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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"

19235 results found.

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

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