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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. Trigger 1062273: Swift detection of 4U 1700-377
  2. GRB 210730A: Campo Imperatore optical observations
  3. GRB 210730A: BOOTES-5/JGT and 2.2m CAHA telescopes optical limit
  4. Swift GRB 210730A: Global MASTER-Net observations report
  5. Fermi trigger No 649390368: Global MASTER-Net observations report
  6. GRB 210730A: TNG optical observations
  7. IceCube-210730A - IceCube observation of a high-energy neutrino candidate track-like event
  8. GRB 210726A: Chandra detection of the X-ray afterglow
  9. GRB 210730A: Fermi GBM observation
  10. Fermi trigger No 649313854: Global MASTER-Net observations report
  11. GRB 210730A: AstroSat CZTI detection
  12. GRB 210730A: Swift-BAT refined analysis
  13. GRB 210730A: Swift-XRT refined Analysis
  14. GRB 210730A: Swift/UVOT Upper Limits
  15. GRB 210724A: Early CAHA 2.2m limit
  16. GRB 210730A: Enhanced Swift-XRT position
  17. GRB 210727A: AstroSat CZTI detection
  18. GRB 210730A: Swift detection of a burst near M82
  19. GRB 210724A: Corrected Swift-XRT enhanced position
  20. Fermi GBM Sub-Threshold Detection of GRB 210725B
  21. GRB 210726A: OSIRIS/GTC observations
  22. GRB 210727A: CALET Gamma-Ray Burst Monitor detection
  23. GRB 210726A: Deep CAHA 2.2m limit
  24. GRB 210726A: 6 GHz VLA radio upper limit
  25. IPN triangulation of GRB 210727A (short)
  26. Fermi GBM Sub-Threshold Detection of GRB 210726A
  27. GRB 210714A: Fermi GBM observation
  28. GRB 210702A: MeerKAT radio detection
  29. GRB 210726A: Swift-XRT refined Analysis
  30. GRB 210726A: Swift-BAT refined analysis
  31. GRB 210726A: Likely a short burst
  32. GRB 210726A: RATIR Optical Upper Limits and Candidate Host Galaxy
  33. GRB 210727A: AGILE/MCAL detection
  34. Fermi trigger No 649072251: Global MASTER-Net observations report
  35. GRB 210727A: BALROG localization (Fermi Trigger 649072251 / GRB 210727410)
  36. GRB 210725A: AbAO optical upper limit
  37. GRB 210724A: Swift/UVOT Upper Limits
  38. GRB 210723A: Swift/UVOT Upper Limits
  39. GRB 210725A: Swift/UVOT Upper Limits
  40. GRB 210725B: Swift/UVOT Upper Limits
  41. GRB 210726A: CAHA 2.2m telescope optical limit
  42. GRB 210726A: Enhanced Swift-XRT position
  43. GRB 210726A: Swift detection of a burst
  44. Swift GRB210726.80: Global MASTER-Net observations report
  45. Fermi trigger No 648959581: Global MASTER-Net observations report
  46. GRB 210725B: Swift-XRT refined Analysis
  47. GRB 210725A: Fermi GBM detection
  48. GRB 210724A: Zeiss-1000 of Koshka observatory, optical upper limit
  49. GRB 210725A: Swift-XRT refined Analysis
  50. GRB 210725B: Swift-BAT refined analysis
  51. GRB 210724A: Swift-XRT refined Analysis
  52. GRB 210725A: Swift-BAT refined analysis
  53. GRB 210724A: Swift-BAT refined analysis
  54. Swift GRB 210725B: Global MASTER-Net observations report
  55. GRB 210724A: Afterglow candidate from OSIRIS/GTC
  56. GRB 210725B: Enhanced Swift-XRT position
  57. GRB 210725A: MITSuME Akeno optical upper limits
  58. GRB 210725B: Swift detection of a burst
  59. GRB 210725A: CALET Gamma-Ray Burst Monitor detection
  60. GRB 210723A: CALET Gamma-Ray Burst Monitor detection
  61. GRB 210722A: continued Assy optical observations
  62. GRB 210722A: Nanshan/NEXT further optical observations
  63. GRB 210725A: KAIT Optical Upper Limit
  64. Fermi trigger No 648868114: Global MASTER-Net observations report
  65. GRB 210725A: Swift detection of a burst
  66. Swift GRB210725.16: Global MASTER-Net observations report
  67. GRB 210723A: Fermi GBM Observation
  68. GRB210724A: MeerLICHT upper limits
  69. GRB 210724A: Swift detection of a burst
  70. Swift GRB210724.84: Global MASTER-Net observations report
  71. GRB 210723A: Swift-BAT refined analysis
  72. GRB 210722A: continued Assy optical observations
  73. GRB 210723A: Swift-XRT refined Analysis
  74. GRB 210722A: D50 optical detection
  75. Swift GRB 210723A: Global MASTER-Net observations report
  76. GRB 210722A: Fermi GBM observation
  77. GRB 210722A: Swift-BAT refined analysis
  78. GRB 210722A: Kitab optical observations, light curve
  79. GRB 210722A: Redshift from OSIRIS/GTC
  80. GRB 210723A: Prompt enhanced Swift-XRT position
  81. GRB 210723A: Swift detection of a burst
  82. GRB 210722A: RATIR Optical Observations
  83. GRB 210722A: Swift-XRT refined Analysis
  84. GRB 210722A: Swift/UVOT Detection
  85. GRB 210722A: GIT optical detection and preliminary analysis
  86. Swift GRB 210722A: Global MASTER-Net observations report
  87. GRB 210702A: ALMA detection of mm-band rebrightening
  88. GRB 210722A: Assy optical detection
  89. GRB 210702A: ATCA detection of radio rebrightening
  90. GRB 210722A: Nanshan/NEXT optical afterglow observations
  91. GRB 210722A: Swift detection of a burst with a bright optical counterpart
  92. Fermi trigger No 648602917: Global MASTER-Net observations report
  93. Fermi-LAT Gamma-ray Observations of IceCube-210717A
  94. GRB 210719A: GECAM detection
  95. IceCube-210717A: No counterpart candidates in INTEGRAL SPI-ACS and IBIS prompt observation
  96. Fermi trigger No 648359752: Global MASTER-Net observations report
  97. Fermi trigger No 648278666: Global MASTER-Net observations report
  98. IceCube-210717A: IceCube observation of a high-energy neutrino candidate track-like event
  99. Konus-Wind detection of GRB 210714A
  100. Fermi trigger No 647942198: MASTER optical afterglow detection

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