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

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