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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').
  1. GRB 210421C: Fermi GBM Final Real-time Localization
  2. GRB 210421B: Fermi GBM Final Localization
  3. Fermi trigger No 640695289: Global MASTER-Net observations report
  4. GRB 210419C: Swift/UVOT Upper Limits
  5. GRB 210420B: Correction to DDOTI Magnitude
  6. GRB 210420B: Ondrejov D50 optical afterglow detection
  7. GRB 210421A: Enhanced Swift-XRT position
  8. GRB 210420B: RATIR Optical and NIR Observations
  9. GRB 210420B: Tautenburg observations
  10. GRB 210420B: Swift/UVOT Detection
  11. GRB 210420B: KAIT Optical Observations
  12. GRB 210413B: MITSuME Okayama optical upper limits
  13. GRB 210419C: MITSuME Akeno optical upper limits
  14. GRB 210420B: DDOTI Detection of the Afterglow
  15. GRB 210421A: DDOTI Upper Limit
  16. GRB 210419C: Swift-BAT refined analysis
  17. Fermi GRB 210420A: Global MASTER-Net observations report
  18. GRB 210420B: update on the BAT trigger time
  19. GRB 210420B: Redshift from GTC
  20. GRB 210420B: Multiband photometry from NOT
  21. GRB 210420B: Montarrenti Observatory optical afterglow detection
  22. Swift GRB 210421A: Global MASTER-Net observations report
  23. GRB 210421A: Swift detection of a burst
  24. GRB 210420B: AST3-3 YaoAn Optical Observation
  25. GRB 210420B: BOOTES-4/MET optical afterglow detection
  26. GRB 210420B: Optical observations
  27. GRB 210420B: MASTER optical counterpart detection
  28. GRB 210420B: Swift detection of a burst
  29. GRB 210419C: RATIR Optical and NIR Upper Limits
  30. GRB 210419C: Montarrenti Observatory Upper Limit
  31. GRB 210419A: Swift/UVOT Upper Limits
  32. GRB 210419C: KAIT Optical Upper Limit
  33. GRB 210419C: Enhanced Swift-XRT position
  34. GRB 210419A: Swift-BAT refined analysis
  35. GRB 210420A: Fermi GBM Final Real-time Localization
  36. Swift GRB210419.98: Global MASTER-Net observations report
  37. GRB 210419A: Swift-XRT refined Analysis
  38. GRB 210419C: Swift detection of a burst
  39. Fermi GRB 210419B: Global MASTER-Net observations report
  40. Swift GRB 210419A: Global MASTER-Net observations report
  41. GRB 210419B: Fermi GBM Final Real-time Localization
  42. GRB 210419A: Enhanced Swift-XRT position
  43. GRB 210419A: LCO Optical Upper Limit
  44. GRB 210419A: Swift detection of a burst
  45. GRB 210413B: Swift-XRT observations
  46. Fermi GBM trigger 640353092/210417494 is not a GRB
  47. GRB 210413B: LOAO optical upper limit
  48. Fermi Gamma-ray Burst Monitor trigger 640303939/210416925 is not a GRB
  49. GRB 210411C: A very significant early X-ray afterglow
  50. IceCube Alert 210416.09: Global MASTER-Net observations report
  51. GRB 210413B: Swift ToO observations
  52. IceCubeCascade-210416a: Kanata Optical Imaging of 3C 279
  53. GRB 210413B: Swift/BAT detection and probable localization of a short burst
  54. GRB 210411B: AstroSat CZTI detection
  55. GRB 210410A: AstroSat CZTI detection
  56. GRB 210410A: A twin of short GRB 090510 with complementary observations
  57. Fermi GRB 210415A: Global MASTER-Net observations report
  58. GRB 210415A: Fermi GBM Final Real-time Localization
  59. GRB 210413A: GECAM detection
  60. GRB 210410A: Swift/UVOT Upper Limits (revision)
  61. GRB 210411C: Swift/UVOT Detection
  62. GRB 210411C: Swift-BAT refined analysis
  63. GRB 210411C: Chilescope optical observations
  64. GRB 210411C: ePESSTO+ NTT optical observations
  65. GRB 210411C: Swift-XRT refined Analysis
  66. GRB 210411C: VLT/X-shooter redshift
  67. GRB 210410A: MITSuME Akeno optical upper limits
  68. Swift GRB 210411C: Global MASTER-Net observations report
  69. GRB 210411C: BOOTES-4/MET optical upper limit
  70. GRB 210411C: LCO Optical Afterglow Candidate
  71. Fermi GRB 210411B: Global MASTER-Net observations report
  72. GRB 210411C: Enhanced Swift-XRT position
  73. GRB 210406A: 10.4m GTC follow-up observation
  74. GRB 210410A: AGILE/MCAL analysis
  75. Konus-Wind detection of GRB 210410A
  76. GRB 210411D: BALROG localization (Fermi Trigger 639851475 / GRB 210411688)
  77. GRB 210411D: Fermi GBM Final Real-time Localization
  78. GRB 210411C: Swift detection of a burst with an optical counterpart
  79. GRB 210410A: Swift-BAT refined analysis
  80. GRB 210411B: Fermi GBM Final Real-time Localization
  81. Fermi GRB 210411A: Global MASTER-Net observations report
  82. GRB 210410A: Swift-XRT refined Analysis
  83. GRB 210411A: Fermi GBM Final Real-time Localization
  84. GRB 210410A: Fermi GBM detection
  85. GRB 210410A: Swift/UVOT Upper Limits
  86. GRB210410A: Joint inspection of RATIR and D50 data
  87. GRB 210406A: Swift-XRT observations
  88. GRB 210410A: RATIR Optical and NIR Observations
  89. GRB 210409A: GECAM detection
  90. GRB 210410A: AGILE detection of a burst
  91. GRB 210410A: Fermi-LAT detection
  92. GRB210410A: Candidate optical afterglow by Ondrejov D50
  93. Fermi GRB 210410A: Global MASTER-Net observations report
  94. GRB 210410A: Swift XRT localization
  95. GRB 210410A: Fermi GBM Final Real-time Localization
  96. Swift Triggers 1042031 and 1042032 are not astrophysical events
  97. GRB 210406A: Mondy optical afterglow candidate
  98. GRB 210406A: Swift ToO observations
  99. GRB 210406B: Fermi GBM detection
  100. Konus-Wind detection of GRB 210406A

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