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GCN Circulars are now part of the new GCN! See news and announcements

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').
  1. GRB 230506B: Swift-XRT refined Analysis
  2. GRB 230506C: Swift-XRT analysis
  3. GRB 230506C: Candidate afterglow observation by D50
  4. GRB 230506C: TSHAO possible afterglow candidate
  5. GRB 230506B: Swift/UVOT Detection
  6. IceCube-230506A: IceCube observation of a high-energy neutrino candidate
  7. GRB 230506C: Swift detection of a burst
  8. Swift GRB230506.71: Global MASTER-Net observations report
  9. GRB 230506B: Swift detection of a burst
  10. GRB 230506B: MASTER optical observations
  11. GRB 230506B: Swift detection of a burst
  12. GRB 230506A: Fermi GBM Final Real-time Localization
  13. GRB 230420A: Mondy optical afterglow detection, TSHAO, CrAO optical upper limit
  14. Fermi trigger No 704837952: Global MASTER-Net observations report
  15. GRB 230430A: A short GRB from a neutron star merger
  16. GRB 230427A: Swift-BAT refined analysis
  17. GRB 230503A: Fermi GBM Final Real-time Localization
  18. Konus-Wind detection of GRB 230430A
  19. IceCube-Cascade 230430A: Upper limits from a search for additional neutrino events in IceCube
  20. IPN triangulation of GRB 230430A (short)
  21. GRB 230420A: AROMA-N Optical Upper Limit
  22. GRB 230430B: Fermi GBM Final Localization
  23. GRB 230430A: Fermi GBM observation
  24. GRB 230430A: AstroSat CZTI detection
  25. GRB 230430A: Fermi GBM Final Real-time Localization
  26. GRB 230427A: NOT optical upper limit
  27. GRB 230427A: TSHAO, SAO RAS, AbAO optical upper limit
  28. GRB 230427A: Swift/UVOT Detection
  29. Duplicate of GCN 33369
  30. GRB 230427A: Gaoyazi/GOT optical upper limit
  31. GRB 230427A: OHP/T193 spectroscopy observations of WISEA J101316.01+481158.7
  32. GRB 230427A: Nanshan/HMT optical upper limit
  33. GRB 230427A: Osservatorio Astronomico Nastro verde upper limit
  34. GRB 230427A: OSIRIS+/GTC observations
  35. GRB 230427A: Swift-XRT refined Analysis
  36. GRB 230426A: VZLUSAT-2 detection
  37. Fermi trigger No 704365743: Global MASTER-Net observations report
  38. GRB 230428A: Fermi GBM Final Real-time Localization
  39. GRB 230427A: GIT optical upper limit
  40. GRB 230427A: Bassano Bresciano Observatory upper limit
  41. GRB 230427A: GMG upper limit
  42. GRB 230427A : OHP/T193 optical upper limit
  43. GRB 230427A: BOOTES-5/JGT afterglow detection
  44. GRB 230423A(trigger #1165354): Swift-BAT refined analysis
  45. GRB 230427A: AKO Upper Limit
  46. Swift GRB230427.44: Global MASTER-Net observations report
  47. GRB 230426A: MASTER OT J023135.16-792104.8 optical counterpart discovery
  48. GRB 230427A: MITSuME Akeno optical upper limits
  49. GRB 230426A: Fermi GBM Detection
  50. GRB 230427A: Enhanced Swift-XRT position
  51. GRB 230427A: Swift detection of a burst with an optical counterpart
  52. GRB 230426A: AstroSat CZTI detection
  53. Fermi trigger No 704233744: Global MASTER-Net observations report
  54. GRB 230426A: Fermi GBM Final Real-time Localization
  55. GRB 230423A: Swift/UVOT Upper Limits
  56. GRB 230425A: Fermi GBM Final Real-time Localization
  57. GRB 230423A: Swift-XRT refined Analysis
  58. GRB 230420A: Lowell Discovery Telescope Optical Detection
  59. GRB 230423A: Swift-XRT afterglow detection
  60. Erroneous submission
  61. Swift Trigger 1165354 is probably not a GRB
  62. GRB 221009A: Late-time JWST Observations and Detection of Supernova Emission
  63. GRB 230421A: Fermi GBM observation
  64. Konus-Wind detection of GRB 230418A
  65. GRB 230420A: Swift/UVOT Upper Limits
  66. GRB 230421: Swift/BAT-GUANO arcminute localization
  67. GRB230420A: VLT optical observation
  68. GRB 230420A: Swift-BAT refined analysis
  69. Duplicate of GCN 33668
  70. GRB 230421A: Fermi GBM Final Real-time Localization
  71. GRB 230420A: Swift-XRT refined Analysis
  72. GRB 230420A: MITSuME Akeno optical observation
  73. GRB 230420A: NOT optical afterglow confirmation
  74. GRB 230420A: Gaoyazi/GOT optical upper limit
  75. GRB 230420A: BOOTES-5/JGT optical afterglow detection
  76. GRB 230420A: LCOGT Optical Upper Limit
  77. GRB 230420A: Enhanced Swift-XRT position
  78. GRB230414B: VIRT Optical Upper Limit
  79. IPN triangulation of GRB 230418A (short)
  80. GRB 230420A: Swift detection of a burst
  81. GRB 230418A: AstroSat CZTI detection
  82. GRB 230418A: AGILE detection
  83. GRB 230402A: Fermi GBM detection
  84. GRB 230419A: Fermi GBM Final Real-time Localization
  85. GRB 230418A: Swift/BAT-GUANO detection outside the coded FOV
  86. GRB 230418A: Fermi GBM Observation
  87. IceCube-Cascade 230417A: Upper limits from a search for additional neutrino events in IceCube
  88. GRB 230402A: Fermi-LAT detection
  89. Fermi-LAT gamma-ray observations of IceCube-230416A
  90. GRB 230414B: Nickel and KAIT telescope optical observations
  91. Duplicate of GCN 33640
  92. Duplicate of GCN 33640
  93. GRB 230414B Swift-BAT refined analysis
  94. Duplicate of GCN 33642
  95. GRB 230415A: Fermi GBM detection
  96. GRB 230414B: Swift/UVOT Detection
  97. GRB 230414B: Osservatorio Astronomico Nastro Verde - Sorrento: optical observations
  98. IceCube-230416A: Upper limits from a search for additional neutrino events in IceCube
  99. GRB 230415A: Swift/BAT-GUANO detection
  100. New GCN Circulars Portal for Rapid Communications on Astronomical Transients is Online
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