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

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