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Optical-UV synchrotron spectrum has been argued to be the primary driver ofthe majority of X-ray spectral changes in the BL Lacertae object OJ 287 duringits low and intermediate X-ray flux state. Here, we focus on the lowestrecorded X-ray flux state of OJ 287 by the Swift facility and report thefinding of a power-law optical-UV spectrum with a photon spectrum of $\rm2.71\pm0.03$ continuing into X-rays. Considering this at X-rays, we found apower-law X-ray spectrum of photon spectral index $\rm 1.22\pm0.20$ thatimproves to $\rm 1.29\pm0.06$ when considering other observations with similarX-ray spectra. This is the hardest reported X-ray spectrum (0.3-10 keV) and isconsistent with the reported Swift-BAT hard X-ray spectrum. We further showthat this X-ray spectrum can reproduce most of the flat X-ray spectra whencombined with the corresponding optical-UV continuum during the low andintermediate flux states strengthening synchrotron as the primary driver ofmost of the X-ray spectral changes in the LBL state of the source. Combinedwith sharp-steepening/cutoff of the optical-UV spectrum during bright phases,the extended-spectrum indicates a comparatively larger emission region andcould be the large-scale jet emission. The optical-UV spectrum implies ahigh-energy power-law particle spectrum of $\rm \sim4.4$ while X-ray implies ahard low-energy particle spectrum of $\rm 1.3-1.6$ which could be the real orcan result from a higher low-energy cut-off in the particle spectrum.

On the Spectral Changes of OJ 287: The Lowest X-ray state Spectrum -- extended at Optical-UV and Hard at X-rays