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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 250504A: VLT/X-shooter upper limits
  2. Fermi GRB 250505A: Global MASTER-Net observations report
  3. GRB 250504A: SVOM/VT upper limit
  4. GRB 250504A: REM optical/NIR observations
  5. GRB 250502A: REM optical/NIR observations
  6. GRB 250505A: Fermi GBM Final Real-time Localization
  7. GRB 250504A: MeerLICHT optical afterglow detection
  8. GRB 250504A: Fermi GBM Observation
  9. GRB 250504A: Enhanced Swift-XRT position
  10. Fermi GRB 250504A: Global MASTER-Net observations report
  11. GRB 250504A: Swift detection of a burst
  12. GRB 250504A: Fermi GBM Final Real-time Localization
  13. Swift GRB250504.98: Global MASTER-Net observations report
  14. GRB 250502A: Swift/UVOT Follow up
  15. GRB 250502A: Mondy and Tien-Shan Optical Observations
  16. GRB 250502A: KAIT optical observations
  17. GRB 250502A: Montarrenti Observatory optical detection
  18. GRB 250502A: Swift-XRT afterglow detection
  19. Fermi trigger No 767975731: Global MASTER-Net observations report
  20. GRB 250502A: NOT optical observations
  21. GRB 250502a: Liverpool Telescope optical follow-up
  22. GRB 250502B: AstroSat CZTI detection
  23. GRB 250502A: AKO Optical Afterglow Detection
  24. GRB 250502A: LCO optical counterpart detection
  25. GRB 250502A: Swift ToO observations
  26. GRB 250502A: Redshift from OSIRIS+/GTC z = 2.163
  27. GRB 250502C: Fermi GBM Final Localization
  28. GRB 250407A: VZLUSAT-2 detection
  29. Fermi-LAT Gamma-ray Observations of IceCube-250429A
  30. GRB 250502B: DDOTI Optical Observations
  31. GRB 250430A: Swift-XRT refined Analysis
  32. GRB 250502A: Early optical counterpart detection by LCO.
  33. GRB 250430A: Swift/UVOT Detection
  34. GRB 250502A: SVOM/VT optical bump
  35. GRB 250502A: TRT optical afterglow confirmation
  36. GRB 250430A: Enhanced Swift-XRT position
  37. Fermi GRB 250502B: Global MASTER-Net observations report
  38. GRB 250430A: Optical Observations via Virtual Telescope Project, Italy
  39. GRB 250502A: SVOM/COLIBRÍ (FM-GFT) Detection of a Bright Optical Counterpart Candidate
  40. GRB 250502B: Fermi GBM Final Real-time Localization
  41. GRB 250502A: SVOM detection of a burst
  42. GRB 250430A: Calapai Observatory, Massa S. Giorgio (Messina), upper limit
  43. GRB 250430A: SVOM/VT optical observations
  44. GRB 250430A: KAIT optical observations
  45. EP250428b: Pan-STARRS follow-up, upper limit on the optical counterpart, and possible host galaxy.
  46. GRB 250430A / EP250430a: J-band upper limits with WINTER
  47. GRB 250430A: NUTTelA-TAO Early Measurements
  48. EP250427a / GRB 250427A: OHP/T193 photometric observations: third visit
  49. GRB 250430A: DDOTI Optical Observations
  50. GRB 250430A: Leavitt Observatory optical upper limit
  51. GRB 250430A: Bassano Bresciano Observatory upper limit
  52. GRB 250430A : MITSuME Akeno optical upper limits
  53. GRB 250430A / EP250430a: VLT/X-shooter spectroscopic redshift z = 0.767
  54. SVOM/sb25043004: EP-FXT observations
  55. EP250430a/GRB 250430A: Einstein Probe WXT detection of the X-ray prompt emission
  56. GRB 250424A: CALET Gamma-Ray Burst Monitor detection
  57. IceCube-250429A: Upper limits from a search for additional neutrino events in IceCube
  58. IceCube-250426A: Upper limits from a search for additional neutrino events in IceCube
  59. GRB 250430A: AKO Optical Afterglow Detection
  60. GRB 250430A: Kanata optical upper limit
  61. EP 250427A: Optical counterpart detection by LCO.
  62. GRB 250430A: Swift detection of a burst with optical counterpart
  63. Swift GRB250430.73: Global MASTER-Net observations report
  64. EP250428b: FTW optical and NIR observations
  65. EP250427a/GRB250427A: HCT optical follow-up
  66. EP250427a / GRB 250427A: OHP/T193 continued photometric observations
  67. SVOM/sb25043004: SVOM detection of a X-ray transient
  68. Fermi trigger No 767623859: Global MASTER-Net observations report
  69. EP250428b: refined analysis of the EP-FXT follow-up observation
  70. EP250428b: GROWTH-India telescope optical upper limit
  71. EP250428b: SVOM/VT upper limit
  72. EP250428b: SAO RAS optical upper limit
  73. EP250428b: LAST optical upper limit
  74. IceCube-250429A - IceCube observation of a high-energy neutrino candidate track-like event
  75. GRB 250427A: Swift/UVOT Detection
  76. EP250428b: Global MASTER-Net observations report
  77. EP250428b: Einstein Probe detection of a fast X-ray transient
  78. Fermi-LAT Gamma-ray Observations of IceCube-250426A
  79. EP250427a / GRB 250427A: OHP/T193 photometric observations
  80. EP250427a: EP-FXT follow-up observations
  81. EP250427a/GRB 250427A: FTW optical and NIR observations of the counterpart
  82. EP250427a: Lesedi optical counterpart detection
  83. EP250427A: COLIBRÍ Continuing Optical Observations
  84. GRB250427A/EP250427a GIT optical afterglow detection:
  85. EP250427a: LT optical counterpart detection
  86. GRB 250427A: Swift-XRT refined Analysis
  87. EP250427a / GRB 250427A: LCO optical counterpart detection
  88. EP250427a / GRB 250427A: VLT/X-shooter redshift confirmation z = 1.520
  89. EP250427A/GRB250427A: Keck/LRIS redshift
  90. EP250427a: REM optical/NIR afterglow detection
  91. GRB 250424A: LCO optical observation
  92. GRB 250427A/ EP250427a: Fermi-GBM Sub-Threshold Detection
  93. EP250427A: COLIBRÍ Optical Detection
  94. EP250427a: TRT optical counterpart detection
  95. EP 250427a: BOOTES-7 optical afterglow candidate
  96. EP250427a: Global MASTER-Net observations report
  97. EP250427a: Einstein Probe detection of a fast X-ray transient
  98. IceCube Alert 250426.74: Global MASTER-Net observations report
  99. GRB 250424A: Swift-BAT refined analysis
  100. IceCube-250426A - IceCube observation of a high-energy neutrino candidate track-like event (duplicate submission)

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