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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"

32495 results found.

  1. GRB 250506A: Swift-XRT observations
  2. Fermi-LAT Gamma-ray Observations of IceCube-250506A
  3. GRB 250507A: SVOM/COLIBRÍ (FM-GFT) optical upper limit
  4. GRB 250506A: Mephisto optical upper limits
  5. GRB 250504A: EIRSAT-1 GMOD Detection
  6. GRB 250506A: Swift ToO observations
  7. GRB 250502A: Bassano Bresciano Observatory upper limit
  8. GRB 250430A: Konus-Wind detection and joint Konus-Wind+Swift-BAT spectral analysis
  9. GRB 250506A: Xinglong 2.16m optical upper limit
  10. SVOM/sb25050601: EP-FXT observations
  11. GRB 250506A: SVOM improved position and MXT detection of a fading X-ray afterglow
  12. GRB 250506A: REM optical/NIR upper limits
  13. GRB 250506A: Fermi GBM Observation
  14. GRB 250506A: Swift XRT observations and possible counterpart detection
  15. GRB 250506A: TRT optical observations
  16. GRB 250506A: SVOM/COLIBRÍ (FM-GFT) Upper Limits on the Optical Counterpart
  17. GRB 250504A: Swift-BAT refined analysis
  18. GRB 250430A: Swift-BAT refined analysis
  19. GRB 250504A: VLT/X-shooter upper limits
  20. Fermi GRB 250505A: Global MASTER-Net observations report
  21. GRB 250504A: SVOM/VT upper limit
  22. GRB 250504A: REM optical/NIR observations
  23. GRB 250502A: REM optical/NIR observations
  24. GRB 250504A: MeerLICHT optical afterglow detection
  25. GRB 250504A: Fermi GBM Observation
  26. Fermi GRB 250504A: Global MASTER-Net observations report
  27. GRB 250502A: Swift/UVOT Follow up
  28. GRB 250502A: Mondy and Tien-Shan Optical Observations
  29. GRB 250502A: KAIT optical observations
  30. GRB 250502A: Montarrenti Observatory optical detection
  31. GRB 250502A: Swift-XRT afterglow detection
  32. GRB 250502A: NOT optical observations
  33. GRB 250502a: Liverpool Telescope optical follow-up
  34. GRB 250502B: AstroSat CZTI detection
  35. GRB 250502A: AKO Optical Afterglow Detection
  36. GRB 250502A: LCO optical counterpart detection
  37. GRB 250502A: Swift ToO observations
  38. GRB 250502A: Redshift from OSIRIS+/GTC z = 2.163
  39. GRB 250407A: VZLUSAT-2 detection
  40. Fermi-LAT Gamma-ray Observations of IceCube-250429A
  41. GRB 250502B: DDOTI Optical Observations
  42. GRB 250502A: Early optical counterpart detection by LCO.
  43. GRB 250430A: Swift/UVOT Detection
  44. GRB 250502A: SVOM/VT optical bump
  45. GRB 250502A: TRT optical afterglow confirmation
  46. Fermi GRB 250502B: Global MASTER-Net observations report
  47. GRB 250430A: Optical Observations via Virtual Telescope Project, Italy
  48. GRB 250430A: Calapai Observatory, Massa S. Giorgio (Messina), upper limit
  49. GRB 250430A: SVOM/VT optical observations
  50. GRB 250430A: KAIT optical observations
  51. EP250428b: Pan-STARRS follow-up, upper limit on the optical counterpart, and possible host galaxy.
  52. GRB 250430A / EP250430a: J-band upper limits with WINTER
  53. GRB 250430A: NUTTelA-TAO Early Measurements
  54. EP250427a / GRB 250427A: OHP/T193 photometric observations: third visit
  55. GRB 250430A: DDOTI Optical Observations
  56. GRB 250430A: Leavitt Observatory optical upper limit
  57. GRB 250430A: Bassano Bresciano Observatory upper limit
  58. GRB 250430A : MITSuME Akeno optical upper limits
  59. GRB 250430A / EP250430a: VLT/X-shooter spectroscopic redshift z = 0.767
  60. SVOM/sb25043004: EP-FXT observations
  61. EP250430a/GRB 250430A: Einstein Probe WXT detection of the X-ray prompt emission
  62. GRB 250424A: CALET Gamma-Ray Burst Monitor detection
  63. IceCube-250429A: Upper limits from a search for additional neutrino events in IceCube
  64. IceCube-250426A: Upper limits from a search for additional neutrino events in IceCube
  65. GRB 250430A: AKO Optical Afterglow Detection
  66. GRB 250430A: Kanata optical upper limit
  67. EP 250427A: Optical counterpart detection by LCO.
  68. EP250428b: FTW optical and NIR observations
  69. EP250427a/GRB250427A: HCT optical follow-up
  70. EP250427a / GRB 250427A: OHP/T193 continued photometric observations
  71. EP250428b: refined analysis of the EP-FXT follow-up observation
  72. EP250428b: GROWTH-India telescope optical upper limit
  73. EP250428b: SVOM/VT upper limit
  74. EP250428b: SAO RAS optical upper limit
  75. EP250428b: LAST optical upper limit
  76. GRB 250427A: Swift/UVOT Detection
  77. EP250428b: Global MASTER-Net observations report
  78. EP250428b: Einstein Probe detection of a fast X-ray transient
  79. Fermi-LAT Gamma-ray Observations of IceCube-250426A
  80. EP250427a / GRB 250427A: OHP/T193 photometric observations
  81. EP250427a: EP-FXT follow-up observations
  82. EP250427a/GRB 250427A: FTW optical and NIR observations of the counterpart
  83. EP250427a: Lesedi optical counterpart detection
  84. EP250427A: COLIBRÍ Continuing Optical Observations
  85. GRB250427A/EP250427a GIT optical afterglow detection:
  86. EP250427a: LT optical counterpart 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. EP250427a: REM optical/NIR afterglow detection
  92. GRB 250424A: LCO optical observation
  93. GRB 250427A/ EP250427a: Fermi-GBM Sub-Threshold Detection
  94. EP250427A: COLIBRÍ Optical Detection
  95. EP250427a: TRT optical counterpart detection
  96. EP250427a: Global MASTER-Net observations report
  97. EP250427a: Einstein Probe detection of a fast X-ray transient
  98. GRB 250424A: Swift-BAT refined analysis
  99. IceCube-250426A - IceCube observation of a high-energy neutrino candidate track-like event (duplicate submission)
  100. GRB 250424A: SVOM/GRM observation of a long burst

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