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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').
  1. EP250427a/GRB 250427A: FTW optical and NIR observations of the counterpart
  2. EP250427a: Lesedi optical counterpart detection
  3. EP250427A: COLIBRÍ Continuing Optical Observations
  4. GRB250427A/EP250427a GIT optical afterglow detection:
  5. EP250427a: LT optical counterpart detection
  6. GRB 250427A: Swift-XRT refined Analysis
  7. EP250427a / GRB 250427A: LCO optical counterpart detection
  8. EP250427a / GRB 250427A: VLT/X-shooter redshift confirmation z = 1.520
  9. EP250427A/GRB250427A: Keck/LRIS redshift
  10. EP250427a: REM optical/NIR afterglow detection
  11. GRB 250424A: LCO optical observation
  12. GRB 250427A/ EP250427a: Fermi-GBM Sub-Threshold Detection
  13. EP250427A: COLIBRÍ Optical Detection
  14. EP250427a: TRT optical counterpart detection
  15. EP 250427a: BOOTES-7 optical afterglow candidate
  16. EP250427a: Global MASTER-Net observations report
  17. EP250427a: Einstein Probe detection of a fast X-ray transient
  18. IceCube Alert 250426.74: Global MASTER-Net observations report
  19. GRB 250424A: Swift-BAT refined analysis
  20. IceCube-250426A - IceCube observation of a high-energy neutrino candidate track-like event (duplicate submission)
  21. IceCube-250426A - IceCube observation of a high-energy neutrino candidate track-like event
  22. GRB 250424A: SVOM/GRM observation of a long burst
  23. GRB 250424A: PRIME near-infrared detection
  24. GRB 250424A: WINTER J-band detection
  25. GRB 250424A: EIRSAT-1 GMOD Detection
  26. IceCube-250416A: Upper limits from a search for additional neutrino events in IceCube
  27. IceCube-250421A: Upper limits from a search for additional neutrino events in IceCube
  28. GRB 250424A: SVOM/VT optical observation
  29. GRB 250419A: Mondy Optical Observations
  30. GRB 250424A: Swift/UVOT Detection
  31. Konus-Wind detection of GRB 250424A
  32. Fermi-LAT gamma-ray observations of IceCube-250421A
  33. GRB 250424A: Skynet Optical Observations
  34. GRB 250424A: Kilonova-Catcher optical afterglow detection
  35. GRB 250419a: Continued Liverpool Telescope observations
  36. GRB 250419A: Liverpool Telescope optical upper limit
  37. GRB 250407A: GRBAlpha detection
  38. GRB 250404A / EP250404a: GRBAlpha detection
  39. GRB 250330B: GRBAlpha detection
  40. GRB 250419A: SVOM/ECLAIRs refined analysis
  41. GRB 250424A: Swift-XRT refined Analysis
  42. GRB 250424A: Enhanced Swift-XRT position
  43. GRB 250424A: AstroSat CZTI detection of a bright long burst
  44. GRB 250424A: COLIBRÍ Detection of a Bright Optical Counterpart
  45. GRB 250424A: BlackGEM optical afterglow detection
  46. GRB 250424A: VLT/X-shooter spectroscopic redshift z = 0.310
  47. GRB 250424A: likely host galaxy
  48. GRB 250424A: DDOTI Afterglow Detection
  49. GRB 250424A: REM optical/NIR afterglow detection
  50. GRB 250424A: Swift detection of a burst with an optical counterpart
  51. Swift GRB250424A: Global MASTER-Net observations report
  52. Swift GRB250424A: Global MASTER-Net OT detection
  53. LIGO/Virgo/KAGRA S250328ae: Subaru/PFS Spectroscopic Follow up and Candidates
  54. EP250421a: Nickel optical upper limit
  55. EP250416a / GRB 250416C: Gemini GMOS-S likely host galaxy redshift z = 0.963
  56. EP250421a: Upper limits from Fermi-GBM Observations
  57. SVOM/sb25042207: XRT observations
  58. SVOM/sb25042207: BOOTES-2 early optical upper limit
  59. SVOM/sb25042207: GOTO optical upper limits
  60. GRB 250421A: AstroSat CZTI detection
  61. SVOM/sb25042207: SVOM detection of an X-ray transient
  62. GRB250419A: VLA radio detection
  63. IceCube-250421A: DDOTI Detection of the LAST Candidate
  64. GRB 250419A: Mephisto Multi-band Optical Detection
  65. GRB 250419A: Calapai Observatory, Massa S. Giorgio (Messina), optical observations.
  66. IC-250421A: LAST optical observations of the IceCube neutrino candidate
  67. EP250421a: NOT optical observations
  68. GRB 250419A: Optical Observations via Virtual Telescope Project
  69. EP250421a: REM optical upper limit
  70. EP250421a: Swift/XRT counterpart detection
  71. EP250421A: COLIBRÍ Optical Upper Limit
  72. GRB 250419A: Mondy Continued Optical Observations
  73. Fermi GRB 250421A: Global MASTER-Net observations report
  74. EP250421a: Global MASTER-Net observations report
  75. GRB 250421B: AstroSat CZTI detection of a bright long burst
  76. EP250421a: Einstein Probe detection of an X-ray transient
  77. EP250421a: Mephisto optical counterpart confirmation
  78. IceCube Alert 250421.71: Global MASTER-Net observations report
  79. IceCube-250421A - IceCube observation of a high-energy neutrino candidate track-like event
  80. IceCube-Cascade 250414A: Upper limits from a search for additional neutrino events in IceCube
  81. EP250421a: JinShan likely optical counterpart
  82. The EP-WXT trigger 01709135179: Kinder optical counterpart candidate
  83. GRB 250421A: Fermi GBM Final Real-time Localization
  84. GRB 250419A: Liverpool Telescope observations
  85. GRB 250419A: LCO optical observation
  86. GRB 250419A: JinShan optical observations
  87. GRB 250419A: SVOM/VT optical continuous observations
  88. GRB 250419A: SVOM/C-GFT optical observations
  89. GRB 250419A: Swift/UVOT Follow up
  90. GRB 250416C / EP250416a: SVOM/GRM observation of a burst
  91. GRB 250419A: LCO optical afterglow multi-band observations
  92. GRB 250419A: Mondy and AbAO Optical Observations
  93. GRB 250419A: Liverpool Telescope observations
  94. GRB 250419A: AKO Optical Afterglow Detection
  95. GRB 250419A: MASTER optical afterglow observation
  96. Fermi-LAT Gamma-ray Observations of IceCube-250416A
  97. GRB 250407A: rest-frame energetics from Konus-Wind observation
  98. GRB 250419A: Swift-XRT localisation
  99. GRB 250407A: GTC/OSIRIS+ spectroscopic redshift z = 1.36
  100. GRB 250419A: VLT/X-shooter spectroscopic redshift z = 0.845

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