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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. EP250421a: Nickel optical upper limit
  2. EP250416a / GRB 250416C: Gemini GMOS-S likely host galaxy redshift z = 0.963
  3. EP250421a: Upper limits from Fermi-GBM Observations
  4. SVOM/sb25042207: XRT observations
  5. SVOM/sb25042207: BOOTES-2 early optical upper limit
  6. SVOM/sb25042207: GOTO optical upper limits
  7. GRB 250421A: AstroSat CZTI detection
  8. SVOM/sb25042207: SVOM detection of an X-ray transient
  9. GRB250419A: VLA radio detection
  10. IceCube-250421A: DDOTI Detection of the LAST Candidate
  11. GRB 250419A: Mephisto Multi-band Optical Detection
  12. GRB 250419A: Calapai Observatory, Massa S. Giorgio (Messina), optical observations.
  13. IC-250421A: LAST optical observations of the IceCube neutrino candidate
  14. EP250421a: NOT optical observations
  15. GRB 250419A: Optical Observations via Virtual Telescope Project
  16. EP250421a: REM optical upper limit
  17. EP250421a: Swift/XRT counterpart detection
  18. EP250421A: COLIBRÍ Optical Upper Limit
  19. GRB 250419A: Mondy Continued Optical Observations
  20. Fermi GRB 250421A: Global MASTER-Net observations report
  21. EP250421a: Global MASTER-Net observations report
  22. GRB 250421B: AstroSat CZTI detection of a bright long burst
  23. EP250421a: Einstein Probe detection of an X-ray transient
  24. EP250421a: Mephisto optical counterpart confirmation
  25. IceCube Alert 250421.71: Global MASTER-Net observations report
  26. IceCube-250421A - IceCube observation of a high-energy neutrino candidate track-like event
  27. IceCube-Cascade 250414A: Upper limits from a search for additional neutrino events in IceCube
  28. EP250421a: JinShan likely optical counterpart
  29. The EP-WXT trigger 01709135179: Kinder optical counterpart candidate
  30. GRB 250421A: Fermi GBM Final Real-time Localization
  31. GRB 250419A: Liverpool Telescope observations
  32. GRB 250419A: LCO optical observation
  33. GRB 250419A: JinShan optical observations
  34. GRB 250419A: SVOM/VT optical continuous observations
  35. GRB 250419A: SVOM/C-GFT optical observations
  36. GRB 250419A: Swift/UVOT Follow up
  37. GRB 250416C / EP250416a: SVOM/GRM observation of a burst
  38. GRB 250419A: LCO optical afterglow multi-band observations
  39. GRB 250419A: Mondy and AbAO Optical Observations
  40. GRB 250419A: Liverpool Telescope observations
  41. GRB 250419A: AKO Optical Afterglow Detection
  42. GRB 250419A: MASTER optical afterglow observation
  43. Fermi-LAT Gamma-ray Observations of IceCube-250416A
  44. GRB 250407A: rest-frame energetics from Konus-Wind observation
  45. GRB 250419A: Swift-XRT localisation
  46. GRB 250407A: GTC/OSIRIS+ spectroscopic redshift z = 1.36
  47. GRB 250419A: VLT/X-shooter spectroscopic redshift z = 0.845
  48. GRB 250419A: Swift-XRT refined Analysis
  49. GRB 250419A: GOTO optical counterpart detection
  50. GRB 250419A: KAIT optical afterglow observations
  51. GRB 250419A: SVOM/VT optical bright counterpart confirmation
  52. GRB 250419A: SVOM/COLIBRÍ (FM-GFT) Detection of the Optical Counterpart
  53. GRB 250419A: SVOM detection of a soft burst
  54. Konus-Wind detection of GRB 250416C (a counterpart of EP250416a)
  55. EP250416a: Swift/XRT counterpart fading
  56. EP250416a: refined EP-WXT and EP-FXT analysis
  57. Konus-Wind detection of GRB 250403A
  58. EP20250416a: Swift/XRT counterpart detection
  59. GRB 250403A: VLT/FORS2 spectroscopic redshift z = 1.847
  60. IceCube-250416A: DDOTI Optical Observations
  61. EP250416a: Gemini South-GMOS optical counterpart
  62. EP250225a: SVOM/VT optical brightening
  63. SVOM/sb25041603 is not a GRB
  64. EP250416a: GSP optical upper limit
  65. EP250416a: Global MASTER-Net observations report
  66. Fermi Gamma-ray Burst Monitor trigger 766505186/250416588 (GRB 250416A) is not a GRB
  67. EP250416a: Einstein Probe detection of an X-ray transient
  68. IceCube-250416A - IceCube observation of a high-energy neutrino candidate track-like event
  69. IceCube-250416A: Global MASTER-Net observations report
  70. Fermi Gamma-ray Burst Monitor trigger 766511207/250416657 is not a GRB
  71. GRB 250416B: Fermi GBM Final Real-time Localization
  72. GRB 250416A: Fermi GBM Final Real-time Localization
  73. SVOM/sb25041603: SVOM/COLIBRÍ (FM-GFT) Upper Limit on the Optical Counterpart
  74. SVOM/sb25041603: SVOM detection of an X-ray transient
  75. Fermi Gamma-ray Burst Monitor trigger 766474855/250416237 is not a GRB
  76. IceCube 250414.324: DDOTI Optical Observations
  77. GRB 250413A: AstroSat CZTI detection
  78. EP250304a: ATCA radio observations
  79. GRB 250412A: AstroSat CZTI detection
  80. EP250404a: Nanshan 0.43m Telescope optical observatios
  81. Fermi trigger No 766148493: Global MASTER-Net observations report
  82. Fermi trigger No 766173972: Global MASTER-Net observations report
  83. GRB 250411A: DDOTI Optical Observations
  84. Fermi GRB 250411A: Global MASTER-Net observations report
  85. GRB 250411A: Fermi GBM Final Real-time Localization
  86. GRB 250407A: Continued KAIT/Nickel optical observations
  87. GRB 250314A: e-MERLIN observations
  88. GRB 250407A: Mondy and AbAO Optical Observations
  89. EP250227a: Further NOT optical observations
  90. GRB 250320B: cubesat Avion detection
  91. IceCube-250406A: Swift-XRT observations
  92. IPN triangulation of GRB 250321D (consistent with the fast X-ray transient EP250321a)
  93. AMON Coincidence Alert from the sub-threshold IceCube-HAWC search NuEm-250409A
  94. IPN triangulation of GRB 250407A
  95. EP250407a: Global MASTER-Net observations report
  96. GRB 250407A: LCO detection of a fading optical counterpart
  97. Fermi-LAT gamma-ray observations of IceCube-250406A
  98. EP250407a: Swift-XRT observations
  99. IceCube-250406A: Upper limits from a search for additional neutrino events in IceCube
  100. Konus-Wind detection of GRB 250407A

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