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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. GRB250419A: VLA radio detection
  2. IceCube-250421A: DDOTI Detection of the LAST Candidate
  3. GRB 250419A: Mephisto Multi-band Optical Detection
  4. GRB 250419A: Calapai Observatory, Massa S. Giorgio (Messina), optical observations.
  5. IC-250421A: LAST optical observations of the IceCube neutrino candidate
  6. EP250421a: NOT optical observations
  7. GRB 250419A: Optical Observations via Virtual Telescope Project
  8. EP250421a: REM optical upper limit
  9. EP250421a: Swift/XRT counterpart detection
  10. EP250421A: COLIBRÍ Optical Upper Limit
  11. GRB 250419A: Mondy Continued Optical Observations
  12. Fermi GRB 250421A: Global MASTER-Net observations report
  13. EP250421a: Global MASTER-Net observations report
  14. GRB 250421B: AstroSat CZTI detection of a bright long burst
  15. EP250421a: Einstein Probe detection of an X-ray transient
  16. EP250421a: Mephisto optical counterpart confirmation
  17. IceCube Alert 250421.71: Global MASTER-Net observations report
  18. IceCube-250421A - IceCube observation of a high-energy neutrino candidate track-like event
  19. IceCube-Cascade 250414A: Upper limits from a search for additional neutrino events in IceCube
  20. EP250421a: JinShan likely optical counterpart
  21. The EP-WXT trigger 01709135179: Kinder optical counterpart candidate
  22. GRB 250421A: Fermi GBM Final Real-time Localization
  23. GRB 250419A: Liverpool Telescope observations
  24. GRB 250419A: LCO optical observation
  25. GRB 250419A: JinShan optical observations
  26. GRB 250419A: SVOM/VT optical continuous observations
  27. GRB 250419A: SVOM/C-GFT optical observations
  28. GRB 250419A: Swift/UVOT Follow up
  29. GRB 250416C / EP250416a: SVOM/GRM observation of a burst
  30. GRB 250419A: LCO optical afterglow multi-band observations
  31. GRB 250419A: Mondy and AbAO Optical Observations
  32. GRB 250419A: Liverpool Telescope observations
  33. GRB 250419A: AKO Optical Afterglow Detection
  34. GRB 250419A: MASTER optical afterglow observation
  35. Fermi-LAT Gamma-ray Observations of IceCube-250416A
  36. GRB 250407A: rest-frame energetics from Konus-Wind observation
  37. GRB 250419A: Swift-XRT localisation
  38. GRB 250407A: GTC/OSIRIS+ spectroscopic redshift z = 1.36
  39. GRB 250419A: VLT/X-shooter spectroscopic redshift z = 0.845
  40. GRB 250419A: Swift-XRT refined Analysis
  41. GRB 250419A: GOTO optical counterpart detection
  42. GRB 250419A: KAIT optical afterglow observations
  43. GRB 250419A: SVOM/VT optical bright counterpart confirmation
  44. GRB 250419A: SVOM/COLIBRÍ (FM-GFT) Detection of the Optical Counterpart
  45. GRB 250419A: SVOM detection of a soft burst
  46. Konus-Wind detection of GRB 250416C (a counterpart of EP250416a)
  47. EP250416a: Swift/XRT counterpart fading
  48. EP250416a: refined EP-WXT and EP-FXT analysis
  49. Konus-Wind detection of GRB 250403A
  50. EP20250416a: Swift/XRT counterpart detection
  51. GRB 250403A: VLT/FORS2 spectroscopic redshift z = 1.847
  52. IceCube-250416A: DDOTI Optical Observations
  53. EP250416a: Gemini South-GMOS optical counterpart
  54. EP250225a: SVOM/VT optical brightening
  55. SVOM/sb25041603 is not a GRB
  56. EP250416a: GSP optical upper limit
  57. EP250416a: Global MASTER-Net observations report
  58. Fermi Gamma-ray Burst Monitor trigger 766505186/250416588 (GRB 250416A) is not a GRB
  59. EP250416a: Einstein Probe detection of an X-ray transient
  60. IceCube-250416A - IceCube observation of a high-energy neutrino candidate track-like event
  61. IceCube-250416A: Global MASTER-Net observations report
  62. Fermi Gamma-ray Burst Monitor trigger 766511207/250416657 is not a GRB
  63. GRB 250416B: Fermi GBM Final Real-time Localization
  64. GRB 250416A: Fermi GBM Final Real-time Localization
  65. SVOM/sb25041603: SVOM/COLIBRÍ (FM-GFT) Upper Limit on the Optical Counterpart
  66. SVOM/sb25041603: SVOM detection of an X-ray transient
  67. Fermi Gamma-ray Burst Monitor trigger 766474855/250416237 is not a GRB
  68. IceCube 250414.324: DDOTI Optical Observations
  69. GRB 250413A: AstroSat CZTI detection
  70. EP250304a: ATCA radio observations
  71. GRB 250412A: AstroSat CZTI detection
  72. EP250404a: Nanshan 0.43m Telescope optical observatios
  73. Fermi trigger No 766148493: Global MASTER-Net observations report
  74. Fermi trigger No 766173972: Global MASTER-Net observations report
  75. GRB 250411A: DDOTI Optical Observations
  76. Fermi GRB 250411A: Global MASTER-Net observations report
  77. GRB 250411A: Fermi GBM Final Real-time Localization
  78. GRB 250407A: Continued KAIT/Nickel optical observations
  79. GRB 250314A: e-MERLIN observations
  80. GRB 250407A: Mondy and AbAO Optical Observations
  81. EP250227a: Further NOT optical observations
  82. GRB 250320B: cubesat Avion detection
  83. IceCube-250406A: Swift-XRT observations
  84. IPN triangulation of GRB 250321D (consistent with the fast X-ray transient EP250321a)
  85. AMON Coincidence Alert from the sub-threshold IceCube-HAWC search NuEm-250409A
  86. IPN triangulation of GRB 250407A
  87. EP250407a: Global MASTER-Net observations report
  88. GRB 250407A: LCO detection of a fading optical counterpart
  89. Fermi-LAT gamma-ray observations of IceCube-250406A
  90. EP250407a: Swift-XRT observations
  91. IceCube-250406A: Upper limits from a search for additional neutrino events in IceCube
  92. Konus-Wind detection of GRB 250407A
  93. GRB 250407A: SVOM/GRM observation of a bright long burst
  94. GRB 250407A: EP-WXT afterglow detection
  95. EP250407a: EP-WXT detection of a fast X-ray transient
  96. GRB 250407A: COLIBRÍ/DDRAGO Detection of the Optical Counterpart
  97. GRB 250407A: KAIT Optical Afterglow Candidate
  98. IceCube-250406A: No candidates from the Zwicky Transient Facility
  99. GRB 250407A: Fermi GBM Detection
  100. GRB 250407A: Swift-XRT afterglow detection

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