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

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