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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. GRB 250424A: Skynet Optical Observations
  2. GRB 250424A: Kilonova-Catcher optical afterglow detection
  3. GRB 250419a: Continued Liverpool Telescope observations
  4. GRB 250419A: Liverpool Telescope optical upper limit
  5. GRB 250407A: GRBAlpha detection
  6. GRB 250404A / EP250404a: GRBAlpha detection
  7. GRB 250330B: GRBAlpha detection
  8. GRB 250419A: SVOM/ECLAIRs refined analysis
  9. GRB 250424A: Swift-XRT refined Analysis
  10. GRB 250424A: Enhanced Swift-XRT position
  11. GRB 250424A: AstroSat CZTI detection of a bright long burst
  12. GRB 250424A: COLIBRÍ Detection of a Bright Optical Counterpart
  13. GRB 250424A: BlackGEM optical afterglow detection
  14. GRB 250424A: VLT/X-shooter spectroscopic redshift z = 0.310
  15. GRB 250424A: likely host galaxy
  16. GRB 250424A: DDOTI Afterglow Detection
  17. GRB 250424A: REM optical/NIR afterglow detection
  18. GRB 250424A: Swift detection of a burst with an optical counterpart
  19. Swift GRB 250424A: Global MASTER-Net observations report
  20. Swift GRB 250424A: Global MASTER-Net OT detection
  21. LIGO/Virgo/KAGRA S250328ae: Subaru/PFS Spectroscopic Follow up and Candidates
  22. EP250421a: Nickel optical upper limit
  23. EP250416a / GRB 250416C: Gemini GMOS-S likely host galaxy redshift z = 0.963
  24. EP250421a: Upper limits from Fermi-GBM Observations
  25. SVOM/sb25042207: XRT observations
  26. SVOM/sb25042207: BOOTES-2 early optical upper limit
  27. SVOM/sb25042207: GOTO optical upper limits
  28. GRB 250421A: AstroSat CZTI detection
  29. SVOM/sb25042207: SVOM detection of an X-ray transient
  30. GRB250419A: VLA radio detection
  31. IceCube-250421A: DDOTI Detection of the LAST Candidate
  32. GRB 250419A: Mephisto Multi-band Optical Detection
  33. GRB 250419A: Calapai Observatory, Massa S. Giorgio (Messina), optical observations.
  34. IC-250421A: LAST optical observations of the IceCube neutrino candidate
  35. EP250421a: NOT optical observations
  36. GRB 250419A: Optical Observations via Virtual Telescope Project
  37. EP250421a: REM optical upper limit
  38. EP250421a: Swift/XRT counterpart detection
  39. EP250421A: COLIBRÍ Optical Upper Limit
  40. GRB 250419A: Mondy Continued Optical Observations
  41. Fermi GRB 250421A: Global MASTER-Net observations report
  42. EP250421a: Global MASTER-Net observations report
  43. GRB 250421B: AstroSat CZTI detection of a bright long burst
  44. EP250421a: Einstein Probe detection of an X-ray transient
  45. EP250421a: Mephisto optical counterpart confirmation
  46. IceCube Alert 250421.71: Global MASTER-Net observations report
  47. IceCube-250421A - IceCube observation of a high-energy neutrino candidate track-like event
  48. IceCube-Cascade 250414A: Upper limits from a search for additional neutrino events in IceCube
  49. EP250421a: JinShan likely optical counterpart
  50. The EP-WXT trigger 01709135179: Kinder optical counterpart candidate
  51. GRB 250421A: Fermi GBM Final Real-time Localization
  52. GRB 250419A: Liverpool Telescope observations
  53. GRB 250419A: LCO optical observation
  54. GRB 250419A: JinShan optical observations
  55. GRB 250419A: SVOM/VT optical continuous observations
  56. GRB 250419A: SVOM/C-GFT optical observations
  57. GRB 250419A: Swift/UVOT Follow up
  58. GRB 250416C / EP250416a: SVOM/GRM observation of a burst
  59. GRB 250419A: LCO optical afterglow multi-band observations
  60. GRB 250419A: Mondy and AbAO Optical Observations
  61. GRB 250419A: Liverpool Telescope observations
  62. GRB 250419A: AKO Optical Afterglow Detection
  63. GRB 250419A: MASTER optical afterglow observation
  64. Fermi-LAT Gamma-ray Observations of IceCube-250416A
  65. GRB 250407A: rest-frame energetics from Konus-Wind observation
  66. GRB 250419A: Swift-XRT localisation
  67. GRB 250407A: GTC/OSIRIS+ spectroscopic redshift z = 1.36
  68. GRB 250419A: VLT/X-shooter spectroscopic redshift z = 0.845
  69. GRB 250419A: Swift-XRT refined Analysis
  70. GRB 250419A: GOTO optical counterpart detection
  71. GRB 250419A: KAIT optical afterglow observations
  72. GRB 250419A: SVOM/VT optical bright counterpart confirmation
  73. GRB 250419A: SVOM/COLIBRÍ (FM-GFT) Detection of the Optical Counterpart
  74. GRB 250419A: SVOM detection of a soft burst
  75. Konus-Wind detection of GRB 250416C (a counterpart of EP250416a)
  76. EP250416a: Swift/XRT counterpart fading
  77. EP250416a: refined EP-WXT and EP-FXT analysis
  78. Konus-Wind detection of GRB 250403A
  79. EP20250416a: Swift/XRT counterpart detection
  80. GRB 250403A: VLT/FORS2 spectroscopic redshift z = 1.847
  81. IceCube-250416A: DDOTI Optical Observations
  82. EP250416a: Gemini South-GMOS optical counterpart
  83. EP250225a: SVOM/VT optical brightening
  84. SVOM/sb25041603 is not a GRB
  85. EP250416a: GSP optical upper limit
  86. EP250416a: Global MASTER-Net observations report
  87. Fermi Gamma-ray Burst Monitor trigger 766505186/250416588 (GRB 250416A) is not a GRB
  88. EP250416a: Einstein Probe detection of an X-ray transient
  89. IceCube-250416A - IceCube observation of a high-energy neutrino candidate track-like event
  90. IceCube-250416A: Global MASTER-Net observations report
  91. Fermi Gamma-ray Burst Monitor trigger 766511207/250416657 is not a GRB
  92. GRB 250416B: Fermi GBM Final Real-time Localization
  93. GRB 250416A: Fermi GBM Final Real-time Localization
  94. SVOM/sb25041603: SVOM/COLIBRÍ (FM-GFT) Upper Limit on the Optical Counterpart
  95. SVOM/sb25041603: SVOM detection of an X-ray transient
  96. Fermi Gamma-ray Burst Monitor trigger 766474855/250416237 is not a GRB
  97. IceCube 250414.324: DDOTI Optical Observations
  98. GRB 250413A: AstroSat CZTI detection
  99. EP250304a: ATCA radio observations
  100. GRB 250412A: AstroSat CZTI detection

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