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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"

2993 results found.

  1. EP250905a: Global MASTER-Net observations report
  2. EP250905a: Einstein Probe detection of an X-ray transient
  3. EP detected a brightening of LMXB 1ES 1735-26.9
  4. EP250827a and EP250827b: Upper limit from Fermi-GBM Observations
  5. EP250903a: Swift-XRT observations
  6. EP#01709201209: Swift-XRT observations
  7. EP250903a: retraction of the LCO candidate, and discovery of the likely counterpart
  8. EP-WXT trigger 01709201209: Liverpool Telescope upper limits
  9. EP250903a: refined analysis of the EP-WXT and EP-FXT observations
  10. The EP-WXT trigger 01709201209 is likely a flaring star
  11. GRB 250903A: EP-FXT counterpart detection
  12. EP250903a: SVOM/VT optical confirmation
  13. EP250901a: Mondy, Assy and SAO RAS optical limits
  14. EP250903a: LCO candidate counterpart discovery
  15. EP250903a: Global MASTER-Net observations report
  16. EP250903a: TRT optical observations
  17. EP250903a: Einstein Probe detection of an X-ray transient
  18. EP 250827B: Detection of supernova counterpart by LCO.
  19. EP/WXT01709201159: GOTO optical follow-up
  20. EP250827b / AT 2025wkm: TRT optical observations
  21. EP250827b: NOT spectroscopic observations and AT 2025wkm classification as a broad-lined type-Ic supernova
  22. GRB 250830B: Swift-XRT afterglow detection
  23. EP250901a: refined analysis of the EP-WXT and EP-FXT observations
  24. GRB 250901A: EP-FXT follow-up observation
  25. EP250901a: Swift-XRT observations
  26. EP250831a: NOT optical observations and tentative afterglow candidate
  27. EP250827b: Contemporaneous detection of EP X-ray flare EP250827b and ZTF transient ZTF25abmpngy/AT2025wkm
  28. EP250901a: Mephisto optical upper limits
  29. EP250901a: Global MASTER-Net observations report
  30. EP250901a: Einstein Probe detection of an X-ray transient
  31. EP250831a: EP-FXT follow-up observation
  32. EP250831a: Swift-XRT observations
  33. EP250831a: Global MASTER-Net observations report
  34. EP250831a: EP-WXT detection of a fast X-ray transient
  35. GRB 250830B: Swift-XRT observations
  36. EP250830a: Global MASTER-Net observations report
  37. EP250830a/GRB 250830B: Einstein Probe detection of an X-ray transient and Swift/XRT follow-up
  38. EP-WXT trigger 01709200994: Liverpool Telescope upper limits
  39. EP-WXT trigger 01709200994: confirmation of a stellar flare by BOOTES-6
  40. The EP-WXT trigger 01709200994 is likely a flaring star
  41. EP250827a: very early ATLAS detections, starting 43 sec after the EP trigger
  42. EP250828a: refined analysis of the EP-WXT and EP-FXT observations
  43. EP250828a: Optical counterpart detection with Kinder observations
  44. EP250828a: Liverpool Telescope upper limits
  45. EP250828a: Global MASTER-Net observations report
  46. EP-WXT trigger 01709200800 : KAIT optical observations
  47. EP250827a: Swift/UVOT Detection
  48. EP250828a: NOT optical counterpart confirmation
  49. EP250828a: SVOM/VT optical candidate
  50. EP250828a: Seimei/TriCCS optical counterpart detection
  51. EP250827a: STEP/T80S Confirmation of fading optical counterpart
  52. EP250828a: Optical upper limit with Kinder observations
  53. EP250827a: LCO observations show fading optical counterpart
  54. EP250828a: Einstein Probe detection of an X-ray transient
  55. EP250827a: Preliminary analysis of the EP-WXT and EP-FXT observations
  56. EP250827a: confirmation of optical rebrightening with LCO
  57. EP250827A: An optical rebrightening was detected by LCO.
  58. EP250827a: Swift-XRT counterpart detection
  59. The EP-WXT trigger 01709200800 is likely a flaring star
  60. EP250827a: TRT optical observations
  61. EP250827a / GRB 250827A: MASTER-OAFA OT observation
  62. EP250827a: Gemini-South redshift z = 1.613
  63. EP250827a: Global MASTER-Net observations report
  64. EP250827a: Gemini-South optical counterpart detection
  65. EP250827a: Einstein Probe detection of an X-ray transient
  66. EP triggers 01709200706 and 01709200707: GOTO confirmation of flaring stars
  67. The EP-WXT trigger 01709200707 is likely a flaring star
  68. The EP-WXT trigger 01709200706 is likely a flaring star
  69. Konus-Wind detection of GRB 250821B
  70. EP250821a: Swift/XRT counterpart fading
  71. EP250821a: VLT X-shooter spectroscopic redshift z = 0.577
  72. EP250821a: SVOM/VT optical observation
  73. EP250821a: Rapidly fading optical source detected in Las Cumbres followup
  74. EP250821a: Swift XRT and UVOT counterpart detection
  75. EP250821a: Preliminary analysis of the EP-WXT and EP-FXT observations
  76. LIGO/Virgo/KAGRA S250818k: EP/FXT observation of AT 2025ulz
  77. EP250821a: Einstein Probe detection of an X-ray transient
  78. GRB 250818B: Kilonova-Catcher optical afterglow detection
  79. GRB 250818B: SAO RAS optical observations
  80. GRB 250818B: EP-FXT counterpart detection
  81. GRB 250813B: Liverpool Telescope optical upper limits
  82. GRB 250813B: SVOM/GRM observation
  83. GRB 250813B: SVOM/VT optical observations
  84. GRB 250813B: EP-FXT counterpart detection
  85. EP250812a: NOT, NTT, and GS observations
  86. EP250812a: Liverpool Telescope upper limits
  87. EP250812a: SVOM/VT optical counterpart
  88. EP250812a: refined analysis of the EP-WXT and EP-FXT observations
  89. GRB 250812A: EP-FXT counterpart detection
  90. EP 250812a: GOTO optical upper limit
  91. EP250812a: Swift-XRT counterpart detection
  92. EP250812a: Einstein Probe detection of an X-ray transient
  93. EP250807a: EP-FXT follow-up observation upper limit
  94. EP250807a: Global MASTER-Net observations report
  95. EP-WXT trigger 01709195487: KAIT confirmation of the stellar flare
  96. Konus-Wind detection of GRB 250807A
  97. GRB 250806A: SVOM/MXT refined analysis
  98. EP250807a: NTT z-band optical upper limit
  99. EP250807a: EP-WXT detection of a fast X-ray transient
  100. EP 250807.979: GOTO optical upper limit

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