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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"

27553 results found.

  1. EP250905a: Einstein Probe detection of an X-ray transient
  2. GRB 250905B: Fermi GBM Final Localization
  3. GRB250904A: Liverpool Telescope upper limits
  4. GRB 250905A: Enhanced Swift-XRT position
  5. GRB 250904A: Swift/UVOT Detection
  6. GRB 250903A: Swift/UVOT detection
  7. GRB 250904A: Swift-XRT refined Analysis
  8. EP detected a brightening of LMXB 1ES 1735-26.9
  9. GRB 250905A: KAIT optical upper limit
  10. GRB 250905A: Swift detection of a burst
  11. GRB 250904A: Enhanced Swift-XRT position
  12. GRB 250904A: TRT optical counterpart detection
  13. GRB 250902B: CALET Gamma-Ray Burst Monitor detection
  14. GRB 250904A: Prompt enhanced Swift-XRT position
  15. GRB 250904A: Swift detection of a burst
  16. GRB 250902A: CALET Gamma-Ray Burst Monitor detection
  17. GRB 250902A: VZLUSAT-2 detection
  18. GRB 250903A: Swift-XRT observations
  19. EP250903a: Swift-XRT observations
  20. EP#01709201209: Swift-XRT observations
  21. EP250903a: retraction of the LCO candidate, and discovery of the likely counterpart
  22. EP-WXT trigger 01709201209: Liverpool Telescope upper limits
  23. GRB 250830C: VZLUSAT-2 detection
  24. GRB 250903A: VLT X-shooter spectroscopic redshift z = 1.590
  25. GRB 250903A: EP-FXT counterpart detection
  26. GRB 250902A: GECAM-B detection
  27. GRB 250903A: LCO optical observation
  28. GRB 250903A: LCO optical afterglow detection
  29. EP250901a: Mondy, Assy and SAO RAS optical limits
  30. Subject GRB 250903A: SVOM/MXT afterglow detection
  31. EP250903a: LCO candidate counterpart discovery
  32. GRB 250903A: TRT optical counterpart detection
  33. GRB 250902B: AstroSat CZTI detection
  34. GRB 250903A: SVOM detection of a burst
  35. EP250903a: Einstein Probe detection of an X-ray transient
  36. EP 250827B: Detection of supernova counterpart by LCO.
  37. EP250827b: continued Liverpool Telescope observations
  38. EP250827b: SVOM/VT observation of AT 2025wkm
  39. GRB 250902A: Fermi GBM Detection
  40. GRB 250901A: Swift/UVOT Upper Limit
  41. GRB 250902B: Fermi GBM Final Real-time Localization
  42. GRB 250830B: Swift-XRT afterglow detection
  43. EP250827b: Liverpool Telescope observations
  44. GRB 250831A (SVOM trigger sb25083102): confirmation of a stellar flare by SVOM/VT
  45. EP250828a: Early near-infrared follow-up with MIRAGE on the MDM 1.3m telescope
  46. EP250901a: refined analysis of the EP-WXT and EP-FXT observations
  47. GRB 250901A: EP-FXT follow-up observation
  48. GRB 250901A: NOT optical observations
  49. GRB 250902A: Fermi GBM Final Real-time Localization
  50. GRB 250901A: SVOM/VT optical afterglow with VHF data
  51. GRB 250901A: Swift-XRT afterglow detection
  52. EP250901a: Swift-XRT observations
  53. GRB 250901A: LCO optical upper limit
  54. EP250827b: Swift observations of AT 2025wkm
  55. EP250831a: NOT optical observations and tentative afterglow candidate
  56. EP250827b: Contemporaneous detection of EP X-ray flare EP250827b and ZTF transient ZTF25abmpngy/AT2025wkm
  57. GRB 250901A: SVOM detection of a burst
  58. GRB 250830C: Insight-HXMT detection
  59. GRB 250830C: GECAM-B detection
  60. GRB 250830C: AstroSat CZTI detection of a long burst
  61. EP250901a: Einstein Probe detection of an X-ray transient
  62. EP250831a: EP-FXT follow-up observation
  63. EP250831a: Swift-XRT observations
  64. IceCube-250831A - IceCube observation of a high-energy neutrino candidate track-like event
  65. EP250831a: EP-WXT detection of a fast X-ray transient
  66. GRB 250831A (SVOM trigger sb25083102) is likely an outburst from star G 272-61
  67. GRB 250831A: Swift-XRT counterpart detection
  68. GRB 250831A: SVOM detection of a soft burst
  69. GRB 250830B: Swift-XRT observations
  70. EP250830a/GRB 250830B: Einstein Probe detection of an X-ray transient and Swift/XRT follow-up
  71. EP-WXT trigger 01709200994: Liverpool Telescope upper limits
  72. GRB 250830B: Swift ToO observations
  73. EP-WXT trigger 01709200994: confirmation of a stellar flare by BOOTES-6
  74. GRB 250830B: MAXI/GSC detection
  75. GRB 250830A / MAXI J0853+337: MAXI/GSC detection
  76. EP250827a: very early ATLAS detections, starting 43 sec after the EP trigger
  77. LIGO/Virgo/KAGRA S250818k: MeerKAT detection of an increase in radio flux from AT2025ulz
  78. GRB 250808B: SVOM detection of a burst through offline search
  79. EP250828a: Optical counterpart detection with Kinder observations
  80. EP250828a: Liverpool Telescope upper limits
  81. EP250828a: KAIT optical upper limit
  82. EP250827a: Swift/UVOT Detection
  83. EP250828a: Seimei/TriCCS optical counterpart detection
  84. GRB 250828B: Swift detection of a burst
  85. EP250827a: STEP/T80S Confirmation of fading optical counterpart
  86. LIGO/Virgo/KAGRA S250818k: uGMRT 1.3 GHz observations of AT2025ulz
  87. GRB 250828A: Fermi GBM Final Localization
  88. EP250828a: Einstein Probe detection of an X-ray transient
  89. GRID detection of GRB 250824A
  90. EP250827a: confirmation of optical rebrightening with LCO
  91. EP250827a: GOTO observation of the optical afterglow
  92. GRB 250827A: Fermi GBM Final Real-time Localization
  93. EP250827a: Swift-XRT counterpart detection
  94. EP250827a: BOOTES-7 early optical dectection
  95. EP250827a / GRB 250827A: MASTER-OAFA OT observation
  96. EP250827a: Las Cumbres independent detection of the optical counterpart
  97. EP250827a: Gemini-South optical counterpart detection
  98. EP250827a: Einstein Probe detection of an X-ray transient
  99. GRB 250806A: HiPERCAM/GTC limits on a possible supernova
  100. GRB 250826A: Fermi GBM Final Real-time Localization

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