Greene & Ho 2007b) and relatively X-ray bright (Greene & Ho 2007a; Miniutti et al. 2009; Desroches et al. 2009; Dong et al. 2012a).

The most extensive multiwavelength studies on low-mass BHs thus far have concentrated, unsurprisingly, on the two prototypes, NGC 4395 and POX 52. Interestingly, the SED of NGC 4395 differs markedly from those of both quasars and typical low-luminosity AGNs (Moran et al. 1999). Specifically, the big blue bump, which dominates the SED of luminous

\[specfit\]

Seyferts and quasars at optical and UV bands, is absent, leading to an optical-to-X-ray spectral index of ${\ensuremath{\alpha_{\rm{ox}}}}=-0.97$ (Dewangan et al. 2008). NGC 4395 is a rare example of a low-mass AGN with a relatively low Eddington ratio (${{\ensuremath{L\mathrm{_{bol}}}}/{\ensuremath{L\mathrm{_{Edd}}}}}$) of $1.2\times10^{-3}$. Most likely because of strong selection effects, optically selected samples of low-mass BHs tend to have higher ${{\ensuremath{L\mathrm{_{bol}}}}/{\ensuremath{L\mathrm{_{Edd}}}}}$, ranging from $\lesssim0.01$ to $\sim1$ with a median of 0.2 (Dong et al. 2012b). POX 52, with $L_{\rm bol}=1.3\times10^{43}$ [erg s$^{-1}$]{} and ${{\ensuremath{L\mathrm{_{bol}}}}/{\ensuremath{L\mathrm{_{Edd}}}}}=0.2
-0.5$, exhibits a much more normal SED that is broadly similar to that of a scaled-down version of radio-quiet quasars (Thornton et al. 2008). The broad-band SED of NGC 4051, a narrow-line Seyfert 1 galaxy with ${\ensuremath{M_\mathrm{BH}}}=(1.7\pm0.5)\times10^6{\ensuremath{M_{\odot}}}$ (Denney et 