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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"

6791 results found.

  1. GRB 250911A: Swift/UVOT Detection
  2. GRB 250910A / EP250910a: Swift-XRT afterglow detection
  3. LIGO/Virgo/KAGRA S250911ac: Identification of a GW compact binary merger candidate
  4. GRB 250702B: Late time Chandra observations
  5. EP#01709240653: Swift-XRT observations
  6. Fermi-LAT Gamma-ray Observations of IceCube-250905A
  7. GRB 250903A: Swift-XRT afterglow detection
  8. EP250905b: EP-FXT follow-up observation
  9. GRB 250905A: Swift-XRT refined Analysis
  10. GRB 250905A: Swift/UVOT Upper Limits
  11. GRB 250903A: Swift/UVOT detection
  12. GRB 250904A: Swift-XRT refined Analysis
  13. GRB 250903A: Swift-XRT observations
  14. EP250903a: Swift-XRT observations
  15. EP#01709201209: Swift-XRT observations
  16. GRB 250903A: LCO optical afterglow detection
  17. EP250903a: LCO candidate counterpart discovery
  18. Fermi-LAT Gamma-ray Observations of IceCube-250831A
  19. GRB 250902A: Fermi GBM Detection
  20. GRB 250901A: Swift/UVOT Upper Limit
  21. GRB 250830B: Swift-XRT afterglow detection
  22. GRB 250901A: EP-FXT follow-up observation
  23. GRB 250901A: SVOM/VT optical afterglow with VHF data
  24. GRB 250901A: Swift-XRT afterglow detection
  25. EP250901a: Swift-XRT observations
  26. EP250831a: NOT optical observations and tentative afterglow candidate
  27. EP250831a: EP-FXT follow-up observation
  28. EP250831a: Swift-XRT observations
  29. EP250831a: EP-WXT detection of a fast X-ray transient
  30. GRB 250831A: Swift-XRT counterpart detection
  31. GRB 250831A: SVOM/VT upper limit with VHF data
  32. GRB 250830B: Swift-XRT observations
  33. EP250828a: Optical counterpart detection with Kinder observations
  34. EP250827a: Swift/UVOT Detection
  35. EP250828a: Optical upper limit with Kinder observations
  36. EP250827a: confirmation of optical rebrightening with LCO
  37. EP250827a: Swift-XRT counterpart detection
  38. EP250827a: Gemini-South redshift z = 1.613
  39. LIGO/Virgo/KAGRA S250818k: SAO RAS BTA z-band observations of AT2025ulz
  40. GRB 250823A: Swift-XRT refined Analysis
  41. LIGO/Virgo/KAGRA S250818k: Swift Observations of AT 2025ulz - Second Epoch
  42. GRB 250823A: Fermi GBM Observation
  43. EP250821a: Swift/XRT counterpart fading
  44. GRB 250821A: Swift-XRT refined Analysis
  45. GRB 250821B: Fermi GBM Detection
  46. LIGO/Virgo/KAGRA S250818k: ENGRAVE observations of AT 2025ulz
  47. EP250821a: Swift XRT and UVOT counterpart detection
  48. GRB 250821A: Prompt enhanced Swift-XRT position
  49. LIGO/Virgo/KAGRA S250818k: EP/FXT observation of AT 2025ulz
  50. GRB 250813B: Swift/UVOT Upper Limit
  51. GRB 250818B: Swift/UVOT Detection
  52. GRB 250818B: SAO RAS optical observations
  53. GRB 250818A: Swift-XRT refined Analysis
  54. GRB 250818B: EP-FXT counterpart detection
  55. GRB 250818A: Fermi GBM Observation
  56. GRB 250818B: Swift-XRT afterglow detection
  57. sb25081602: Swift-XRT observations
  58. LIGO/Virgo/KAGRA S250813k: Swift XRT observations, 2 X-ray sources
  59. GRB 250814A: P200/WIRC observations of the afterglow candidate
  60. GRB 250814A: Swift-XRT refined Analysis
  61. GRB 240814A: Fermi GBM Observation
  62. GRB 250814A: Possible afterglow candidate from P200/WIRC
  63. GRB 250813B: Fermi GBM Observation
  64. GRB 250814A: Optical observations with MDM Hiltner 2.4m telescope
  65. GRB 250813B: EP-FXT counterpart detection
  66. Fermi-LAT Gamma-ray Observations of IceCube-250813A
  67. GRB 250813B: Swift-XRT afterglow detection
  68. GRB 250812A: Swift/UVOT Detection
  69. EP250812a: Swift-XRT counterpart detection
  70. GRB 250812A: SVOM/COLIBRÍ (FM-GFT) optical observations
  71. GRB 250812A: Swift-XRT afterglow detection
  72. Fermi-LAT Gamma-ray Observations of IceCube-250804A
  73. GRB 250809A: Swift-XRT refined Analysis
  74. GRB 250702B: Chandra X-ray Detection
  75. GRB 250808A: Fermi GBM Observation
  76. GRB 250808A: Swift-XRT candidate counterpart detection
  77. GRB 250807A: Swift-XRT refined Analysis
  78. GRB 250807B: Swift-XRT refined Analysis
  79. Swift GRB250807.65: Global MASTER-Net observations report
  80. GRB 250806A: EP-FXT observation
  81. EP#01709198415/EP250806a: Swift-XRT observations
  82. EP250802a: EP-FXT follow-up observation
  83. GRB 250806A: Swift-XRT counterpart detection
  84. GRB 250806A: SVOM/VT optical upper limit
  85. GRB 250805A: Swift-XRT refined Analysis
  86. GRB 250804B: Swift-XRT observations
  87. EP250802a: GROWTH-India Telescope optical upper limit
  88. GRB 250727A: Swift-XRT afterglow confirmation and refined analysis
  89. LIGO/Virgo/KAGRA S250727dc: Swift-XRT observations, 8 X-ray sources
  90. GRB 250728A: Swift-XRT observations
  91. GRB 250728A: Fermi GBM Observation
  92. GRB 250727A: Swift-XRT observations
  93. GRB 250725A: Swift-XRT refined Analysis
  94. GRB 250725A: Fermi GBM Observation
  95. Konus-Wind detection of GRB 250725A
  96. GRB 250725A: Fermi-LAT detection
  97. Swift GRB 250725A: Global MASTER-Net observations report
  98. SVOM J195836+32283 is not a real source
  99. GRB 250721A: Fermi GBM Observation
  100. SVOM J195836+32283/sb25072103: Swift XRT/UVOT upper limits

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