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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. Fermi GRB 250421A: Global MASTER-Net observations report
  2. EP250421a: Global MASTER-Net observations report
  3. GRB 250421B: AstroSat CZTI detection of a bright long burst
  4. EP250421a: Einstein Probe detection of an X-ray transient
  5. EP250421a: Mephisto optical counterpart confirmation
  6. IceCube Alert 250421.71: Global MASTER-Net observations report
  7. IceCube-250421A - IceCube observation of a high-energy neutrino candidate track-like event
  8. IceCube-Cascade 250414A: Upper limits from a search for additional neutrino events in IceCube
  9. EP250421a: JinShan likely optical counterpart
  10. The EP-WXT trigger 01709135179: Kinder optical counterpart candidate
  11. GRB 250421A: Fermi GBM Final Real-time Localization
  12. GRB 250419A: Liverpool Telescope observations
  13. GRB 250419A: LCO optical observation
  14. GRB 250419A: JinShan optical observations
  15. GRB 250419A: SVOM/VT optical continuous observations
  16. GRB 250419A: SVOM/C-GFT optical observations
  17. GRB 250419A: Swift/UVOT Follow up
  18. GRB 250416C / EP250416a: SVOM/GRM observation of a burst
  19. GRB 250419A: LCO optical afterglow multi-band observations
  20. GRB 250419A: Mondy and AbAO Optical Observations
  21. GRB 250419A: Liverpool Telescope observations
  22. GRB 250419A: AKO Optical Afterglow Detection
  23. GRB 250419A: MASTER optical afterglow observation
  24. Fermi-LAT Gamma-ray Observations of IceCube-250416A
  25. GRB 250407A: rest-frame energetics from Konus-Wind observation
  26. GRB 250419A: Swift-XRT localisation
  27. GRB 250407A: GTC/OSIRIS+ spectroscopic redshift z = 1.36
  28. GRB 250419A: VLT/X-shooter spectroscopic redshift z = 0.845
  29. GRB 250419A: Swift-XRT refined Analysis
  30. GRB 250419A: GOTO optical counterpart detection
  31. GRB 250419A: KAIT optical afterglow observations
  32. GRB 250419A: SVOM/VT optical bright counterpart confirmation
  33. GRB 250419A: SVOM/COLIBRÍ (FM-GFT) Detection of the Optical Counterpart
  34. GRB 250419A: SVOM detection of a soft burst
  35. Konus-Wind detection of GRB 250416C (a counterpart of EP250416a)
  36. EP250416a: Swift/XRT counterpart fading
  37. EP250416a: refined EP-WXT and EP-FXT analysis
  38. Konus-Wind detection of GRB 250403A
  39. EP20250416a: Swift/XRT counterpart detection
  40. GRB 250403A: VLT/FORS2 spectroscopic redshift z = 1.847
  41. IceCube-250416A: DDOTI Optical Observations
  42. EP250416a: Gemini South-GMOS optical counterpart
  43. EP250225a: SVOM/VT optical brightening
  44. SVOM/sb25041603 is not a GRB
  45. EP250416a: GSP optical upper limit
  46. EP250416a: Global MASTER-Net observations report
  47. Fermi Gamma-ray Burst Monitor trigger 766505186/250416588 (GRB 250416A) is not a GRB
  48. EP250416a: Einstein Probe detection of an X-ray transient
  49. IceCube-250416A - IceCube observation of a high-energy neutrino candidate track-like event
  50. IceCube-250416A: Global MASTER-Net observations report
  51. Fermi Gamma-ray Burst Monitor trigger 766511207/250416657 is not a GRB
  52. GRB 250416B: Fermi GBM Final Real-time Localization
  53. GRB 250416A: Fermi GBM Final Real-time Localization
  54. SVOM/sb25041603: SVOM/COLIBRÍ (FM-GFT) Upper Limit on the Optical Counterpart
  55. SVOM/sb25041603: SVOM detection of an X-ray transient
  56. Fermi Gamma-ray Burst Monitor trigger 766474855/250416237 is not a GRB
  57. IceCube 250414.324: DDOTI Optical Observations
  58. GRB 250413A: AstroSat CZTI detection
  59. EP250304a: ATCA radio observations
  60. GRB 250412A: AstroSat CZTI detection
  61. EP250404a: Nanshan 0.43m Telescope optical observatios
  62. Fermi trigger No 766148493: Global MASTER-Net observations report
  63. Fermi trigger No 766173972: Global MASTER-Net observations report
  64. GRB 250411A: DDOTI Optical Observations
  65. Fermi GRB 250411A: Global MASTER-Net observations report
  66. GRB 250411A: Fermi GBM Final Real-time Localization
  67. GRB 250407A: Continued KAIT/Nickel optical observations
  68. GRB 250314A: e-MERLIN observations
  69. GRB 250407A: Mondy and AbAO Optical Observations
  70. EP250227a: Further NOT optical observations
  71. GRB 250320B: cubesat Avion detection
  72. IceCube-250406A: Swift-XRT observations
  73. IPN triangulation of GRB 250321D (consistent with the fast X-ray transient EP250321a)
  74. AMON Coincidence Alert from the sub-threshold IceCube-HAWC search NuEm-250409A
  75. IPN triangulation of GRB 250407A
  76. EP250407a: Global MASTER-Net observations report
  77. GRB 250407A: LCO detection of a fading optical counterpart
  78. Fermi-LAT gamma-ray observations of IceCube-250406A
  79. EP250407a: Swift-XRT observations
  80. IceCube-250406A: Upper limits from a search for additional neutrino events in IceCube
  81. Konus-Wind detection of GRB 250407A
  82. GRB 250407A: SVOM/GRM observation of a bright long burst
  83. GRB 250407A: EP-WXT afterglow detection
  84. EP250407a: EP-WXT detection of a fast X-ray transient
  85. GRB 250407A: COLIBRÍ/DDRAGO Detection of the Optical Counterpart
  86. GRB 250407A: KAIT Optical Afterglow Candidate
  87. IceCube-250406A: No candidates from the Zwicky Transient Facility
  88. GRB 250407A: Fermi GBM Detection
  89. GRB 250407A: Swift-XRT afterglow detection
  90. Fermi GRB 250407A: Global MASTER-Net observations report
  91. GRB 250407A: Swift ToO observations
  92. GRB 250407A: SRG/ART-XC afterglow detection
  93. LIGO/Virgo/KAGRA S250331o: Upper limits from Swift/BAT-GUANO
  94. IceCube 250406A: DDOTI Optical Observations of the Refined Position
  95. Konus-Wind detection of GRB 250406B (short/hard)
  96. IPN triangulation of GRB 250406B (short/hard)
  97. GRB 250407A: BALROG localization (Fermi Trigger 765733706 / GRB 250407659)
  98. GRB 250407A: Fermi GBM Final Real-time Localization
  99. IceCube-250406A - IceCube observation of a high-energy neutrino candidate track-like event
  100. IceCube 250406.951: COLIBRÍ/DDRAGO Optical Upper Limit

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