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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 250419A: SVOM/VT optical bright counterpart confirmation
  2. GRB 250419A: SVOM/COLIBRÍ (FM-GFT) Detection of the Optical Counterpart
  3. GRB 250419A: SVOM detection of a soft burst
  4. Konus-Wind detection of GRB 250416C (a counterpart of EP250416a)
  5. EP250416a: Swift/XRT counterpart fading
  6. EP250416a: refined EP-WXT and EP-FXT analysis
  7. Konus-Wind detection of GRB 250403A
  8. EP20250416a: Swift/XRT counterpart detection
  9. GRB 250403A: VLT/FORS2 spectroscopic redshift z = 1.847
  10. IceCube-250416A: DDOTI Optical Observations
  11. EP250416a: Gemini South-GMOS optical counterpart
  12. EP250225a: SVOM/VT optical brightening
  13. SVOM/sb25041603 is not a GRB
  14. EP250416a: GSP optical upper limit
  15. EP250416a: Global MASTER-Net observations report
  16. Fermi Gamma-ray Burst Monitor trigger 766505186/250416588 (GRB 250416A) is not a GRB
  17. EP250416a: Einstein Probe detection of an X-ray transient
  18. IceCube-250416A - IceCube observation of a high-energy neutrino candidate track-like event
  19. IceCube-250416A: Global MASTER-Net observations report
  20. Fermi Gamma-ray Burst Monitor trigger 766511207/250416657 is not a GRB
  21. GRB 250416B: Fermi GBM Final Real-time Localization
  22. GRB 250416A: Fermi GBM Final Real-time Localization
  23. SVOM/sb25041603: SVOM/COLIBRÍ (FM-GFT) Upper Limit on the Optical Counterpart
  24. SVOM/sb25041603: SVOM detection of an X-ray transient
  25. Fermi Gamma-ray Burst Monitor trigger 766474855/250416237 is not a GRB
  26. IceCube 250414.324: DDOTI Optical Observations
  27. GRB 250413A: AstroSat CZTI detection
  28. EP250304a: ATCA radio observations
  29. GRB 250412A: AstroSat CZTI detection
  30. EP250404a: Nanshan 0.43m Telescope optical observatios
  31. Fermi trigger No 766148493: Global MASTER-Net observations report
  32. Fermi trigger No 766173972: Global MASTER-Net observations report
  33. GRB 250411A: DDOTI Optical Observations
  34. Fermi GRB 250411A: Global MASTER-Net observations report
  35. GRB 250411A: Fermi GBM Final Real-time Localization
  36. GRB 250407A: Continued KAIT/Nickel optical observations
  37. GRB 250314A: e-MERLIN observations
  38. GRB 250407A: Mondy and AbAO Optical Observations
  39. EP250227a: Further NOT optical observations
  40. GRB 250320B: cubesat Avion detection
  41. IceCube-250406A: Swift-XRT observations
  42. IPN triangulation of GRB 250321D (consistent with the fast X-ray transient EP250321a)
  43. AMON Coincidence Alert from the sub-threshold IceCube-HAWC search NuEm-250409A
  44. IPN triangulation of GRB 250407A
  45. EP250407a: Global MASTER-Net observations report
  46. GRB 250407A: LCO detection of a fading optical counterpart
  47. Fermi-LAT gamma-ray observations of IceCube-250406A
  48. EP250407a: Swift-XRT observations
  49. IceCube-250406A: Upper limits from a search for additional neutrino events in IceCube
  50. Konus-Wind detection of GRB 250407A
  51. GRB 250407A: SVOM/GRM observation of a bright long burst
  52. GRB 250407A: EP-WXT afterglow detection
  53. EP250407a: EP-WXT detection of a fast X-ray transient
  54. GRB 250407A: COLIBRÍ/DDRAGO Detection of the Optical Counterpart
  55. GRB 250407A: KAIT Optical Afterglow Candidate
  56. IceCube-250406A: No candidates from the Zwicky Transient Facility
  57. GRB 250407A: Fermi GBM Detection
  58. GRB 250407A: Swift-XRT afterglow detection
  59. Fermi GRB 250407A: Global MASTER-Net observations report
  60. GRB 250407A: Swift ToO observations
  61. GRB 250407A: SRG/ART-XC afterglow detection
  62. LIGO/Virgo/KAGRA S250331o: Upper limits from Swift/BAT-GUANO
  63. IceCube 250406A: DDOTI Optical Observations of the Refined Position
  64. Konus-Wind detection of GRB 250406B (short/hard)
  65. IPN triangulation of GRB 250406B (short/hard)
  66. GRB 250407A: BALROG localization (Fermi Trigger 765733706 / GRB 250407659)
  67. GRB 250407A: Fermi GBM Final Real-time Localization
  68. IceCube-250406A - IceCube observation of a high-energy neutrino candidate track-like event
  69. IceCube 250406.951: COLIBRÍ/DDRAGO Optical Upper Limit
  70. IceCube 250406.951: DDOTI Optical Observations
  71. GRB 250406A: AstroSat CZTI detection
  72. IceCube Alert 250406.95: Global MASTER-Net observations report
  73. Fermi trigger No 765663719: Global MASTER-Net observations report
  74. EP250404a: Multi-band Optical Observations from UCAS-70 and XL-C14
  75. Fermi GRB 250406A: Global MASTER-Net observations report
  76. GRB 250404A: Calapai Observatory, Massa S. Giorgio (Messina), optical observations.
  77. GRB 250406A: Fermi GBM Final Real-time Localization
  78. EP250404a / GRB 250404A: Montarrenti Observatory optical observations
  79. Fermi trigger No 765619921: Global MASTER-Net observations report
  80. Fermi Gamma-ray Burst Monitor trigger 765619921/250406342 is not a GRB
  81. GRB 250404A / EP250404a: RC500 INASAN-Kislovodsk optical upper limit
  82. GRB 250404A / EP250404a: SVOM/GWAC-F60 and F50 observations
  83. EP250404a / GRB 250404A: J band observations by SYSU 80cm telescope
  84. Konus-Wind detection of GRB 250404A / EP250404a
  85. GRB 250404A / EP250404a: Mondy optical observations
  86. EP250404a: refined analysis of the EP-WXT and EP-FXT observations
  87. GRB 250404A / EP250404a: GMG spectroscopic redshift at z ~ 2.627
  88. GRB 250404A / EP250404a: Leavitt Observatory optical counterpart detection
  89. GRB 250402A: Calapai Observatory, Massa S. Giorgio (Messina), optical observations.
  90. EP250402a: Optical upper limit with PD 1.3m observations
  91. GRB 250404A / EP250404a: NOT optical observations
  92. GRB 250331D: Swift-XRT afterglow detection
  93. GRB 250404B: AstroSat CZTI detection of a short burst
  94. GRB 250403A: AstroSat CZTI detection
  95. EP250404a: Osservatorio Astronomico "Nastro Verde" optical observations: detection of an optical counterpart
  96. EP250404a: REM optical/NIR observations
  97. EP250404a: Seimei/TriCCS optical counterpart detection
  98. EP250404A: COLIBRÍ/DDRAGO Optical Observations
  99. EP250404A / GRB250404A: Ondrejov D50 optical afterglow detection
  100. EP250404a: LCO optical counterpart detection

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