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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"

20958 results found.

  1. GRB 250419A: Calapai Observatory, Massa S. Giorgio (Messina), optical observations.
  2. IC-250421A: LAST optical observations of the IceCube neutrino candidate
  3. EP250421a: NOT optical observations
  4. GRB 250419A: Optical Observations via Virtual Telescope Project
  5. EP250421a: REM optical upper limit
  6. EP250421a: Swift/XRT counterpart detection
  7. EP250421A: COLIBRÍ Optical Upper Limit
  8. GRB 250419A: Mondy Continued Optical Observations
  9. Fermi GRB 250421A: Global MASTER-Net observations report
  10. EP250421a: Global MASTER-Net observations report
  11. EP250421a: Mephisto optical counterpart confirmation
  12. IceCube Alert 250421.71: Global MASTER-Net observations report
  13. EP250421a: JinShan likely optical counterpart
  14. The EP-WXT trigger 01709135179: Kinder optical counterpart candidate
  15. GRB 250419A: Liverpool Telescope observations
  16. GRB 250419A: LCO optical observation
  17. GRB 250419A: JinShan optical observations
  18. GRB 250419A: SVOM/VT optical continuous observations
  19. GRB 250419A: SVOM/C-GFT optical observations
  20. GRB 250419A: Swift/UVOT Follow up
  21. GRB 250419A: LCO optical afterglow multi-band observations
  22. GRB 250419A: Mondy and AbAO Optical Observations
  23. GRB 250419A: Liverpool Telescope observations
  24. GRB 250419A: AKO Optical Afterglow Detection
  25. GRB 250419A: MASTER optical afterglow observation
  26. Fermi-LAT Gamma-ray Observations of IceCube-250416A
  27. GRB 250407A: GTC/OSIRIS+ spectroscopic redshift z = 1.36
  28. GRB 250419A: VLT/X-shooter spectroscopic redshift z = 0.845
  29. GRB 250419A: GOTO optical counterpart detection
  30. GRB 250419A: KAIT optical afterglow observations
  31. GRB 250419A: SVOM/COLIBRÍ (FM-GFT) Detection of the Optical Counterpart
  32. EP250416a: Swift/XRT counterpart fading
  33. EP250416a: refined EP-WXT and EP-FXT analysis
  34. EP20250416a: Swift/XRT counterpart detection
  35. GRB 250403A: VLT/FORS2 spectroscopic redshift z = 1.847
  36. IceCube-250416A: DDOTI Optical Observations
  37. EP250416a: Gemini South-GMOS optical counterpart
  38. EP250225a: SVOM/VT optical brightening
  39. EP250416a: GSP optical upper limit
  40. EP250416a: Global MASTER-Net observations report
  41. IceCube-250416A: Global MASTER-Net observations report
  42. IceCube 250414.324: DDOTI Optical Observations
  43. EP250304a: ATCA radio observations
  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 250407A: Continued KAIT/Nickel optical observations
  50. GRB 250314A: e-MERLIN observations
  51. GRB 250407A: Mondy and AbAO Optical Observations
  52. EP250227a: Further NOT optical observations
  53. IceCube-250406A: Swift-XRT observations
  54. AMON Coincidence Alert from the sub-threshold IceCube-HAWC search NuEm-250409A
  55. EP250407a: Global MASTER-Net observations report
  56. GRB 250407A: LCO detection of a fading optical counterpart
  57. Fermi-LAT gamma-ray observations of IceCube-250406A
  58. EP250407a: Swift-XRT observations
  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: Swift-XRT afterglow detection
  64. Fermi GRB 250407A: Global MASTER-Net observations report
  65. GRB 250407A: Swift ToO observations
  66. IceCube 250406A: DDOTI Optical Observations of the Refined Position
  67. IceCube 250406.951: COLIBRÍ/DDRAGO Optical Upper Limit
  68. IceCube 250406.951: DDOTI Optical Observations
  69. IceCube Alert 250406.95: Global MASTER-Net observations report
  70. Fermi trigger No 765663719: Global MASTER-Net observations report
  71. EP250404a: Multi-band Optical Observations from UCAS-70 and XL-C14
  72. Fermi GRB 250406A: Global MASTER-Net observations report
  73. GRB 250404A: Calapai Observatory, Massa S. Giorgio (Messina), optical observations.
  74. EP250404a / GRB 250404A: Montarrenti Observatory optical observations
  75. Fermi trigger No 765619921: Global MASTER-Net observations report
  76. GRB 250404A / EP250404a: SVOM/GWAC-F60 and F50 observations
  77. EP250404a / GRB 250404A: J band observations by SYSU 80cm telescope
  78. GRB 250404A / EP250404a: Mondy optical observations
  79. EP250404a: refined analysis of the EP-WXT and EP-FXT observations
  80. GRB 250404A / EP250404a: Leavitt Observatory optical counterpart detection
  81. GRB 250402A: Calapai Observatory, Massa S. Giorgio (Messina), optical observations.
  82. EP250402a: Optical upper limit with PD 1.3m observations
  83. GRB 250404A / EP250404a: NOT optical observations
  84. GRB 250331D: Swift-XRT afterglow detection
  85. EP250404a: Osservatorio Astronomico "Nastro Verde" optical observations: detection of an optical counterpart
  86. EP250404a: REM optical/NIR observations
  87. EP250404a: Seimei/TriCCS optical counterpart detection
  88. EP250404A: COLIBRÍ/DDRAGO Optical Observations
  89. EP250404A / GRB250404A: Ondrejov D50 optical afterglow detection
  90. EP250404a: LCO optical counterpart detection
  91. Fermi GRB 250404A: Global MASTER-Net observations report
  92. EP250404a: Xinglong decaying optical counterpart
  93. GRB 250403A: Montarrenti Observatory optical detection
  94. EP250404a: Global MASTER-Net observations report
  95. GRB 250403A: KAIT optical observations
  96. EP250404a: AKO Optical Afterglow Detection
  97. EP250404a: LAST detection of optical counterpart
  98. GRB 250403A: Fermi GBM observations
  99. EP250404a: Mephisto multi-band optical detection
  100. EP250321A: J band upper limit by SYSU 80cm telescope

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