  There is mounting evidence that supermassive black holes form and grow in
bulgeless galaxies. However, a robust determination of the fraction of AGNs in
bulgeless galaxies, an important constraint to models of supermassive black
hole seed formation and merger-free models of AGN fueling, is unknown, since
optical studies have been shown to be incomplete for low mass AGNs. In a recent
study using the Wide-field Infrared Survey Explorer, we discovered hundreds of
bulgeless galaxies that display mid-infrared signatures of extremely hot dust
suggestive of powerful accreting massive black holes, despite having no
signatures of black hole activity at optical wavelengths. Here we report X-ray
follow-up observations of J122434.66+555522.3, a nearby (z=0.052) isolated
bulgeless galaxy that contains an unresolved X-ray source detected at the 3
sigma level by XMM-Newton with an observed luminosity uncorrected for intrinsic
absorption of L{2-10~keV}=1.1+/-0.4 10^40 ergs/s. Ground-based near-infrared
spectroscopy with the Large Binocular Telescope together with multiwavelength
observations from ultraviolet to millimeter wavelengths together suggest that
J1224+5555 harbors a highly absorbed AGN with an intrinsic absorption of ~NH
>10^24 cm^-2. The hard X-ray luminosity of the putative AGN corrected for
absorption is L{2-10~keV}~3x10^42 ergs/s, which, depending on the bolometric
correction factor, corresponds to a bolometric luminosity of the AGN of
6x10^43ergs/s - 3x10^44 erg/s, and a lower mass limit for the black hole of
MBH~2x10^6 Msun, based on the Eddington limit.
