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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"

36149 results found.

  1. EP250404a: Nanshan/HMT optical counterpart detection
  2. EP250404a: Einstein Probe detection of an X-ray transient
  3. GRB 250404A: Fermi GBM Final Real-time Localization
  4. GRB 250402A: Mondy optical observations
  5. GRB 250403A: Swift/UVOT Detection
  6. GRB 250402A: Swift/UVOT Upper Limits
  7. GRB 250403A: SVOM/VT optical observation
  8. GRB 250403A: REM NIR afterglow detection
  9. GRB 250403A: LCO optical counterpart detection
  10. GRB 250403A: JinShan optical observations
  11. GRB 250402A: EP-FXT afterglow detection
  12. GRB 250403A: Optical counterpart detection by LCO.
  13. GRB 250403A: Swift-XRT observations
  14. GRB 250322A: 10 GHz VLA radio upper limits
  15. Fermi GRB 250403A: Global MASTER-Net observations report
  16. GRB 250403A: GOTO optical counterpart follow-up observations
  17. GRB 250402A: NUTTelA-TAO Early Optical Limits
  18. GRB 250403A: GMG Optical Observation
  19. GRB 250403A: 1.6m Mephisto multi-band optical detection
  20. GRB 250402A: Fermi GBM Observation
  21. GRB 250403A: SVOM/C-GFT optical observations
  22. GRB 250403A: GOTO detection of the optical afterglow
  23. GRB 250402A: Swift-XRT observations
  24. GRB 250403A : SVOM detection of a burst
  25. GRB 250403A: Fermi GBM Final Real-time Localization
  26. GRB 250225B: VLT host galaxy redshift z = 0.950
  27. GRB250402A: SVOM/COLIBRÍ (FM-GFT) Detection of the Optical Counterpart
  28. GRB 250402A: VLT/FORS2 spectroscopic redshift z = 2.823
  29. GRB 250402A: REM optical/NIR upper limits
  30. GRB 250402A: LCO optical counterpart detection
  31. GRB 250402A: refined SVOM/MXT data analysis
  32. GRB 250402B: AstroSat CZTI detection of a short burst
  33. GRB 250402A: SVOM/VT optical counterpart
  34. GRB 250402A: SVOM detection of a burst
  35. GRB 250331C: Calapai Observatory, Massa S. Giorgio (Messina), upper limit
  36. GRB 250314A: ALMA detection
  37. GRB 250329B: Swift/UVOT Upper Limit
  38. GRB 250329A: Swift/UVOT Upper Limit
  39. GRB 250327B: Swift/UVOT Detection
  40. GRB 250327A: Swift/UVOT Upper Limits
  41. GRB 250331E: SVOM/GRM observation
  42. GRB 250327B: Kilonova-Catcher Observations
  43. GRB250331D: AbAO optical observations
  44. GRB 250331D: Fermi GBM observation
  45. GRB 250331C: Swift/UVOT Upper Limits
  46. GRB 250331B: Swift/UVOT Upper Limits
  47. GRB 250328A: AbAO AS-32 Optical Observations
  48. GRB 250219A: NOT candidate host galaxy detection
  49. GRB 250322B: GRBAlpha detection
  50. GRB 250331D: Swift-XRT observations
  51. GRB 250331C: Swift-XRT refined Analysis
  52. GRB 250331B: Swift-XRT refined Analysis
  53. GRB 250331B: Swift-XRT refined Analysis
  54. GRB 250322B possible detection by the AstroSat Satellite
  55. GRB 250330B: SVOM/GRM observation of a short burst
  56. Fermi GRB 250331E: Global MASTER-Net observations report
  57. Fermi GRB 250331D: Global MASTER-Net observations report
  58. GRB 250330B: EIRSAT-1 GMOD Detection
  59. GRB 250331E: Fermi GBM Final Real-time Localization
  60. GRB 250327A Swift-BAT refined analysis
  61. GRB 250329A: AbAO, Mondy and SAO RAS optical upper limits
  62. GRB 250329B: CAHA 2.2m telescope optical limit
  63. GRB 250331D: Swift ToO observations
  64. Swift GRB 250331C: Global MASTER-Net observations report
  65. Swift GRB 250331B: Global MASTER-Net observations report
  66. GRB 250331D: Swift/BAT-GUANO arcminute localization of a burst during slew
  67. Konus-Wind detection of GRB 250327B
  68. GRB 250331C: Enhanced Swift-XRT position
  69. IceCube-250330A: Upper limits from a search for additional neutrino events in IceCube
  70. GRB 250331B: Enhanced Swift-XRT position
  71. GRB 250320C : SVOM detection of a burst through offline search
  72. GRB 250329B: Swift-XRT confirmation of fading
  73. GRB 250330A: VLT/FORS2 Afterglow Detection
  74. GRB20250327B: 45th Parallel Observatory upper limit
  75. GRB 250328A: Swift/UVOT Detection
  76. GRB 250328A: Swift-XRT refined Analysis
  77. GRB 250330A: Fermi GBM Observation
  78. GRB 250331C: COLIBRÍ/DDRAGO optical upper limit
  79. GRB 250331B: COLIBRÍ/DDRAGO optical upper limit
  80. GRB 250331D: Fermi GBM Final Real-time Localization
  81. GRB 250331C: Prompt enhanced Swift-XRT position
  82. GRB 250331C: Swift detection of a burst
  83. GRB 250331B: Swift detection of a burst
  84. GRB 250330A: SVOM/VT optical upper limit
  85. GRB 250331A: MAXI/GSC detection
  86. GRB 250314A: VLA detection
  87. Fermi GRB 250330B: Global MASTER-Net observations report
  88. GRB 250330B: Fermi GBM Final Real-time Localization
  89. Fermi GRB 250330A: Global MASTER-Net observations report
  90. GRB 250330A: BOOTES-7 early optical upper limit
  91. GRB 250330A: Swift/UVOT Upper Limits
  92. GRB 250330A: Swift-XRT afterglow detection
  93. GRB 250328A: 1.6m Mephisto optical observations
  94. GRB 250329B: SVOM/COLIBRÍ (F-GFT) optical upper limit
  95. GRB 250330A: Fermi GBM Final Localization
  96. GRB 250330A: VLT/FORS2 Optical Observations
  97. GRB 250330A: Prompt Swift-XRT position
  98. GRB 250329B: Swift-XRT afterglow detection
  99. GRB 250330A: Swift detection of a burst
  100. GRB 250328A: A fading optical afterglow confirmed by SVOM/VT

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