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Swift monitoring of NGC 5548: X-ray reprocessing and short-term UV/optical variability

McHardy, I. M ; Cameron, D. T ; Dwelly, T ; Connolly, S ; Lira, P ; Emmanoulopoulos, D ; Gelbord, J ; Breedt, E ; Arevalo, P ; Uttley, P

Monthly notices of the Royal Astronomical Society, 2014-10, Vol.444 (2), p.1469-1474 [Periódico revisado por pares]

London: Oxford University Press

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  • Título:
    Swift monitoring of NGC 5548: X-ray reprocessing and short-term UV/optical variability
  • Autor: McHardy, I. M ; Cameron, D. T ; Dwelly, T ; Connolly, S ; Lira, P ; Emmanoulopoulos, D ; Gelbord, J ; Breedt, E ; Arevalo, P ; Uttley, P
  • Assuntos: Accretion disks ; Black holes ; Star & galaxy formation ; Ultraviolet astronomy ; X-ray astronomy
  • É parte de: Monthly notices of the Royal Astronomical Society, 2014-10, Vol.444 (2), p.1469-1474
  • Notas: ObjectType-Article-1
    SourceType-Scholarly Journals-1
    ObjectType-Feature-2
    content type line 23
  • Descrição: Lags measured from correlated X-ray/UV/optical monitoring of AGN allow us to determine whether UV/optical variability is driven by reprocessing of X-rays or X-ray variability is driven by UV/optical seed photon variations. We present the results of the largest study to date of the relationship between the X-ray, UV and optical variability in an AGN with 554 observations, over a 750 d period, of the Seyfert 1 galaxy NGC 5548 with Swift. There is a good overall correlation between the X-ray and UV/optical bands, particularly on short time-scales (tens of days). The UV/optical bands lag the X-ray band with lags which are proportional to wavelength raised to the power 1.23 ± 0.31. This power is very close to the power (4/3) expected if short time-scale UV/optical variability is driven by reprocessing of X-rays by a surrounding accretion disc. The observed lags, however, are longer than expected from a standard Shakura–Sunyaev accretion disc with X-ray heating, given the currently accepted black hole mass and accretion rate values, but can be explained with a slightly larger mass and accretion rate, and a generally hotter disc. Some long-term UV/optical variations are not paralleled exactly in the X-rays, suggesting an additional component to the UV/optical variability arising perhaps from accretion rate perturbations propagating inwards through the disc.
  • Editor: London: Oxford University Press
  • Idioma: Inglês
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