spectral-timing analysis may be able to determine how much each of the spectral components is oscillating. Such an analysis, however, is beyond the scope of this initial work.

Eddington limits
----------------

Finally, we note that our analysis of the light curve, the spectral evolution, and the timing behavior all indicate that each time interval where the [*NICER*]{}count-rate of [SAX J1808]{}is between 13,000 [ct[s$^{-1}$]{}]{}and 14,000 [ct[s$^{-1}$]{}]{}is somehow special. At these count rates, the burst rise pauses, the dip reaches its minimum, and burst oscillations appear. The bolometric flux measured at these times was $(1.43\pm0.09){\ensuremath{\times 10^{-7}} }$[[erg[s$^{-1}$]{}[cm$^{-2}$]{}]{}]{}, which corresponds to a luminosity of $(2.08\pm0.13){\ensuremath{\times 10^{38}} }$[[erg[s$^{-1}$]{}]{}]{}. We note that this luminosity is consistent with the expected local Eddington limit of a hydrogen envelope of a neutron star [@Lewin1993].

For spherically symmetric emission, the Eddington luminosity as measured by the observer is predicted as [@Lewin1993; @Suleimanov2017] $$L_{\rm edd} = \frac{4\pi GMc}{\kappa_{\rm T}}\frac{1}{(1+z)},$$ where $M$ is the neutron star mass, $G$ the gravitational constant, $c$ the speed of light, and $z$ the gravitational redshift. Finally, $\kappa_{\rm T}=0.2(1+X)\,{\rm cm}^2$[g$^{-1}$]{} is the Thomson electron scattering opacity, with $X$ the hydrogen abundance in the atmospheric layer. Hence, we expect that the flux level at which PRE occurs 