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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 250510A: follow-up observation with EP-FXT
  2. GRB 250510B: Swift/BAT-GUANO localization skymap of a burst
  3. GRB 250510B: Fermi GBM Final Localization
  4. GRB 250510A: SVOM/COLIBRÍ (FM-GFT) optical upper limit
  5. GRB 250509A: Swift-XRT refined Analysis
  6. GRB 250510A: SVOM possible detection of a burst
  7. GRB 250507A: J-band observations with WINTER (duplicate submission)
  8. GRB 250507A: J-band observations with WINTER
  9. EP250508a: SVOM/VT optical candidate fading
  10. GRB 250509A: Enhanced Swift-XRT position
  11. GRB 250509A: Prompt enhanced Swift-XRT position
  12. Fermi GRB 250509A: Global MASTER-Net observations report
  13. Swift GRB 250509A: Global MASTER-Net observations report
  14. GRB 250509A: Swift detection of a burst
  15. GRB 250509A: Fermi GBM Final Real-time Localization
  16. GRB 250506A: NOT optical upper limits
  17. EP250508a: Liverpool Telescope optical upper limits
  18. EP250508a: follow-up observation with EP-FXT
  19. EP250508a: SVOM/VT optical candidate
  20. EP250508a: KAIT optical upper limit
  21. GRB 250507A: KAIT optical upper limit
  22. EP250508a: refined analysis of the EP-WXT and EP-FXT observations
  23. GRB 250505B: SVOM/GRM observation of a short burst
  24. GRB 250502A: Calapai Observatory, Massa S. Giorgio (Messina), optical observation.
  25. GRB 250506A: GECAM detection
  26. EP250508a: REM optical/NIR observations
  27. GRB 250506A: Swift-XRT afterglow detection
  28. EP250508a: Global MASTER-Net observations report
  29. GRB 250506A: SVOM/VT optical upper limit
  30. EP250508a: COLIBRÍ Optical Limit
  31. EP250508a: Einstein Probe detection of an X-ray transient
  32. GRB 250507A: Swift-XRT refined Analysis
  33. IceCube-250506A: Upper limits from a search for additional neutrino events in IceCube
  34. GRB 250506A: Swift/UVOT Upper Limits
  35. GRB 250427B : SVOM detection of a burst through offline search
  36. GRB 250507A: follow-up observation with EP-FXT
  37. GRB 250430A / EP250430a: AstroSat CZTI detection
  38. EP#01709175213/IGR J19566+0326: Swift-XRT detection
  39. GRB 250506A: SVOM/COLIBRÍ (FM-GFT) optical upper limit
  40. GRB 250507A: refined SVOM/MXT data analysis
  41. GRB 250507A: REM optical/NIR observations
  42. GRB 250507A: SVOM/VT optical upper limit
  43. GRB 250506A: Swift-XRT observations
  44. Fermi-LAT Gamma-ray Observations of IceCube-250506A
  45. GRB 250507A: SVOM/COLIBRÍ (FM-GFT) optical upper limit
  46. EP-WXT trigger 01709175213: a new X-ray outburst of LMXB MAXI J1957+032
  47. GRB 250507A: SVOM detection of a long burst
  48. GRB 250506A: Mephisto optical upper limits
  49. GRB 250504A: EIRSAT-1 GMOD Detection
  50. GRB 250506A: Swift ToO observations
  51. GRB 250502A: Bassano Bresciano Observatory upper limit
  52. IceCube-250506A - IceCube observation of a high-energy neutrino candidate track-like event
  53. IceCube Alert 250506.59: Global MASTER-Net observations report
  54. GRB 250430A: Konus-Wind detection and joint Konus-Wind+Swift-BAT spectral analysis
  55. GRB 250506A: Xinglong 2.16m optical upper limit
  56. SVOM/sb25050601: EP-FXT observations
  57. GRB 250506A: SVOM improved position and MXT detection of a fading X-ray afterglow
  58. GRB 250506A: REM optical/NIR upper limits
  59. GRB 250506A: Fermi GBM Observation
  60. GRB 250506A: Swift XRT observations and possible counterpart detection
  61. GRB 250506A: TRT optical observations
  62. GRB 250506A: SVOM/COLIBRÍ (FM-GFT) Upper Limits on the Optical Counterpart
  63. GRB 250506A: SVOM detection of a burst
  64. GRB 250504A: Swift-BAT refined analysis
  65. GRB 250430A: Swift-BAT refined analysis
  66. GRB 250506A: Fermi GBM Final Real-time Localization
  67. GRB 250504A: Swift-XRT refined Analysis
  68. GRB 250504A: VLT/X-shooter upper limits
  69. Fermi GRB 250505A: Global MASTER-Net observations report
  70. GRB 250504A: SVOM/VT upper limit
  71. GRB 250504A: REM optical/NIR observations
  72. GRB 250502A: REM optical/NIR observations
  73. GRB 250505A: Fermi GBM Final Real-time Localization
  74. GRB 250504A: MeerLICHT optical afterglow detection
  75. GRB 250504A: Fermi GBM Observation
  76. GRB 250504A: Enhanced Swift-XRT position
  77. Fermi GRB 250504A: Global MASTER-Net observations report
  78. GRB 250504A: Swift detection of a burst
  79. GRB 250504A: Fermi GBM Final Real-time Localization
  80. Swift GRB250504.98: Global MASTER-Net observations report
  81. GRB 250502A: Swift/UVOT Follow up
  82. GRB 250502A: Mondy and Tien-Shan Optical Observations
  83. GRB 250502A: KAIT optical observations
  84. GRB 250502A: Montarrenti Observatory optical detection
  85. GRB 250502A: Swift-XRT afterglow detection
  86. Fermi trigger No 767975731: Global MASTER-Net observations report
  87. GRB 250502A: NOT optical observations
  88. GRB 250502a: Liverpool Telescope optical follow-up
  89. GRB 250502B: AstroSat CZTI detection
  90. GRB 250502A: AKO Optical Afterglow Detection
  91. GRB 250502A: LCO optical counterpart detection
  92. GRB 250502A: Swift ToO observations
  93. GRB 250502A: Redshift from OSIRIS+/GTC z = 2.163
  94. GRB 250502C: Fermi GBM Final Localization
  95. GRB 250407A: VZLUSAT-2 detection
  96. Fermi-LAT Gamma-ray Observations of IceCube-250429A
  97. GRB 250502B: DDOTI Optical Observations
  98. GRB 250430A: Swift-XRT refined Analysis
  99. GRB 250502A: Early optical counterpart detection by LCO.
  100. GRB 250430A: Swift/UVOT Detection

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