A soft X-ray reverberation lag in ESO 113-G010. (arXiv:1210.7874v1 [astro-ph.HE])

A soft X-ray reverberation lag in ESO 113-G010. (arXiv:1210.7874v1 [astro-ph.HE]):
Reverberation lags have recently been discovered in a handful of nearby,
variable AGN. Here, we analyze a ~100 ksec archival XMM-Newton observation of
the highly variable AGN, ESO 113-G010 in order to search for lags between hard
(1.5 - 4.5 keV) and soft (0.3 - 0.9 keV) energy bands. At the lowest
frequencies available in the lightcurve, we find hard lags where the power-law
dominated hard band lags the soft band where the reflection fraction is high.
However, at higher frequencies in the range 2E-4 - 3E-4 Hz we find a soft lag
of 325 +/- 89 seconds at greater than the 3.5-sigma level. The general
evolution from hard to soft lags as the frequency increases is similar to other
AGN where soft lags have been detected. We interpret this soft lag as due to
reverberation, with the reflection component responding to variability in the
power-law. For a black hole mass of 7E6 M_solar this corresponds to a
light-crossing time of ~9 GM/c^3, however, dilution effects mean that the
intrinsic lag is likely longer than this. Based on recent black hole
mass-scaling for lag properties, the lag amplitude and frequency are more
consistent with a black hole a few times more massive than the best estimates,
though flux-dependent effects could easily add scatter this large.