cross-sections of @Verner1996, `diskbb` [@Makishima1986] is a multi-color disk blackbody component, and `nthcomp` [@Zdziarski1996; @Zycki1999] is a thermal Comptonization component. We used an absorption column density of $N_H =
  2.1{\ensuremath{\times 10^{21}} }$[cm$^{-2}$]{} [@Papitto2009; @DiSalvo2019], and electron temperature of [30]{}keV [@DiSalvo2019]. We further tied the `nthcomp` photon seed temperature to the disk temperature. Our best-fit had a reduced $\chi^2$ ([$\chi^2_r$]{}) of 1.04 for 375 degrees of freedom (dof), yielding an inner disk temperature of $kT=0.70\pm0.07$ keV and a power-law photon index of $\Gamma=2.0\pm0.4$. Using the `cflux` model we further measured the unabsorbed $1-10$ keV flux to be $(2.85 \pm
  0.05){\ensuremath{\times 10^{-10}} }\,{{\rm erg{\,s\ensuremath{^{-1}}\xspace}{\,cm\ensuremath{^{-2}}\xspace}}\xspace}$, from which we extrapolate a bolometric flux ($0.01-100$keV) of [$(4.7 \pm 0.5){\ensuremath{\times 10^{-10}} }\,{{\rm erg{\,s\ensuremath{^{-1}}\xspace}{\,cm\ensuremath{^{-2}}\xspace}}\xspace}$]{}. Assuming a distance of $3.5$kpc [@Galloway2006], a 1.4[$M_{\odot}$]{}neutron star mass, and a 10km radius, this corresponds to a mass accretion rate of $\dot M =
  2.9{\ensuremath{\times 10^{-11}} }\,{\ensuremath{M_{\odot}}\xspace}$[yr$^{-1}$]{}, which is $\approx0.3\%$ of the Eddington rate.

Burst spectroscopy {#sec:spectra}
------------------

![ Top: burst spectra at four epochs during the X-ray burst. Bottom: the residuals of the best fit models, showing the ratio of the data over the model prediction. In each case we have set the normalization of the emission line components to zero, 