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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"

6788 results found.

  1. GRB 251025B: Swift-XRT confirmation of fading
  2. GRB 251026B: Swift-XRT observations of GOTO25jgl/AT2025absf
  3. Fermi-LAT Gamma-ray Observations of IceCube-251025A
  4. GRB 251023B: Swift-UVOT Upper Limits
  5. GRB 251027A: Swift-XRT observations
  6. GRB 251026A: Swift-XRT observations
  7. GRB 251025B: ULL-ASTRO-MASTER optical counterpart detection with IAC80 telescope at Teide Observatory
  8. GRB 251025B: Swift-XRT afterglow detection
  9. GRB 251024A: Swift-XRT refined Analysis
  10. GRB 251025B: SVOM/VT optical observations with VHF data
  11. GRB 251022A: Swift-XRT detection of GOTO25iym
  12. EP251023b: Global MASTER-Net observations report
  13. GRB 251022A: Fermi GBM Observation
  14. EP251023a: ULL-ASTRO-MASTER detection of the optical afterglow with LCO 40-cm telescope at Teide Observatory
  15. EP#01709247298: Swift-XRT counterpart detection
  16. GRB 251013C: further SAO RAS optical observations
  17. EP251023a: GSP Optical Counterpart Detection
  18. GRB 251022A: Fermi-LAT detection
  19. GRB 251016B: Fermi GBM Detection
  20. Fermi-LAT gamma-ray observations of IceCube-251018A
  21. GRB 251016A: Fermi GBM Observation
  22. GRB 251018A: Fermi GBM Observation
  23. GRB 251018A: Swift-XRT refined Analysis
  24. GRB 251016A: Swift-XRT afterglow detection
  25. GRB 251016A: Swift/UVOT Detection
  26. GRB 251017A: Swift-XRT refined Analysis
  27. GRB 251011A: Fermi GBM Observation
  28. sb25101602: Swift-XRT counterpart detection
  29. GRB 251014A: Swift-XRT observations
  30. Fermi-LAT Gamma-ray Observations of IceCube-251014A
  31. GRB 251013D: Swift/UVOT Observations
  32. GRB 251013C: Swift/UVOT Detection
  33. GRB 251013D: Swift-XRT observations
  34. GRB 251014B: Swift-XRT observations
  35. GRB 251014D: Swift-XRT afterglow detection
  36. GRB 251013D: Fermi GBM Observation
  37. GRB 251013C: Early and late-time optical counterpart detection by LCO
  38. GRB 251013C: Fermi GBM Observation
  39. GRB 251013C NUTTelA-TAO / BSTI Early Measurements
  40. GRB 251013C: ULL-ASTRO-MASTER detection of the optical afterglow with the LCO 40-cm telescope at Sutherland Observatory
  41. GRB 251014A: SAO RAS optical upper limit
  42. GRB 251014A: Fermi GBM Observation
  43. GRB 251013C: Swift-XRT counterpart detection
  44. GRB 251013C: SAO RAS optical observations
  45. GRB 251011B: Swift-XRT refined Analysis
  46. GRB 251011B: Fermi GBM Observation
  47. GRB 251006A: Fermi GBM Observation
  48. GRB 251003A: Fermi GBM Observation
  49. GRB 251006B: Fermi GBM Observation
  50. GRB 251006B/EP251006a: EP-FXT afterglow detection
  51. GRB 251007A: Swift-XRT refined Analysis
  52. GRB 251007B: Swift-XRT refined Analysis
  53. EP251003a: LCO and VST fading optical counterpart
  54. GRB 251006B/EP251006a: EP-FXT follow-up observation
  55. GRB 251005C: Swift-XRT refined Analysis
  56. GRB 251005C: Fermi GBM Observation
  57. GRB 251002A: Swift/UVOT detection
  58. GRB 251003A: Swift-XRT refined Analysis
  59. GRB 251002A: Fermi GBM Observation
  60. GRB 251002A: Swift-XRT afterglow detection
  61. GRB 251002A: ULL-ASTRO-MASTER early detection of the optical afterglow with the LCO 40-cm telescope at Sutherland Observatory
  62. GRB 251001B: Swift-XRT refined Analysis
  63. GRB 251001B: Fermi GBM Observation
  64. GRB 251001A: Fermi GBM Detection
  65. Fermi-LAT Gamma-ray Observations of IceCube-250926A
  66. GRB 250925A: Swift-XRT refined Analysis
  67. GRB 250920C: ULL-ASTRO-MASTER early detection of the optical afterglow with LCO 40-cm telescope at Siding Spring Observatory
  68. GRB 250925A: Swift/UVOT Upper Limits
  69. GRB 250925A: Optical Observations via Virtual Telescope Project, Italy
  70. GRB 250925A: GROWTH-India Telescope Upper Limits
  71. GRB 250924A: Swift-XRT refined Analysis
  72. Konus-Wind detection of GRB 250920C
  73. GRB 250920B: SAO RAS optical observations
  74. GRB 250920C: Swift-XRT refined Analysis
  75. GRB 250916A: SAO RAS Zeiss-1000 optical observations
  76. GRB 250920B: Fermi GBM Observation
  77. GRB 250920A: Fermi GBM Detection
  78. GRB 250920C: Fermi GBM Observation
  79. GRB 250920B: Swift-XRT refined Analysis
  80. Konus-Wind detection of GRB 250919A
  81. GRB 250919A: Fermi GBM Observation
  82. GRB 250919A: Swift-XRT afterglow detection
  83. GRB 250919A: Fermi-LAT detection
  84. GRB 250916A: Fermi GBM Observation
  85. GRB 250917B: VLT/HAWK-I near-infrared observations
  86. GRB 250916A: Swift-XRT observations
  87. EP250916a: EP-FXT follow-up observation
  88. GRB 250916A: MAO/AZT-22 optical observations
  89. GRB 250916A: SAO RAS optical observations
  90. GRB 250917B: Fermi GBM Observation
  91. GRB 250917B: Swift-XRT observations
  92. GRB 250912A: Swift-XRT observations
  93. GRB 250912A: Fermi GBM Observation
  94. EP250911a: SAO RAS optical observations
  95. GRB 250911A: Swift-XRT refined Analysis
  96. EP250911a: Swift-XRT observations
  97. EP250911a: Optical detection with Kinder observations
  98. GRB 250911A: Swift/UVOT Detection
  99. GRB 250910A / EP250910a: Swift-XRT afterglow detection
  100. LIGO/Virgo/KAGRA S250911ac: Identification of a GW compact binary merger candidate

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