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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"

14820 results found.

  1. EP250905a: Liverpool Telescope observations
  2. EP250905b: EP-WXT detection of a fast X-ray transient
  3. EP250905a: FTW one optical and multiple NIR counterpart candidates
  4. EP250905a: JinShan likely optical counterpart detection
  5. IceCube-250905A - IceCube observation of a high-energy neutrino candidate track-like event
  6. EP250905a: Einstein Probe detection of an X-ray transient
  7. GRB 250905B: Fermi GBM Final Localization
  8. GRB 250904A: Swift/UVOT Detection
  9. GRB 250903A: Swift/UVOT detection
  10. EP detected a brightening of LMXB 1ES 1735-26.9
  11. GRB 250905A: Swift detection of a burst
  12. GRB 250904A: TRT optical counterpart detection
  13. GRB 250902B: CALET Gamma-Ray Burst Monitor detection
  14. EP250827b: Gemini Spectroscopic Confirmation of AT2025wkm as a Ic-BL Supernova
  15. GRB 250904A: Swift detection of a burst
  16. GRB 250902A: CALET Gamma-Ray Burst Monitor detection
  17. GRB 250902A: VZLUSAT-2 detection
  18. EP250903a: retraction of the LCO candidate, and discovery of the likely counterpart
  19. EP-WXT trigger 01709201209: Liverpool Telescope upper limits
  20. GRB 250830C: VZLUSAT-2 detection
  21. GRB 250903A: VLT X-shooter spectroscopic redshift z = 1.590
  22. GRB 250903A: EP-FXT counterpart detection
  23. GRB 250902A: GECAM-B detection
  24. GRB 250903A: LCO optical afterglow detection
  25. Subject GRB 250903A: SVOM/MXT afterglow detection
  26. GRB 250903A: TRT optical counterpart detection
  27. GRB 250902B: AstroSat CZTI detection
  28. GRB 250903A: SVOM detection of a burst
  29. EP250903a: TRT optical observations
  30. EP250903a: Einstein Probe detection of an X-ray transient
  31. EP 250827B: Detection of supernova counterpart by LCO.
  32. EP250827b / AT 2025wkm: TRT optical observations
  33. EP250827b: continued Liverpool Telescope observations
  34. EP250827b: SVOM/VT observation of AT 2025wkm
  35. GRB 250902A: Fermi GBM Detection
  36. GRB 250902B: Fermi GBM Final Real-time Localization
  37. GRB 250830B: Swift-XRT afterglow detection
  38. EP250827b: Liverpool Telescope observations
  39. EP250828a: Early near-infrared follow-up with MIRAGE on the MDM 1.3m telescope
  40. EP250901a: refined analysis of the EP-WXT and EP-FXT observations
  41. GRB 250901A: EP-FXT follow-up observation
  42. GRB 250902A: Fermi GBM Final Real-time Localization
  43. GRB 250901A: Swift-XRT afterglow detection
  44. EP250831a: NOT optical observations and tentative afterglow candidate
  45. EP250827b: Contemporaneous detection of EP X-ray flare EP250827b and ZTF transient ZTF25abmpngy/AT2025wkm
  46. GRB 250901A: SVOM detection of a burst
  47. GRB 250830C: Insight-HXMT detection
  48. GRB 250830C: GECAM-B detection
  49. GRB 250830C: AstroSat CZTI detection of a long burst
  50. EP250901a: Einstein Probe detection of an X-ray transient
  51. EP250831a: EP-FXT follow-up observation
  52. IceCube-250831A - IceCube observation of a high-energy neutrino candidate track-like event
  53. EP250831a: EP-WXT detection of a fast X-ray transient
  54. GRB 250831A: Swift-XRT counterpart detection
  55. GRB 250831A: SVOM detection of a soft burst
  56. EP250830a/GRB 250830B: Einstein Probe detection of an X-ray transient and Swift/XRT follow-up
  57. EP-WXT trigger 01709200994: Liverpool Telescope upper limits
  58. EP-WXT trigger 01709200994: confirmation of a stellar flare by BOOTES-6
  59. GRB 250830B: MAXI/GSC detection
  60. GRB 250830A / MAXI J0853+337: MAXI/GSC detection
  61. EP250827a: very early ATLAS detections, starting 43 sec after the EP trigger
  62. LIGO/Virgo/KAGRA S250818k: MeerKAT detection of an increase in radio flux from AT2025ulz
  63. GRB 250808B: SVOM detection of a burst through offline search
  64. EP250828a: Optical counterpart detection with Kinder observations
  65. EP250828a: Liverpool Telescope upper limits
  66. EP250827a: Swift/UVOT Detection
  67. EP250828a: NOT optical counterpart confirmation
  68. EP250828a: Seimei/TriCCS optical counterpart detection
  69. GRB 250828B: Swift detection of a burst
  70. EP250827a: STEP/T80S Confirmation of fading optical counterpart
  71. LIGO/Virgo/KAGRA S250818k: uGMRT 1.3 GHz observations of AT2025ulz
  72. GRB 250828A: Fermi GBM Final Localization
  73. EP250828a: Einstein Probe detection of an X-ray transient
  74. GRID detection of GRB 250824A
  75. GRB 250827A: Fermi GBM Final Real-time Localization
  76. EP250827a: Swift-XRT counterpart detection
  77. EP250827a: TRT optical observations
  78. EP250827a: BOOTES-7 early optical dectection
  79. EP250827a / GRB 250827A: MASTER-OAFA OT observation
  80. EP250827a: Las Cumbres independent detection of the optical counterpart
  81. EP250827a: Gemini-South optical counterpart detection
  82. EP250827a: Einstein Probe detection of an X-ray transient
  83. GRB 250806A: HiPERCAM/GTC limits on a possible supernova
  84. GRB 250826A: Fermi GBM Final Real-time Localization
  85. LIGO/Virgo/KAGRA S250818k: VLA upper limits on AT2025ulz
  86. GRB 250821B: AstroSat CZTI detection
  87. GRB 250819A: AstroSat CZTI detection
  88. GRB 250821B: Insight-HXMT detection
  89. LIGO/Virgo/KAGRA S250818k: Swift Observations of AT 2025ulz - Second Epoch
  90. GRB 250824B: Fermi GBM Final Real-time Localization
  91. GRB 250824A: Fermi GBM Final Real-time Localization
  92. GRB 250823A: Swift/UVOT Detection
  93. GRB 250818B: MeerKAT Detection
  94. GRB 250823A: LCOGT Optical Detection
  95. GRB 250823A: BOOTES6/DPRT early optical detection
  96. GRB 250823A: Liverpool Telescope optical detection
  97. GRB 250823A: Swift detection of a burst
  98. GRB 250823A: Fermi GBM Final Real-time Localization
  99. Konus-Wind detection of GRB 250821B
  100. LIGO/Virgo/KAGRA S250818k: Rebrightening detected with Gemini/GMOS

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