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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"

36188 results found.

  1. GRB 260330A: Fermi GBM Final Real-time Localization
  2. GRB 260327A: Insight-HXMT/HE detection
  3. GRB 260326A: Insight-HXMT/HE detection
  4. GRID detection of GRB 260326A
  5. GRB 260310A: Gemini-North Spectral Confirmation of Supernova Features
  6. SMA Detection of GRB 260310A / AT 2026fgk
  7. GRB 260307B: ATCA Radio Upper Limits
  8. GRB 260327A: AstroSat CZTI detection of a long burst
  9. GRB 260310A / AT 2026fgk: COLIBRÍ photometric evidence of the emerging supernova
  10. GRB 260310A: OSIRIS+/GTC spectroscopic detection of the associated BL-Ic, SN 2026fgk
  11. GRB 260310A / AT2026fgk: Late-time infrared detection with MIRAGE on the MDM 1.3m telescope
  12. IPN triangulation of GRB 260320A
  13. GRB 260310A / AT2026fgk: R- and I-band observations with the PKU 60 cm optical telescope
  14. GRB 260326A: Fermi GBM Detection
  15. GRB 260325A: Fermi GBM Final Localization
  16. GRB 260326A: Fermi GBM Final Real-time Localization
  17. EP260321a: Upper limits from a neutrino search with IceCube
  18. Fermi Gamma-ray Burst Monitor trigger 796145512/260325647 is not a GRB
  19. GRB 260310A/AT2026fgk: Kilonova-Catcher late optical afterglow detection at about 15 days post trigger time
  20. IPN triangulation of GRB 260316B
  21. GRID detection of GRB 260320A
  22. Fermi Gamma-ray Burst Monitor trigger 796060650/260324665 is not a GRB
  23. EP260321a: VLT/FORS2 spectroscopy confirmation of an associated type Ic-BL supernova SN 2026gzf
  24. GRB 260310A: LBT optical observations
  25. EP260321A: Mondy optical observations
  26. GRB 260321A: SVOM/COLIBRÍ (FM-GFT) optical upper limits at the FXT positions
  27. GRB 260316B: CALET Gamma-Ray Burst Monitor detection
  28. Fermi GRB 260323A: Global MASTER-Net observations report
  29. GRB 260323A: Fermi GBM Final Real-time Localization
  30. GRB260310A: Palomar 60-inch photometry of an extremely bright late-time afterglow with a temporal break at 8 days
  31. GRB 260310A/AT2026fgk: Detection of temporal steepening in Einstein Probe X-ray data
  32. GRB 260322A: Fermi GBM Final Localization
  33. GRB 260320A: Glowbug gamma-ray detection
  34. Fermi Gamma-ray Burst Monitor trigger 795918973/260323025 is not a GRB
  35. GRB 260321A: EP-FXT follow-up observation
  36. GRB 260321A: SVOM/VT optical upper limits
  37. GRB 260321A: SVOM/COLIBRÍ (FM-GFT) optical upper limit
  38. GRB 260320A: Insight-HXMT/HE detection
  39. GRB 260310A: continued optical observation at Mondy
  40. Fermi GBM Sub-Threshold Detection of GRB 260321A
  41. GRB 260321A: SVOM detection of a burst
  42. GRB 260310A / AT2026fgk: ABObservatory and NOCTIS new optical observations
  43. GRB 260318A: Glowbug gamma-ray detection
  44. GRB 260310A / AT 2026fgk: KAIT optical observations
  45. GRB 260320A: NuSTAR detection of prompt emission
  46. GRB 260310A / AT2026fgk: NuSTAR follow-up detection
  47. EP-WXT trigger 01709258989: KAIT confirmation of a stellar flare
  48. GRB 260310A / AT 2026fgk: FTW optical and NIR observations show no rebrightening
  49. GRB 260310A: no evidence of re-brightening up to 9.6 days in optical observation at Mondy
  50. GRB 260310A / AT 2026fgk: COLIBRÍ evidence of a late rebrightening
  51. GRB 260310A/AT2026fgk: LBT near-infrared observations
  52. NOEMA Detection of GRB 260310A / AT 2026fgk
  53. GRB 260318A: SVOM/GRM observation
  54. GRB 260310A: classification as long GRB based on Eiso, Ep, and T_90
  55. GRB 260318A: GECAM-B observation
  56. Fermi GRB 260318A: Global MASTER-Net observations report
  57. GRB 260318A: Fermi GBM Final Real-time Localization
  58. Fermi Gamma-ray Burst Monitor trigger 795096033/260312500 (GRB 260313A) is unlikely to be a GRB
  59. GRB 260316A / EP260316a: COLIBRÍ optical followup of counterpart candidate
  60. GRB 260310A / AT 2026fgk: radio detection with the VLA
  61. GRB 260310A / AT2026fgk: SVOM/VT optical observations
  62. GRB 260310A / AT2026fgk: LCO optical observations
  63. GRB 260317A: Fermi GBM Final Localization
  64. GRB 260316B: GECAM-B observation
  65. GRB 260316B: SVOM/GRM observation
  66. EP260316a / GRB 260316A: SVOM/VT optical upper limits
  67. GRB 260316B: AstroSat CZTI detection
  68. IceCube-260315A: Upper limits from a search for additional neutrino events in IceCube
  69. GRB 260316B: Fermi GBM Final Real-time Localization
  70. EP260316a / GRB 260316A : Fermi-GBM Sub-Threshold Detection
  71. GRB 260314A: Glowbug gamma-ray detection
  72. GRB 260310A / AT2026fgk: 1.3m DFOT optical observations
  73. GRB 260310A / AT2026fgk: ABObservatory and NOCTIS optical observations
  74. GRB 260310A / AT 2026fgk: iTelescope optical observations
  75. GRID detection of GRB 260312B
  76. IceCube-260315A - IceCube observation of a high-energy neutrino candidate track-like event
  77. GRB 260314A: GECAM-B observation of a burst
  78. Fermi Gamma-ray Burst Monitor trigger 795185313/260314534 is not a GRB
  79. GRB 260310A / AT2026fgk: SAO RAS optical observations
  80. GRB 260310A/AT2026fgk: radio detection at 15GHz
  81. GRB 260310A / AT2026fgk: TNG NIR detection
  82. GRB 260310A / AT2026fgk: OASDG optical observations
  83. GRB 260310A / AT2026fgk: Multiband optical follow-up with Kinder observations
  84. GRB 260310A / AT 2026fgk: COLIBRÍ continuing optical observations
  85. GRB 260310A / AT2026fgk: further CAHA 1.23m telescope optical observations suggest shallow decay
  86. Fermi GRB 260314A: Global MASTER-Net observations report
  87. Fermi GRB 260313A: Global MASTER-Net observations report
  88. GRB 260314A: Fermi GBM Final Real-time Localization
  89. GRB 260310A/AT 2026fgk: WINTER NIR Detections
  90. GRB 260313A: A Correction to the Fermi GBM Final Localization
  91. GRB 260310A: Einstein Probe Follow-up X-ray Telescope (FXT) Detection
  92. GRB 260310A/AT 2026fgk: J-band observations by the SYSU 80 cm infrared telescope
  93. GRB 260310B: Insight-HXMT/HE detection
  94. GRB 260310A/AT 2026fgk: DDOTI Optical Detection
  95. GRB 260310A: NOT optical polarimetry
  96. GRB 260312B: AstroSat CZTI detection
  97. Swift BAT trigger 1500295: A solar flare
  98. GRB 260313A: Fermi GBM Final Real-time Localization
  99. GRB 260310A/AT 2026fgk: Bok spectroscopic observation
  100. Swift BAT trigger 1500287: A solar flare

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