style="font-variant:small-caps;">cor\_sax</span>$^{-0.633}$, where <span style="font-variant:small-caps;">cor\_sax</span>[^1] gives the cut-off rigidity of the Earth’s magnetic field, in units of GeV[c$^{-1}$]{}. We then applied the <span style="font-variant:small-caps;">barycorr</span> tool to correct the observed event times to the Solar System barycenter, where we used the JPL DE405 planetary ephemeris [@Standish1998] and the optical coordinates of @Hartman2008. Finally, we estimated the background contributions to our data from [*NICER*]{}observations of the [*RXTE*]{}blank-field regions [@Jahoda2006].

Analysis and Results {#sec:results}
====================

The X-ray burst onset, $t_0$, occurred on MJD 58716.089362 TDB, which was $442{{\rm\,s}\xspace}$ into a $1063{{\rm\,s}\xspace}$ continuous exposure. In the following we focus our analysis on this exposure and express all times with respect to the noted onset time.

Light curve and phenomenology
-----------------------------

At $t_0$ the $0.3-10$ keV count-rate increased rapidly from an averaged $125$ [ct[s$^{-1}$]{}]{}to $\approx34,000$[ct[s$^{-1}$]{}]{}over a timespan of $\approx4.3{{\rm\,s}\xspace}$. The peak rate was maintained for $\approx3.6{{\rm\,s}\xspace}$, before the burst began to decay. The subsequent decay progressed on a minute-long time scale: at $t\simeq64{{\rm\,s}\xspace}$ the burst rate had dropped to below 5% of the peak rate, and by the end of the available exposure, at $t=621{{\rm\,s}\xspace}$, the source flux had fallen to $172$ [ct[s$^{-1}$]{}]{}. [ While this rate was slightly higher than the averaged preburst rate, the 