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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: rest-frame energetics from Konus-Wind observation
  2. GRB 250419A: Swift-XRT localisation
  3. GRB 250407A: GTC/OSIRIS+ spectroscopic redshift z = 1.36
  4. GRB 250419A: VLT/X-shooter spectroscopic redshift z = 0.845
  5. GRB 250419A: Swift-XRT refined Analysis
  6. GRB 250419A: GOTO optical counterpart detection
  7. GRB 250419A: KAIT optical afterglow observations
  8. GRB 250419A: SVOM/VT optical bright counterpart confirmation
  9. GRB 250419A: SVOM/COLIBRÍ (FM-GFT) Detection of the Optical Counterpart
  10. GRB 250419A: SVOM detection of a soft burst
  11. Konus-Wind detection of GRB 250416C (a counterpart of EP250416a)
  12. EP250416a: Swift/XRT counterpart fading
  13. EP250416a: refined EP-WXT and EP-FXT analysis
  14. Konus-Wind detection of GRB 250403A
  15. EP20250416a: Swift/XRT counterpart detection
  16. GRB 250403A: VLT/FORS2 spectroscopic redshift z = 1.847
  17. IceCube-250416A: DDOTI Optical Observations
  18. EP250416a: Gemini South-GMOS optical counterpart
  19. EP250225a: SVOM/VT optical brightening
  20. SVOM/sb25041603 is not a GRB
  21. EP250416a: GSP optical upper limit
  22. EP250416a: Global MASTER-Net observations report
  23. Fermi Gamma-ray Burst Monitor trigger 766505186/250416588 (GRB 250416A) is not a GRB
  24. EP250416a: Einstein Probe detection of an X-ray transient
  25. IceCube-250416A - IceCube observation of a high-energy neutrino candidate track-like event
  26. IceCube-250416A: Global MASTER-Net observations report
  27. Fermi Gamma-ray Burst Monitor trigger 766511207/250416657 is not a GRB
  28. GRB 250416B: Fermi GBM Final Real-time Localization
  29. GRB 250416A: Fermi GBM Final Real-time Localization
  30. SVOM/sb25041603: SVOM/COLIBRÍ (FM-GFT) Upper Limit on the Optical Counterpart
  31. SVOM/sb25041603: SVOM detection of an X-ray transient
  32. Fermi Gamma-ray Burst Monitor trigger 766474855/250416237 is not a GRB
  33. IceCube 250414.324: DDOTI Optical Observations
  34. GRB 250413A: AstroSat CZTI detection
  35. EP250304a: ATCA radio observations
  36. GRB 250412A: AstroSat CZTI detection
  37. EP250404a: Nanshan 0.43m Telescope optical observatios
  38. Fermi trigger No 766148493: Global MASTER-Net observations report
  39. Fermi trigger No 766173972: Global MASTER-Net observations report
  40. GRB 250411A: DDOTI Optical Observations
  41. Fermi GRB 250411A: Global MASTER-Net observations report
  42. GRB 250411A: Fermi GBM Final Real-time Localization
  43. GRB 250407A: Continued KAIT/Nickel optical observations
  44. GRB 250314A: e-MERLIN observations
  45. GRB 250407A: Mondy and AbAO Optical Observations
  46. EP250227a: Further NOT optical observations
  47. GRB 250320B: cubesat Avion detection
  48. IceCube-250406A: Swift-XRT observations
  49. IPN triangulation of GRB 250321D (consistent with the fast X-ray transient EP250321a)
  50. AMON Coincidence Alert from the sub-threshold IceCube-HAWC search NuEm-250409A
  51. IPN triangulation of GRB 250407A
  52. EP250407a: Global MASTER-Net observations report
  53. GRB 250407A: LCO detection of a fading optical counterpart
  54. Fermi-LAT gamma-ray observations of IceCube-250406A
  55. EP250407a: Swift-XRT observations
  56. IceCube-250406A: Upper limits from a search for additional neutrino events in IceCube
  57. Konus-Wind detection of GRB 250407A
  58. GRB 250407A: SVOM/GRM observation of a bright long burst
  59. GRB 250407A: EP-WXT afterglow detection
  60. EP250407a: EP-WXT detection of a fast X-ray transient
  61. GRB 250407A: COLIBRÍ/DDRAGO Detection of the Optical Counterpart
  62. GRB 250407A: KAIT Optical Afterglow Candidate
  63. IceCube-250406A: No candidates from the Zwicky Transient Facility
  64. GRB 250407A: Fermi GBM Detection
  65. GRB 250407A: Swift-XRT afterglow detection
  66. Fermi GRB 250407A: Global MASTER-Net observations report
  67. GRB 250407A: Swift ToO observations
  68. GRB 250407A: SRG/ART-XC afterglow detection
  69. LIGO/Virgo/KAGRA S250331o: Upper limits from Swift/BAT-GUANO
  70. IceCube 250406A: DDOTI Optical Observations of the Refined Position
  71. Konus-Wind detection of GRB 250406B (short/hard)
  72. IPN triangulation of GRB 250406B (short/hard)
  73. GRB 250407A: BALROG localization (Fermi Trigger 765733706 / GRB 250407659)
  74. GRB 250407A: Fermi GBM Final Real-time Localization
  75. IceCube-250406A - IceCube observation of a high-energy neutrino candidate track-like event
  76. IceCube 250406.951: COLIBRÍ/DDRAGO Optical Upper Limit
  77. IceCube 250406.951: DDOTI Optical Observations
  78. GRB 250406A: AstroSat CZTI detection
  79. IceCube Alert 250406.95: Global MASTER-Net observations report
  80. Fermi trigger No 765663719: Global MASTER-Net observations report
  81. EP250404a: Multi-band Optical Observations from UCAS-70 and XL-C14
  82. Fermi GRB 250406A: Global MASTER-Net observations report
  83. GRB 250404A: Calapai Observatory, Massa S. Giorgio (Messina), optical observations.
  84. GRB 250406A: Fermi GBM Final Real-time Localization
  85. EP250404a / GRB 250404A: Montarrenti Observatory optical observations
  86. Fermi trigger No 765619921: Global MASTER-Net observations report
  87. Fermi Gamma-ray Burst Monitor trigger 765619921/250406342 is not a GRB
  88. GRB 250404A / EP250404a: RC500 INASAN-Kislovodsk optical upper limit
  89. GRB 250404A / EP250404a: SVOM/GWAC-F60 and F50 observations
  90. EP250404a / GRB 250404A: J band observations by SYSU 80cm telescope
  91. Konus-Wind detection of GRB 250404A / EP250404a
  92. GRB 250404A / EP250404a: Mondy optical observations
  93. EP250404a: refined analysis of the EP-WXT and EP-FXT observations
  94. GRB 250404A / EP250404a: GMG spectroscopic redshift at z ~ 2.627
  95. GRB 250404A / EP250404a: Leavitt Observatory optical counterpart detection
  96. GRB 250402A: Calapai Observatory, Massa S. Giorgio (Messina), optical observations.
  97. EP250402a: Optical upper limit with PD 1.3m observations
  98. GRB 250404A / EP250404a: NOT optical observations
  99. GRB 250331D: Swift-XRT afterglow detection
  100. GRB 250404B: AstroSat CZTI detection of a short burst

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