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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: Swift ToO observations
  2. GRB 250407A: SRG/ART-XC afterglow detection
  3. LIGO/Virgo/KAGRA S250331o: Upper limits from Swift/BAT-GUANO
  4. IceCube 250406A: DDOTI Optical Observations of the Refined Position
  5. Konus-Wind detection of GRB 250406B (short/hard)
  6. IPN triangulation of GRB 250406B (short/hard)
  7. GRB 250407A: BALROG localization (Fermi Trigger 765733706 / GRB 250407659)
  8. GRB 250407A: Fermi GBM Final Real-time Localization
  9. IceCube-250406A - IceCube observation of a high-energy neutrino candidate track-like event
  10. IceCube 250406.951: COLIBRÍ/DDRAGO Optical Upper Limit
  11. IceCube 250406.951: DDOTI Optical Observations
  12. GRB 250406A: AstroSat CZTI detection
  13. IceCube Alert 250406.95: Global MASTER-Net observations report
  14. Fermi trigger No 765663719: Global MASTER-Net observations report
  15. EP250404a: Multi-band Optical Observations from UCAS-70 and XL-C14
  16. Fermi GRB 250406A: Global MASTER-Net observations report
  17. GRB 250404A: Calapai Observatory, Massa S. Giorgio (Messina), optical observations.
  18. GRB 250406A: Fermi GBM Final Real-time Localization
  19. EP250404a / GRB 250404A: Montarrenti Observatory optical observations
  20. Fermi trigger No 765619921: Global MASTER-Net observations report
  21. Fermi Gamma-ray Burst Monitor trigger 765619921/250406342 is not a GRB
  22. GRB 250404A / EP250404a: RC500 INASAN-Kislovodsk optical upper limit
  23. GRB 250404A / EP250404a: SVOM/GWAC-F60 and F50 observations
  24. EP250404a / GRB 250404A: J band observations by SYSU 80cm telescope
  25. Konus-Wind detection of GRB 250404A / EP250404a
  26. GRB 250404A / EP250404a: Mondy optical observations
  27. EP250404a: refined analysis of the EP-WXT and EP-FXT observations
  28. GRB 250404A / EP250404a: GMG spectroscopic redshift at z ~ 2.627
  29. GRB 250404A / EP250404a: Leavitt Observatory optical counterpart detection
  30. GRB 250402A: Calapai Observatory, Massa S. Giorgio (Messina), optical observations.
  31. EP250402a: Optical upper limit with PD 1.3m observations
  32. GRB 250404A / EP250404a: NOT optical observations
  33. GRB 250331D: Swift-XRT afterglow detection
  34. GRB 250404B: AstroSat CZTI detection of a short burst
  35. GRB 250403A: AstroSat CZTI detection
  36. EP250404a: Osservatorio Astronomico "Nastro Verde" optical observations: detection of an optical counterpart
  37. EP250404a: REM optical/NIR observations
  38. EP250404a: Seimei/TriCCS optical counterpart detection
  39. EP250404A: COLIBRÍ/DDRAGO Optical Observations
  40. EP250404A / GRB250404A: Ondrejov D50 optical afterglow detection
  41. EP250404a: LCO optical counterpart detection
  42. Fermi GRB 250404A: Global MASTER-Net observations report
  43. EP250404a: Xinglong decaying optical counterpart
  44. GRB 250403A: Montarrenti Observatory optical detection
  45. GRB 250404A: Fermi GBM Detection
  46. EP250404a: Global MASTER-Net observations report
  47. GRB 250403A: KAIT optical observations
  48. EP250404a: AKO Optical Afterglow Detection
  49. EP250404a: LAST detection of optical counterpart
  50. GRB 250402A: Swift/BAT-GUANO localization skymap of a burst
  51. EP250404a: Xinglong-2.16m spectroscopic redshift
  52. GRB 250403A: Fermi GBM observations
  53. GRB 250327B: VIRT Optical Upper Limit
  54. EP250404a: Mephisto multi-band optical detection
  55. GRB 250331C Swift-BAT refined analysis
  56. GRB 250331B Swift-BAT refined analysis
  57. GRB 250330A Swift-BAT refined analysis
  58. EP250321A: J band upper limit by SYSU 80cm telescope
  59. EP250404a: BOOTES-4/JGT optical afterglow detection
  60. EP250404a: Nanshan/HMT optical counterpart detection
  61. EP250404a: Einstein Probe detection of an X-ray transient
  62. GRB 250404A: Fermi GBM Final Real-time Localization
  63. GRB 250402A: Mondy optical observations
  64. GRB 250403A: Swift/UVOT Detection
  65. GRB 250402A: Swift/UVOT Upper Limits
  66. EP250402a: Optical upper limit with Kinder observations
  67. GRB 250403A: SVOM/VT optical observation
  68. GRB 250403A: REM NIR afterglow detection
  69. GRB 250403A: LCO optical counterpart detection
  70. IceCube-250330A: MASTER detection of PKS 2032+107 blazar flare with Zhirkov effect
  71. GRB 250403A: JinShan optical observations
  72. GRB 250402A: EP-FXT afterglow detection
  73. GRB 250403A: Optical counterpart detection by LCO.
  74. EP250402a: EP-FXT follow-up observations
  75. GRB 250403A: Swift-XRT observations
  76. GRB 250322A: 10 GHz VLA radio upper limits
  77. Fermi GRB 250403A: Global MASTER-Net observations report
  78. GRB 250403A: GOTO optical counterpart follow-up observations
  79. GRB 250402A: NUTTelA-TAO Early Optical Limits
  80. GRB 250403A: GMG Optical Observation
  81. GRB 250403A: 1.6m Mephisto multi-band optical detection
  82. GRB 250402A: Fermi GBM Observation
  83. GRB 250403A: SVOM/C-GFT optical observations
  84. GRB 250403A: GOTO detection of the optical afterglow
  85. GRB 250402A: Swift-XRT observations
  86. GRB 250403A : SVOM detection of a burst
  87. GRB 250403A: Fermi GBM Final Real-time Localization
  88. GRB 250225B: VLT host galaxy redshift z = 0.950
  89. GRB250402A: SVOM/COLIBRÍ (FM-GFT) Detection of the Optical Counterpart
  90. GRB 250402A: VLT/FORS2 spectroscopic redshift z = 2.823
  91. GRB 250402A: REM optical/NIR upper limits
  92. GRB 250402A: LCO optical counterpart detection
  93. GRB 250402A: refined SVOM/MXT data analysis
  94. The EP-WXT trigger 01709133862 is a flaring star
  95. EP250402a: Einstein Probe detection of a fast X-ray transient
  96. GRB 250402B: AstroSat CZTI detection of a short burst
  97. GRB 250402A: SVOM/VT optical counterpart
  98. GRB 250402A: SVOM detection of a burst
  99. GRB 250331C: Calapai Observatory, Massa S. Giorgio (Messina), upper limit
  100. GRB 250314A: ALMA detection

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