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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. Fermi-LAT Gamma-ray Observations of IceCube-250506A
  2. GRB 250507A: SVOM/COLIBRÍ (FM-GFT) optical upper limit
  3. EP-WXT trigger 01709175213: a new X-ray outburst of LMXB MAXI J1957+032
  4. GRB 250507A: SVOM detection of a long burst
  5. GRB 250506A: Mephisto optical upper limits
  6. GRB 250504A: EIRSAT-1 GMOD Detection
  7. GRB 250506A: Swift ToO observations
  8. GRB 250502A: Bassano Bresciano Observatory upper limit
  9. IceCube-250506A - IceCube observation of a high-energy neutrino candidate track-like event
  10. IceCube Alert 250506.59: Global MASTER-Net observations report
  11. GRB 250430A: Konus-Wind detection and joint Konus-Wind+Swift-BAT spectral analysis
  12. GRB 250506A: Xinglong 2.16m optical upper limit
  13. SVOM/sb25050601: EP-FXT observations
  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. Swift GRB250504.98: Global MASTER-Net observations report
  38. GRB 250502A: Swift/UVOT Follow up
  39. GRB 250502A: Mondy and Tien-Shan Optical Observations
  40. GRB 250502A: KAIT optical observations
  41. GRB 250502A: Montarrenti Observatory optical detection
  42. GRB 250502A: Swift-XRT afterglow detection
  43. Fermi trigger No 767975731: Global MASTER-Net observations report
  44. GRB 250502A: NOT optical observations
  45. GRB 250502a: Liverpool Telescope optical follow-up
  46. GRB 250502B: AstroSat CZTI detection
  47. GRB 250502A: AKO Optical Afterglow Detection
  48. GRB 250502A: LCO optical counterpart detection
  49. GRB 250502A: Swift ToO observations
  50. GRB 250502A: Redshift from OSIRIS+/GTC z = 2.163
  51. GRB 250502C: Fermi GBM Final Localization
  52. GRB 250407A: VZLUSAT-2 detection
  53. Fermi-LAT Gamma-ray Observations of IceCube-250429A
  54. GRB 250502B: DDOTI Optical Observations
  55. GRB 250430A: Swift-XRT refined Analysis
  56. GRB 250502A: Early optical counterpart detection by LCO.
  57. GRB 250430A: Swift/UVOT Detection
  58. GRB 250502A: SVOM/VT optical bump
  59. GRB 250502A: TRT optical afterglow confirmation
  60. GRB 250430A: Enhanced Swift-XRT position
  61. Fermi GRB 250502B: Global MASTER-Net observations report
  62. GRB 250430A: Optical Observations via Virtual Telescope Project, Italy
  63. GRB 250502A: SVOM/COLIBRÍ (FM-GFT) Detection of a Bright Optical Counterpart Candidate
  64. GRB 250502B: Fermi GBM Final Real-time Localization
  65. GRB 250502A: SVOM detection of a burst
  66. GRB 250430A: Calapai Observatory, Massa S. Giorgio (Messina), upper limit
  67. GRB 250430A: SVOM/VT optical observations
  68. GRB 250430A: KAIT optical observations
  69. EP250428b: Pan-STARRS follow-up, upper limit on the optical counterpart, and possible host galaxy.
  70. GRB 250430A / EP250430a: J-band upper limits with WINTER
  71. GRB 250430A: NUTTelA-TAO Early Measurements
  72. EP250427a / GRB 250427A: OHP/T193 photometric observations: third visit
  73. GRB 250430A: DDOTI Optical Observations
  74. GRB 250430A: Leavitt Observatory optical upper limit
  75. GRB 250430A: Bassano Bresciano Observatory upper limit
  76. GRB 250430A : MITSuME Akeno optical upper limits
  77. GRB 250430A / EP250430a: VLT/X-shooter spectroscopic redshift z = 0.767
  78. SVOM/sb25043004: EP-FXT observations
  79. EP250430a/GRB 250430A: Einstein Probe WXT detection of the X-ray prompt emission
  80. GRB 250424A: CALET Gamma-Ray Burst Monitor detection
  81. IceCube-250429A: Upper limits from a search for additional neutrino events in IceCube
  82. IceCube-250426A: Upper limits from a search for additional neutrino events in IceCube
  83. GRB 250430A: AKO Optical Afterglow Detection
  84. GRB 250430A: Kanata optical upper limit
  85. EP 250427A: Optical counterpart detection by LCO.
  86. GRB 250430A: Swift detection of a burst with optical counterpart
  87. Swift GRB250430.73: Global MASTER-Net observations report
  88. EP250428b: FTW optical and NIR observations
  89. EP250427a/GRB250427A: HCT optical follow-up
  90. EP250427a / GRB 250427A: OHP/T193 continued photometric observations
  91. SVOM/sb25043004: SVOM detection of a X-ray transient
  92. Fermi trigger No 767623859: Global MASTER-Net observations report
  93. EP250428b: refined analysis of the EP-FXT follow-up observation
  94. EP250428b: GROWTH-India telescope optical upper limit
  95. EP250428b: SVOM/VT upper limit
  96. EP250428b: SAO RAS optical upper limit
  97. EP250428b: LAST optical upper limit
  98. IceCube-250429A - IceCube observation of a high-energy neutrino candidate track-like event
  99. GRB 250427A: Swift/UVOT Detection
  100. EP250428b: Global MASTER-Net observations report

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