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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"

12054 results found.

  1. Fermi GRB 260417B: Global MASTER-Net observations report
  2. EP260417b: GROWTH-India Telescope optical upper limit
  3. EP260417a: Global MASTER-Net observations report
  4. Fermi GRB 260417A: Global MASTER-Net observations report
  5. EP260416a: KAIT optical upper limit
  6. EP260416a: Global MASTER-Net observations report
  7. Fermi trigger No 797912738: Global MASTER-Net observations report
  8. Fermi GRB 260413A: Global MASTER-Net observations report
  9. Fermi GRB 260412A: Global MASTER-Net observations report
  10. GRB 260410A: COLIBRÍ optical upper limit
  11. EP-WXT01709259790: Optical Upper limits with kinder observations
  12. EP-WXT01709259790: Xinglong optical upper limit
  13. EP260409a: SVOM/VT optical upper limits
  14. EP260409a: COLIBRÍ optical upper limits
  15. EP260409a: Global MASTER-Net observations report
  16. EP260402a / GRB 260402A: Mephisto optical upper limits
  17. EP-WXT01709259586: Xinglong optical upper limit
  18. EP260403a: Mephisto optical upper limits
  19. EP260402a/GRB 260402A: Xinglong optical upper limit
  20. EP260321a: Upper limits from VLA radio observations
  21. EP260321a: uGMRT observations
  22. EP260405a: GMOS-N optical upper limits
  23. EP260405a: SVOM/VT optical upper limits
  24. EP260405a: Global MASTER-Net observations report
  25. EP260405a: Einstein Probe detection of a fast X-ray transient
  26. EP260405a / EP-WXT 11900672904: COLIBRÍ optical upper limits
  27. Fermi trigger No 797039833: Global MASTER-Net observations report
  28. GRB 260330B: SVOM/VT optical candidate
  29. EP260402a/GRB 260402A: Jinshan near-infrared upper limit
  30. GRB 260402A: WINTER J-band upper limit
  31. GRB260402A: GROWTH-India Telescope optical upper limit
  32. GRB 260402A / EP260402a: SVOM/VT optical upper limits
  33. EP260402a/GRB 260402A: SVOM/C-GFT upper limit
  34. GRB 260402A: Kilonova-Catcher optical upper limit
  35. GRB 260402A: SVOM/COLIBRÍ (FM-GFT) optical upper limit
  36. Fermi GRB 260401A: Global MASTER-Net observations report
  37. GRB 260401A: MAXI/GSC detection
  38. EP260329b: Mondy and Assy-Turgen optical upper limits
  39. EP260327a: Xinglong optical upper limit
  40. GRB 260330B: SVOM/VT optical upper limits
  41. Konus-Wind detection of GRB 260320A
  42. GRB 260321A: SVOM/ECLAIRs refined analysis
  43. EP260329b: J-band upper limits with WINTER
  44. EP260329a: J-band upper limit with WINTER
  45. GRB 260330B: LCO optical upper limits
  46. EP260329a: COLIBRÍ optical upper limit
  47. EP260329a: EP-FXT follow up observation
  48. EP260329b: Global MASTER-Net observations report
  49. Fermi trigger No 796485221: Global MASTER-Net observations report
  50. EP260329b: Optical follow-up with Kinder observations
  51. EP260329a: Optical upper limit with Kinder observations
  52. EP260327a: refined analysis of the EP-WXT and autonomous EP-FXT observations
  53. EP260327a: SVOM/VT optical upper limits
  54. GRB 260307B: ATCA Radio Upper Limits
  55. EP260327a: WINTER J-band upper limit
  56. EP260327a: COLIBRÍ optical upper limits
  57. EP260327a: Gemini-North optical upper limits
  58. EP260327a: Global MASTER-Net observations report
  59. EP260321a: Upper limits from a neutrino search with IceCube
  60. GRB 260321A: SVOM/COLIBRÍ (FM-GFT) optical upper limits at the FXT positions
  61. Fermi GRB 260323A: Global MASTER-Net observations report
  62. GRB260310A: Palomar 60-inch photometry of an extremely bright late-time afterglow with a temporal break at 8 days
  63. EP260321a: Early TRT rising followed by JinShan decaying and then re-rising
  64. EP260321a: ZTF and Rubin detections of the candidate optical counterpart to EP260321a
  65. EP260321a: further Kinder optical observations
  66. GRB 260321A: SVOM/VT optical upper limits
  67. EP260321a: Las Cumbres upper limit
  68. GRB 260321A: SVOM/COLIBRÍ (FM-GFT) optical upper limit
  69. EP260321a: COLIBRÍ optical upper limit on any supernova shock breakout emission
  70. EP260321a: SVOM/VT optical upper limit
  71. EP260321a: Kinder observations detect a blue variable star and set limits on a source from the z =0.034 galaxy within the error circle
  72. EP260321a: Global MASTER-Net observations report
  73. Fermi GRB 260318A: Global MASTER-Net observations report
  74. EP260316a / GRB 260316A: SVOM/VT optical upper limits
  75. Fermi-LAT Gamma-ray Observations of IceCube-260315A
  76. IceCube-260315A: Upper limits from a search for additional neutrino events in IceCube
  77. EP260316a: Xinglong optical upper limit
  78. EP260316a: optical upper limit with Kinder observations
  79. EP260314a: Xinglong optical upper limit
  80. EP260314a: optical upper limit with Kinder observations
  81. IceCube Alert-260315A/AT2026fpm Automatic MASTER optical blue counterpart candidate
  82. EP260314a: COLIBRÍ optical upper limit
  83. EP260314a: BOOTES-6/DPR optical upper limits at early times
  84. EP260314a: Global MASTER-Net observations report
  85. Fermi trigger No 795185313: Global MASTER-Net observations report
  86. IceCube Alert 260315A: Global MASTER-Net observations report
  87. The EP-WXT trigger 01709258851: Las Cumbres upper limit
  88. GRB 260310A/AT2026fgk: radio detection at 15GHz
  89. Fermi GRB 260314A: Global MASTER-Net observations report
  90. Fermi GRB 260313A: Global MASTER-Net observations report
  91. GRB 260310A: NOT optical polarimetry
  92. Fermi GRB 260312B: Global MASTER-Net observations report
  93. Fermi GRB 260311B: Global MASTER-Net observations report
  94. EP260306a: Mondy optical upper limit
  95. Fermi GRB 260310B: Global MASTER-Net observations report
  96. Fermi GRB 260310A: Global MASTER-Net observations report
  97. GRB 260307B: Mephisto optical upper limits
  98. GRB 260307B: SVOM/VT upper limit with X band data analysis
  99. Fermi GRB 260307A: Global MASTER-Net observations report
  100. GRB260307B: GROWTH-India Telescope optical upper limit

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