Anomalously Steep Reddening Law in Quasars: An Exceptional Example
  Observed in IRAS14026+4341
  A fraction of the heavily reddened quasars require a reddening curve which is
even steeper than that of the Small Magellanic Cloud. In this paper, we
thoroughly characterize the anomalously steep reddening law in quasars, via an
exceptional example observed in IRAS 14026+4341. By comparing the observed
spectrum to the quasar composite spectrum, we derive a reddening curve in the
rest-frame wavelength range of 1200 {\AA}--10000 {\AA}. It is featured with a
steep rise at wavelengths shorter than 3000 {\AA}, but no significant reddening
at longer wavelengths. The absence of dust reddening in optical continuum is
confirmed by the normal broad-line Balmer decrement (the H$\alpha$/H$\beta$
ratio) in IRAS 14026+4341. The anomalous reddening curve can be satisfactorily
reproduced by a dust model containing silicate grains in a power-law size
distribution, $dn(a)/da \propto a^{-1.4}$, truncated at a maximum size
$a_{max}=70 {\rm nm}$. The unusual size distribution may be caused by the
destruction of large "stardust" grains by quasar activities or a different dust
formation mechanism (i.e., the in situ formation of dust grains in quasar
outflows). It is also possible that the analogies of the dust grains observed
toward the Galactic center is responsible for the steep reddening curve. In
addition, we find that IRAS 14026+4341 is a weak emission-line quasar (i.e.,
PHL 1811 analogies) with heavy dust reddening and blueshifted broad absorption
lines.
