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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 210410A: Global MASTER-Net observations report
  2. GRB 210410A: Swift XRT localization
  3. GRB 210410A: Fermi GBM Final Real-time Localization
  4. Swift Triggers 1042031 and 1042032 are not astrophysical events
  5. GRB 210406A: Mondy optical afterglow candidate
  6. GRB 210406A: Swift ToO observations
  7. GRB 210406B: Fermi GBM detection
  8. Konus-Wind detection of GRB 210406A
  9. GRB 210406A: Fermi GBM detection
  10. GRB 210406A: Mondy optical upper limit
  11. GRB 210406A: Konkoly Obs. optical upper limit
  12. GRB 210406A: BOOTES-4/MET optical upper limit
  13. GRB 210406A: A long GRB detected by INTEGRAL
  14. Integral GRB210406.72: Global MASTER-Net observations report
  15. GRB 210402A: MASTER prompt and follow up optical observation
  16. GRB 210402A: Swift/UVOT Upper Limits
  17. GRB 210402A: Fermi GBM detection
  18. GRB 210402A: Further NOT optical observations
  19. GRB 210402A: Swift-BAT refined analysis
  20. GRB 210404.141: DDOTI Upper Limits
  21. GRB 210207B: Prompt and very late time observations with HCT.
  22. GRB 210401A: GECAM detection
  23. GRB 210402A: NOT optical afterglow candidate
  24. Fermi trigger No 639199407: Global MASTER-Net observations report
  25. GRB 210402A: BOOTES-network early optical upper limit
  26. GRB 210403A: Swift-BAT refined analysis
  27. GRB 210402A: LBT observations
  28. GRB 210402A: DDOTI Upper Limits
  29. Swift GRB210403.35: Global MASTER-Net observations report
  30. GRB 210402A: Swift-XRT refined Analysis
  31. GRB 210330A: AstroSat CZTI detection
  32. GRB 210403A: Swift detection of a burst
  33. GRB 210402A: Montarrenti Observatory upper limit
  34. GRB 210328A: AstroSat CZTI detection
  35. GRB 210402A: NOT optical upper limits
  36. Konus-Wind detection of GRB 210401A
  37. GRB 210402A: Swift detection of a burst
  38. Fermi trigger No 639093861: Global MASTER-Net observations report
  39. Swift GRB210402.92: Global MASTER-Net observations report
  40. Fermi GRB 210401A: Global MASTER-Net observations report
  41. GRB 210401A: Fermi GBM Final Real-time Localization
  42. GRB 210330A: MASTER optical observation
  43. GRB 210328A: GECAM detection
  44. GRB 210330A: GECAM detection
  45. GRB 210324A: AstroSat CZTI detection
  46. GRB 210324C: AstroSat CZTI detection
  47. GRB 210328A: BALROG localization (Fermi Trigger / GRB 210328865)
  48. GRB 210328A: Fermi GBM Final Real-time Localization
  49. GRB 210326A: Insight-HXMT/HE detection
  50. GRB 210326A: Fermi GBM Final Localization
  51. Fermi trigger No 638414549: Global MASTER-Net observations report
  52. Konus-Wind detection of GRB 210324C
  53. IPN triangulation of GRB 210324C
  54. GRB 210323A: Insight-HXMT/HE detection
  55. GRB 210321A: OSN Upper Limit
  56. GRB 210323A: MASTER optical observation
  57. Fermi GRB 210324C: Global MASTER-Net observations report
  58. Fermi GRB 210324B: Global MASTER-Net observations report
  59. GRB 210323A: Swift-BAT refined analysis
  60. GRB 210323A: Gemini-North Optical Source Detection
  61. GRB 210324C: BALROG localization (Fermi Trigger 638308803 / GRB 210324833)
  62. GRB 210324C: Fermi GBM Final Real-time Localization
  63. Short GRB 210323A: GTC Observations
  64. GRB 210312B: OSN Afterglow Observations
  65. GRB 210324B: Fermi GBM Final Real-time Localization
  66. GRB 210323B: Swift ToO observations
  67. Konus-Wind detection of GRB 210323A (short)
  68. GRB 210323A: Swift/UVOT Upper Limits
  69. GRB 210323A: Classification and redshift estimation
  70. GRB 210323A: Kitab optical upper limit
  71. GRB 210323A: Fermi GBM detection
  72. GRB 210323A: Mondy optical observations, counterpart detection
  73. GRB 210324A: Fermi GBM Final Real-time Localization
  74. GRB 210318A: Swift/UVOT Upper Limits
  75. GRB 210323A: Swift-XRT refined Analysis
  76. GRB 210323A: Enhanced Swift-XRT position
  77. GRB 210323A: NOT optical afterglow candidate
  78. Swift GRB 210323A: Global MASTER-Net observations report
  79. GRB 210323B: Swift/BAT-GUANO detection and possible arcminute localization
  80. GRB 210323A: Nanshan/NEXT optical upper limit
  81. GRB 210323A: Swift detection of a short burst
  82. Fermi GBM trigger 637977270/210320996 is not a GRB
  83. GRB 210321A: Swift/UVOT Detection
  84. Konus-Wind detection of GRB 210321A
  85. GRB 210318B: Swift/UVOT Upper Limits
  86. GRB 210321A: DDOTI Position Correction
  87. IceCube Alert 210322.11: Global MASTER-Net observations report
  88. GRB 210321A: CrAO optical upper limit
  89. GRB 210321A: Swift-BAT refined analysis
  90. IceCube 135113_19489408.amon: Swift-XRT observations
  91. GRB 210321A: Mondy optical observations
  92. IceCube Astrotrack Bronze 135113_19489408.amon is likely background
  93. GRB 210321A: Xinglong GWAC-F60A optical observation
  94. GRB 210321A: Swift-XRT refined Analysis
  95. GRB 210321A: Redshift from OSIRIS/GTC
  96. GRB 210321A: NOT optical afterglow detection and redshift limit
  97. GRB 210321A: MASTER optical observation
  98. MAXI GRB210320.89: Global MASTER-Net observations report
  99. GRB 210321A: Enhanced Swift-XRT position
  100. GRB 210321A: DDOTI Afterglow Confirmation

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