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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. ZTF21aayokph (AT2021lfa): Nanshan/NEXT optical upper limit
  2. GRB 210506A: Swift/BAT-GUANO detection and possible arcminute localization of a short hard burst
  3. GRB 210504A: Lowell Discovery Telescope optical observations
  4. ZTF21aayokph (AT2021lfa): Redshift from Gemini South
  5. GRB 210504A: VLT X-shooter redshift
  6. GRB 210424B: AstroSat CZTI detection
  7. GRB 210504A: Swift-XRT refined Analysis
  8. RATIR Observations of ZTF21aayokph (AT2021lfa)
  9. DDOTI Observations of ZTF21aayokph (AT2021lfa)
  10. GRB 210504A: Swift-BAT refined analysis
  11. ZTF and LT observations of ZTF21aayokph (AT2021lfa), a fast-fading red transient
  12. GRB 210504A: NOT optical afterglow detection
  13. GRB 210504A: MITSuME Akeno optical upper limits
  14. Fermi GRB 210503A: DDOTI Upper Limits on the Afterglow
  15. GRB 210504A: AST3-3 YaoAn Optical Upper Limit
  16. GRB 210504A: Swift/UVOT Detection
  17. GRB 210504A: BOOTES-4/MET optical upper limit
  18. Swift GRB210504.58: Global MASTER-Net observations report
  19. GRB 210504A: update on the BAT trigger time and burst duration
  20. GRB 210504A: Swift detection of a burst
  21. Fermi GRB 210503A: Global MASTER-Net observations report
  22. GRB 210503A: Fermi GBM Final Real-time Localization
  23. Swift GRB210502.74: Global MASTER-Net observations report
  24. Swift Detection of MAXI J1803-298 including an optical counterpart
  25. MAXI GRB210501.83: Global MASTER-Net observations report
  26. Fermi GRB 210501A: Global MASTER-Net observations report
  27. Fermi trigger No 641601187: Global MASTER-Net observations report
  28. GRB 210430A: BOOTES-1 optical limit
  29. GRB 210424B: MITSuME Akeno optical upper limits
  30. GRB 210501A: Fermi GBM Final Real-time Localization
  31. GRB 210430A: Swift-BAT refined analysis
  32. Fermi GRB 210430B: Global MASTER-Net observations report
  33. GRB 210430B: Fermi GBM Final Real-time Localization
  34. Swift GRB210430.45: Global MASTER-Net observations report
  35. GRB 210430A: Swift detection of a burst
  36. GRB 210424B: CALET Gamma-Ray Burst Monitor detection
  37. GRB 210413B: Swift/UVOT Observations
  38. Konus-Wind detection of GRB 210424B
  39. Delayed GRB GCN Notices from Swift
  40. IPN triangulation of GRB 210424B (short/hard)
  41. GRB 210323B: Swift-XRT observations
  42. Swift Trigger 1045571 is not a GRB
  43. GRB 210427A: GECAM detection
  44. GRB 210427A: BALROG localization (Fermi Trigger / GRB 210427206)
  45. Fermi GRB 210427A: Global MASTER-Net observations report
  46. GRB 210427A: Fermi GBM Final Real-time Localization
  47. GRB 210422B: Fermi GBM Final Localization
  48. GRB 210420B: Assy optical observations
  49. Fermi trigger No 640975205: Global MASTER-Net observations report
  50. GRB 210425A: GECAM detection
  51. GRB 210424.694: DDOTI Upper Limits on the Afterglow
  52. GRB 210422A: Swift-BAT refined analysis
  53. GRB 210424A: Fermi GBM Final Real-time Localization
  54. GRB 210420B: follow-up photometry of optical afterglow at INASAN/Simeiz
  55. GRB 210420B: Zeiss-1000 of Koshka optical observations
  56. GRB 210421A: Swift-BAT refined analysis
  57. GRB 210421B: Swift-XRT observations
  58. GRB 210421B: AstroSat CZTI detection
  59. GRB 210420B: continued Tautenburg observations
  60. GRB 210421A: GECAM detection
  61. GRB 210421B: AstroSat CZTI detection
  62. Swift GRB210422.74: Global MASTER-Net observations report
  63. GRB 210422A: Swift detection of a burst
  64. GRB 210421A: Swift/UVOT Upper Limits
  65. GRB 210420B: Correction to AST3-3 YaoAn magnitude
  66. GRB 210420B: follow-up photometry of the optical afterglow at Konkoly
  67. GRB 210421A: MITSuME Akeno optical upper limits
  68. GRB 210419B: AstroSat CZTI detection
  69. Fermi Gamma-ray Burst Monitor trigger 210421C is not a GRB
  70. GRB 210420B: Swift-BAT refined analysis
  71. GRB 210421B: Swift ToO observations
  72. GRB 210421B: Swift/BAT-GUANO detection and arcminute localization
  73. GRB 210420B: Swift-XRT refined Analysis
  74. GRB 210421A: Swift-XRT refined Analysis
  75. GRB 210421B: Correction of GRB Type to "Likely Long GRB"
  76. Fermi GRB 210421C: Global MASTER-Net observations report
  77. GRB 210420B: Montarrenti Observatory follow-up observations
  78. GRB 210421C: Fermi GBM Final Real-time Localization
  79. GRB 210421B: Fermi GBM Final Localization
  80. Fermi trigger No 640695289: Global MASTER-Net observations report
  81. GRB 210419C: Swift/UVOT Upper Limits
  82. GRB 210420B: Correction to DDOTI Magnitude
  83. GRB 210420B: Ondrejov D50 optical afterglow detection
  84. GRB 210421A: Enhanced Swift-XRT position
  85. GRB 210420B: RATIR Optical and NIR Observations
  86. GRB 210420B: Tautenburg observations
  87. GRB 210420B: Swift/UVOT Detection
  88. GRB 210420B: KAIT Optical Observations
  89. GRB 210413B: MITSuME Okayama optical upper limits
  90. GRB 210419C: MITSuME Akeno optical upper limits
  91. GRB 210420B: DDOTI Detection of the Afterglow
  92. GRB 210421A: DDOTI Upper Limit
  93. GRB 210419C: Swift-BAT refined analysis
  94. Fermi GRB 210420A: Global MASTER-Net observations report
  95. GRB 210420B: update on the BAT trigger time
  96. GRB 210420B: Redshift from GTC
  97. GRB 210420B: Multiband photometry from NOT
  98. GRB 210420B: Montarrenti Observatory optical afterglow detection
  99. Swift GRB 210421A: Global MASTER-Net observations report
  100. GRB 210421A: Swift detection of a burst

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