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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: Early TRT rising followed by JinShan decaying and then re-rising
  2. GRB 260321A: EP-FXT follow-up observation
  3. The EP-WXT trigger 01709259045 is likely a flaring star
  4. EP260321a: ZTF and Rubin detections of the candidate optical counterpart to EP260321a
  5. EP260321a: GOTO detection of blue variable source
  6. EP260321a: VLT imaging and spectroscopy show the variable source to be at z = 0.0343
  7. EP260321a: further Kinder optical observations
  8. GRB 260321A: SVOM/VT optical upper limits
  9. EP260321a: Las Cumbres upper limit
  10. GRB 260321A: SVOM/COLIBRÍ (FM-GFT) optical upper limit
  11. GRB 260320A: Insight-HXMT/HE detection
  12. EP260321a: COLIBRÍ optical upper limit on any supernova shock breakout emission
  13. EP260321a: refined analysis of the EP-WXT and EP-FXT observations, implying a possible supernova shock breakout candidate
  14. EP260321a: SVOM/VT optical upper limit
  15. GRB 260310A: continued optical observation at Mondy
  16. Fermi GBM Sub-Threshold Detection of GRB 260321A
  17. GRB 260321A: SVOM detection of a burst
  18. EP260321a: Kinder observations detect a blue variable star and set limits on a source from the z =0.034 galaxy within the error circle
  19. EP260321a: Global MASTER-Net observations report
  20. EP260321a: Einstein Probe detection of an X-ray transient
  21. GRB 260310A / AT2026fgk: ABObservatory and NOCTIS new optical observations
  22. GRB 260318A: Glowbug gamma-ray detection
  23. GRB 260310A / AT 2026fgk: KAIT optical observations
  24. GRB 260320A: NuSTAR detection of prompt emission
  25. GRB 260310A / AT2026fgk: NuSTAR follow-up detection
  26. EP-WXT trigger 01709258989: KAIT confirmation of a stellar flare
  27. GRB 260310A / AT 2026fgk: FTW optical and NIR observations show no rebrightening
  28. GRB 260310A: no evidence of re-brightening up to 9.6 days in optical observation at Mondy
  29. GRB 260310A / AT 2026fgk: COLIBRÍ evidence of a late rebrightening
  30. GRB 260310A/AT2026fgk: LBT near-infrared observations
  31. NOEMA Detection of GRB 260310A / AT 2026fgk
  32. EP-WXT trigger 01709258989: confirmation of a stellar flare by BOOTES-7
  33. GRB 260318A: SVOM/GRM observation
  34. The EP-WXT trigger 01709258989 is likely a flaring star
  35. GRB 260310A: classification as long GRB based on Eiso, Ep, and T_90
  36. GRB 260318A: GECAM-B observation
  37. GRB260310A/AT2026fgk: Further optical observation from 1.3m DFOT
  38. Fermi GRB 260318A: Global MASTER-Net observations report
  39. GRB 260318A: Fermi GBM Final Real-time Localization
  40. IceCube-260315A: No Candidate Transients from the Zwicky Transient Facility
  41. Fermi Gamma-ray Burst Monitor trigger 795096033/260312500 (GRB 260313A) is unlikely to be a GRB
  42. GRB 260316A / EP260316a: COLIBRÍ optical followup of counterpart candidate
  43. GRB 260310A / AT 2026fgk: radio detection with the VLA
  44. GRB 260310A / AT2026fgk: SVOM/VT optical observations
  45. GRB 260310A / AT2026fgk: LCO optical observations
  46. IceCube-260315A/AT2026fpm: EP-FXT follow-up observation
  47. GRB 260317A: Fermi GBM Final Localization
  48. GRB 260316B: GECAM-B observation
  49. GRB 260316B: SVOM/GRM observation
  50. EP260316a / GRB 260316A: SVOM/VT optical upper limits
  51. EP260316a: COLIBRÍ faint optical counterpart candidate
  52. Fermi-LAT Gamma-ray Observations of IceCube-260315A
  53. GRB 260316B: AstroSat CZTI detection
  54. EP260316a: refined analysis of the EP-WXT and EP-FXT observations
  55. IceCube-260315A: Upper limits from a search for additional neutrino events in IceCube
  56. EP260316a: Xinglong optical upper limit
  57. GRB 260316B: Fermi GBM Final Real-time Localization
  58. EP260316a: optical upper limit with Kinder observations
  59. EP260316a / GRB 260316A : Fermi-GBM Sub-Threshold Detection
  60. GRB 260314A: Glowbug gamma-ray detection
  61. The EP-WXT trigger 00199258890 (EP260316a): a correction to the trigger time and FXT automatic follow-up
  62. IceCube-260315A: COLIBRÍ optical observations
  63. EP260314a: Xinglong optical upper limit
  64. EP260314a: optical upper limit with Kinder observations
  65. IceCube Alert-260315A/AT2026fpm Automatic MASTER optical blue counterpart candidate
  66. GRB 260310A / AT2026fgk: 1.3m DFOT optical observations
  67. GRB 260310A / AT2026fgk: ABObservatory and NOCTIS optical observations
  68. GRB 260310A / AT 2026fgk: iTelescope optical observations
  69. EP260314a: COLIBRÍ optical upper limit
  70. GRID detection of GRB 260312B
  71. IceCube-260315A - IceCube observation of a high-energy neutrino candidate track-like event
  72. EP260314a: refined analysis of the EP-WXT and EP-FXT observations
  73. EP260314a: BOOTES-6/DPR optical upper limits at early times
  74. EP260314a: Global MASTER-Net observations report
  75. EP260314a: SVOM/VT optical candidate
  76. Fermi trigger No 795185313: Global MASTER-Net observations report
  77. IceCube Alert 260315A: Global MASTER-Net observations report
  78. EP260314a: Einstein Probe detection of an X-ray transient
  79. The EP-WXT trigger 01709258851: Las Cumbres upper limit
  80. GRB 260314A: GECAM-B observation of a burst
  81. Fermi Gamma-ray Burst Monitor trigger 795185313/260314534 is not a GRB
  82. GRB 260310A / AT2026fgk: SAO RAS optical observations
  83. GRB 260310A/AT2026fgk: radio detection at 15GHz
  84. GRB 260310A / AT2026fgk: TNG NIR detection
  85. GRB 260310A / AT2026fgk: OASDG optical observations
  86. GRB 260310A / AT2026fgk: Multiband optical follow-up with Kinder observations
  87. GRB 260310A / AT 2026fgk: COLIBRÍ continuing optical observations
  88. GRB 260310A / AT2026fgk: further CAHA 1.23m telescope optical observations suggest shallow decay
  89. Fermi GRB 260314A: Global MASTER-Net observations report
  90. Fermi GRB 260313A: Global MASTER-Net observations report
  91. GRB 260314A: Fermi GBM Final Real-time Localization
  92. GRB 260310A/AT 2026fgk: WINTER NIR Detections
  93. GRB 260313A: A Correction to the Fermi GBM Final Localization
  94. GRB 260310A: Einstein Probe Follow-up X-ray Telescope (FXT) Detection
  95. GRB 260310A/AT 2026fgk: J-band observations by the SYSU 80 cm infrared telescope
  96. GRB 260310B: Insight-HXMT/HE detection
  97. GRB 260310A/AT 2026fgk: DDOTI Optical Detection
  98. GRB 260310A: NOT optical polarimetry
  99. GRB 260312B: AstroSat CZTI detection
  100. Swift BAT trigger 1500295: A solar flare

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