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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. EP250227a: Further NOT optical observations
  2. GRB 250320B: cubesat Avion detection
  3. IceCube-250406A: Swift-XRT observations
  4. IPN triangulation of GRB 250321D (consistent with the fast X-ray transient EP250321a)
  5. AMON Coincidence Alert from the sub-threshold IceCube-HAWC search NuEm-250409A
  6. IPN triangulation of GRB 250407A
  7. EP250407a: Global MASTER-Net observations report
  8. GRB 250407A: LCO detection of a fading optical counterpart
  9. Fermi-LAT gamma-ray observations of IceCube-250406A
  10. EP250407a: Swift-XRT observations
  11. IceCube-250406A: Upper limits from a search for additional neutrino events in IceCube
  12. Konus-Wind detection of GRB 250407A
  13. GRB 250407A: SVOM/GRM observation of a bright long burst
  14. GRB 250407A: EP-WXT afterglow detection
  15. EP250407a: EP-WXT detection of a fast X-ray transient
  16. GRB 250407A: COLIBRÍ/DDRAGO Detection of the Optical Counterpart
  17. GRB 250407A: KAIT Optical Afterglow Candidate
  18. IceCube-250406A: No candidates from the Zwicky Transient Facility
  19. GRB 250407A: Fermi GBM Detection
  20. GRB 250407A: Swift-XRT afterglow detection
  21. Fermi GRB 250407A: Global MASTER-Net observations report
  22. GRB 250407A: Swift ToO observations
  23. GRB 250407A: SRG/ART-XC afterglow detection
  24. LIGO/Virgo/KAGRA S250331o: Upper limits from Swift/BAT-GUANO
  25. IceCube 250406A: DDOTI Optical Observations of the Refined Position
  26. Konus-Wind detection of GRB 250406B (short/hard)
  27. IPN triangulation of GRB 250406B (short/hard)
  28. GRB 250407A: BALROG localization (Fermi Trigger 765733706 / GRB 250407659)
  29. GRB 250407A: Fermi GBM Final Real-time Localization
  30. IceCube-250406A - IceCube observation of a high-energy neutrino candidate track-like event
  31. IceCube 250406.951: COLIBRÍ/DDRAGO Optical Upper Limit
  32. IceCube 250406.951: DDOTI Optical Observations
  33. GRB 250406A: AstroSat CZTI detection
  34. IceCube Alert 250406.95: Global MASTER-Net observations report
  35. Fermi trigger No 765663719: Global MASTER-Net observations report
  36. EP250404a: Multi-band Optical Observations from UCAS-70 and XL-C14
  37. Fermi GRB 250406A: Global MASTER-Net observations report
  38. GRB 250404A: Calapai Observatory, Massa S. Giorgio (Messina), optical observations.
  39. GRB 250406A: Fermi GBM Final Real-time Localization
  40. EP250404a / GRB 250404A: Montarrenti Observatory optical observations
  41. Fermi trigger No 765619921: Global MASTER-Net observations report
  42. Fermi Gamma-ray Burst Monitor trigger 765619921/250406342 is not a GRB
  43. GRB 250404A / EP250404a: RC500 INASAN-Kislovodsk optical upper limit
  44. GRB 250404A / EP250404a: SVOM/GWAC-F60 and F50 observations
  45. EP250404a / GRB 250404A: J band observations by SYSU 80cm telescope
  46. Konus-Wind detection of GRB 250404A / EP250404a
  47. GRB 250404A / EP250404a: Mondy optical observations
  48. EP250404a: refined analysis of the EP-WXT and EP-FXT observations
  49. GRB 250404A / EP250404a: GMG spectroscopic redshift at z ~ 2.627
  50. GRB 250404A / EP250404a: Leavitt Observatory optical counterpart detection
  51. GRB 250402A: Calapai Observatory, Massa S. Giorgio (Messina), optical observations.
  52. EP250402a: Optical upper limit with PD 1.3m observations
  53. GRB 250404A / EP250404a: NOT optical observations
  54. GRB 250331D: Swift-XRT afterglow detection
  55. GRB 250404B: AstroSat CZTI detection of a short burst
  56. GRB 250403A: AstroSat CZTI detection
  57. EP250404a: Osservatorio Astronomico "Nastro Verde" optical observations: detection of an optical counterpart
  58. EP250404a: REM optical/NIR observations
  59. EP250404a: Seimei/TriCCS optical counterpart detection
  60. EP250404A: COLIBRÍ/DDRAGO Optical Observations
  61. EP250404A / GRB250404A: Ondrejov D50 optical afterglow detection
  62. EP250404a: LCO optical counterpart detection
  63. Fermi GRB 250404A: Global MASTER-Net observations report
  64. EP250404a: Xinglong decaying optical counterpart
  65. GRB 250403A: Montarrenti Observatory optical detection
  66. GRB 250404A: Fermi GBM Detection
  67. EP250404a: Global MASTER-Net observations report
  68. GRB 250403A: KAIT optical observations
  69. EP250404a: AKO Optical Afterglow Detection
  70. EP250404a: LAST detection of optical counterpart
  71. GRB 250402A: Swift/BAT-GUANO localization skymap of a burst
  72. EP250404a: Xinglong-2.16m spectroscopic redshift
  73. GRB 250403A: Fermi GBM observations
  74. GRB 250327B: VIRT Optical Upper Limit
  75. EP250404a: Mephisto multi-band optical detection
  76. GRB 250331C Swift-BAT refined analysis
  77. GRB 250331B Swift-BAT refined analysis
  78. GRB 250330A Swift-BAT refined analysis
  79. EP250321A: J band upper limit by SYSU 80cm telescope
  80. EP250404a: BOOTES-4/JGT optical afterglow detection
  81. EP250404a: Nanshan/HMT optical counterpart detection
  82. EP250404a: Einstein Probe detection of an X-ray transient
  83. GRB 250404A: Fermi GBM Final Real-time Localization
  84. GRB 250402A: Mondy optical observations
  85. GRB 250403A: Swift/UVOT Detection
  86. GRB 250402A: Swift/UVOT Upper Limits
  87. EP250402a: Optical upper limit with Kinder observations
  88. GRB 250403A: SVOM/VT optical observation
  89. GRB 250403A: REM NIR afterglow detection
  90. GRB 250403A: LCO optical counterpart detection
  91. IceCube-250330A: MASTER detection of PKS 2032+107 blazar flare with Zhirkov effect
  92. GRB 250403A: JinShan optical observations
  93. GRB 250402A: EP-FXT afterglow detection
  94. GRB 250403A: Optical counterpart detection by LCO.
  95. EP250402a: EP-FXT follow-up observations
  96. GRB 250403A: Swift-XRT observations
  97. GRB 250322A: 10 GHz VLA radio upper limits
  98. Fermi GRB 250403A: Global MASTER-Net observations report
  99. GRB 250403A: GOTO optical counterpart follow-up observations
  100. GRB 250402A: NUTTelA-TAO Early Optical Limits

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