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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. Fermi trigger No 766173972: Global MASTER-Net observations report
  2. GRB 250411A: DDOTI Optical Observations
  3. Fermi GRB 250411A: Global MASTER-Net observations report
  4. GRB 250411A: Fermi GBM Final Real-time Localization
  5. GRB 250407A: Continued KAIT/Nickel optical observations
  6. GRB 250314A: e-MERLIN observations
  7. GRB 250407A: Mondy and AbAO Optical Observations
  8. EP250227a: Further NOT optical observations
  9. GRB 250320B: cubesat Avion detection
  10. IceCube-250406A: Swift-XRT observations
  11. IPN triangulation of GRB 250321D (consistent with the fast X-ray transient EP250321a)
  12. AMON Coincidence Alert from the sub-threshold IceCube-HAWC search NuEm-250409A
  13. IPN triangulation of GRB 250407A
  14. EP250407a: Global MASTER-Net observations report
  15. GRB 250407A: LCO detection of a fading optical counterpart
  16. Fermi-LAT gamma-ray observations of IceCube-250406A
  17. EP250407a: Swift-XRT observations
  18. IceCube-250406A: Upper limits from a search for additional neutrino events in IceCube
  19. Konus-Wind detection of GRB 250407A
  20. GRB 250407A: SVOM/GRM observation of a bright long burst
  21. GRB 250407A: EP-WXT afterglow detection
  22. EP250407a: EP-WXT detection of a fast X-ray transient
  23. GRB 250407A: COLIBRÍ/DDRAGO Detection of the Optical Counterpart
  24. GRB 250407A: KAIT Optical Afterglow Candidate
  25. IceCube-250406A: No candidates from the Zwicky Transient Facility
  26. GRB 250407A: Fermi GBM Detection
  27. GRB 250407A: Swift-XRT afterglow detection
  28. Fermi GRB 250407A: Global MASTER-Net observations report
  29. GRB 250407A: Swift ToO observations
  30. GRB 250407A: SRG/ART-XC afterglow detection
  31. LIGO/Virgo/KAGRA S250331o: Upper limits from Swift/BAT-GUANO
  32. IceCube 250406A: DDOTI Optical Observations of the Refined Position
  33. Konus-Wind detection of GRB 250406B (short/hard)
  34. IPN triangulation of GRB 250406B (short/hard)
  35. GRB 250407A: BALROG localization (Fermi Trigger 765733706 / GRB 250407659)
  36. GRB 250407A: Fermi GBM Final Real-time Localization
  37. IceCube-250406A - IceCube observation of a high-energy neutrino candidate track-like event
  38. IceCube 250406.951: COLIBRÍ/DDRAGO Optical Upper Limit
  39. IceCube 250406.951: DDOTI Optical Observations
  40. GRB 250406A: AstroSat CZTI detection
  41. IceCube Alert 250406.95: Global MASTER-Net observations report
  42. Fermi trigger No 765663719: Global MASTER-Net observations report
  43. EP250404a: Multi-band Optical Observations from UCAS-70 and XL-C14
  44. Fermi GRB 250406A: Global MASTER-Net observations report
  45. GRB 250404A: Calapai Observatory, Massa S. Giorgio (Messina), optical observations.
  46. GRB 250406A: Fermi GBM Final Real-time Localization
  47. EP250404a / GRB 250404A: Montarrenti Observatory optical observations
  48. Fermi trigger No 765619921: Global MASTER-Net observations report
  49. Fermi Gamma-ray Burst Monitor trigger 765619921/250406342 is not a GRB
  50. GRB 250404A / EP250404a: RC500 INASAN-Kislovodsk optical upper limit
  51. GRB 250404A / EP250404a: SVOM/GWAC-F60 and F50 observations
  52. EP250404a / GRB 250404A: J band observations by SYSU 80cm telescope
  53. Konus-Wind detection of GRB 250404A / EP250404a
  54. GRB 250404A / EP250404a: Mondy optical observations
  55. EP250404a: refined analysis of the EP-WXT and EP-FXT observations
  56. GRB 250404A / EP250404a: GMG spectroscopic redshift at z ~ 2.627
  57. GRB 250404A / EP250404a: Leavitt Observatory optical counterpart detection
  58. GRB 250402A: Calapai Observatory, Massa S. Giorgio (Messina), optical observations.
  59. EP250402a: Optical upper limit with PD 1.3m observations
  60. GRB 250404A / EP250404a: NOT optical observations
  61. GRB 250331D: Swift-XRT afterglow detection
  62. GRB 250404B: AstroSat CZTI detection of a short burst
  63. GRB 250403A: AstroSat CZTI detection
  64. EP250404a: Osservatorio Astronomico "Nastro Verde" optical observations: detection of an optical counterpart
  65. EP250404a: REM optical/NIR observations
  66. EP250404a: Seimei/TriCCS optical counterpart detection
  67. EP250404A: COLIBRÍ/DDRAGO Optical Observations
  68. EP250404A / GRB250404A: Ondrejov D50 optical afterglow detection
  69. EP250404a: LCO optical counterpart detection
  70. Fermi GRB 250404A: Global MASTER-Net observations report
  71. EP250404a: Xinglong decaying optical counterpart
  72. GRB 250403A: Montarrenti Observatory optical detection
  73. GRB 250404A: Fermi GBM Detection
  74. EP250404a: Global MASTER-Net observations report
  75. GRB 250403A: KAIT optical observations
  76. EP250404a: AKO Optical Afterglow Detection
  77. EP250404a: LAST detection of optical counterpart
  78. GRB 250402A: Swift/BAT-GUANO localization skymap of a burst
  79. EP250404a: Xinglong-2.16m spectroscopic redshift
  80. GRB 250403A: Fermi GBM observations
  81. GRB 250327B: VIRT Optical Upper Limit
  82. EP250404a: Mephisto multi-band optical detection
  83. GRB 250331C Swift-BAT refined analysis
  84. GRB 250331B Swift-BAT refined analysis
  85. GRB 250330A Swift-BAT refined analysis
  86. EP250321A: J band upper limit by SYSU 80cm telescope
  87. EP250404a: BOOTES-4/JGT optical afterglow detection
  88. EP250404a: Nanshan/HMT optical counterpart detection
  89. EP250404a: Einstein Probe detection of an X-ray transient
  90. GRB 250404A: Fermi GBM Final Real-time Localization
  91. GRB 250402A: Mondy optical observations
  92. GRB 250403A: Swift/UVOT Detection
  93. GRB 250402A: Swift/UVOT Upper Limits
  94. EP250402a: Optical upper limit with Kinder observations
  95. GRB 250403A: SVOM/VT optical observation
  96. GRB 250403A: REM NIR afterglow detection
  97. GRB 250403A: LCO optical counterpart detection
  98. IceCube-250330A: MASTER detection of PKS 2032+107 blazar flare with Zhirkov effect
  99. GRB 250403A: JinShan optical observations
  100. GRB 250402A: EP-FXT afterglow detection

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