X-ray flaring in PDS 456 observed in a high-flux state
Date Issued
2017
Author(s)
Abstract
We present an analysis of a $190$\,ks (net exposure) \textit{Suzaku}
observation, carried out in 2007, of the nearby ($z=0.184$) luminous (L$_{\rm
bol}\sim10^{47}$\,erg\,s$^{-1}$) quasar PDS\,456. In this observation, the
intrinsically steep bare continuum is revealed compared to subsequent
observations, carried out in 2011 and 2013, where the source is fainter, harder
and more absorbed. We detected two pairs of prominent hard and soft flares,
restricted to the first and second half of the observation respectively. The
flares occur on timescales of the order of $\sim50$\,ks, which is equivalent to
a light-crossing distance of $\sim10\,R_{\rm g}$ in PDS\,456. From the spectral
variability observed during the flares, we find that the continuum changes
appear to be dominated by two components: (i) a variable soft component
($<2$\,keV), which may be related to the Comptonized tail of the disc emission,
and (ii) a variable hard power-law component ($>2$\,keV). The photon index of
the latter power-law component appears to respond to changes in the soft band
flux, increasing during the soft X-ray flares. Here the softening of the
spectra, observed during the flares, may be due to Compton cooling of the disc
corona induced by the increased soft X-ray photon seed flux. In contrast, we
rule out partial covering absorption as the physical mechanism behind the
observed short timescale spectral variability, as the timescales are likely too
short to be accounted for by absorption variability.
Volume
465
Issue
3
Start page
2804
Issn Identifier
0035-8711
Rights
open.access
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