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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"

15986 results found.

  1. GRB 250916A: Swift-XRT observations
  2. GRB 250916A: MAO/AZT-22 optical observations
  3. GRB 250916A: SAO RAS optical observations
  4. GRB 250916A : GIT optical observations
  5. GRB250917B: WFST optical observations
  6. GRB 250916A: GOTO optical counterpart candidate
  7. EP250827b: VLA Observations
  8. LIGO/Virgo/KAGRA S250818k: HCT optical follow-up
  9. GRB 250912A: SVOM/COLIBRÍ (FM-GFT) optical observations
  10. GRB 250912A: VLT observations
  11. GRB 250912A:SVOM/VT optical upper limit
  12. GRB 250912A: LCO optical upper limit
  13. EP250908c: tentative VLT/FORS2 redshift z = 2.87
  14. EP250911a: refined analysis of the EP-WXT and EP-FXT observations
  15. GRB 250910B: SVOM/GRM observation
  16. EP250911a: SVOM/VT optical observation
  17. GRB 250911A: MASTER optical counterpart observations
  18. EP250911a: SAO RAS optical observations
  19. EP250911a: Swift-XRT observations
  20. EP250911a: Optical detection with Kinder observations
  21. GRB 250910A / EP250910a: Swift-XRT afterglow detection
  22. GRB 250910A / EP250910a : VLT/HAWK-I NIR counterpart discovery
  23. EP250911a: COLIBRÍ optical observations
  24. EP250911a: LCO optical counterpart discovery
  25. GRB 250911A: COLIBRÍ optical counterpart candidate
  26. GRB 250910A / EP250910a: VLT/HAWK-I near-infrared observations
  27. GRB 250910A: SVOM/VT optical upper limit
  28. EP250908C: GROND observation of the fading optical counterpart
  29. GRB 250910A: LCO optical upper limit
  30. EP250908c: SVOM/VT optical observation
  31. EP250908c: VLT/FORS2 optical counterpart identification
  32. EP250908b: SVOM/VT optical candidate (Coordinate supplement for GCN 41758)
  33. EP250908b: SVOM/VT optical candidate
  34. EP#01709240652 (possibly EP250908a): FTW optical and NIR observations
  35. GRB 250903A: Swift-XRT afterglow detection
  36. EP250905a: Liverpool Telescope i-band upper limits
  37. LIGO/Virgo/KAGRA S250830bp: DECam DESGW Epoch 2 Candidates
  38. EP250905a: Liverpool Telescope observations
  39. EP250905a: FTW one optical and multiple NIR counterpart candidates
  40. EP250905a: JinShan likely optical counterpart detection
  41. GRB 250905A: Swift/UVOT Upper Limits
  42. GRB250904A: Liverpool Telescope upper limits
  43. GRB 250903A: Swift/UVOT detection
  44. GRB 250905A: KAIT optical upper limit
  45. GRB 250904A: TRT optical counterpart detection
  46. EP250827b: Gemini Spectroscopic Confirmation of AT2025wkm as a Ic-BL Supernova
  47. GRB 250903A: Swift-XRT observations
  48. EP250903a: Swift-XRT observations
  49. EP250903a: retraction of the LCO candidate, and discovery of the likely counterpart
  50. GRB 250903A: VLT X-shooter spectroscopic redshift z = 1.590
  51. GRB 250903A: EP-FXT counterpart detection
  52. GRB 250903A: LCO optical observation
  53. GRB 250903A: LCO optical afterglow detection
  54. GRB 250903A: SVOM/VT optical confirmation with VHF data
  55. EP250903a: SVOM/VT optical confirmation
  56. EP250901a: Mondy, Assy and SAO RAS optical limits
  57. Subject GRB 250903A: SVOM/MXT afterglow detection
  58. GRB 250903A: TRT optical counterpart detection
  59. GRB 250903A: SVOM detection of a burst
  60. EP250903a: TRT optical observations
  61. EP 250827B: Detection of supernova counterpart by LCO.
  62. EP/WXT01709201159: GOTO optical follow-up
  63. EP250827b / AT 2025wkm: TRT optical observations
  64. EP250827b: NOT spectroscopic observations and AT 2025wkm classification as a broad-lined type-Ic supernova
  65. GRB 250902B: SVOM/GRM observation
  66. GRB 250901A: Swift/UVOT Upper Limit
  67. GRB 250902A: SVOM/GRM observation
  68. EP250828a: Early near-infrared follow-up with MIRAGE on the MDM 1.3m telescope
  69. GRB 250901A: EP-FXT follow-up observation
  70. GRB 250901A: NOT optical observations
  71. GRB 250901A: SVOM/VT optical afterglow with VHF data
  72. GRB 250901A: LCO optical upper limit
  73. EP250827b: Swift observations of AT 2025wkm
  74. LIGO/Virgo/KAGRA S250830bp: DECam DESGW Epoch 1 Candidates
  75. EP250831a: NOT optical observations and tentative afterglow candidate
  76. EP250827b: FTW Observations of AT 2025wkm
  77. EP250827b: Contemporaneous detection of EP X-ray flare EP250827b and ZTF transient ZTF25abmpngy/AT2025wkm
  78. EP250901a: Mephisto optical upper limits
  79. GRB 250831A: SVOM/COLIBRÍ (FM-GFT) optical upper limit
  80. EP250821a: SOAR observations
  81. EP250827a: very early ATLAS detections, starting 43 sec after the EP trigger
  82. EP250828a: refined analysis of the EP-WXT and EP-FXT observations
  83. EP250828a: Optical counterpart detection with Kinder observations
  84. EP250828a: Liverpool Telescope upper limits
  85. EP-WXT trigger 01709200800 : KAIT optical observations
  86. EP250828a: KAIT optical upper limit
  87. EP250827a: Swift/UVOT Detection
  88. EP250828a: NOT optical counterpart confirmation
  89. EP250828a: SVOM/VT optical candidate
  90. EP250828a: Seimei/TriCCS optical counterpart detection
  91. EP250827a: STEP/T80S Confirmation of fading optical counterpart
  92. EP250828a: Optical upper limit with Kinder observations
  93. EP250827a: LCO observations show fading optical counterpart
  94. EP250827A: VLT/X-shooter redshift confirmation
  95. EP250827a: confirmation of optical rebrightening with LCO
  96. EP250827a: GOTO observation of the optical afterglow
  97. GRB 250826A: SVOM/GRM observation
  98. EP250827A: An optical rebrightening was detected by LCO.
  99. EP250827a: Swift-XRT counterpart detection
  100. EP250827a: TRT optical observations

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