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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. EP-WXT trigger 01709259112: confirmation of a stellar flare by BOOTES-5 & BOOTES-7
  2. GRB 260316B: CALET Gamma-Ray Burst Monitor detection
  3. The EP-WXT trigger 01709259112 is likely a flaring star
  4. Fermi GRB 260323A: Global MASTER-Net observations report
  5. GRB 260323A: Fermi GBM Final Real-time Localization
  6. GRB260310A: Palomar 60-inch photometry of an extremely bright late-time afterglow with a temporal break at 8 days
  7. GRB 260310A/AT2026fgk: Detection of temporal steepening in Einstein Probe X-ray data
  8. GRB 260322A: Fermi GBM Final Localization
  9. GRB 260320A: Glowbug gamma-ray detection
  10. EP260321a / AT2026gzf: VLT/X-shooter detection of supernova-like spectral features at z = 0.0344
  11. EP260321a: COLIBRÍ further optical observations and brightening
  12. Fermi Gamma-ray Burst Monitor trigger 795918973/260323025 is not a GRB
  13. EP260321a: Continued brightening from Kinder follow-up of the emerging supernova candidate
  14. EP260214b: ATCA 6 GHz detection
  15. EP260321a: Early TRT rising followed by JinShan decaying and then re-rising
  16. GRB 260321A: EP-FXT follow-up observation
  17. The EP-WXT trigger 01709259045 is likely a flaring star
  18. EP260321a: ZTF and Rubin detections of the candidate optical counterpart to EP260321a
  19. EP260321a: GOTO detection of blue variable source
  20. EP260321a: VLT imaging and spectroscopy show the variable source to be at z = 0.0343
  21. EP260321a: further Kinder optical observations
  22. GRB 260321A: SVOM/VT optical upper limits
  23. EP260321a: Las Cumbres upper limit
  24. GRB 260321A: SVOM/COLIBRÍ (FM-GFT) optical upper limit
  25. GRB 260320A: Insight-HXMT/HE detection
  26. EP260321a: COLIBRÍ optical upper limit on any supernova shock breakout emission
  27. EP260321a: refined analysis of the EP-WXT and EP-FXT observations, implying a possible supernova shock breakout candidate
  28. EP260321a: SVOM/VT optical upper limit
  29. GRB 260310A: continued optical observation at Mondy
  30. Fermi GBM Sub-Threshold Detection of GRB 260321A
  31. GRB 260321A: SVOM detection of a burst
  32. EP260321a: Kinder observations detect a blue variable star and set limits on a source from the z =0.034 galaxy within the error circle
  33. EP260321a: Global MASTER-Net observations report
  34. EP260321a: Einstein Probe detection of an X-ray transient
  35. GRB 260310A / AT2026fgk: ABObservatory and NOCTIS new optical observations
  36. GRB 260318A: Glowbug gamma-ray detection
  37. GRB 260310A / AT 2026fgk: KAIT optical observations
  38. GRB 260320A: NuSTAR detection of prompt emission
  39. GRB 260310A / AT2026fgk: NuSTAR follow-up detection
  40. EP-WXT trigger 01709258989: KAIT confirmation of a stellar flare
  41. GRB 260310A / AT 2026fgk: FTW optical and NIR observations show no rebrightening
  42. GRB 260310A: no evidence of re-brightening up to 9.6 days in optical observation at Mondy
  43. GRB 260310A / AT 2026fgk: COLIBRÍ evidence of a late rebrightening
  44. GRB 260310A/AT2026fgk: LBT near-infrared observations
  45. NOEMA Detection of GRB 260310A / AT 2026fgk
  46. EP-WXT trigger 01709258989: confirmation of a stellar flare by BOOTES-7
  47. GRB 260318A: SVOM/GRM observation
  48. The EP-WXT trigger 01709258989 is likely a flaring star
  49. GRB 260310A: classification as long GRB based on Eiso, Ep, and T_90
  50. GRB 260318A: GECAM-B observation
  51. GRB260310A/AT2026fgk: Further optical observation from 1.3m DFOT
  52. Fermi GRB 260318A: Global MASTER-Net observations report
  53. GRB 260318A: Fermi GBM Final Real-time Localization
  54. IceCube-260315A: No Candidate Transients from the Zwicky Transient Facility
  55. Fermi Gamma-ray Burst Monitor trigger 795096033/260312500 (GRB 260313A) is unlikely to be a GRB
  56. GRB 260316A / EP260316a: COLIBRÍ optical followup of counterpart candidate
  57. GRB 260310A / AT 2026fgk: radio detection with the VLA
  58. GRB 260310A / AT2026fgk: SVOM/VT optical observations
  59. GRB 260310A / AT2026fgk: LCO optical observations
  60. IceCube-260315A/AT2026fpm: EP-FXT follow-up observation
  61. GRB 260317A: Fermi GBM Final Localization
  62. GRB 260316B: GECAM-B observation
  63. GRB 260316B: SVOM/GRM observation
  64. EP260316a / GRB 260316A: SVOM/VT optical upper limits
  65. EP260316a: COLIBRÍ faint optical counterpart candidate
  66. Fermi-LAT Gamma-ray Observations of IceCube-260315A
  67. GRB 260316B: AstroSat CZTI detection
  68. EP260316a: refined analysis of the EP-WXT and EP-FXT observations
  69. IceCube-260315A: Upper limits from a search for additional neutrino events in IceCube
  70. EP260316a: Xinglong optical upper limit
  71. GRB 260316B: Fermi GBM Final Real-time Localization
  72. EP260316a: optical upper limit with Kinder observations
  73. EP260316a / GRB 260316A : Fermi-GBM Sub-Threshold Detection
  74. GRB 260314A: Glowbug gamma-ray detection
  75. The EP-WXT trigger 00199258890 (EP260316a): a correction to the trigger time and FXT automatic follow-up
  76. IceCube-260315A: COLIBRÍ optical observations
  77. EP260314a: Xinglong optical upper limit
  78. EP260314a: optical upper limit with Kinder observations
  79. IceCube Alert-260315A/AT2026fpm Automatic MASTER optical blue counterpart candidate
  80. GRB 260310A / AT2026fgk: 1.3m DFOT optical observations
  81. GRB 260310A / AT2026fgk: ABObservatory and NOCTIS optical observations
  82. GRB 260310A / AT 2026fgk: iTelescope optical observations
  83. EP260314a: COLIBRÍ optical upper limit
  84. GRID detection of GRB 260312B
  85. IceCube-260315A - IceCube observation of a high-energy neutrino candidate track-like event
  86. EP260314a: refined analysis of the EP-WXT and EP-FXT observations
  87. EP260314a: BOOTES-6/DPR optical upper limits at early times
  88. EP260314a: Global MASTER-Net observations report
  89. EP260314a: SVOM/VT optical candidate
  90. Fermi trigger No 795185313: Global MASTER-Net observations report
  91. IceCube Alert 260315A: Global MASTER-Net observations report
  92. EP260314a: Einstein Probe detection of an X-ray transient
  93. The EP-WXT trigger 01709258851: Las Cumbres upper limit
  94. GRB 260314A: GECAM-B observation of a burst
  95. Fermi Gamma-ray Burst Monitor trigger 795185313/260314534 is not a GRB
  96. GRB 260310A / AT2026fgk: SAO RAS optical observations
  97. GRB 260310A/AT2026fgk: radio detection at 15GHz
  98. GRB 260310A / AT2026fgk: TNG NIR detection
  99. GRB 260310A / AT2026fgk: OASDG optical observations
  100. GRB 260310A / AT2026fgk: Multiband optical follow-up with Kinder observations

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