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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"

23838 results found.

  1. GRB 250430A: Calapai Observatory, Massa S. Giorgio (Messina), upper limit
  2. GRB 250430A: KAIT optical observations
  3. GRB 250430A: NUTTelA-TAO Early Measurements
  4. EP250427a / GRB 250427A: OHP/T193 photometric observations: third visit
  5. GRB 250430A: DDOTI Optical Observations
  6. GRB 250430A: Leavitt Observatory optical upper limit
  7. GRB 250430A: Bassano Bresciano Observatory upper limit
  8. GRB 250430A : MITSuME Akeno optical upper limits
  9. GRB 250430A / EP250430a: VLT/X-shooter spectroscopic redshift z = 0.767
  10. SVOM/sb25043004: EP-FXT observations
  11. EP250430a/GRB 250430A: Einstein Probe WXT detection of the X-ray prompt emission
  12. GRB 250424A: CALET Gamma-Ray Burst Monitor detection
  13. GRB 250430A: AKO Optical Afterglow Detection
  14. GRB 250430A: Kanata optical upper limit
  15. EP 250427A: Optical counterpart detection by LCO.
  16. GRB 250430A: Swift detection of a burst with optical counterpart
  17. Swift GRB250430.73: Global MASTER-Net observations report
  18. EP250428b: FTW optical and NIR observations
  19. EP250427a/GRB250427A: HCT optical follow-up
  20. EP250427a / GRB 250427A: OHP/T193 continued photometric observations
  21. SVOM/sb25043004: SVOM detection of a X-ray transient
  22. Fermi trigger No 767623859: Global MASTER-Net observations report
  23. EP250428b: GROWTH-India telescope optical upper limit
  24. EP250428b: Global MASTER-Net observations report
  25. EP250427a / GRB 250427A: OHP/T193 photometric observations
  26. EP250427a: EP-FXT follow-up observations
  27. EP250427a/GRB 250427A: FTW optical and NIR observations of the counterpart
  28. EP250427a: Lesedi optical counterpart detection
  29. EP250427A: COLIBRÍ Continuing Optical Observations
  30. GRB250427A/EP250427a GIT optical afterglow detection:
  31. GRB 250427A: Swift-XRT refined Analysis
  32. EP250427a / GRB 250427A: LCO optical counterpart detection
  33. EP250427a / GRB 250427A: VLT/X-shooter redshift confirmation z = 1.520
  34. EP250427a: REM optical/NIR afterglow detection
  35. GRB 250424A: LCO optical observation
  36. GRB 250427A/ EP250427a: Fermi-GBM Sub-Threshold Detection
  37. EP250427A: COLIBRÍ Optical Detection
  38. EP250427a: TRT optical counterpart detection
  39. EP250427a: Global MASTER-Net observations report
  40. IceCube Alert 250426.74: Global MASTER-Net observations report
  41. GRB 250424A: Swift-BAT refined analysis
  42. GRB 250424A: SVOM/GRM observation of a long burst
  43. GRB 250424A: PRIME near-infrared detection
  44. GRB 250424A: WINTER J-band detection
  45. GRB 250424A: EIRSAT-1 GMOD Detection
  46. GRB 250419A: Mondy Optical Observations
  47. GRB 250424A: Swift/UVOT Detection
  48. Konus-Wind detection of GRB 250424A
  49. GRB 250424A: Kilonova-Catcher optical afterglow detection
  50. GRB 250419a: Continued Liverpool Telescope observations
  51. GRB 250419A: Liverpool Telescope optical upper limit
  52. GRB 250330B: GRBAlpha detection
  53. GRB 250424A: Swift-XRT refined Analysis
  54. GRB 250424A: AstroSat CZTI detection of a bright long burst
  55. GRB 250424A: COLIBRÍ Detection of a Bright Optical Counterpart
  56. GRB 250424A: BlackGEM optical afterglow detection
  57. GRB 250424A: VLT/X-shooter spectroscopic redshift z = 0.310
  58. GRB 250424A: likely host galaxy
  59. GRB 250424A: DDOTI Afterglow Detection
  60. GRB 250424A: REM optical/NIR afterglow detection
  61. GRB 250424A: Swift detection of a burst with an optical counterpart
  62. Swift GRB250424A: Global MASTER-Net observations report
  63. Swift GRB250424A: Global MASTER-Net OT detection
  64. EP250421a: Nickel optical upper limit
  65. EP250421a: Upper limits from Fermi-GBM Observations
  66. SVOM/sb25042207: XRT observations
  67. SVOM/sb25042207: GOTO optical upper limits
  68. SVOM/sb25042207: SVOM detection of an X-ray transient
  69. IceCube-250421A: DDOTI Detection of the LAST Candidate
  70. GRB 250419A: Mephisto Multi-band Optical Detection
  71. EP250421a: NOT optical observations
  72. EP250421a: REM optical upper limit
  73. EP250421a: Swift/XRT counterpart detection
  74. EP250421A: COLIBRÍ Optical Upper Limit
  75. GRB 250419A: Mondy Continued Optical Observations
  76. Fermi GRB 250421A: Global MASTER-Net observations report
  77. EP250421a: Global MASTER-Net observations report
  78. EP250421a: Einstein Probe detection of an X-ray transient
  79. EP250421a: Mephisto optical counterpart confirmation
  80. IceCube Alert 250421.71: Global MASTER-Net observations report
  81. EP250421a: JinShan likely optical counterpart
  82. The EP-WXT trigger 01709135179: Kinder optical counterpart candidate
  83. GRB 250421A: Fermi GBM Final Real-time Localization
  84. GRB 250419A: Liverpool Telescope observations
  85. GRB 250419A: LCO optical observation
  86. GRB 250419A: JinShan optical observations
  87. GRB 250419A: SVOM/VT optical continuous observations
  88. GRB 250419A: SVOM/C-GFT optical observations
  89. GRB 250419A: Swift/UVOT Follow up
  90. GRB 250419A: LCO optical afterglow multi-band observations
  91. GRB 250419A: Mondy and AbAO Optical Observations
  92. GRB 250419A: AKO Optical Afterglow Detection
  93. GRB 250419A: MASTER optical afterglow observation
  94. GRB 250407A: GTC/OSIRIS+ spectroscopic redshift z = 1.36
  95. GRB 250419A: Swift-XRT refined Analysis
  96. GRB 250419A: GOTO optical counterpart detection
  97. GRB 250419A: KAIT optical afterglow observations
  98. GRB 250419A: SVOM/VT optical bright counterpart confirmation
  99. GRB 250419A: SVOM/COLIBRÍ (FM-GFT) Detection of the Optical Counterpart
  100. GRB 250419A: SVOM detection of a soft burst

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