b: COLIBRÍ optical observations
  17. EP260329a: Optical upper limit with Kinder observations
  18. EP260329b: LCO optical observations of the counterpart
  19. GRB 260326A: Insight-HXMT/HE detection
  20. EP260329b: Einstein Probe detection of an X-ray transient
  21. EP260329a: Einstein Probe detection of an X-ray transient
  22. EP-WXT trigger 01709259209: TRT optical counterpart detection
  23. The EP-WXT trigger 01709259209 (EP260329b?): Las Cumbres discovery of the optical counterpart
  24. GRID detection of GRB 260326A
  25. GRB 260310A: Gemini-North Spectral Confirmation of Supernova Features
  26. EP260327a: refined analysis of the EP-WXT and autonomous EP-FXT observations
  27. EP260327a: SVOM/VT optical upper limits
  28. SMA Detection of GRB 260310A / AT 2026fgk
  29. GRB 260307B: ATCA Radio Upper Limits
  30. EP260327a: WINTER J-band upper limit
  31. EP260327a: COLIBRÍ optical upper limits
  32. GRB 260327A: AstroSat CZTI detection of a long burst
  33. EP260327a: Gemini-North optical upper limits
  34. EP260324a: GROWTH-India Telescope optical observation
  35. EP260327a: Global MASTER-Net observations report
  36. EP260327a: Einstein Probe detection of an X-ray transient
  37. GRB 260310A / AT 2026fgk: COLIBRÍ photometric evidence of the emerging supernova
  38. GRB 260310A: OSIRIS+/GTC spectroscopic detection of the associated BL-Ic, SN 2026fgk
  39. The EP-WXT trigger 01709259173 is likely a flaring star
  40. GRB 260310A / AT2026fgk: Late-time infrared detection with MIRAGE on the MDM 1.3m telescope
  41. IPN triangulation of GRB 260320A
  42. EP260324a: ZTF discovery of the optical counterpart ZTF26aapviim/AT2026hir
  43. GRB 260310A / AT2026fgk: R- and I-band observations with the PKU 60 cm optical telescope
  44. GRB 260326A: Fermi GBM Detection
  45. EP260321a: JinShan near-infrared observations
  46. GRB 260325A: Fermi GBM Final Localization
  47. GRB 260326A: Fermi GBM Final Real-time Localization
  48. EP260321a: Upper limits from a neutrino search with IceCube
  49. Fermi Gamma-ray Burst Monitor trigger 796145512/260325647 is not a GRB
  50. GRB 260310A/AT2026fgk: Kilonova-Catcher late optical afterglow detection at about 15 days post trigger time
  51. IPN triangulation of GRB 260316B
  52. EP260321a: J-band observations by the SYSU 80 cm infrared telescope
  53. GRID detection of GRB 260320A
  54. EP260321a: Gemini-South confirmation of a supernova (duplicate submission)
  55. EP260321a: Gemini-South confirmation of a supernova
  56. Fermi Gamma-ray Burst Monitor trigger 796060650/260324665 is not a GRB
  57. EP260321a: VLT/FORS2 spectroscopy confirmation of an associated type Ic-BL supernova SN 2026gzf
  58. GRB 260310A: LBT optical observations
  59. EP260321A: Mondy optical observations
  60. GRB 260321A: SVOM/COLIBRÍ (FM-GFT) optical upper limits at the FXT positions
  61. EP-WXT trigger 01709259112: confirmation of a stellar flare by BOOTES-5 & BOOTES-7
  62. GRB 260316B: CALET Gamma-Ray Burst Monitor detection
  63. The EP-WXT trigger 01709259112 is likely a flaring star
  64. Fermi GRB 260323A: Global MASTER-Net observations report
  65. GRB 260323A: Fermi GBM Final Real-time Localization
  66. GRB260310A: Palomar 60-inch photometry of an extremely bright late-time afterglow with a temporal break at 8 days
  67. GRB 260310A/AT2026fgk: Detection of temporal steepening in Einstein Probe X-ray data
  68. GRB 260322A: Fermi GBM Final Localization
  69. GRB 260320A: Glowbug gamma-ray detection
  70. EP260321a / AT2026gzf: VLT/X-shooter detection of supernova-like spectral features at z = 0.0344
  71. EP260321a: COLIBRÍ further optical observations and brightening
  72. Fermi Gamma-ray Burst Monitor trigger 795918973/260323025 is not a GRB
  73. EP260321a: Continued brightening from Kinder follow-up of the emerging supernova candidate
  74. EP260214b: ATCA 6 GHz detection
  75. EP260321a: Early TRT rising followed by JinShan decaying and then re-rising
  76. GRB 260321A: EP-FXT follow-up observation
  77. The EP-WXT trigger 01709259045 is likely a flaring star
  78. EP260321a: ZTF and Rubin detections of the candidate optical counterpart to EP260321a
  79. EP260321a: GOTO detection of blue variable source
  80. EP260321a: VLT imaging and spectroscopy show the variable source to be at z = 0.0343
  81. EP260321a: further Kinder optical observations
  82. GRB 260321A: SVOM/VT optical upper limits
  83. EP260321a: Las Cumbres upper limit
  84. GRB 260321A: SVOM/COLIBRÍ (FM-GFT) optical upper limit
  85. GRB 260320A: Insight-HXMT/HE detection
  86. EP260321a: COLIBRÍ optical upper limit on any supernova shock breakout emission
  87. EP260321a: refined analysis of the EP-WXT and EP-FXT observations, implying a possible supernova shock breakout candidate
  88. EP260321a: SVOM/VT optical upper limit
  89. GRB 260310A: continued optical observation at Mondy
  90. Fermi GBM Sub-Threshold Detection of GRB 260321A
  91. GRB 260321A: SVOM detection of a burst
  92. EP260321a: Kinder observations detect a blue variable star and set limits on a source from the z =0.034 galaxy within the error circle
  93. EP260321a: Global MASTER-Net observations report
  94. EP260321a: Einstein Probe detection of an X-ray transient
  95. GRB 260310A / AT2026fgk: ABObservatory and NOCTIS new optical observations
  96. GRB 260318A: Glowbug gamma-ray detection
  97. GRB 260310A / AT 2026fgk: KAIT optical observations
  98. GRB 260320A: NuSTAR detection of prompt emission
  99. GRB 260310A / AT2026fgk: NuSTAR follow-up detection
  100. EP-WXT trigger 01709258989: KAIT confirmation of a stellar flare

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