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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"

32541 results found.

  1. EP250511a: Mephisto optical upper limits
  2. GRB 250506A: GRBAlpha detection
  3. GRB 250512B: SVOM detection of a burst
  4. EP250511a: REM optical/NIR observations
  5. EP250511a: Einstein Probe follow-up obsevation and refined analysis
  6. EP250511a: SVOM/VT optical candidate comfirmation
  7. EP250511a: Global MASTER-Net observations report
  8. EP250511a: COLIBRÍ optical counterpart candidate
  9. EP250511a: BOOTES-5 optical upper limit
  10. EP250508a: Gemini NIR upper limits
  11. GRB 250510B: Fermi GBM Observation
  12. Fermi GRB 250510C: Global MASTER-Net observations report
  13. Fermi GRB 250510B: Global MASTER-Net observations report
  14. GRB 250510A: Swift-XRT observations
  15. GRB 250509A: Fermi GBM Observation
  16. IceCube-250506A: No Transient Candidates from the Zwicky Transient Facility
  17. GRB 250510A: follow-up observation with EP-FXT
  18. GRB 250510B: Swift/BAT-GUANO localization skymap of a burst
  19. GRB 250510A: SVOM/COLIBRÍ (FM-GFT) optical upper limit
  20. GRB 250507A: J-band observations with WINTER (duplicate submission)
  21. GRB 250507A: J-band observations with WINTER
  22. EP250508a: SVOM/VT optical candidate fading
  23. Fermi GRB 250509A: Global MASTER-Net observations report
  24. Swift GRB 250509A: Global MASTER-Net observations report
  25. GRB 250506A: NOT optical upper limits
  26. EP250508a: Liverpool Telescope optical upper limits
  27. EP250508a: follow-up observation with EP-FXT
  28. EP250508a: SVOM/VT optical candidate
  29. EP250508a: KAIT optical upper limit
  30. GRB 250507A: KAIT optical upper limit
  31. EP250508a: refined analysis of the EP-WXT and EP-FXT observations
  32. GRB 250502A: Calapai Observatory, Massa S. Giorgio (Messina), optical observation.
  33. GRB 250506A: GECAM detection
  34. EP250508a: REM optical/NIR observations
  35. EP250508a: Global MASTER-Net observations report
  36. GRB 250506A: SVOM/VT optical upper limit
  37. EP250508a: COLIBRÍ Optical Limit
  38. GRB 250507A: Swift-XRT refined Analysis
  39. IceCube-250506A: Upper limits from a search for additional neutrino events in IceCube
  40. GRB 250506A: Swift/UVOT Upper Limits
  41. GRB 250507A: follow-up observation with EP-FXT
  42. GRB 250430A / EP250430a: AstroSat CZTI detection
  43. EP#01709175213/IGR J19566+0326: Swift-XRT detection
  44. GRB 250506A: SVOM/COLIBRÍ (FM-GFT) optical upper limit
  45. GRB 250507A: refined SVOM/MXT data analysis
  46. GRB 250507A: REM optical/NIR observations
  47. GRB 250507A: SVOM/VT optical upper limit
  48. GRB 250506A: Swift-XRT observations
  49. Fermi-LAT Gamma-ray Observations of IceCube-250506A
  50. GRB 250507A: SVOM/COLIBRÍ (FM-GFT) optical upper limit
  51. GRB 250506A: Mephisto optical upper limits
  52. GRB 250504A: EIRSAT-1 GMOD Detection
  53. GRB 250506A: Swift ToO observations
  54. GRB 250502A: Bassano Bresciano Observatory upper limit
  55. GRB 250430A: Konus-Wind detection and joint Konus-Wind+Swift-BAT spectral analysis
  56. GRB 250506A: Xinglong 2.16m optical upper limit
  57. SVOM/sb25050601: EP-FXT observations
  58. GRB 250506A: SVOM improved position and MXT detection of a fading X-ray afterglow
  59. GRB 250506A: REM optical/NIR upper limits
  60. GRB 250506A: Fermi GBM Observation
  61. GRB 250506A: Swift XRT observations and possible counterpart detection
  62. GRB 250506A: TRT optical observations
  63. GRB 250506A: SVOM/COLIBRÍ (FM-GFT) Upper Limits on the Optical Counterpart
  64. GRB 250504A: Swift-BAT refined analysis
  65. GRB 250430A: Swift-BAT refined analysis
  66. GRB 250504A: VLT/X-shooter upper limits
  67. Fermi GRB 250505A: Global MASTER-Net observations report
  68. GRB 250504A: SVOM/VT upper limit
  69. GRB 250504A: REM optical/NIR observations
  70. GRB 250502A: REM optical/NIR observations
  71. GRB 250504A: MeerLICHT optical afterglow detection
  72. GRB 250504A: Fermi GBM Observation
  73. Fermi GRB 250504A: Global MASTER-Net observations report
  74. GRB 250502A: Swift/UVOT Follow up
  75. GRB 250502A: Mondy and Tien-Shan Optical Observations
  76. GRB 250502A: KAIT optical observations
  77. GRB 250502A: Montarrenti Observatory optical detection
  78. GRB 250502A: Swift-XRT afterglow detection
  79. GRB 250502A: NOT optical observations
  80. GRB 250502a: Liverpool Telescope optical follow-up
  81. GRB 250502B: AstroSat CZTI detection
  82. GRB 250502A: AKO Optical Afterglow Detection
  83. GRB 250502A: LCO optical counterpart detection
  84. GRB 250502A: Swift ToO observations
  85. GRB 250502A: Redshift from OSIRIS+/GTC z = 2.163
  86. GRB 250407A: VZLUSAT-2 detection
  87. Fermi-LAT Gamma-ray Observations of IceCube-250429A
  88. GRB 250502B: DDOTI Optical Observations
  89. GRB 250502A: Early optical counterpart detection by LCO.
  90. GRB 250430A: Swift/UVOT Detection
  91. GRB 250502A: SVOM/VT optical bump
  92. GRB 250502A: TRT optical afterglow confirmation
  93. Fermi GRB 250502B: Global MASTER-Net observations report
  94. GRB 250430A: Optical Observations via Virtual Telescope Project, Italy
  95. GRB 250430A: Calapai Observatory, Massa S. Giorgio (Messina), upper limit
  96. GRB 250430A: SVOM/VT optical observations
  97. GRB 250430A: KAIT optical observations
  98. EP250428b: Pan-STARRS follow-up, upper limit on the optical counterpart, and possible host galaxy.
  99. GRB 250430A / EP250430a: J-band upper limits with WINTER
  100. GRB 250430A: NUTTelA-TAO Early Measurements

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