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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. Fermi GRB 260323A: Global MASTER-Net observations report
  2. GRB 260323A: Fermi GBM Final Real-time Localization
  3. GRB260310A: Palomar 60-inch photometry of an extremely bright late-time afterglow with a temporal break at 8 days
  4. GRB 260310A/AT2026fgk: Detection of temporal steepening in Einstein Probe X-ray data
  5. GRB 260322A: Fermi GBM Final Localization
  6. GRB 260320A: Glowbug gamma-ray detection
  7. EP260321a / AT2026gzf: VLT/X-shooter detection of supernova-like spectral features at z = 0.0344
  8. EP260321a: COLIBRÍ further optical observations and brightening
  9. Fermi Gamma-ray Burst Monitor trigger 795918973/260323025 is not a GRB
  10. EP260321a: Continued brightening from Kinder follow-up of the emerging supernova candidate
  11. EP260214b: ATCA 6 GHz detection
  12. EP260321a: Early TRT rising followed by JinShan decaying and then re-rising
  13. GRB 260321A: EP-FXT follow-up observation
  14. The EP-WXT trigger 01709259045 is likely a flaring star
  15. EP260321a: ZTF and Rubin detections of the candidate optical counterpart to EP260321a
  16. EP260321a: GOTO detection of blue variable source
  17. EP260321a: VLT imaging and spectroscopy show the variable source to be at z = 0.0343
  18. EP260321a: further Kinder optical observations
  19. GRB 260321A: SVOM/VT optical upper limits
  20. EP260321a: Las Cumbres upper limit
  21. GRB 260321A: SVOM/COLIBRÍ (FM-GFT) optical upper limit
  22. GRB 260320A: Insight-HXMT/HE detection
  23. EP260321a: COLIBRÍ optical upper limit on any supernova shock breakout emission
  24. EP260321a: refined analysis of the EP-WXT and EP-FXT observations, implying a possible supernova shock breakout candidate
  25. EP260321a: SVOM/VT optical upper limit
  26. GRB 260310A: continued optical observation at Mondy
  27. Fermi GBM Sub-Threshold Detection of GRB 260321A
  28. GRB 260321A: SVOM detection of a burst
  29. EP260321a: Kinder observations detect a blue variable star and set limits on a source from the z =0.034 galaxy within the error circle
  30. EP260321a: Global MASTER-Net observations report
  31. EP260321a: Einstein Probe detection of an X-ray transient
  32. GRB 260310A / AT2026fgk: ABObservatory and NOCTIS new optical observations
  33. GRB 260318A: Glowbug gamma-ray detection
  34. GRB 260310A / AT 2026fgk: KAIT optical observations
  35. GRB 260320A: NuSTAR detection of prompt emission
  36. GRB 260310A / AT2026fgk: NuSTAR follow-up detection
  37. EP-WXT trigger 01709258989: KAIT confirmation of a stellar flare
  38. GRB 260310A / AT 2026fgk: FTW optical and NIR observations show no rebrightening
  39. GRB 260310A: no evidence of re-brightening up to 9.6 days in optical observation at Mondy
  40. GRB 260310A / AT 2026fgk: COLIBRÍ evidence of a late rebrightening
  41. GRB 260310A/AT2026fgk: LBT near-infrared observations
  42. NOEMA Detection of GRB 260310A / AT 2026fgk
  43. EP-WXT trigger 01709258989: confirmation of a stellar flare by BOOTES-7
  44. GRB 260318A: SVOM/GRM observation
  45. The EP-WXT trigger 01709258989 is likely a flaring star
  46. GRB 260310A: classification as long GRB based on Eiso, Ep, and T_90
  47. GRB 260318A: GECAM-B observation
  48. GRB260310A/AT2026fgk: Further optical observation from 1.3m DFOT
  49. Fermi GRB 260318A: Global MASTER-Net observations report
  50. GRB 260318A: Fermi GBM Final Real-time Localization
  51. IceCube-260315A: No Candidate Transients from the Zwicky Transient Facility
  52. Fermi Gamma-ray Burst Monitor trigger 795096033/260312500 (GRB 260313A) is unlikely to be a GRB
  53. GRB 260316A / EP260316a: COLIBRÍ optical followup of counterpart candidate
  54. GRB 260310A / AT 2026fgk: radio detection with the VLA
  55. GRB 260310A / AT2026fgk: SVOM/VT optical observations
  56. GRB 260310A / AT2026fgk: LCO optical observations
  57. IceCube-260315A/AT2026fpm: EP-FXT follow-up observation
  58. GRB 260317A: Fermi GBM Final Localization
  59. GRB 260316B: GECAM-B observation
  60. GRB 260316B: SVOM/GRM observation
  61. EP260316a / GRB 260316A: SVOM/VT optical upper limits
  62. EP260316a: COLIBRÍ faint optical counterpart candidate
  63. Fermi-LAT Gamma-ray Observations of IceCube-260315A
  64. GRB 260316B: AstroSat CZTI detection
  65. EP260316a: refined analysis of the EP-WXT and EP-FXT observations
  66. IceCube-260315A: Upper limits from a search for additional neutrino events in IceCube
  67. EP260316a: Xinglong optical upper limit
  68. GRB 260316B: Fermi GBM Final Real-time Localization
  69. EP260316a: optical upper limit with Kinder observations
  70. EP260316a / GRB 260316A : Fermi-GBM Sub-Threshold Detection
  71. GRB 260314A: Glowbug gamma-ray detection
  72. The EP-WXT trigger 00199258890 (EP260316a): a correction to the trigger time and FXT automatic follow-up
  73. IceCube-260315A: COLIBRÍ optical observations
  74. EP260314a: Xinglong optical upper limit
  75. EP260314a: optical upper limit with Kinder observations
  76. IceCube Alert-260315A/AT2026fpm Automatic MASTER optical blue counterpart candidate
  77. GRB 260310A / AT2026fgk: 1.3m DFOT optical observations
  78. GRB 260310A / AT2026fgk: ABObservatory and NOCTIS optical observations
  79. GRB 260310A / AT 2026fgk: iTelescope optical observations
  80. EP260314a: COLIBRÍ optical upper limit
  81. GRID detection of GRB 260312B
  82. IceCube-260315A - IceCube observation of a high-energy neutrino candidate track-like event
  83. EP260314a: refined analysis of the EP-WXT and EP-FXT observations
  84. EP260314a: BOOTES-6/DPR optical upper limits at early times
  85. EP260314a: Global MASTER-Net observations report
  86. EP260314a: SVOM/VT optical candidate
  87. Fermi trigger No 795185313: Global MASTER-Net observations report
  88. IceCube Alert 260315A: Global MASTER-Net observations report
  89. EP260314a: Einstein Probe detection of an X-ray transient
  90. The EP-WXT trigger 01709258851: Las Cumbres upper limit
  91. GRB 260314A: GECAM-B observation of a burst
  92. Fermi Gamma-ray Burst Monitor trigger 795185313/260314534 is not a GRB
  93. GRB 260310A / AT2026fgk: SAO RAS optical observations
  94. GRB 260310A/AT2026fgk: radio detection at 15GHz
  95. GRB 260310A / AT2026fgk: TNG NIR detection
  96. GRB 260310A / AT2026fgk: OASDG optical observations
  97. GRB 260310A / AT2026fgk: Multiband optical follow-up with Kinder observations
  98. GRB 260310A / AT 2026fgk: COLIBRÍ continuing optical observations
  99. GRB 260310A / AT2026fgk: further CAHA 1.23m telescope optical observations suggest shallow decay
  100. Fermi GRB 260314A: Global MASTER-Net observations report

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