Abstract

We present one of the largest multiwavelength studies of simultaneous optical-to-X-ray spectral energy distributions (SEDs) of unobscured (N-H < 10(22) cm(-2)) active galactic nuclei (AGN) in the local Universe. Using a representative sample of hard-X-ray-selected AGN from the 70-month Swift/BAT catalog, with optical/UV photometric data from Swift/UVOT and X-ray spectral data from Swift/XRT, we constructed broadband SEDs of 236 nearby AGN (0.001 < z < 0.3). We employed GALFIT to estimate host galaxy contamination in the optical/UV and determine the intrinsic AGN fluxes. We used an absorbed power law with a reflection component to model the X-ray spectra and a dust-reddened multi-temperature blackbody to fit the optical/UV SED. We calculated intrinsic luminosities at multiple wavelengths, total bolometric luminosities (L-bol), optical-to-X-ray spectral indices (alpha(ox)), and multiple bolometric corrections (kappa(lambda)) in the optical, UV, and X-rays. We used black hole masses obtained by reverberation mapping and the virial method to estimate Eddington ratios (lambda(Edd)) for all our AGN. We confirm the tight correlation (scatter = 0.45 dex) between UV (2500 & Aring;) and X-ray (2 keV) luminosity for our sample. We observe a significant decrease in alpha(ox) with L-bol and lambda(Edd), suggesting that brighter sources emit more UV photons per X-rays. We report a second-order regression relation (scatter = 0.15 dex) between the 2-10 keV bolometric correction (kappa(2 - 10)) and alpha(ox), which is useful to compute L-bol in the absence of multiband SEDs. We also investigate the dependence of optical/UV bolometric corrections on the physical properties of AGN and obtain a significant increase in the UV bolometric corrections (kappa(W2) and kappa(M2)) with L-bol and lambda(Edd), unlike those in the optical (kappa(V) and kappa(B)), which are constant across five orders of L-bol and lambda(Edd). We obtain significant dispersions (similar to 0.1-1 dex) in all bolometric corrections, and hence recommend using appropriate relations with observed quantities while including the reported scatter, instead of their median values.