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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"

44330 results found.

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

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