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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"

19334 results found.

  1. GRB 250823A: Swift-BAT refined analysis
  2. GRB 250823A: Swift-XRT refined Analysis
  3. LIGO/Virgo/KAGRA S250818k: Swift Observations of AT 2025ulz - Second Epoch
  4. GRB 250823A: COLIBRÍ optical observations
  5. GRB 250823A: SVOM/VT optical observation
  6. GRB 250823A: Swift/UVOT Detection
  7. GRB 250823A: NOT optical observations
  8. GRB 250823A: Fermi GBM Observation
  9. GRB 250818B: MeerKAT Detection
  10. GRB 250823A: Enhanced Swift-XRT position
  11. GRB 250823A: LCOGT Optical Detection
  12. GRB 250823A: BOOTES6/DPRT early optical detection
  13. GRB 250823A: Liverpool Telescope optical detection
  14. GRB 250823A: Swift detection of a burst
  15. Swift GRB250823.84: Global MASTER-Net observations report
  16. GRB 250821A: Kilonova-Catcher optical upper limits
  17. EP250821a: Swift/XRT counterpart fading
  18. GRB 250821A: Swift-BAT refined analysis
  19. EP250821a: Swift/UVOT further observations.
  20. GRB 250821A: VLT/FORS2 Optical Observation
  21. GRB 250821A: GECAM-B detection
  22. EP250821a: SVOM/VT optical observation
  23. GRB 250821A: NOT z-band upper limit
  24. GRB 250821A: Swift-XRT refined Analysis
  25. Swift GRB 250821A: Global MASTER-Net observations report
  26. GRB 250821A: Enhanced Swift-XRT position
  27. GRB 250821A: Swift/UVOT Upper Limits
  28. EP250821a: Rapidly fading optical source detected in Las Cumbres followup
  29. EP250821a: Swift XRT and UVOT counterpart detection
  30. GRB 250821A: LCOGT Optical Upper Limits
  31. GRB 250814A: CMO SAI and SAO RAS izJ observations.
  32. GRB 250821A: Prompt enhanced Swift-XRT position
  33. GRB 250821A: Swift detection of a burst
  34. LIGO/Virgo/KAGRA S250818k: Swift observations of AT 2025ulz
  35. GRB 250814A: Swift/UVOT Upper Limits
  36. GRB 250813B: Swift/UVOT Upper Limit
  37. IPN triangulation of GRB 250814C (short)
  38. IPN triangulation of GRB 250804B (short)
  39. GRB 250818B: Kilonova-Catcher optical afterglow detection
  40. GRB 250818A: AstroSat CZTI detection
  41. GRB 250818B: Swift/UVOT Detection
  42. GRB 250818B: SAO RAS optical observations
  43. Swift GRB 250818A: Global MASTER-Net observations report
  44. GRB 250818A: Swift-XRT refined Analysis
  45. GRB 250818A: Swift-BAT refined analysis
  46. GRB 250818B: Keck redshift of the optical afterglow
  47. GRB 250818A: Swift/UVOT Upper Limits
  48. GRB 250818A: Enhanced Swift-XRT position
  49. GRB 250818A: Fermi GBM Observation
  50. GRB 250818B: SVOM/VT optical observation
  51. GRB 250814A: Further GRAWITA TNG NIR observations
  52. GRB 250818B: Swift-XRT afterglow detection
  53. GRB 250818A: Swift detection of a burst
  54. sb25081602: Swift-XRT observations
  55. GRB 250814A: Swift-BAT refined analysis
  56. GRB 250814A: Further COLIBRÍ optical upper limit
  57. GRB 250814A: detection of the afterglow candidate with Liverpool Telescope
  58. GRB 250814A: GRAWITA TNG NIR observations
  59. GRB 250814A: Mondy optical observations of the candidate counterpart to LVK S250814bg
  60. GRB250814A: TRT optical upper limits
  61. GRB 250814C: SVOM/GRM observation of a short burst
  62. LIGO/Virgo/KAGRA S250813k: Swift XRT observations, 2 X-ray sources
  63. GRB 250813B: SVOM/GRM observation
  64. GRB 250814A: P200/WIRC observations of the afterglow candidate
  65. GRB 250814A: possible optical afterglow candidate at Spanish observatories
  66. GRB 250814A: KAIT optical upper limit
  67. GRB 250814A: Swift-XRT refined Analysis
  68. GRB 240814A: Fermi GBM Observation
  69. GRB 250814A: Possible afterglow candidate from P200/WIRC
  70. GRB 250814A: Optical observations with MDM Hiltner 2.4m telescope
  71. Swift GRB250814.32: Global MASTER-Net observations report
  72. GRB 250814A: J-band upper limit from WINTER
  73. GRB 250813B: SVOM/VT optical observations
  74. GRB 250814A: COLIBRÍ optical upper limit
  75. LIGO/Virgo/KAGRA S250814bg: Identification of a GW compact binary merger candidate possibly associated with GRB 250814A detected by Fermi GBM and Swift BAT
  76. GRB 250814A: DDOTI Optical Upper Limit
  77. GRB 250813B: Swift-XRT afterglow detection
  78. GRB 250814A: Swift detection of a burst coincident with a subthreshold GW trigger
  79. EP250812a: NOT, NTT, and GS observations
  80. GRB 250812A: Swift/UVOT Detection
  81. EP250812a: SVOM/VT optical counterpart
  82. GRB 250812A: Swift ToO observations
  83. GRB 250807B: Swift-BAT refined analysis
  84. EP 250812a: GOTO optical upper limit
  85. GRB 250812A: Kilonova-Catcher optical afterglow detection
  86. EP250812a: Swift-XRT counterpart detection
  87. GRB 250812A: SVOM/VT optical afterglow confirmation
  88. GRB 250812A: Swift-XRT afterglow detection
  89. GRB 250809A: Swift-BAT refined analysis
  90. GRB 250807A: Swift-BAT refined analysis
  91. GRB 250809A: Swift/UVOT Detection
  92. Corrected Swift-XRT Refined Analysis of GRB 250809A
  93. GRB 250809A: Swift-XRT refined Analysis
  94. GRB 250807B: SVOM/VT optical observation
  95. GRB 250809A: LCOGT Optical Upper Limits
  96. GRB 250702B: Chandra X-ray Detection
  97. GRB 250808A: VLT X-shooter candidate counterpart
  98. GRB 250809A: Prompt enhanced Swift-XRT position
  99. GRB 250809A: Swift detection of a gamma ray burst
  100. GRB 250808A: Swift-XRT candidate counterpart detection

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