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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 trigger No 767623859: Global MASTER-Net observations report
  2. EP250428b: refined analysis of the EP-FXT follow-up observation
  3. EP250428b: GROWTH-India telescope optical upper limit
  4. EP250428b: SVOM/VT upper limit
  5. EP250428b: SAO RAS optical upper limit
  6. EP250428b: LAST optical upper limit
  7. IceCube-250429A - IceCube observation of a high-energy neutrino candidate track-like event
  8. GRB 250427A: Swift/UVOT Detection
  9. EP250428b: Global MASTER-Net observations report
  10. EP250428b: Einstein Probe detection of a fast X-ray transient
  11. Fermi-LAT Gamma-ray Observations of IceCube-250426A
  12. EP250427a / GRB 250427A: OHP/T193 photometric observations
  13. EP250427a: EP-FXT follow-up observations
  14. EP250427a/GRB 250427A: FTW optical and NIR observations of the counterpart
  15. EP250427a: Lesedi optical counterpart detection
  16. EP250427A: COLIBRÍ Continuing Optical Observations
  17. GRB250427A/EP250427a GIT optical afterglow detection:
  18. EP250427a: LT optical counterpart detection
  19. GRB 250427A: Swift-XRT refined Analysis
  20. EP250427a / GRB 250427A: LCO optical counterpart detection
  21. EP250427a / GRB 250427A: VLT/X-shooter redshift confirmation z = 1.520
  22. EP250427A/GRB250427A: Keck/LRIS redshift
  23. EP250427a: REM optical/NIR afterglow detection
  24. GRB 250424A: LCO optical observation
  25. GRB 250427A/ EP250427a: Fermi-GBM Sub-Threshold Detection
  26. EP250427A: COLIBRÍ Optical Detection
  27. EP250427a: TRT optical counterpart detection
  28. EP 250427a: BOOTES-7 optical afterglow candidate
  29. EP250427a: Global MASTER-Net observations report
  30. EP250427a: Einstein Probe detection of a fast X-ray transient
  31. IceCube Alert 250426.74: Global MASTER-Net observations report
  32. GRB 250424A: Swift-BAT refined analysis
  33. IceCube-250426A - IceCube observation of a high-energy neutrino candidate track-like event (duplicate submission)
  34. IceCube-250426A - IceCube observation of a high-energy neutrino candidate track-like event
  35. GRB 250424A: SVOM/GRM observation of a long burst
  36. GRB 250424A: PRIME near-infrared detection
  37. GRB 250424A: WINTER J-band detection
  38. GRB 250424A: EIRSAT-1 GMOD Detection
  39. IceCube-250416A: Upper limits from a search for additional neutrino events in IceCube
  40. IceCube-250421A: Upper limits from a search for additional neutrino events in IceCube
  41. GRB 250424A: SVOM/VT optical observation
  42. GRB 250419A: Mondy Optical Observations
  43. GRB 250424A: Swift/UVOT Detection
  44. Konus-Wind detection of GRB 250424A
  45. Fermi-LAT gamma-ray observations of IceCube-250421A
  46. GRB 250424A: Skynet Optical Observations
  47. GRB 250424A: Kilonova-Catcher optical afterglow detection
  48. GRB 250419a: Continued Liverpool Telescope observations
  49. GRB 250419A: Liverpool Telescope optical upper limit
  50. GRB 250407A: GRBAlpha detection
  51. GRB 250404A / EP250404a: GRBAlpha detection
  52. GRB 250330B: GRBAlpha detection
  53. GRB 250419A: SVOM/ECLAIRs refined analysis
  54. GRB 250424A: Swift-XRT refined Analysis
  55. GRB 250424A: Enhanced Swift-XRT position
  56. GRB 250424A: AstroSat CZTI detection of a bright long burst
  57. GRB 250424A: COLIBRÍ Detection of a Bright Optical Counterpart
  58. GRB 250424A: BlackGEM optical afterglow detection
  59. GRB 250424A: VLT/X-shooter spectroscopic redshift z = 0.310
  60. GRB 250424A: likely host galaxy
  61. GRB 250424A: DDOTI Afterglow Detection
  62. GRB 250424A: REM optical/NIR afterglow detection
  63. GRB 250424A: Swift detection of a burst with an optical counterpart
  64. Swift GRB 250424A: Global MASTER-Net observations report
  65. Swift GRB 250424A: Global MASTER-Net OT detection
  66. LIGO/Virgo/KAGRA S250328ae: Subaru/PFS Spectroscopic Follow up and Candidates
  67. EP250421a: Nickel optical upper limit
  68. EP250416a / GRB 250416C: Gemini GMOS-S likely host galaxy redshift z = 0.963
  69. EP250421a: Upper limits from Fermi-GBM Observations
  70. SVOM/sb25042207: XRT observations
  71. SVOM/sb25042207: BOOTES-2 early optical upper limit
  72. SVOM/sb25042207: GOTO optical upper limits
  73. GRB 250421A: AstroSat CZTI detection
  74. SVOM/sb25042207: SVOM detection of an X-ray transient
  75. GRB250419A: VLA radio detection
  76. IceCube-250421A: DDOTI Detection of the LAST Candidate
  77. GRB 250419A: Mephisto Multi-band Optical Detection
  78. GRB 250419A: Calapai Observatory, Massa S. Giorgio (Messina), optical observations.
  79. IC-250421A: LAST optical observations of the IceCube neutrino candidate
  80. EP250421a: NOT optical observations
  81. GRB 250419A: Optical Observations via Virtual Telescope Project
  82. EP250421a: REM optical upper limit
  83. EP250421a: Swift/XRT counterpart detection
  84. EP250421A: COLIBRÍ Optical Upper Limit
  85. GRB 250419A: Mondy Continued Optical Observations
  86. Fermi GRB 250421A: Global MASTER-Net observations report
  87. EP250421a: Global MASTER-Net observations report
  88. GRB 250421B: AstroSat CZTI detection of a bright long burst
  89. EP250421a: Einstein Probe detection of an X-ray transient
  90. EP250421a: Mephisto optical counterpart confirmation
  91. IceCube Alert 250421.71: Global MASTER-Net observations report
  92. IceCube-250421A - IceCube observation of a high-energy neutrino candidate track-like event
  93. IceCube-Cascade 250414A: Upper limits from a search for additional neutrino events in IceCube
  94. EP250421a: JinShan likely optical counterpart
  95. The EP-WXT trigger 01709135179: Kinder optical counterpart candidate
  96. GRB 250421A: Fermi GBM Final Real-time Localization
  97. GRB 250419A: Liverpool Telescope observations
  98. GRB 250419A: LCO optical observation
  99. GRB 250419A: JinShan optical observations
  100. GRB 250419A: SVOM/VT optical continuous observations

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