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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"
  1. EP260618a: Liverpool Telescope optical observations
  2. GRB 260619A: NOT optical observations
  3. GRB 260618B: LCO optical observations
  4. The EP-WXT trigger 01709271197 is likely a flaring star
  5. EP260618a: JinShan optical observations
  6. GRB 260616B/EP260616a: SVOM/GRM detection of a burst
  7. GRB 260618B: Fermi GBM Observation
  8. IceCube-Cascade 260618A: Upper limits from a search for additional neutrino events in IceCube
  9. GRB 260619A: TRT optical counterpart confirmation
  10. GRB 260610B: Further GRANDMA Optical Observations and re-brightening detection
  11. GRB 260604B: 239Alferov CubeSat detection
  12. GRB 260604A: 239Alferov CubeSat detection
  13. GRB 260610B: VLT/FORS2 spectroscopic observation suggests the non-thermal nature of the optical rebrightening
  14. GRB 260619A: SVOM/VT optical counterpart confirmation
  15. Fermi-LAT Gamma-ray Observations of IceCube-260610A
  16. GRB 260618B: SVOM/VT optical candidate
  17. GRB 260618B: SVOM/VT optical candidate (duplicate Submission of 45001)
  18. GRB 260619A: SVOM/COLIBRÍ (FM-GFT) optical counterpart candidate
  19. Konus-Wind detection of GRB 260617A
  20. GRB 260616B: AstroSat CZTI detection
  21. GRB 260616A: AstroSat CZTI detection
  22. GRB 260616A: SVOM/GRM observation
  23. EP260618a: OHP/T193 optical observations
  24. GRB 260610B/AT2026owq: 1.3m DFOT optical rebrightening detection
  25. GRB 260619A: Kilonova-Catcher optical upper limit
  26. EP260618a: EP-FXT follow-up observation
  27. EP260618a: LCO optical counterpart confirmation
  28. GRB 260617A: CALET Gamma-Ray Burst Monitor detection
  29. EP260618a: COLIBRÍ optical counterpart candidate
  30. GRB 260616A: NuSTAR detection of prompt emission
  31. GRB 260614B: NuSTAR detection of prompt emission
  32. GRB 260619A: SVOM possible detection of a faint burst
  33. IceCube-260610A: Upper limits from a search for additional neutrino events in IceCube
  34. GRB 260618B: Fermi-LAT detection
  35. IPN triangulation of GRB 260617A (short)
  36. GRB 260610B/AT 2026owq: FTW optical and NIR observations
  37. GRB 260616A: Insight-HXMT detection
  38. GRB 260618B: Fermi GBM Final Real-time Localization
  39. EP260618a: EP-WXT detection of an X-ray transient
  40. GRB 260610B: AbAO optical observations
  41. EP260616a/GRB 260616B: EP-FXT follow-up observation
  42. GRB 260506B: cubesat Avion detection
  43. GRB 260616C: GECAM-B observation of a burst
  44. GRB 260618A: Fermi GBM Final Real-time Localization
  45. GRB 260617A: Fermi GBM Detection
  46. GRB 260616A: Fermi GBM Observation
  47. GRB 260617A: Fermi GBM Final Real-time Localization (Duplicate Submission)
  48. GRB 260617A: Fermi GBM Final Real-time Localization
  49. Konus-Wind detection of GRB 260616B/EP260616a
  50. Konus-Wind detection of GRB 260616A
  51. GRB 260616B: CALET Gamma-Ray Burst Monitor detection
  52. EP260616a/GRB260616B: COLIBRÍ optical upper limit
  53. GRB 260616A: GECAM-B observation
  54. GRB 260610B / AT2026owq: SAO RAS optical observations of possible re-brightening
  55. GRB 260429A: cubesat Avion detection
  56. GRB260616C: MAXI/GSC detection
  57. GRB 260616A: Fermi-LAT detection
  58. GRB 260610B / AT 2026owq: Liverpool Telescope confirmation of continuing optical rebrightening
  59. GRB 260610B / AT 2026owq: COLIBRÍ further observations and confirmation of the rebrigthening
  60. GRB 260614A: AstroSat CZTI detection
  61. EP260616a: EP-WXT detection of a fast X-ray transient
  62. GRB 260610B / AT 2026owq: Possible re-brightening identified from Pan-STARRS observations
  63. The EP-WXT trigger 01709270148 is likely a flaring star
  64. GRB 260616B: Fermi GBM Detection
  65. GRB 260604C: GRANDMA late observations with CFHT/MegaCam
  66. GRB 260616B: BALROG localization (Fermi Trigger 803286321 / GRB 260616295)
  67. The EP-WXT trigger 01709269893 is likely a flaring star
  68. GRB 260616A: BALROG localization (Fermi Trigger 803272919 / GRB 260616140)
  69. GRB 260616A: Fermi GBM Final Real-time Localization
  70. GRB 260614B: SVOM/ECLAIRs refined analysis
  71. GRB 260610B: Terskol optical observations
  72. GRB 260614B: GECAM-B observation
  73. GRB 260610B: SVOM/GRM observation
  74. GRB 260614B: SVOM/VT optical afterglow confirmation
  75. GRB 260614B: Fermi GBM Observation
  76. GRB 260610B: ALMA detection
  77. GRB 260614A: GECAM-B observation
  78. GRB 260614B: SVOM/VT optical candidate from VHF data
  79. GRB 260614B: SVOM detection of a burst
  80. GRB 260614B: Fermi GBM Final Real-time Localization
  81. GRB 260611B: SVOM/GRM detection
  82. GRB 260614A: Fermi GBM Final Localization
  83. The EP-WXT trigger 01709269488 is likely a flaring star
  84. GRB 260603C: AstroSat CZTI detection
  85. GRB 260610B: further Liverpool Telescope optical observations
  86. GRB 260610B: Fermi GBM Observation
  87. GRB 260610B / AT2026owq: GRANDMA optical observations
  88. GRB 260610B / AT2026owq: further SAO RAS optical observations
  89. EP260605a: COLIBRÍ optical upper limits
  90. GRB 260610b: Liverpool Telescope optical observations
  91. EP260610b: Liverpool Telescope optical upper limits
  92. IceCube-260610A: No candidates from the Zwicky Transient Facility
  93. IceCube-260610A: EP-FXT follow-up observation
  94. GRB 260611B: CALET Gamma-Ray Burst Monitor detection
  95. The EP-WXT trigger 01709269176: SVOM/C-GFT confirmation of a stellar flare
  96. GRB 260610B / AT2026owq: SVOM/VT optical observations
  97. GRB 260610B / AT2026owq: OASDG optical observations
  98. GRB 260610B: IAC-80 Optical observations
  99. GRB 260610B / AT2026owq: SAO RAS optical observations
  100. GRB 260611B: Fermi GBM Final Real-time Localization

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