6.3 \times 10^5 \left(\dot{M}/\dot{M}_{\rm Edd}\right)^{1/4}
M_8^{-1/4} \left(r/R_{\rm S} \right)^{-3/4}\ {\rm K,}$$ where $M_8$ is the black hole mass in units of $10^8\,M_{\odot}$ and $R_{\rm S}$ is the Schwarzschild radius (Shakura & Sunyaev 1973). The temperature of the inner regions of the disk scales like $M^{-1/4}$, so the strength of the soft X-rays in NLS1s might plausibly be ascribed to a low central mass and a high accretion-rate flow.

One way to distinguish among various explanations of the NLS1 phenomenon is to measure the size of the BLR, which can be done via reverberation-mapping techniques (Blandford & McKee 1982; Peterson 1993; Netzer & Peterson 1997). It is usually assumed that the variability of an emission-line $L(t)$ to a variable continuum $C(t)$ can be linearized to the form $$\label{eq:TF}
\delta L(t) = \int \Psi(\tau)\ \delta C(t-\tau)\ d\tau,$$ where $\Psi(\tau)$ is the “transfer function,” which depends on the geometry and reprocessing physics of the BLR. A representative time scale for response of a line can be found by a simple cross-correlation of the continuum and emission-line light curves. By convolving eq. (\[eq:TF\]) with $C(t)$, one obtains the cross-correlation function $$\CCF(\tau) = \int \Psi(\tau') \ACF(\tau-\tau')\ d\tau',$$ where $\ACF(\tau)$ is the continuum autocorrelation function (Penston 