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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"

44422 results found.

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

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