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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: likely host galaxy
  2. GRB 250424A: DDOTI Afterglow Detection
  3. GRB 250424A: REM optical/NIR afterglow detection
  4. GRB 250424A: Swift detection of a burst with an optical counterpart
  5. Swift GRB 250424A: Global MASTER-Net observations report
  6. Swift GRB 250424A: Global MASTER-Net OT detection
  7. LIGO/Virgo/KAGRA S250328ae: Subaru/PFS Spectroscopic Follow up and Candidates
  8. EP250421a: Nickel optical upper limit
  9. EP250416a / GRB 250416C: Gemini GMOS-S likely host galaxy redshift z = 0.963
  10. EP250421a: Upper limits from Fermi-GBM Observations
  11. SVOM/sb25042207: XRT observations
  12. SVOM/sb25042207: BOOTES-2 early optical upper limit
  13. SVOM/sb25042207: GOTO optical upper limits
  14. GRB 250421A: AstroSat CZTI detection
  15. SVOM/sb25042207: SVOM detection of an X-ray transient
  16. GRB250419A: VLA radio detection
  17. IceCube-250421A: DDOTI Detection of the LAST Candidate
  18. GRB 250419A: Mephisto Multi-band Optical Detection
  19. GRB 250419A: Calapai Observatory, Massa S. Giorgio (Messina), optical observations.
  20. IC-250421A: LAST optical observations of the IceCube neutrino candidate
  21. EP250421a: NOT optical observations
  22. GRB 250419A: Optical Observations via Virtual Telescope Project
  23. EP250421a: REM optical upper limit
  24. EP250421a: Swift/XRT counterpart detection
  25. EP250421A: COLIBRÍ Optical Upper Limit
  26. GRB 250419A: Mondy Continued Optical Observations
  27. Fermi GRB 250421A: Global MASTER-Net observations report
  28. EP250421a: Global MASTER-Net observations report
  29. GRB 250421B: AstroSat CZTI detection of a bright long burst
  30. EP250421a: Einstein Probe detection of an X-ray transient
  31. EP250421a: Mephisto optical counterpart confirmation
  32. IceCube Alert 250421.71: Global MASTER-Net observations report
  33. IceCube-250421A - IceCube observation of a high-energy neutrino candidate track-like event
  34. IceCube-Cascade 250414A: Upper limits from a search for additional neutrino events in IceCube
  35. EP250421a: JinShan likely optical counterpart
  36. The EP-WXT trigger 01709135179: Kinder optical counterpart candidate
  37. GRB 250421A: Fermi GBM Final Real-time Localization
  38. GRB 250419A: Liverpool Telescope observations
  39. GRB 250419A: LCO optical observation
  40. GRB 250419A: JinShan optical observations
  41. GRB 250419A: SVOM/VT optical continuous observations
  42. GRB 250419A: SVOM/C-GFT optical observations
  43. GRB 250419A: Swift/UVOT Follow up
  44. GRB 250416C / EP250416a: SVOM/GRM observation of a burst
  45. GRB 250419A: LCO optical afterglow multi-band observations
  46. GRB 250419A: Mondy and AbAO Optical Observations
  47. GRB 250419A: Liverpool Telescope observations
  48. GRB 250419A: AKO Optical Afterglow Detection
  49. GRB 250419A: MASTER optical afterglow observation
  50. Fermi-LAT Gamma-ray Observations of IceCube-250416A
  51. GRB 250407A: rest-frame energetics from Konus-Wind observation
  52. GRB 250419A: Swift-XRT localisation
  53. GRB 250407A: GTC/OSIRIS+ spectroscopic redshift z = 1.36
  54. GRB 250419A: VLT/X-shooter spectroscopic redshift z = 0.845
  55. GRB 250419A: Swift-XRT refined Analysis
  56. GRB 250419A: GOTO optical counterpart detection
  57. GRB 250419A: KAIT optical afterglow observations
  58. GRB 250419A: SVOM/VT optical bright counterpart confirmation
  59. GRB 250419A: SVOM/COLIBRÍ (FM-GFT) Detection of the Optical Counterpart
  60. GRB 250419A: SVOM detection of a soft burst
  61. Konus-Wind detection of GRB 250416C (a counterpart of EP250416a)
  62. EP250416a: Swift/XRT counterpart fading
  63. EP250416a: refined EP-WXT and EP-FXT analysis
  64. Konus-Wind detection of GRB 250403A
  65. EP20250416a: Swift/XRT counterpart detection
  66. GRB 250403A: VLT/FORS2 spectroscopic redshift z = 1.847
  67. IceCube-250416A: DDOTI Optical Observations
  68. EP250416a: Gemini South-GMOS optical counterpart
  69. EP250225a: SVOM/VT optical brightening
  70. SVOM/sb25041603 is not a GRB
  71. EP250416a: GSP optical upper limit
  72. EP250416a: Global MASTER-Net observations report
  73. Fermi Gamma-ray Burst Monitor trigger 766505186/250416588 (GRB 250416A) is not a GRB
  74. EP250416a: Einstein Probe detection of an X-ray transient
  75. IceCube-250416A - IceCube observation of a high-energy neutrino candidate track-like event
  76. IceCube-250416A: Global MASTER-Net observations report
  77. Fermi Gamma-ray Burst Monitor trigger 766511207/250416657 is not a GRB
  78. GRB 250416B: Fermi GBM Final Real-time Localization
  79. GRB 250416A: Fermi GBM Final Real-time Localization
  80. SVOM/sb25041603: SVOM/COLIBRÍ (FM-GFT) Upper Limit on the Optical Counterpart
  81. SVOM/sb25041603: SVOM detection of an X-ray transient
  82. Fermi Gamma-ray Burst Monitor trigger 766474855/250416237 is not a GRB
  83. IceCube 250414.324: DDOTI Optical Observations
  84. GRB 250413A: AstroSat CZTI detection
  85. EP250304a: ATCA radio observations
  86. GRB 250412A: AstroSat CZTI detection
  87. EP250404a: Nanshan 0.43m Telescope optical observatios
  88. Fermi trigger No 766148493: Global MASTER-Net observations report
  89. Fermi trigger No 766173972: Global MASTER-Net observations report
  90. GRB 250411A: DDOTI Optical Observations
  91. Fermi GRB 250411A: Global MASTER-Net observations report
  92. GRB 250411A: Fermi GBM Final Real-time Localization
  93. GRB 250407A: Continued KAIT/Nickel optical observations
  94. GRB 250314A: e-MERLIN observations
  95. GRB 250407A: Mondy and AbAO Optical Observations
  96. EP250227a: Further NOT optical observations
  97. GRB 250320B: cubesat Avion detection
  98. IceCube-250406A: Swift-XRT observations
  99. IPN triangulation of GRB 250321D (consistent with the fast X-ray transient EP250321a)
  100. AMON Coincidence Alert from the sub-threshold IceCube-HAWC search NuEm-250409A

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