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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"

32419 results found.

  1. GRB 250506A: SVOM/COLIBRÍ (FM-GFT) optical upper limit
  2. GRB 250507A: refined SVOM/MXT data analysis
  3. GRB 250507A: REM optical/NIR observations
  4. GRB 250507A: SVOM/VT optical upper limit
  5. GRB 250506A: Swift-XRT observations
  6. GRB 250507A: SVOM/COLIBRÍ (FM-GFT) optical upper limit
  7. GRB 250507A: SVOM detection of a long burst
  8. GRB 250506A: Mephisto optical upper limits
  9. GRB 250504A: EIRSAT-1 GMOD Detection
  10. GRB 250506A: Swift ToO observations
  11. GRB 250502A: Bassano Bresciano Observatory upper limit
  12. GRB 250430A: Konus-Wind detection and joint Konus-Wind+Swift-BAT spectral analysis
  13. GRB 250506A: Xinglong 2.16m optical upper limit
  14. GRB 250506A: SVOM improved position and MXT detection of a fading X-ray afterglow
  15. GRB 250506A: REM optical/NIR upper limits
  16. GRB 250506A: Fermi GBM Observation
  17. GRB 250506A: Swift XRT observations and possible counterpart detection
  18. GRB 250506A: TRT optical observations
  19. GRB 250506A: SVOM/COLIBRÍ (FM-GFT) Upper Limits on the Optical Counterpart
  20. GRB 250506A: SVOM detection of a burst
  21. GRB 250504A: Swift-BAT refined analysis
  22. GRB 250430A: Swift-BAT refined analysis
  23. GRB 250506A: Fermi GBM Final Real-time Localization
  24. GRB 250504A: Swift-XRT refined Analysis
  25. GRB 250504A: VLT/X-shooter upper limits
  26. Fermi GRB 250505A: Global MASTER-Net observations report
  27. GRB 250504A: SVOM/VT upper limit
  28. GRB 250504A: REM optical/NIR observations
  29. GRB 250502A: REM optical/NIR observations
  30. GRB 250505A: Fermi GBM Final Real-time Localization
  31. GRB 250504A: MeerLICHT optical afterglow detection
  32. GRB 250504A: Fermi GBM Observation
  33. GRB 250504A: Enhanced Swift-XRT position
  34. Fermi GRB 250504A: Global MASTER-Net observations report
  35. GRB 250504A: Swift detection of a burst
  36. GRB 250504A: Fermi GBM Final Real-time Localization
  37. GRB 250502A: Swift/UVOT Follow up
  38. GRB 250502A: Mondy and Tien-Shan Optical Observations
  39. GRB 250502A: KAIT optical observations
  40. GRB 250502A: Montarrenti Observatory optical detection
  41. GRB 250502A: Swift-XRT afterglow detection
  42. GRB 250502A: NOT optical observations
  43. GRB 250502a: Liverpool Telescope optical follow-up
  44. GRB 250502B: AstroSat CZTI detection
  45. GRB 250502A: AKO Optical Afterglow Detection
  46. GRB 250502A: LCO optical counterpart detection
  47. GRB 250502A: Swift ToO observations
  48. GRB 250502A: Redshift from OSIRIS+/GTC z = 2.163
  49. GRB 250502C: Fermi GBM Final Localization
  50. GRB 250407A: VZLUSAT-2 detection
  51. GRB 250502B: DDOTI Optical Observations
  52. GRB 250430A: Swift-XRT refined Analysis
  53. GRB 250502A: Early optical counterpart detection by LCO.
  54. GRB 250430A: Swift/UVOT Detection
  55. GRB 250502A: SVOM/VT optical bump
  56. GRB 250502A: TRT optical afterglow confirmation
  57. GRB 250430A: Enhanced Swift-XRT position
  58. Fermi GRB 250502B: Global MASTER-Net observations report
  59. GRB 250430A: Optical Observations via Virtual Telescope Project, Italy
  60. GRB 250502A: SVOM/COLIBRÍ (FM-GFT) Detection of a Bright Optical Counterpart Candidate
  61. GRB 250502B: Fermi GBM Final Real-time Localization
  62. GRB 250502A: SVOM detection of a burst
  63. GRB 250430A: Calapai Observatory, Massa S. Giorgio (Messina), upper limit
  64. GRB 250430A: SVOM/VT optical observations
  65. GRB 250430A: KAIT optical observations
  66. GRB 250430A / EP250430a: J-band upper limits with WINTER
  67. GRB 250430A: NUTTelA-TAO Early Measurements
  68. EP250427a / GRB 250427A: OHP/T193 photometric observations: third visit
  69. GRB 250430A: DDOTI Optical Observations
  70. GRB 250430A: Leavitt Observatory optical upper limit
  71. GRB 250430A: Bassano Bresciano Observatory upper limit
  72. GRB 250430A : MITSuME Akeno optical upper limits
  73. GRB 250430A / EP250430a: VLT/X-shooter spectroscopic redshift z = 0.767
  74. EP250430a/GRB 250430A: Einstein Probe WXT detection of the X-ray prompt emission
  75. GRB 250424A: CALET Gamma-Ray Burst Monitor detection
  76. GRB 250430A: AKO Optical Afterglow Detection
  77. GRB 250430A: Kanata optical upper limit
  78. EP 250427A: Optical counterpart detection by LCO.
  79. GRB 250430A: Swift detection of a burst with optical counterpart
  80. EP250427a / GRB 250427A: OHP/T193 continued photometric observations
  81. EP250428b: SAO RAS optical upper limit
  82. GRB 250427A: Swift/UVOT Detection
  83. EP250427a / GRB 250427A: OHP/T193 photometric observations
  84. EP250427a: EP-FXT follow-up observations
  85. EP250427a/GRB 250427A: FTW optical and NIR observations of the counterpart
  86. GRB250427A/EP250427a GIT optical afterglow detection:
  87. GRB 250427A: Swift-XRT refined Analysis
  88. EP250427a / GRB 250427A: LCO optical counterpart detection
  89. EP250427a / GRB 250427A: VLT/X-shooter redshift confirmation z = 1.520
  90. EP250427A/GRB250427A: Keck/LRIS redshift
  91. GRB 250424A: LCO optical observation
  92. GRB 250427A/ EP250427a: Fermi-GBM Sub-Threshold Detection
  93. GRB 250424A: Swift-BAT refined analysis
  94. GRB 250424A: SVOM/GRM observation of a long burst
  95. GRB 250424A: PRIME near-infrared detection
  96. GRB 250424A: WINTER J-band detection
  97. GRB 250424A: EIRSAT-1 GMOD Detection
  98. GRB 250424A: SVOM/VT optical observation
  99. GRB 250419A: Mondy Optical Observations
  100. GRB 250424A: Swift/UVOT Detection

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