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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. GRB 250506A: GECAM detection
  2. EP250508a: REM optical/NIR observations
  3. GRB 250506A: Swift-XRT afterglow detection
  4. EP250508a: Global MASTER-Net observations report
  5. GRB 250506A: SVOM/VT optical upper limit
  6. EP250508a: COLIBRÍ Optical Limit
  7. EP250508a: Einstein Probe detection of an X-ray transient
  8. GRB 250507A: Swift-XRT refined Analysis
  9. IceCube-250506A: Upper limits from a search for additional neutrino events in IceCube
  10. GRB 250506A: Swift/UVOT Upper Limits
  11. GRB 250427B : SVOM detection of a burst through offline search
  12. GRB 250507A: follow-up observation with EP-FXT
  13. GRB 250430A / EP250430a: AstroSat CZTI detection
  14. EP#01709175213/IGR J19566+0326: Swift-XRT detection
  15. GRB 250506A: SVOM/COLIBRÍ (FM-GFT) optical upper limit
  16. GRB 250507A: refined SVOM/MXT data analysis
  17. GRB 250507A: REM optical/NIR observations
  18. GRB 250507A: SVOM/VT optical upper limit
  19. GRB 250506A: Swift-XRT observations
  20. Fermi-LAT Gamma-ray Observations of IceCube-250506A
  21. GRB 250507A: SVOM/COLIBRÍ (FM-GFT) optical upper limit
  22. EP-WXT trigger 01709175213: a new X-ray outburst of LMXB MAXI J1957+032
  23. GRB 250507A: SVOM detection of a long burst
  24. GRB 250506A: Mephisto optical upper limits
  25. GRB 250504A: EIRSAT-1 GMOD Detection
  26. GRB 250506A: Swift ToO observations
  27. GRB 250502A: Bassano Bresciano Observatory upper limit
  28. IceCube-250506A - IceCube observation of a high-energy neutrino candidate track-like event
  29. IceCube Alert 250506.59: Global MASTER-Net observations report
  30. GRB 250430A: Konus-Wind detection and joint Konus-Wind+Swift-BAT spectral analysis
  31. GRB 250506A: Xinglong 2.16m optical upper limit
  32. SVOM/sb25050601: EP-FXT observations
  33. GRB 250506A: SVOM improved position and MXT detection of a fading X-ray afterglow
  34. GRB 250506A: REM optical/NIR upper limits
  35. GRB 250506A: Fermi GBM Observation
  36. GRB 250506A: Swift XRT observations and possible counterpart detection
  37. GRB 250506A: TRT optical observations
  38. GRB 250506A: SVOM/COLIBRÍ (FM-GFT) Upper Limits on the Optical Counterpart
  39. GRB 250506A: SVOM detection of a burst
  40. GRB 250504A: Swift-BAT refined analysis
  41. GRB 250430A: Swift-BAT refined analysis
  42. GRB 250506A: Fermi GBM Final Real-time Localization
  43. GRB 250504A: Swift-XRT refined Analysis
  44. GRB 250504A: VLT/X-shooter upper limits
  45. Fermi GRB 250505A: Global MASTER-Net observations report
  46. GRB 250504A: SVOM/VT upper limit
  47. GRB 250504A: REM optical/NIR observations
  48. GRB 250502A: REM optical/NIR observations
  49. GRB 250505A: Fermi GBM Final Real-time Localization
  50. GRB 250504A: MeerLICHT optical afterglow detection
  51. GRB 250504A: Fermi GBM Observation
  52. GRB 250504A: Enhanced Swift-XRT position
  53. Fermi GRB 250504A: Global MASTER-Net observations report
  54. GRB 250504A: Swift detection of a burst
  55. GRB 250504A: Fermi GBM Final Real-time Localization
  56. Swift GRB250504.98: Global MASTER-Net observations report
  57. GRB 250502A: Swift/UVOT Follow up
  58. GRB 250502A: Mondy and Tien-Shan Optical Observations
  59. GRB 250502A: KAIT optical observations
  60. GRB 250502A: Montarrenti Observatory optical detection
  61. GRB 250502A: Swift-XRT afterglow detection
  62. Fermi trigger No 767975731: Global MASTER-Net observations report
  63. GRB 250502A: NOT optical observations
  64. GRB 250502a: Liverpool Telescope optical follow-up
  65. GRB 250502B: AstroSat CZTI detection
  66. GRB 250502A: AKO Optical Afterglow Detection
  67. GRB 250502A: LCO optical counterpart detection
  68. GRB 250502A: Swift ToO observations
  69. GRB 250502A: Redshift from OSIRIS+/GTC z = 2.163
  70. GRB 250502C: Fermi GBM Final Localization
  71. GRB 250407A: VZLUSAT-2 detection
  72. Fermi-LAT Gamma-ray Observations of IceCube-250429A
  73. GRB 250502B: DDOTI Optical Observations
  74. GRB 250430A: Swift-XRT refined Analysis
  75. GRB 250502A: Early optical counterpart detection by LCO.
  76. GRB 250430A: Swift/UVOT Detection
  77. GRB 250502A: SVOM/VT optical bump
  78. GRB 250502A: TRT optical afterglow confirmation
  79. GRB 250430A: Enhanced Swift-XRT position
  80. Fermi GRB 250502B: Global MASTER-Net observations report
  81. GRB 250430A: Optical Observations via Virtual Telescope Project, Italy
  82. GRB 250502A: SVOM/COLIBRÍ (FM-GFT) Detection of a Bright Optical Counterpart Candidate
  83. GRB 250502B: Fermi GBM Final Real-time Localization
  84. GRB 250502A: SVOM detection of a burst
  85. GRB 250430A: Calapai Observatory, Massa S. Giorgio (Messina), upper limit
  86. GRB 250430A: SVOM/VT optical observations
  87. GRB 250430A: KAIT optical observations
  88. EP250428b: Pan-STARRS follow-up, upper limit on the optical counterpart, and possible host galaxy.
  89. GRB 250430A / EP250430a: J-band upper limits with WINTER
  90. GRB 250430A: NUTTelA-TAO Early Measurements
  91. EP250427a / GRB 250427A: OHP/T193 photometric observations: third visit
  92. GRB 250430A: DDOTI Optical Observations
  93. GRB 250430A: Leavitt Observatory optical upper limit
  94. GRB 250430A: Bassano Bresciano Observatory upper limit
  95. GRB 250430A : MITSuME Akeno optical upper limits
  96. GRB 250430A / EP250430a: VLT/X-shooter spectroscopic redshift z = 0.767
  97. SVOM/sb25043004: EP-FXT observations
  98. EP250430a/GRB 250430A: Einstein Probe WXT detection of the X-ray prompt emission
  99. GRB 250424A: CALET Gamma-Ray Burst Monitor detection
  100. IceCube-250429A: Upper limits from a search for additional neutrino events in IceCube

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