BASS
K. K. Gupta, Cláudio Ricci, Matthew J. Temple, A. Tortosa, Michael Koss, Roberto J. Assef, F. E. Bauer, R. F. Mushotzky, F. Ricci, Y. Ueda, A. F. Rojas, Benny Trakhtenbrot, Chin-Shin Chang, Kyuseok Oh, Ruancun Li, T. Kawamuro, Y. Díaz, Meredith C. Powell, Daniel Stern, C. M. Urry, Fiona Harrison, S. B. Cenko
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 ( α ox ), and multiple bolometric corrections ( κ λ ) in the optical, UV, and X-rays. We used black hole masses obtained by reverberation mapping and the virial method to estimate Eddington ratios ( λ Edd ) for all our AGN. We confirm the tight correlation (scatter = 0.45 dex) between UV (2500 Å) and X-ray (2 keV) luminosity for our sample. We observe a significant decrease in α ox with L bol and λ 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 ( κ 2 − 10 ) and α 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 ( κ W2 and κ M2 ) with L bol and λ Edd , unlike those in the optical ( κ V and κ B ), which are constant across five orders of L bol and λ Edd . We obtain significant dispersions (∼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.