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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').
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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"

32508 results found.

  1. EP250508a: REM optical/NIR observations
  2. EP250508a: Global MASTER-Net observations report
  3. GRB 250506A: SVOM/VT optical upper limit
  4. EP250508a: COLIBRÍ Optical Limit
  5. GRB 250507A: Swift-XRT refined Analysis
  6. IceCube-250506A: Upper limits from a search for additional neutrino events in IceCube
  7. GRB 250506A: Swift/UVOT Upper Limits
  8. GRB 250507A: follow-up observation with EP-FXT
  9. GRB 250430A / EP250430a: AstroSat CZTI detection
  10. EP#01709175213/IGR J19566+0326: Swift-XRT detection
  11. GRB 250506A: SVOM/COLIBRÍ (FM-GFT) optical upper limit
  12. GRB 250507A: refined SVOM/MXT data analysis
  13. GRB 250507A: REM optical/NIR observations
  14. GRB 250507A: SVOM/VT optical upper limit
  15. GRB 250506A: Swift-XRT observations
  16. Fermi-LAT Gamma-ray Observations of IceCube-250506A
  17. GRB 250507A: SVOM/COLIBRÍ (FM-GFT) optical upper limit
  18. GRB 250506A: Mephisto optical upper limits
  19. GRB 250504A: EIRSAT-1 GMOD Detection
  20. GRB 250506A: Swift ToO observations
  21. GRB 250502A: Bassano Bresciano Observatory upper limit
  22. GRB 250430A: Konus-Wind detection and joint Konus-Wind+Swift-BAT spectral analysis
  23. GRB 250506A: Xinglong 2.16m optical upper limit
  24. SVOM/sb25050601: EP-FXT observations
  25. GRB 250506A: SVOM improved position and MXT detection of a fading X-ray afterglow
  26. GRB 250506A: REM optical/NIR upper limits
  27. GRB 250506A: Fermi GBM Observation
  28. GRB 250506A: Swift XRT observations and possible counterpart detection
  29. GRB 250506A: TRT optical observations
  30. GRB 250506A: SVOM/COLIBRÍ (FM-GFT) Upper Limits on the Optical Counterpart
  31. GRB 250504A: Swift-BAT refined analysis
  32. GRB 250430A: Swift-BAT refined analysis
  33. GRB 250504A: VLT/X-shooter upper limits
  34. Fermi GRB 250505A: Global MASTER-Net observations report
  35. GRB 250504A: SVOM/VT upper limit
  36. GRB 250504A: REM optical/NIR observations
  37. GRB 250502A: REM optical/NIR observations
  38. GRB 250504A: MeerLICHT optical afterglow detection
  39. GRB 250504A: Fermi GBM Observation
  40. Fermi GRB 250504A: Global MASTER-Net observations report
  41. GRB 250502A: Swift/UVOT Follow up
  42. GRB 250502A: Mondy and Tien-Shan Optical Observations
  43. GRB 250502A: KAIT optical observations
  44. GRB 250502A: Montarrenti Observatory optical detection
  45. GRB 250502A: Swift-XRT afterglow detection
  46. GRB 250502A: NOT optical observations
  47. GRB 250502a: Liverpool Telescope optical follow-up
  48. GRB 250502B: AstroSat CZTI detection
  49. GRB 250502A: AKO Optical Afterglow Detection
  50. GRB 250502A: LCO optical counterpart detection
  51. GRB 250502A: Swift ToO observations
  52. GRB 250502A: Redshift from OSIRIS+/GTC z = 2.163
  53. GRB 250407A: VZLUSAT-2 detection
  54. Fermi-LAT Gamma-ray Observations of IceCube-250429A
  55. GRB 250502B: DDOTI Optical Observations
  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. Fermi GRB 250502B: Global MASTER-Net observations report
  61. GRB 250430A: Optical Observations via Virtual Telescope Project, Italy
  62. GRB 250430A: Calapai Observatory, Massa S. Giorgio (Messina), upper limit
  63. GRB 250430A: SVOM/VT optical observations
  64. GRB 250430A: KAIT optical observations
  65. EP250428b: Pan-STARRS follow-up, upper limit on the optical counterpart, and possible host galaxy.
  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. SVOM/sb25043004: EP-FXT observations
  75. EP250430a/GRB 250430A: Einstein Probe WXT detection of the X-ray prompt emission
  76. GRB 250424A: CALET Gamma-Ray Burst Monitor detection
  77. IceCube-250429A: Upper limits from a search for additional neutrino events in IceCube
  78. IceCube-250426A: Upper limits from a search for additional neutrino events in IceCube
  79. GRB 250430A: AKO Optical Afterglow Detection
  80. GRB 250430A: Kanata optical upper limit
  81. EP 250427A: Optical counterpart detection by LCO.
  82. EP250428b: FTW optical and NIR observations
  83. EP250427a/GRB250427A: HCT optical follow-up
  84. EP250427a / GRB 250427A: OHP/T193 continued photometric observations
  85. EP250428b: refined analysis of the EP-FXT follow-up observation
  86. EP250428b: GROWTH-India telescope optical upper limit
  87. EP250428b: SVOM/VT upper limit
  88. EP250428b: SAO RAS optical upper limit
  89. EP250428b: LAST optical upper limit
  90. GRB 250427A: Swift/UVOT Detection
  91. EP250428b: Global MASTER-Net observations report
  92. EP250428b: Einstein Probe detection of a fast X-ray transient
  93. Fermi-LAT Gamma-ray Observations of IceCube-250426A
  94. EP250427a / GRB 250427A: OHP/T193 photometric observations
  95. EP250427a: EP-FXT follow-up observations
  96. EP250427a/GRB 250427A: FTW optical and NIR observations of the counterpart
  97. EP250427a: Lesedi optical counterpart detection
  98. EP250427A: COLIBRÍ Continuing Optical Observations
  99. GRB250427A/EP250427a GIT optical afterglow detection:
  100. EP250427a: LT optical counterpart detection

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