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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: Gemini-South confirmation of a supernova
  2. EP260321a: Gemini-South confirmation of a supernova
  3. Fermi Gamma-ray Burst Monitor trigger 796060650/260324665 is not a GRB
  4. EP260321a: VLT/FORS2 spectroscopy confirmation of an associated type Ic-BL supernova SN 2026gzf
  5. GRB 260310A: LBT optical observations
  6. EP260321A: Mondy optical observations
  7. GRB 260321A: SVOM/COLIBRÍ (FM-GFT) optical upper limits at the FXT positions
  8. EP-WXT trigger 01709259112: confirmation of a stellar flare by BOOTES-5 & BOOTES-7
  9. GRB 260316B: CALET Gamma-Ray Burst Monitor detection
  10. The EP-WXT trigger 01709259112 is likely a flaring star
  11. Fermi GRB 260323A: Global MASTER-Net observations report
  12. GRB 260323A: Fermi GBM Final Real-time Localization
  13. GRB260310A: Palomar 60-inch photometry of an extremely bright late-time afterglow with a temporal break at 8 days
  14. GRB 260310A/AT2026fgk: Detection of temporal steepening in Einstein Probe X-ray data
  15. GRB 260322A: Fermi GBM Final Localization
  16. GRB 260320A: Glowbug gamma-ray detection
  17. EP260321a / AT2026gzf: VLT/X-shooter detection of supernova-like spectral features at z = 0.0344
  18. EP260321a: COLIBRÍ further optical observations and brightening
  19. Fermi Gamma-ray Burst Monitor trigger 795918973/260323025 is not a GRB
  20. EP260321a: Continued brightening from Kinder follow-up of the emerging supernova candidate
  21. EP260214b: ATCA 6 GHz detection
  22. EP260321a: Early TRT rising followed by JinShan decaying and then re-rising
  23. GRB 260321A: EP-FXT follow-up observation
  24. The EP-WXT trigger 01709259045 is likely a flaring star
  25. EP260321a: ZTF and Rubin detections of the candidate optical counterpart to EP260321a
  26. EP260321a: GOTO detection of blue variable source
  27. EP260321a: VLT imaging and spectroscopy show the variable source to be at z = 0.0343
  28. EP260321a: further Kinder optical observations
  29. GRB 260321A: SVOM/VT optical upper limits
  30. EP260321a: Las Cumbres upper limit
  31. GRB 260321A: SVOM/COLIBRÍ (FM-GFT) optical upper limit
  32. GRB 260320A: Insight-HXMT/HE detection
  33. EP260321a: COLIBRÍ optical upper limit on any supernova shock breakout emission
  34. EP260321a: refined analysis of the EP-WXT and EP-FXT observations, implying a possible supernova shock breakout candidate
  35. EP260321a: SVOM/VT optical upper limit
  36. GRB 260310A: continued optical observation at Mondy
  37. Fermi GBM Sub-Threshold Detection of GRB 260321A
  38. GRB 260321A: SVOM detection of a burst
  39. EP260321a: Kinder observations detect a blue variable star and set limits on a source from the z =0.034 galaxy within the error circle
  40. EP260321a: Global MASTER-Net observations report
  41. EP260321a: Einstein Probe detection of an X-ray transient
  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. EP-WXT trigger 01709258989: confirmation of a stellar flare by BOOTES-7
  54. GRB 260318A: SVOM/GRM observation
  55. The EP-WXT trigger 01709258989 is likely a flaring star
  56. GRB 260310A: classification as long GRB based on Eiso, Ep, and T_90
  57. GRB 260318A: GECAM-B observation
  58. GRB260310A/AT2026fgk: Further optical observation from 1.3m DFOT
  59. Fermi GRB 260318A: Global MASTER-Net observations report
  60. GRB 260318A: Fermi GBM Final Real-time Localization
  61. IceCube-260315A: No Candidate Transients from the Zwicky Transient Facility
  62. Fermi Gamma-ray Burst Monitor trigger 795096033/260312500 (GRB 260313A) is unlikely to be a GRB
  63. GRB 260316A / EP260316a: COLIBRÍ optical followup of counterpart candidate
  64. GRB 260310A / AT 2026fgk: radio detection with the VLA
  65. GRB 260310A / AT2026fgk: SVOM/VT optical observations
  66. GRB 260310A / AT2026fgk: LCO optical observations
  67. IceCube-260315A/AT2026fpm: EP-FXT follow-up observation
  68. GRB 260317A: Fermi GBM Final Localization
  69. GRB 260316B: GECAM-B observation
  70. GRB 260316B: SVOM/GRM observation
  71. EP260316a / GRB 260316A: SVOM/VT optical upper limits
  72. EP260316a: COLIBRÍ faint optical counterpart candidate
  73. Fermi-LAT Gamma-ray Observations of IceCube-260315A
  74. GRB 260316B: AstroSat CZTI detection
  75. EP260316a: refined analysis of the EP-WXT and EP-FXT observations
  76. IceCube-260315A: Upper limits from a search for additional neutrino events in IceCube
  77. EP260316a: Xinglong optical upper limit
  78. GRB 260316B: Fermi GBM Final Real-time Localization
  79. EP260316a: optical upper limit with Kinder observations
  80. EP260316a / GRB 260316A : Fermi-GBM Sub-Threshold Detection
  81. GRB 260314A: Glowbug gamma-ray detection
  82. The EP-WXT trigger 00199258890 (EP260316a): a correction to the trigger time and FXT automatic follow-up
  83. IceCube-260315A: COLIBRÍ optical observations
  84. EP260314a: Xinglong optical upper limit
  85. EP260314a: optical upper limit with Kinder observations
  86. IceCube Alert-260315A/AT2026fpm Automatic MASTER optical blue counterpart candidate
  87. GRB 260310A / AT2026fgk: 1.3m DFOT optical observations
  88. GRB 260310A / AT2026fgk: ABObservatory and NOCTIS optical observations
  89. GRB 260310A / AT 2026fgk: iTelescope optical observations
  90. EP260314a: COLIBRÍ optical upper limit
  91. GRID detection of GRB 260312B
  92. IceCube-260315A - IceCube observation of a high-energy neutrino candidate track-like event
  93. EP260314a: refined analysis of the EP-WXT and EP-FXT observations
  94. EP260314a: BOOTES-6/DPR optical upper limits at early times
  95. EP260314a: Global MASTER-Net observations report
  96. EP260314a: SVOM/VT optical candidate
  97. Fermi trigger No 795185313: Global MASTER-Net observations report
  98. IceCube Alert 260315A: Global MASTER-Net observations report
  99. EP260314a: Einstein Probe detection of an X-ray transient
  100. The EP-WXT trigger 01709258851: Las Cumbres upper limit

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