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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 250407A: KAIT Optical Afterglow Candidate
  2. IceCube-250406A: No candidates from the Zwicky Transient Facility
  3. GRB 250407A: Fermi GBM Detection
  4. GRB 250407A: Swift-XRT afterglow detection
  5. Fermi GRB 250407A: Global MASTER-Net observations report
  6. GRB 250407A: Swift ToO observations
  7. GRB 250407A: SRG/ART-XC afterglow detection
  8. LIGO/Virgo/KAGRA S250331o: Upper limits from Swift/BAT-GUANO
  9. IceCube 250406A: DDOTI Optical Observations of the Refined Position
  10. Konus-Wind detection of GRB 250406B (short/hard)
  11. IPN triangulation of GRB 250406B (short/hard)
  12. GRB 250407A: BALROG localization (Fermi Trigger 765733706 / GRB 250407659)
  13. GRB 250407A: Fermi GBM Final Real-time Localization
  14. IceCube-250406A - IceCube observation of a high-energy neutrino candidate track-like event
  15. IceCube 250406.951: COLIBRÍ/DDRAGO Optical Upper Limit
  16. IceCube 250406.951: DDOTI Optical Observations
  17. GRB 250406A: AstroSat CZTI detection
  18. IceCube Alert 250406.95: Global MASTER-Net observations report
  19. Fermi trigger No 765663719: Global MASTER-Net observations report
  20. EP250404a: Multi-band Optical Observations from UCAS-70 and XL-C14
  21. Fermi GRB 250406A: Global MASTER-Net observations report
  22. GRB 250404A: Calapai Observatory, Massa S. Giorgio (Messina), optical observations.
  23. GRB 250406A: Fermi GBM Final Real-time Localization
  24. EP250404a / GRB 250404A: Montarrenti Observatory optical observations
  25. Fermi trigger No 765619921: Global MASTER-Net observations report
  26. Fermi Gamma-ray Burst Monitor trigger 765619921/250406342 is not a GRB
  27. GRB 250404A / EP250404a: RC500 INASAN-Kislovodsk optical upper limit
  28. GRB 250404A / EP250404a: SVOM/GWAC-F60 and F50 observations
  29. EP250404a / GRB 250404A: J band observations by SYSU 80cm telescope
  30. Konus-Wind detection of GRB 250404A / EP250404a
  31. GRB 250404A / EP250404a: Mondy optical observations
  32. EP250404a: refined analysis of the EP-WXT and EP-FXT observations
  33. GRB 250404A / EP250404a: GMG spectroscopic redshift at z ~ 2.627
  34. GRB 250404A / EP250404a: Leavitt Observatory optical counterpart detection
  35. GRB 250402A: Calapai Observatory, Massa S. Giorgio (Messina), optical observations.
  36. EP250402a: Optical upper limit with PD 1.3m observations
  37. GRB 250404A / EP250404a: NOT optical observations
  38. GRB 250331D: Swift-XRT afterglow detection
  39. GRB 250404B: AstroSat CZTI detection of a short burst
  40. GRB 250403A: AstroSat CZTI detection
  41. EP250404a: Osservatorio Astronomico "Nastro Verde" optical observations: detection of an optical counterpart
  42. EP250404a: REM optical/NIR observations
  43. EP250404a: Seimei/TriCCS optical counterpart detection
  44. EP250404A: COLIBRÍ/DDRAGO Optical Observations
  45. EP250404A / GRB250404A: Ondrejov D50 optical afterglow detection
  46. EP250404a: LCO optical counterpart detection
  47. Fermi GRB 250404A: Global MASTER-Net observations report
  48. EP250404a: Xinglong decaying optical counterpart
  49. GRB 250403A: Montarrenti Observatory optical detection
  50. GRB 250404A: Fermi GBM Detection
  51. EP250404a: Global MASTER-Net observations report
  52. GRB 250403A: KAIT optical observations
  53. EP250404a: AKO Optical Afterglow Detection
  54. EP250404a: LAST detection of optical counterpart
  55. GRB 250402A: Swift/BAT-GUANO localization skymap of a burst
  56. EP250404a: Xinglong-2.16m spectroscopic redshift
  57. GRB 250403A: Fermi GBM observations
  58. GRB 250327B: VIRT Optical Upper Limit
  59. EP250404a: Mephisto multi-band optical detection
  60. GRB 250331C Swift-BAT refined analysis
  61. GRB 250331B Swift-BAT refined analysis
  62. GRB 250330A Swift-BAT refined analysis
  63. EP250321A: J band upper limit by SYSU 80cm telescope
  64. EP250404a: BOOTES-4/JGT optical afterglow detection
  65. EP250404a: Nanshan/HMT optical counterpart detection
  66. EP250404a: Einstein Probe detection of an X-ray transient
  67. GRB 250404A: Fermi GBM Final Real-time Localization
  68. GRB 250402A: Mondy optical observations
  69. GRB 250403A: Swift/UVOT Detection
  70. GRB 250402A: Swift/UVOT Upper Limits
  71. EP250402a: Optical upper limit with Kinder observations
  72. GRB 250403A: SVOM/VT optical observation
  73. GRB 250403A: REM NIR afterglow detection
  74. GRB 250403A: LCO optical counterpart detection
  75. IceCube-250330A: MASTER detection of PKS 2032+107 blazar flare with Zhirkov effect
  76. GRB 250403A: JinShan optical observations
  77. GRB 250402A: EP-FXT afterglow detection
  78. GRB 250403A: Optical counterpart detection by LCO.
  79. EP250402a: EP-FXT follow-up observations
  80. GRB 250403A: Swift-XRT observations
  81. GRB 250322A: 10 GHz VLA radio upper limits
  82. Fermi GRB 250403A: Global MASTER-Net observations report
  83. GRB 250403A: GOTO optical counterpart follow-up observations
  84. GRB 250402A: NUTTelA-TAO Early Optical Limits
  85. GRB 250403A: GMG Optical Observation
  86. GRB 250403A: 1.6m Mephisto multi-band optical detection
  87. GRB 250402A: Fermi GBM Observation
  88. GRB 250403A: SVOM/C-GFT optical observations
  89. GRB 250403A: GOTO detection of the optical afterglow
  90. GRB 250402A: Swift-XRT observations
  91. GRB 250403A : SVOM detection of a burst
  92. GRB 250403A: Fermi GBM Final Real-time Localization
  93. GRB 250225B: VLT host galaxy redshift z = 0.950
  94. GRB250402A: SVOM/COLIBRÍ (FM-GFT) Detection of the Optical Counterpart
  95. GRB 250402A: VLT/FORS2 spectroscopic redshift z = 2.823
  96. GRB 250402A: REM optical/NIR upper limits
  97. GRB 250402A: LCO optical counterpart detection
  98. GRB 250402A: refined SVOM/MXT data analysis
  99. The EP-WXT trigger 01709133862 is a flaring star
  100. EP250402a: Einstein Probe detection of a fast X-ray transient

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