Soft X-ray emission in Parkes Quasars.

1
Soft X-ray emission inParkes Quasars.

• Is there dust in radio quasars?

M.Whiting1, R.Webster1, P.Francis2.
1Astrophysics group, School of Physics,
University of Melbourne, Australia. 2Dept.
Physics Theoretical Physics, Australian
National University
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Red quasars.

• Parkes quasars are known to be reddened.
  (Webster et al. 1995, Nature,375, 469 Francis
  et al. 1999, PASA, in prep.)
• Is reddening caused by synchrotron emission or
  absorption by dust?
• If due to dust, then the associated molecular gas
  will absorb soft X-rays.
• Expect optical-X-ray slope to change with the
  amount of reddening. (Masci et al. 1999, ApJ,
  510, 709)

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New Observational Data.

• Optical / Near Infrared near simultaneous
  broadband photometry in B, V, R, I, J, H, and K
  bands. (Francis et al. 1999, PASA, in prep.)
• X-rays ROSAT observations (not simultaneous
  with optical) - integrated flux and photon index.
  (Siebert et al. 1998, MNRAS, 361, 261)

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Fitting.

• Detailed fit to optical / NIR data with dust
  synchrotron models.
• Find sources where dust is better fit than
  synchrotron.
• Get value of AV (in rest frame) for dusty sources.

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Optical-X-ray Index.

• Observed (dust-absorbed) optical-X-ray slope
• Expressed in terms of optical depths, which are
  functions of AV, and intrinsic (unabsorbed)
  slope.
• Get relationship between aBX and AV.

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Predictions.(After Masci et al. 1999, ApJ, 510,
709)

• Gas to dust ratio gives
• Extinction coefficients
• Intrinsic slope
• Gives, with errors

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Results.

• Plot rest-frame optical-X-ray slopes as a
  function of AV.
• Correlations exist at 99 C.L.
• Best fit lines

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X-ray - optical slope vs. AV.
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Conclusions.

• We have identified Parkes sources that are likely
  to be dusty.
• The optical-X-ray slope in these sources agrees
  with the prediction made by soft X-ray
  absorption.
• This provides good evidence that dust is
  affecting an identifiable population of radio
  quasars.

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