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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"

19593 results found.

  1. GRB 250509A: Fermi GBM Observation
  2. GRB 250510B: Swift/BAT-GUANO localization skymap of a burst
  3. GRB 250509A: Swift-XRT refined Analysis
  4. GRB 250507A: J-band observations with WINTER
  5. GRB 250509A: Enhanced Swift-XRT position
  6. GRB 250509A: Prompt enhanced Swift-XRT position
  7. Swift GRB 250509A: Global MASTER-Net observations report
  8. GRB 250509A: Swift detection of a burst
  9. GRB 250506A: NOT optical upper limits
  10. GRB 250506A: GECAM detection
  11. GRB 250506A: Swift-XRT afterglow detection
  12. GRB 250507A: Swift-XRT refined Analysis
  13. GRB 250506A: Swift/UVOT Upper Limits
  14. GRB 250430A / EP250430a: AstroSat CZTI detection
  15. EP#01709175213/IGR J19566+0326: Swift-XRT detection
  16. GRB 250506A: Swift-XRT observations
  17. EP-WXT trigger 01709175213: a new X-ray outburst of LMXB MAXI J1957+032
  18. GRB 250504A: EIRSAT-1 GMOD Detection
  19. GRB 250506A: Swift ToO observations
  20. GRB 250430A: Konus-Wind detection and joint Konus-Wind+Swift-BAT spectral analysis
  21. GRB 250506A: SVOM improved position and MXT detection of a fading X-ray afterglow
  22. GRB 250506A: Swift XRT observations and possible counterpart detection
  23. GRB 250506A: TRT optical observations
  24. GRB 250504A: Swift-BAT refined analysis
  25. GRB 250430A: Swift-BAT refined analysis
  26. GRB 250504A: Swift-XRT refined Analysis
  27. GRB 250504A: VLT/X-shooter upper limits
  28. GRB 250504A: SVOM/VT upper limit
  29. GRB 250504A: REM optical/NIR observations
  30. GRB 250504A: MeerLICHT optical afterglow detection
  31. GRB 250504A: Fermi GBM Observation
  32. GRB 250504A: Enhanced Swift-XRT position
  33. GRB 250504A: Swift detection of a burst
  34. Swift GRB250504.98: Global MASTER-Net observations report
  35. GRB 250502A: Swift/UVOT Follow up
  36. GRB 250502A: Swift-XRT afterglow detection
  37. GRB 250502A: Swift ToO observations
  38. GRB 250430A: Swift-XRT refined Analysis
  39. GRB 250430A: Swift/UVOT Detection
  40. GRB 250430A: Enhanced Swift-XRT position
  41. GRB 250430A: Calapai Observatory, Massa S. Giorgio (Messina), upper limit
  42. GRB 250430A: DDOTI Optical Observations
  43. GRB 250430A: Leavitt Observatory optical upper limit
  44. GRB 250430A: Bassano Bresciano Observatory upper limit
  45. GRB 250430A : MITSuME Akeno optical upper limits
  46. GRB 250430A / EP250430a: VLT/X-shooter spectroscopic redshift z = 0.767
  47. EP250430a/GRB 250430A: Einstein Probe WXT detection of the X-ray prompt emission
  48. GRB 250424A: CALET Gamma-Ray Burst Monitor detection
  49. GRB 250430A: AKO Optical Afterglow Detection
  50. GRB 250430A: Swift detection of a burst with optical counterpart
  51. Swift GRB250430.73: Global MASTER-Net observations report
  52. GRB 250427A: Swift/UVOT Detection
  53. EP250427a: EP-FXT follow-up observations
  54. GRB 250427A: Swift-XRT refined Analysis
  55. GRB 250424A: LCO optical observation
  56. GRB 250424A: Swift-BAT refined analysis
  57. GRB 250424A: SVOM/GRM observation of a long burst
  58. GRB 250424A: PRIME near-infrared detection
  59. GRB 250424A: WINTER J-band detection
  60. GRB 250424A: EIRSAT-1 GMOD Detection
  61. GRB 250424A: Swift/UVOT Detection
  62. Konus-Wind detection of GRB 250424A
  63. GRB 250424A: Skynet Optical Observations
  64. GRB 250424A: Kilonova-Catcher optical afterglow detection
  65. GRB 250424A: Swift-XRT refined Analysis
  66. GRB 250424A: Enhanced Swift-XRT position
  67. GRB 250424A: AstroSat CZTI detection of a bright long burst
  68. GRB 250424A: COLIBRÍ Detection of a Bright Optical Counterpart
  69. GRB 250424A: BlackGEM optical afterglow detection
  70. GRB 250424A: VLT/X-shooter spectroscopic redshift z = 0.310
  71. GRB 250424A: likely host galaxy
  72. GRB 250424A: DDOTI Afterglow Detection
  73. GRB 250424A: REM optical/NIR afterglow detection
  74. GRB 250424A: Swift detection of a burst with an optical counterpart
  75. Swift GRB 250424A: Global MASTER-Net observations report
  76. Swift GRB 250424A: Global MASTER-Net OT detection
  77. SVOM/sb25042207: XRT observations
  78. EP250421a: NOT optical observations
  79. EP250421a: Swift/XRT counterpart detection
  80. GRB 250419A: Swift/UVOT Follow up
  81. GRB 250419A: LCO optical afterglow multi-band observations
  82. GRB 250419A: Mondy and AbAO Optical Observations
  83. GRB 250419A: Swift-XRT localisation
  84. GRB 250419A: Swift-XRT refined Analysis
  85. EP250416a: Swift/XRT counterpart fading
  86. EP20250416a: Swift/XRT counterpart detection
  87. GRB 250407A: Mondy and AbAO Optical Observations
  88. IceCube-250406A: Swift-XRT observations
  89. IPN triangulation of GRB 250407A
  90. GRB 250407A: LCO detection of a fading optical counterpart
  91. EP250407a: Swift-XRT observations
  92. Konus-Wind detection of GRB 250407A
  93. GRB 250407A: SVOM/GRM observation of a bright long burst
  94. GRB 250407A: EP-WXT afterglow detection
  95. GRB 250407A: COLIBRÍ/DDRAGO Detection of the Optical Counterpart
  96. GRB 250407A: Fermi GBM Detection
  97. GRB 250407A: Swift-XRT afterglow detection
  98. GRB 250407A: Swift ToO observations
  99. GRB 250407A: SRG/ART-XC afterglow detection
  100. LIGO/Virgo/KAGRA S250331o: Upper limits from Swift/BAT-GUANO

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