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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 250416C / EP250416a: SVOM/GRM observation of a burst
  2. GRB 250419A: LCO optical afterglow multi-band observations
  3. GRB 250419A: Mondy and AbAO Optical Observations
  4. GRB 250419A: Liverpool Telescope observations
  5. GRB 250419A: AKO Optical Afterglow Detection
  6. GRB 250419A: MASTER optical afterglow observation
  7. Fermi-LAT Gamma-ray Observations of IceCube-250416A
  8. GRB 250407A: rest-frame energetics from Konus-Wind observation
  9. GRB 250419A: Swift-XRT localisation
  10. GRB 250407A: GTC/OSIRIS+ spectroscopic redshift z = 1.36
  11. GRB 250419A: VLT/X-shooter spectroscopic redshift z = 0.845
  12. GRB 250419A: Swift-XRT refined Analysis
  13. GRB 250419A: GOTO optical counterpart detection
  14. GRB 250419A: KAIT optical afterglow observations
  15. GRB 250419A: SVOM/VT optical bright counterpart confirmation
  16. GRB 250419A: SVOM/COLIBRÍ (FM-GFT) Detection of the Optical Counterpart
  17. GRB 250419A: SVOM detection of a soft burst
  18. Konus-Wind detection of GRB 250416C (a counterpart of EP250416a)
  19. EP250416a: Swift/XRT counterpart fading
  20. EP250416a: refined EP-WXT and EP-FXT analysis
  21. Konus-Wind detection of GRB 250403A
  22. EP20250416a: Swift/XRT counterpart detection
  23. GRB 250403A: VLT/FORS2 spectroscopic redshift z = 1.847
  24. IceCube-250416A: DDOTI Optical Observations
  25. EP250416a: Gemini South-GMOS optical counterpart
  26. EP250225a: SVOM/VT optical brightening
  27. SVOM/sb25041603 is not a GRB
  28. EP250416a: GSP optical upper limit
  29. EP250416a: Global MASTER-Net observations report
  30. Fermi Gamma-ray Burst Monitor trigger 766505186/250416588 (GRB 250416A) is not a GRB
  31. EP250416a: Einstein Probe detection of an X-ray transient
  32. IceCube-250416A - IceCube observation of a high-energy neutrino candidate track-like event
  33. IceCube-250416A: Global MASTER-Net observations report
  34. Fermi Gamma-ray Burst Monitor trigger 766511207/250416657 is not a GRB
  35. GRB 250416B: Fermi GBM Final Real-time Localization
  36. GRB 250416A: Fermi GBM Final Real-time Localization
  37. SVOM/sb25041603: SVOM/COLIBRÍ (FM-GFT) Upper Limit on the Optical Counterpart
  38. SVOM/sb25041603: SVOM detection of an X-ray transient
  39. Fermi Gamma-ray Burst Monitor trigger 766474855/250416237 is not a GRB
  40. IceCube 250414.324: DDOTI Optical Observations
  41. GRB 250413A: AstroSat CZTI detection
  42. EP250304a: ATCA radio observations
  43. GRB 250412A: AstroSat CZTI detection
  44. EP250404a: Nanshan 0.43m Telescope optical observatios
  45. Fermi trigger No 766148493: Global MASTER-Net observations report
  46. Fermi trigger No 766173972: Global MASTER-Net observations report
  47. GRB 250411A: DDOTI Optical Observations
  48. Fermi GRB 250411A: Global MASTER-Net observations report
  49. GRB 250411A: Fermi GBM Final Real-time Localization
  50. GRB 250407A: Continued KAIT/Nickel optical observations
  51. GRB 250314A: e-MERLIN observations
  52. GRB 250407A: Mondy and AbAO Optical Observations
  53. EP250227a: Further NOT optical observations
  54. GRB 250320B: cubesat Avion detection
  55. IceCube-250406A: Swift-XRT observations
  56. IPN triangulation of GRB 250321D (consistent with the fast X-ray transient EP250321a)
  57. AMON Coincidence Alert from the sub-threshold IceCube-HAWC search NuEm-250409A
  58. IPN triangulation of GRB 250407A
  59. EP250407a: Global MASTER-Net observations report
  60. GRB 250407A: LCO detection of a fading optical counterpart
  61. Fermi-LAT gamma-ray observations of IceCube-250406A
  62. EP250407a: Swift-XRT observations
  63. IceCube-250406A: Upper limits from a search for additional neutrino events in IceCube
  64. Konus-Wind detection of GRB 250407A
  65. GRB 250407A: SVOM/GRM observation of a bright long burst
  66. GRB 250407A: EP-WXT afterglow detection
  67. EP250407a: EP-WXT detection of a fast X-ray transient
  68. GRB 250407A: COLIBRÍ/DDRAGO Detection of the Optical Counterpart
  69. GRB 250407A: KAIT Optical Afterglow Candidate
  70. IceCube-250406A: No candidates from the Zwicky Transient Facility
  71. GRB 250407A: Fermi GBM Detection
  72. GRB 250407A: Swift-XRT afterglow detection
  73. Fermi GRB 250407A: Global MASTER-Net observations report
  74. GRB 250407A: Swift ToO observations
  75. GRB 250407A: SRG/ART-XC afterglow detection
  76. LIGO/Virgo/KAGRA S250331o: Upper limits from Swift/BAT-GUANO
  77. IceCube 250406A: DDOTI Optical Observations of the Refined Position
  78. Konus-Wind detection of GRB 250406B (short/hard)
  79. IPN triangulation of GRB 250406B (short/hard)
  80. GRB 250407A: BALROG localization (Fermi Trigger 765733706 / GRB 250407659)
  81. GRB 250407A: Fermi GBM Final Real-time Localization
  82. IceCube-250406A - IceCube observation of a high-energy neutrino candidate track-like event
  83. IceCube 250406.951: COLIBRÍ/DDRAGO Optical Upper Limit
  84. IceCube 250406.951: DDOTI Optical Observations
  85. GRB 250406A: AstroSat CZTI detection
  86. IceCube Alert 250406.95: Global MASTER-Net observations report
  87. Fermi trigger No 765663719: Global MASTER-Net observations report
  88. EP250404a: Multi-band Optical Observations from UCAS-70 and XL-C14
  89. Fermi GRB 250406A: Global MASTER-Net observations report
  90. GRB 250404A: Calapai Observatory, Massa S. Giorgio (Messina), optical observations.
  91. GRB 250406A: Fermi GBM Final Real-time Localization
  92. EP250404a / GRB 250404A: Montarrenti Observatory optical observations
  93. Fermi trigger No 765619921: Global MASTER-Net observations report
  94. Fermi Gamma-ray Burst Monitor trigger 765619921/250406342 is not a GRB
  95. GRB 250404A / EP250404a: RC500 INASAN-Kislovodsk optical upper limit
  96. GRB 250404A / EP250404a: SVOM/GWAC-F60 and F50 observations
  97. EP250404a / GRB 250404A: J band observations by SYSU 80cm telescope
  98. Konus-Wind detection of GRB 250404A / EP250404a
  99. GRB 250404A / EP250404a: Mondy optical observations
  100. EP250404a: refined analysis of the EP-WXT and EP-FXT observations

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