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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 260326A: Fermi GBM Final Real-time Localization
  2. EP260321a: Upper limits from a neutrino search with IceCube
  3. Fermi Gamma-ray Burst Monitor trigger 796145512/260325647 is not a GRB
  4. GRB 260310A/AT2026fgk: Kilonova-Catcher late optical afterglow detection at about 15 days post trigger time
  5. IPN triangulation of GRB 260316B
  6. EP260321a: J-band observations by the SYSU 80 cm infrared telescope
  7. GRID detection of GRB 260320A
  8. EP260321a: Gemini-South confirmation of a supernova (duplicate submission)
  9. EP260321a: Gemini-South confirmation of a supernova
  10. Fermi Gamma-ray Burst Monitor trigger 796060650/260324665 is not a GRB
  11. EP260321a: VLT/FORS2 spectroscopy confirmation of an associated type Ic-BL supernova SN 2026gzf
  12. GRB 260310A: LBT optical observations
  13. EP260321A: Mondy optical observations
  14. GRB 260321A: SVOM/COLIBRÍ (FM-GFT) optical upper limits at the FXT positions
  15. EP-WXT trigger 01709259112: confirmation of a stellar flare by BOOTES-5 & BOOTES-7
  16. GRB 260316B: CALET Gamma-Ray Burst Monitor detection
  17. The EP-WXT trigger 01709259112 is likely a flaring star
  18. Fermi GRB 260323A: Global MASTER-Net observations report
  19. GRB 260323A: Fermi GBM Final Real-time Localization
  20. GRB260310A: Palomar 60-inch photometry of an extremely bright late-time afterglow with a temporal break at 8 days
  21. GRB 260310A/AT2026fgk: Detection of temporal steepening in Einstein Probe X-ray data
  22. GRB 260322A: Fermi GBM Final Localization
  23. GRB 260320A: Glowbug gamma-ray detection
  24. EP260321a / AT2026gzf: VLT/X-shooter detection of supernova-like spectral features at z = 0.0344
  25. EP260321a: COLIBRÍ further optical observations and brightening
  26. Fermi Gamma-ray Burst Monitor trigger 795918973/260323025 is not a GRB
  27. EP260321a: Continued brightening from Kinder follow-up of the emerging supernova candidate
  28. EP260214b: ATCA 6 GHz detection
  29. EP260321a: Early TRT rising followed by JinShan decaying and then re-rising
  30. GRB 260321A: EP-FXT follow-up observation
  31. The EP-WXT trigger 01709259045 is likely a flaring star
  32. EP260321a: ZTF and Rubin detections of the candidate optical counterpart to EP260321a
  33. EP260321a: GOTO detection of blue variable source
  34. EP260321a: VLT imaging and spectroscopy show the variable source to be at z = 0.0343
  35. EP260321a: further Kinder optical observations
  36. GRB 260321A: SVOM/VT optical upper limits
  37. EP260321a: Las Cumbres upper limit
  38. GRB 260321A: SVOM/COLIBRÍ (FM-GFT) optical upper limit
  39. GRB 260320A: Insight-HXMT/HE detection
  40. EP260321a: COLIBRÍ optical upper limit on any supernova shock breakout emission
  41. EP260321a: refined analysis of the EP-WXT and EP-FXT observations, implying a possible supernova shock breakout candidate
  42. EP260321a: SVOM/VT optical upper limit
  43. GRB 260310A: continued optical observation at Mondy
  44. Fermi GBM Sub-Threshold Detection of GRB 260321A
  45. GRB 260321A: SVOM detection of a burst
  46. EP260321a: Kinder observations detect a blue variable star and set limits on a source from the z =0.034 galaxy within the error circle
  47. EP260321a: Global MASTER-Net observations report
  48. EP260321a: Einstein Probe detection of an X-ray transient
  49. GRB 260310A / AT2026fgk: ABObservatory and NOCTIS new optical observations
  50. GRB 260318A: Glowbug gamma-ray detection
  51. GRB 260310A / AT 2026fgk: KAIT optical observations
  52. GRB 260320A: NuSTAR detection of prompt emission
  53. GRB 260310A / AT2026fgk: NuSTAR follow-up detection
  54. EP-WXT trigger 01709258989: KAIT confirmation of a stellar flare
  55. GRB 260310A / AT 2026fgk: FTW optical and NIR observations show no rebrightening
  56. GRB 260310A: no evidence of re-brightening up to 9.6 days in optical observation at Mondy
  57. GRB 260310A / AT 2026fgk: COLIBRÍ evidence of a late rebrightening
  58. GRB 260310A/AT2026fgk: LBT near-infrared observations
  59. NOEMA Detection of GRB 260310A / AT 2026fgk
  60. EP-WXT trigger 01709258989: confirmation of a stellar flare by BOOTES-7
  61. GRB 260318A: SVOM/GRM observation
  62. The EP-WXT trigger 01709258989 is likely a flaring star
  63. GRB 260310A: classification as long GRB based on Eiso, Ep, and T_90
  64. GRB 260318A: GECAM-B observation
  65. GRB260310A/AT2026fgk: Further optical observation from 1.3m DFOT
  66. Fermi GRB 260318A: Global MASTER-Net observations report
  67. GRB 260318A: Fermi GBM Final Real-time Localization
  68. IceCube-260315A: No Candidate Transients from the Zwicky Transient Facility
  69. Fermi Gamma-ray Burst Monitor trigger 795096033/260312500 (GRB 260313A) is unlikely to be a GRB
  70. GRB 260316A / EP260316a: COLIBRÍ optical followup of counterpart candidate
  71. GRB 260310A / AT 2026fgk: radio detection with the VLA
  72. GRB 260310A / AT2026fgk: SVOM/VT optical observations
  73. GRB 260310A / AT2026fgk: LCO optical observations
  74. IceCube-260315A/AT2026fpm: EP-FXT follow-up observation
  75. GRB 260317A: Fermi GBM Final Localization
  76. GRB 260316B: GECAM-B observation
  77. GRB 260316B: SVOM/GRM observation
  78. EP260316a / GRB 260316A: SVOM/VT optical upper limits
  79. EP260316a: COLIBRÍ faint optical counterpart candidate
  80. Fermi-LAT Gamma-ray Observations of IceCube-260315A
  81. GRB 260316B: AstroSat CZTI detection
  82. EP260316a: refined analysis of the EP-WXT and EP-FXT observations
  83. IceCube-260315A: Upper limits from a search for additional neutrino events in IceCube
  84. EP260316a: Xinglong optical upper limit
  85. GRB 260316B: Fermi GBM Final Real-time Localization
  86. EP260316a: optical upper limit with Kinder observations
  87. EP260316a / GRB 260316A : Fermi-GBM Sub-Threshold Detection
  88. GRB 260314A: Glowbug gamma-ray detection
  89. The EP-WXT trigger 00199258890 (EP260316a): a correction to the trigger time and FXT automatic follow-up
  90. IceCube-260315A: COLIBRÍ optical observations
  91. EP260314a: Xinglong optical upper limit
  92. EP260314a: optical upper limit with Kinder observations
  93. IceCube Alert-260315A/AT2026fpm Automatic MASTER optical blue counterpart candidate
  94. GRB 260310A / AT2026fgk: 1.3m DFOT optical observations
  95. GRB 260310A / AT2026fgk: ABObservatory and NOCTIS optical observations
  96. GRB 260310A / AT 2026fgk: iTelescope optical observations
  97. EP260314a: COLIBRÍ optical upper limit
  98. GRID detection of GRB 260312B
  99. IceCube-260315A - IceCube observation of a high-energy neutrino candidate track-like event
  100. EP260314a: refined analysis of the EP-WXT and EP-FXT observations

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