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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 250430A: Swift-BAT refined analysis
  2. GRB 250506A: Fermi GBM Final Real-time Localization
  3. GRB 250504A: Swift-XRT refined Analysis
  4. GRB 250504A: VLT/X-shooter upper limits
  5. Fermi GRB 250505A: Global MASTER-Net observations report
  6. GRB 250504A: SVOM/VT upper limit
  7. GRB 250504A: REM optical/NIR observations
  8. GRB 250502A: REM optical/NIR observations
  9. GRB 250505A: Fermi GBM Final Real-time Localization
  10. GRB 250504A: MeerLICHT optical afterglow detection
  11. GRB 250504A: Fermi GBM Observation
  12. GRB 250504A: Enhanced Swift-XRT position
  13. Fermi GRB 250504A: Global MASTER-Net observations report
  14. GRB 250504A: Swift detection of a burst
  15. GRB 250504A: Fermi GBM Final Real-time Localization
  16. Swift GRB250504.98: Global MASTER-Net observations report
  17. GRB 250502A: Swift/UVOT Follow up
  18. GRB 250502A: Mondy and Tien-Shan Optical Observations
  19. GRB 250502A: KAIT optical observations
  20. GRB 250502A: Montarrenti Observatory optical detection
  21. GRB 250502A: Swift-XRT afterglow detection
  22. Fermi trigger No 767975731: Global MASTER-Net observations report
  23. GRB 250502A: NOT optical observations
  24. GRB 250502a: Liverpool Telescope optical follow-up
  25. GRB 250502B: AstroSat CZTI detection
  26. GRB 250502A: AKO Optical Afterglow Detection
  27. GRB 250502A: LCO optical counterpart detection
  28. GRB 250502A: Swift ToO observations
  29. GRB 250502A: Redshift from OSIRIS+/GTC z = 2.163
  30. GRB 250502C: Fermi GBM Final Localization
  31. GRB 250407A: VZLUSAT-2 detection
  32. Fermi-LAT Gamma-ray Observations of IceCube-250429A
  33. GRB 250502B: DDOTI Optical Observations
  34. GRB 250430A: Swift-XRT refined Analysis
  35. GRB 250502A: Early optical counterpart detection by LCO.
  36. GRB 250430A: Swift/UVOT Detection
  37. GRB 250502A: SVOM/VT optical bump
  38. GRB 250502A: TRT optical afterglow confirmation
  39. GRB 250430A: Enhanced Swift-XRT position
  40. Fermi GRB 250502B: Global MASTER-Net observations report
  41. GRB 250430A: Optical Observations via Virtual Telescope Project, Italy
  42. GRB 250502A: SVOM/COLIBRÍ (FM-GFT) Detection of a Bright Optical Counterpart Candidate
  43. GRB 250502B: Fermi GBM Final Real-time Localization
  44. GRB 250502A: SVOM detection of a burst
  45. GRB 250430A: Calapai Observatory, Massa S. Giorgio (Messina), upper limit
  46. GRB 250430A: SVOM/VT optical observations
  47. GRB 250430A: KAIT optical observations
  48. EP250428b: Pan-STARRS follow-up, upper limit on the optical counterpart, and possible host galaxy.
  49. GRB 250430A / EP250430a: J-band upper limits with WINTER
  50. GRB 250430A: NUTTelA-TAO Early Measurements
  51. EP250427a / GRB 250427A: OHP/T193 photometric observations: third visit
  52. GRB 250430A: DDOTI Optical Observations
  53. GRB 250430A: Leavitt Observatory optical upper limit
  54. GRB 250430A: Bassano Bresciano Observatory upper limit
  55. GRB 250430A : MITSuME Akeno optical upper limits
  56. GRB 250430A / EP250430a: VLT/X-shooter spectroscopic redshift z = 0.767
  57. SVOM/sb25043004: EP-FXT observations
  58. EP250430a/GRB 250430A: Einstein Probe WXT detection of the X-ray prompt emission
  59. GRB 250424A: CALET Gamma-Ray Burst Monitor detection
  60. IceCube-250429A: Upper limits from a search for additional neutrino events in IceCube
  61. IceCube-250426A: Upper limits from a search for additional neutrino events in IceCube
  62. GRB 250430A: AKO Optical Afterglow Detection
  63. GRB 250430A: Kanata optical upper limit
  64. EP 250427A: Optical counterpart detection by LCO.
  65. GRB 250430A: Swift detection of a burst with optical counterpart
  66. Swift GRB250430.73: Global MASTER-Net observations report
  67. EP250428b: FTW optical and NIR observations
  68. EP250427a/GRB250427A: HCT optical follow-up
  69. EP250427a / GRB 250427A: OHP/T193 continued photometric observations
  70. SVOM/sb25043004: SVOM detection of a X-ray transient
  71. Fermi trigger No 767623859: Global MASTER-Net observations report
  72. EP250428b: refined analysis of the EP-FXT follow-up observation
  73. EP250428b: GROWTH-India telescope optical upper limit
  74. EP250428b: SVOM/VT upper limit
  75. EP250428b: SAO RAS optical upper limit
  76. EP250428b: LAST optical upper limit
  77. IceCube-250429A - IceCube observation of a high-energy neutrino candidate track-like event
  78. GRB 250427A: Swift/UVOT Detection
  79. EP250428b: Global MASTER-Net observations report
  80. EP250428b: Einstein Probe detection of a fast X-ray transient
  81. Fermi-LAT Gamma-ray Observations of IceCube-250426A
  82. EP250427a / GRB 250427A: OHP/T193 photometric observations
  83. EP250427a: EP-FXT follow-up observations
  84. EP250427a/GRB 250427A: FTW optical and NIR observations of the counterpart
  85. EP250427a: Lesedi optical counterpart detection
  86. EP250427A: COLIBRÍ Continuing Optical Observations
  87. GRB250427A/EP250427a GIT optical afterglow detection:
  88. EP250427a: LT optical counterpart detection
  89. GRB 250427A: Swift-XRT refined Analysis
  90. EP250427a / GRB 250427A: LCO optical counterpart detection
  91. EP250427a / GRB 250427A: VLT/X-shooter redshift confirmation z = 1.520
  92. EP250427A/GRB250427A: Keck/LRIS redshift
  93. EP250427a: REM optical/NIR afterglow detection
  94. GRB 250424A: LCO optical observation
  95. GRB 250427A/ EP250427a: Fermi-GBM Sub-Threshold Detection
  96. EP250427A: COLIBRÍ Optical Detection
  97. EP250427a: TRT optical counterpart detection
  98. EP 250427a: BOOTES-7 optical afterglow candidate
  99. EP250427a: Global MASTER-Net observations report
  100. EP250427a: Einstein Probe detection of a fast X-ray transient

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