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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. EP260321a / AT2026gzf: VLT/X-shooter detection of supernova-like spectral features at z = 0.0344
  2. EP260321a: COLIBRÍ further optical observations and brightening
  3. Fermi Gamma-ray Burst Monitor trigger 795918973/260323025 is not a GRB
  4. EP260321a: Continued brightening from Kinder follow-up of the emerging supernova candidate
  5. EP260214b: ATCA 6 GHz detection
  6. EP260321a: Early TRT rising followed by JinShan decaying and then re-rising
  7. GRB 260321A: EP-FXT follow-up observation
  8. The EP-WXT trigger 01709259045 is likely a flaring star
  9. EP260321a: ZTF and Rubin detections of the candidate optical counterpart to EP260321a
  10. EP260321a: GOTO detection of blue variable source
  11. EP260321a: VLT imaging and spectroscopy show the variable source to be at z = 0.0343
  12. EP260321a: further Kinder optical observations
  13. GRB 260321A: SVOM/VT optical upper limits
  14. EP260321a: Las Cumbres upper limit
  15. GRB 260321A: SVOM/COLIBRÍ (FM-GFT) optical upper limit
  16. GRB 260320A: Insight-HXMT/HE detection
  17. EP260321a: COLIBRÍ optical upper limit on any supernova shock breakout emission
  18. EP260321a: refined analysis of the EP-WXT and EP-FXT observations, implying a possible supernova shock breakout candidate
  19. EP260321a: SVOM/VT optical upper limit
  20. GRB 260310A: continued optical observation at Mondy
  21. Fermi GBM Sub-Threshold Detection of GRB 260321A
  22. GRB 260321A: SVOM detection of a burst
  23. EP260321a: Kinder observations detect a blue variable star and set limits on a source from the z =0.034 galaxy within the error circle
  24. EP260321a: Global MASTER-Net observations report
  25. EP260321a: Einstein Probe detection of an X-ray transient
  26. GRB 260310A / AT2026fgk: ABObservatory and NOCTIS new optical observations
  27. GRB 260318A: Glowbug gamma-ray detection
  28. GRB 260310A / AT 2026fgk: KAIT optical observations
  29. GRB 260320A: NuSTAR detection of prompt emission
  30. GRB 260310A / AT2026fgk: NuSTAR follow-up detection
  31. EP-WXT trigger 01709258989: KAIT confirmation of a stellar flare
  32. GRB 260310A / AT 2026fgk: FTW optical and NIR observations show no rebrightening
  33. GRB 260310A: no evidence of re-brightening up to 9.6 days in optical observation at Mondy
  34. GRB 260310A / AT 2026fgk: COLIBRÍ evidence of a late rebrightening
  35. GRB 260310A/AT2026fgk: LBT near-infrared observations
  36. NOEMA Detection of GRB 260310A / AT 2026fgk
  37. EP-WXT trigger 01709258989: confirmation of a stellar flare by BOOTES-7
  38. GRB 260318A: SVOM/GRM observation
  39. The EP-WXT trigger 01709258989 is likely a flaring star
  40. GRB 260310A: classification as long GRB based on Eiso, Ep, and T_90
  41. GRB 260318A: GECAM-B observation
  42. GRB260310A/AT2026fgk: Further optical observation from 1.3m DFOT
  43. Fermi GRB 260318A: Global MASTER-Net observations report
  44. GRB 260318A: Fermi GBM Final Real-time Localization
  45. IceCube-260315A: No Candidate Transients from the Zwicky Transient Facility
  46. Fermi Gamma-ray Burst Monitor trigger 795096033/260312500 (GRB 260313A) is unlikely to be a GRB
  47. GRB 260316A / EP260316a: COLIBRÍ optical followup of counterpart candidate
  48. GRB 260310A / AT 2026fgk: radio detection with the VLA
  49. GRB 260310A / AT2026fgk: SVOM/VT optical observations
  50. GRB 260310A / AT2026fgk: LCO optical observations
  51. IceCube-260315A/AT2026fpm: EP-FXT follow-up observation
  52. GRB 260317A: Fermi GBM Final Localization
  53. GRB 260316B: GECAM-B observation
  54. GRB 260316B: SVOM/GRM observation
  55. EP260316a / GRB 260316A: SVOM/VT optical upper limits
  56. EP260316a: COLIBRÍ faint optical counterpart candidate
  57. Fermi-LAT Gamma-ray Observations of IceCube-260315A
  58. GRB 260316B: AstroSat CZTI detection
  59. EP260316a: refined analysis of the EP-WXT and EP-FXT observations
  60. IceCube-260315A: Upper limits from a search for additional neutrino events in IceCube
  61. EP260316a: Xinglong optical upper limit
  62. GRB 260316B: Fermi GBM Final Real-time Localization
  63. EP260316a: optical upper limit with Kinder observations
  64. EP260316a / GRB 260316A : Fermi-GBM Sub-Threshold Detection
  65. GRB 260314A: Glowbug gamma-ray detection
  66. The EP-WXT trigger 00199258890 (EP260316a): a correction to the trigger time and FXT automatic follow-up
  67. IceCube-260315A: COLIBRÍ optical observations
  68. EP260314a: Xinglong optical upper limit
  69. EP260314a: optical upper limit with Kinder observations
  70. IceCube Alert-260315A/AT2026fpm Automatic MASTER optical blue counterpart candidate
  71. GRB 260310A / AT2026fgk: 1.3m DFOT optical observations
  72. GRB 260310A / AT2026fgk: ABObservatory and NOCTIS optical observations
  73. GRB 260310A / AT 2026fgk: iTelescope optical observations
  74. EP260314a: COLIBRÍ optical upper limit
  75. GRID detection of GRB 260312B
  76. IceCube-260315A - IceCube observation of a high-energy neutrino candidate track-like event
  77. EP260314a: refined analysis of the EP-WXT and EP-FXT observations
  78. EP260314a: BOOTES-6/DPR optical upper limits at early times
  79. EP260314a: Global MASTER-Net observations report
  80. EP260314a: SVOM/VT optical candidate
  81. Fermi trigger No 795185313: Global MASTER-Net observations report
  82. IceCube Alert 260315A: Global MASTER-Net observations report
  83. EP260314a: Einstein Probe detection of an X-ray transient
  84. The EP-WXT trigger 01709258851: Las Cumbres upper limit
  85. GRB 260314A: GECAM-B observation of a burst
  86. Fermi Gamma-ray Burst Monitor trigger 795185313/260314534 is not a GRB
  87. GRB 260310A / AT2026fgk: SAO RAS optical observations
  88. GRB 260310A/AT2026fgk: radio detection at 15GHz
  89. GRB 260310A / AT2026fgk: TNG NIR detection
  90. GRB 260310A / AT2026fgk: OASDG optical observations
  91. GRB 260310A / AT2026fgk: Multiband optical follow-up with Kinder observations
  92. GRB 260310A / AT 2026fgk: COLIBRÍ continuing optical observations
  93. GRB 260310A / AT2026fgk: further CAHA 1.23m telescope optical observations suggest shallow decay
  94. Fermi GRB 260314A: Global MASTER-Net observations report
  95. Fermi GRB 260313A: Global MASTER-Net observations report
  96. GRB 260314A: Fermi GBM Final Real-time Localization
  97. GRB 260310A/AT 2026fgk: WINTER NIR Detections
  98. GRB 260313A: A Correction to the Fermi GBM Final Localization
  99. GRB 260310A: Einstein Probe Follow-up X-ray Telescope (FXT) Detection
  100. GRB 260310A/AT 2026fgk: J-band observations by the SYSU 80 cm infrared telescope

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