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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: AstroSat CZTI detection of a bright long burst
  2. GRB 250424A: COLIBRÍ Detection of a Bright Optical Counterpart
  3. GRB 250424A: BlackGEM optical afterglow detection
  4. GRB 250424A: VLT/X-shooter spectroscopic redshift z = 0.310
  5. GRB 250424A: likely host galaxy
  6. GRB 250424A: DDOTI Afterglow Detection
  7. GRB 250424A: REM optical/NIR afterglow detection
  8. GRB 250424A: Swift detection of a burst with an optical counterpart
  9. Swift GRB250424A: Global MASTER-Net observations report
  10. Swift GRB250424A: Global MASTER-Net OT detection
  11. LIGO/Virgo/KAGRA S250328ae: Subaru/PFS Spectroscopic Follow up and Candidates
  12. EP250421a: Nickel optical upper limit
  13. EP250416a / GRB 250416C: Gemini GMOS-S likely host galaxy redshift z = 0.963
  14. EP250421a: Upper limits from Fermi-GBM Observations
  15. SVOM/sb25042207: XRT observations
  16. SVOM/sb25042207: BOOTES-2 early optical upper limit
  17. SVOM/sb25042207: GOTO optical upper limits
  18. GRB 250421A: AstroSat CZTI detection
  19. SVOM/sb25042207: SVOM detection of an X-ray transient
  20. GRB250419A: VLA radio detection
  21. IceCube-250421A: DDOTI Detection of the LAST Candidate
  22. GRB 250419A: Mephisto Multi-band Optical Detection
  23. GRB 250419A: Calapai Observatory, Massa S. Giorgio (Messina), optical observations.
  24. IC-250421A: LAST optical observations of the IceCube neutrino candidate
  25. EP250421a: NOT optical observations
  26. GRB 250419A: Optical Observations via Virtual Telescope Project
  27. EP250421a: REM optical upper limit
  28. EP250421a: Swift/XRT counterpart detection
  29. EP250421A: COLIBRÍ Optical Upper Limit
  30. GRB 250419A: Mondy Continued Optical Observations
  31. Fermi GRB 250421A: Global MASTER-Net observations report
  32. EP250421a: Global MASTER-Net observations report
  33. GRB 250421B: AstroSat CZTI detection of a bright long burst
  34. EP250421a: Einstein Probe detection of an X-ray transient
  35. EP250421a: Mephisto optical counterpart confirmation
  36. IceCube Alert 250421.71: Global MASTER-Net observations report
  37. IceCube-250421A - IceCube observation of a high-energy neutrino candidate track-like event
  38. IceCube-Cascade 250414A: Upper limits from a search for additional neutrino events in IceCube
  39. EP250421a: JinShan likely optical counterpart
  40. The EP-WXT trigger 01709135179: Kinder optical counterpart candidate
  41. GRB 250421A: Fermi GBM Final Real-time Localization
  42. GRB 250419A: Liverpool Telescope observations
  43. GRB 250419A: LCO optical observation
  44. GRB 250419A: JinShan optical observations
  45. GRB 250419A: SVOM/VT optical continuous observations
  46. GRB 250419A: SVOM/C-GFT optical observations
  47. GRB 250419A: Swift/UVOT Follow up
  48. GRB 250416C / EP250416a: SVOM/GRM observation of a burst
  49. GRB 250419A: LCO optical afterglow multi-band observations
  50. GRB 250419A: Mondy and AbAO Optical Observations
  51. GRB 250419A: Liverpool Telescope observations
  52. GRB 250419A: AKO Optical Afterglow Detection
  53. GRB 250419A: MASTER optical afterglow observation
  54. Fermi-LAT Gamma-ray Observations of IceCube-250416A
  55. GRB 250407A: rest-frame energetics from Konus-Wind observation
  56. GRB 250419A: Swift-XRT localisation
  57. GRB 250407A: GTC/OSIRIS+ spectroscopic redshift z = 1.36
  58. GRB 250419A: VLT/X-shooter spectroscopic redshift z = 0.845
  59. GRB 250419A: Swift-XRT refined Analysis
  60. GRB 250419A: GOTO optical counterpart detection
  61. GRB 250419A: KAIT optical afterglow observations
  62. GRB 250419A: SVOM/VT optical bright counterpart confirmation
  63. GRB 250419A: SVOM/COLIBRÍ (FM-GFT) Detection of the Optical Counterpart
  64. GRB 250419A: SVOM detection of a soft burst
  65. Konus-Wind detection of GRB 250416C (a counterpart of EP250416a)
  66. EP250416a: Swift/XRT counterpart fading
  67. EP250416a: refined EP-WXT and EP-FXT analysis
  68. Konus-Wind detection of GRB 250403A
  69. EP20250416a: Swift/XRT counterpart detection
  70. GRB 250403A: VLT/FORS2 spectroscopic redshift z = 1.847
  71. IceCube-250416A: DDOTI Optical Observations
  72. EP250416a: Gemini South-GMOS optical counterpart
  73. EP250225a: SVOM/VT optical brightening
  74. SVOM/sb25041603 is not a GRB
  75. EP250416a: GSP optical upper limit
  76. EP250416a: Global MASTER-Net observations report
  77. Fermi Gamma-ray Burst Monitor trigger 766505186/250416588 (GRB 250416A) is not a GRB
  78. EP250416a: Einstein Probe detection of an X-ray transient
  79. IceCube-250416A - IceCube observation of a high-energy neutrino candidate track-like event
  80. IceCube-250416A: Global MASTER-Net observations report
  81. Fermi Gamma-ray Burst Monitor trigger 766511207/250416657 is not a GRB
  82. GRB 250416B: Fermi GBM Final Real-time Localization
  83. GRB 250416A: Fermi GBM Final Real-time Localization
  84. SVOM/sb25041603: SVOM/COLIBRÍ (FM-GFT) Upper Limit on the Optical Counterpart
  85. SVOM/sb25041603: SVOM detection of an X-ray transient
  86. Fermi Gamma-ray Burst Monitor trigger 766474855/250416237 is not a GRB
  87. IceCube 250414.324: DDOTI Optical Observations
  88. GRB 250413A: AstroSat CZTI detection
  89. EP250304a: ATCA radio observations
  90. GRB 250412A: AstroSat CZTI detection
  91. EP250404a: Nanshan 0.43m Telescope optical observatios
  92. Fermi trigger No 766148493: Global MASTER-Net observations report
  93. Fermi trigger No 766173972: Global MASTER-Net observations report
  94. GRB 250411A: DDOTI Optical Observations
  95. Fermi GRB 250411A: Global MASTER-Net observations report
  96. GRB 250411A: Fermi GBM Final Real-time Localization
  97. GRB 250407A: Continued KAIT/Nickel optical observations
  98. GRB 250314A: e-MERLIN observations
  99. GRB 250407A: Mondy and AbAO Optical Observations
  100. EP250227a: Further NOT optical observations

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