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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. IC-250421A: LAST optical observations of the IceCube neutrino candidate
  2. EP250421a: NOT optical observations
  3. GRB 250419A: Optical Observations via Virtual Telescope Project
  4. EP250421a: REM optical upper limit
  5. EP250421a: Swift/XRT counterpart detection
  6. EP250421A: COLIBRÍ Optical Upper Limit
  7. GRB 250419A: Mondy Continued Optical Observations
  8. Fermi GRB 250421A: Global MASTER-Net observations report
  9. EP250421a: Global MASTER-Net observations report
  10. GRB 250421B: AstroSat CZTI detection of a bright long burst
  11. EP250421a: Einstein Probe detection of an X-ray transient
  12. EP250421a: Mephisto optical counterpart confirmation
  13. IceCube Alert 250421.71: Global MASTER-Net observations report
  14. IceCube-250421A - IceCube observation of a high-energy neutrino candidate track-like event
  15. IceCube-Cascade 250414A: Upper limits from a search for additional neutrino events in IceCube
  16. EP250421a: JinShan likely optical counterpart
  17. The EP-WXT trigger 01709135179: Kinder optical counterpart candidate
  18. GRB 250421A: Fermi GBM Final Real-time Localization
  19. GRB 250419A: Liverpool Telescope observations
  20. GRB 250419A: LCO optical observation
  21. GRB 250419A: JinShan optical observations
  22. GRB 250419A: SVOM/VT optical continuous observations
  23. GRB 250419A: SVOM/C-GFT optical observations
  24. GRB 250419A: Swift/UVOT Follow up
  25. GRB 250416C / EP250416a: SVOM/GRM observation of a burst
  26. GRB 250419A: LCO optical afterglow multi-band observations
  27. GRB 250419A: Mondy and AbAO Optical Observations
  28. GRB 250419A: Liverpool Telescope observations
  29. GRB 250419A: AKO Optical Afterglow Detection
  30. GRB 250419A: MASTER optical afterglow observation
  31. Fermi-LAT Gamma-ray Observations of IceCube-250416A
  32. GRB 250407A: rest-frame energetics from Konus-Wind observation
  33. GRB 250419A: Swift-XRT localisation
  34. GRB 250407A: GTC/OSIRIS+ spectroscopic redshift z = 1.36
  35. GRB 250419A: VLT/X-shooter spectroscopic redshift z = 0.845
  36. GRB 250419A: Swift-XRT refined Analysis
  37. GRB 250419A: GOTO optical counterpart detection
  38. GRB 250419A: KAIT optical afterglow observations
  39. GRB 250419A: SVOM/VT optical bright counterpart confirmation
  40. GRB 250419A: SVOM/COLIBRÍ (FM-GFT) Detection of the Optical Counterpart
  41. GRB 250419A: SVOM detection of a soft burst
  42. Konus-Wind detection of GRB 250416C (a counterpart of EP250416a)
  43. EP250416a: Swift/XRT counterpart fading
  44. EP250416a: refined EP-WXT and EP-FXT analysis
  45. Konus-Wind detection of GRB 250403A
  46. EP20250416a: Swift/XRT counterpart detection
  47. GRB 250403A: VLT/FORS2 spectroscopic redshift z = 1.847
  48. IceCube-250416A: DDOTI Optical Observations
  49. EP250416a: Gemini South-GMOS optical counterpart
  50. EP250225a: SVOM/VT optical brightening
  51. SVOM/sb25041603 is not a GRB
  52. EP250416a: GSP optical upper limit
  53. EP250416a: Global MASTER-Net observations report
  54. Fermi Gamma-ray Burst Monitor trigger 766505186/250416588 (GRB 250416A) is not a GRB
  55. EP250416a: Einstein Probe detection of an X-ray transient
  56. IceCube-250416A - IceCube observation of a high-energy neutrino candidate track-like event
  57. IceCube-250416A: Global MASTER-Net observations report
  58. Fermi Gamma-ray Burst Monitor trigger 766511207/250416657 is not a GRB
  59. GRB 250416B: Fermi GBM Final Real-time Localization
  60. GRB 250416A: Fermi GBM Final Real-time Localization
  61. SVOM/sb25041603: SVOM/COLIBRÍ (FM-GFT) Upper Limit on the Optical Counterpart
  62. SVOM/sb25041603: SVOM detection of an X-ray transient
  63. Fermi Gamma-ray Burst Monitor trigger 766474855/250416237 is not a GRB
  64. IceCube 250414.324: DDOTI Optical Observations
  65. GRB 250413A: AstroSat CZTI detection
  66. EP250304a: ATCA radio observations
  67. GRB 250412A: AstroSat CZTI detection
  68. EP250404a: Nanshan 0.43m Telescope optical observatios
  69. Fermi trigger No 766148493: Global MASTER-Net observations report
  70. Fermi trigger No 766173972: Global MASTER-Net observations report
  71. GRB 250411A: DDOTI Optical Observations
  72. Fermi GRB 250411A: Global MASTER-Net observations report
  73. GRB 250411A: Fermi GBM Final Real-time Localization
  74. GRB 250407A: Continued KAIT/Nickel optical observations
  75. GRB 250314A: e-MERLIN observations
  76. GRB 250407A: Mondy and AbAO Optical Observations
  77. EP250227a: Further NOT optical observations
  78. GRB 250320B: cubesat Avion detection
  79. IceCube-250406A: Swift-XRT observations
  80. IPN triangulation of GRB 250321D (consistent with the fast X-ray transient EP250321a)
  81. AMON Coincidence Alert from the sub-threshold IceCube-HAWC search NuEm-250409A
  82. IPN triangulation of GRB 250407A
  83. EP250407a: Global MASTER-Net observations report
  84. GRB 250407A: LCO detection of a fading optical counterpart
  85. Fermi-LAT gamma-ray observations of IceCube-250406A
  86. EP250407a: Swift-XRT observations
  87. IceCube-250406A: Upper limits from a search for additional neutrino events in IceCube
  88. Konus-Wind detection of GRB 250407A
  89. GRB 250407A: SVOM/GRM observation of a bright long burst
  90. GRB 250407A: EP-WXT afterglow detection
  91. EP250407a: EP-WXT detection of a fast X-ray transient
  92. GRB 250407A: COLIBRÍ/DDRAGO Detection of the Optical Counterpart
  93. GRB 250407A: KAIT Optical Afterglow Candidate
  94. IceCube-250406A: No candidates from the Zwicky Transient Facility
  95. GRB 250407A: Fermi GBM Detection
  96. GRB 250407A: Swift-XRT afterglow detection
  97. Fermi GRB 250407A: Global MASTER-Net observations report
  98. GRB 250407A: Swift ToO observations
  99. GRB 250407A: SRG/ART-XC afterglow detection
  100. LIGO/Virgo/KAGRA S250331o: Upper limits from Swift/BAT-GUANO

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