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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"

27031 results found.

  1. EP260329a: EP-FXT follow up observation
  2. EP260329a: NOT optical counterpart candidate
  3. EP260329b: Global MASTER-Net observations report
  4. Fermi trigger No 796485221: Global MASTER-Net observations report
  5. GRB 260327A: Insight-HXMT/HE detection
  6. EP260329b: Optical follow-up with Kinder observations
  7. EP 260329b: COLIBRÍ optical observations
  8. EP260329a: Optical upper limit with Kinder observations
  9. EP260329b: LCO optical observations of the counterpart
  10. GRB 260326A: Insight-HXMT/HE detection
  11. EP260329b: Einstein Probe detection of an X-ray transient
  12. EP260329a: Einstein Probe detection of an X-ray transient
  13. EP-WXT trigger 01709259209: TRT optical counterpart detection
  14. The EP-WXT trigger 01709259209 (EP260329b?): Las Cumbres discovery of the optical counterpart
  15. EP260327a: refined analysis of the EP-WXT and autonomous EP-FXT observations
  16. EP260327a: SVOM/VT optical upper limits
  17. EP260327a: WINTER J-band upper limit
  18. EP260327a: COLIBRÍ optical upper limits
  19. EP260327a: Gemini-North optical upper limits
  20. EP260324a: GROWTH-India Telescope optical observation
  21. EP260327a: Global MASTER-Net observations report
  22. EP260327a: Einstein Probe detection of an X-ray transient
  23. GRB 260310A / AT 2026fgk: COLIBRÍ photometric evidence of the emerging supernova
  24. GRB 260310A / AT2026fgk: Late-time infrared detection with MIRAGE on the MDM 1.3m telescope
  25. EP260324a: ZTF discovery of the optical counterpart ZTF26aapviim/AT2026hir
  26. GRB 260310A / AT2026fgk: R- and I-band observations with the PKU 60 cm optical telescope
  27. GRB 260326A: Fermi GBM Detection
  28. EP260321a: JinShan near-infrared observations
  29. EP260321a: Upper limits from a neutrino search with IceCube
  30. GRB 260310A/AT2026fgk: Kilonova-Catcher late optical afterglow detection at about 15 days post trigger time
  31. EP260321a: J-band observations by the SYSU 80 cm infrared telescope
  32. GRB 260321A: SVOM/COLIBRÍ (FM-GFT) optical upper limits at the FXT positions
  33. EP-WXT trigger 01709259112: confirmation of a stellar flare by BOOTES-5 & BOOTES-7
  34. Fermi GRB 260323A: Global MASTER-Net observations report
  35. GRB260310A: Palomar 60-inch photometry of an extremely bright late-time afterglow with a temporal break at 8 days
  36. GRB 260320A: Glowbug gamma-ray detection
  37. EP260321a: COLIBRÍ further optical observations and brightening
  38. EP260321a: Continued brightening from Kinder follow-up of the emerging supernova candidate
  39. EP260321a: Early TRT rising followed by JinShan decaying and then re-rising
  40. GRB 260321A: EP-FXT follow-up observation
  41. EP260321a: GOTO detection of blue variable source
  42. EP260321a: VLT imaging and spectroscopy show the variable source to be at z = 0.0343
  43. EP260321a: further Kinder optical observations
  44. GRB 260321A: SVOM/VT optical upper limits
  45. EP260321a: Las Cumbres upper limit
  46. GRB 260321A: SVOM/COLIBRÍ (FM-GFT) optical upper limit
  47. EP260321a: COLIBRÍ optical upper limit on any supernova shock breakout emission
  48. EP260321a: refined analysis of the EP-WXT and EP-FXT observations, implying a possible supernova shock breakout candidate
  49. EP260321a: SVOM/VT optical upper limit
  50. Fermi GBM Sub-Threshold Detection of GRB 260321A
  51. EP260321a: Kinder observations detect a blue variable star and set limits on a source from the z =0.034 galaxy within the error circle
  52. EP260321a: Global MASTER-Net observations report
  53. EP260321a: Einstein Probe detection of an X-ray transient
  54. GRB 260318A: Glowbug gamma-ray detection
  55. GRB 260310A / AT 2026fgk: KAIT optical observations
  56. GRB 260320A: NuSTAR detection of prompt emission
  57. EP-WXT trigger 01709258989: KAIT confirmation of a stellar flare
  58. GRB 260310A: no evidence of re-brightening up to 9.6 days in optical observation at Mondy
  59. GRB 260310A / AT 2026fgk: COLIBRÍ evidence of a late rebrightening
  60. EP-WXT trigger 01709258989: confirmation of a stellar flare by BOOTES-7
  61. GRB 260318A: SVOM/GRM observation
  62. GRB 260310A: classification as long GRB based on Eiso, Ep, and T_90
  63. GRB260310A/AT2026fgk: Further optical observation from 1.3m DFOT
  64. Fermi GRB 260318A: Global MASTER-Net observations report
  65. GRB 260316A / EP260316a: COLIBRÍ optical followup of counterpart candidate
  66. GRB 260310A / AT 2026fgk: radio detection with the VLA
  67. GRB 260310A / AT2026fgk: SVOM/VT optical observations
  68. GRB 260310A / AT2026fgk: LCO optical observations
  69. GRB 260316B: SVOM/GRM observation
  70. EP260316a / GRB 260316A: SVOM/VT optical upper limits
  71. EP260316a: COLIBRÍ faint optical counterpart candidate
  72. Fermi-LAT Gamma-ray Observations of IceCube-260315A
  73. EP260316a: refined analysis of the EP-WXT and EP-FXT observations
  74. IceCube-260315A: Upper limits from a search for additional neutrino events in IceCube
  75. EP260316a: Xinglong optical upper limit
  76. EP260316a: optical upper limit with Kinder observations
  77. EP260316a / GRB 260316A : Fermi-GBM Sub-Threshold Detection
  78. GRB 260314A: Glowbug gamma-ray detection
  79. The EP-WXT trigger 00199258890 (EP260316a): a correction to the trigger time and FXT automatic follow-up
  80. IceCube-260315A: COLIBRÍ optical observations
  81. EP260314a: Xinglong optical upper limit
  82. EP260314a: optical upper limit with Kinder observations
  83. IceCube Alert-260315A/AT2026fpm Automatic MASTER optical blue counterpart candidate
  84. GRB 260310A / AT2026fgk: 1.3m DFOT optical observations
  85. GRB 260310A / AT 2026fgk: iTelescope optical observations
  86. EP260314a: COLIBRÍ optical upper limit
  87. EP260314a: refined analysis of the EP-WXT and EP-FXT observations
  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. GRB 260310A / AT2026fgk: SAO RAS optical observations
  94. GRB 260310A / AT2026fgk: Multiband optical follow-up with Kinder observations
  95. GRB 260310A / AT 2026fgk: COLIBRÍ continuing optical observations
  96. Fermi GRB 260314A: Global MASTER-Net observations report
  97. Fermi GRB 260313A: Global MASTER-Net observations report
  98. GRB 260310A/AT 2026fgk: WINTER NIR Detections
  99. GRB 260310A/AT 2026fgk: J-band observations by the SYSU 80 cm infrared telescope
  100. GRB 260310A/AT 2026fgk: DDOTI Optical Detection

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