Transcript Soft X-ray emission in Parkes Quasars.

Soft X-ray emission in
Parkes Quasars.
Is there dust in radio quasars?
M.Whiting1, R.Webster1, P.Francis2.
1Astrophysics
2Dept.
group, School of Physics, University of Melbourne, Australia.
Physics & Theoretical Physics, Australian National University
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)
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)
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.
Optical-X-ray Index.
• Observed (dust-absorbed) optical-X-ray slope:
a BX o
 X  B
 a BX i 
ln( X /  B )
• Expressed in terms of optical depths, which are
functions of AV, and intrinsic (unabsorbed)
slope.
• Get relationship between aBX and AV.
Predictions.
(After Masci et al. 1999, ApJ, 510, 709)
• Gas to dust ratio gives:
• Extinction coefficients:
 B  1.229 AV
• Intrinsic slope :
1keV  0.46 AV
 K  0.104 AV
a KX i  1.0
a BX i  1.3
• Gives, with errors:
a BX  1.3  0.13
a KX  1.0  0.05
0.3
0.2
0.3
0.2
0.03
AV
0.04
AV
0.03
0.02
Results.
• Plot rest-frame optical-X-ray slopes as a
function of AV.
• Correlations exist at 99% C.L.
• Best fit lines :
a BX  1.505  0.143 AV
a KX  0.826  0.053 AV
X-ray - optical slope vs. AV.
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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