absolute astrometry can be shifted by up to 0.6 arcsec due to pointing uncertainties.

### *Chandra* ULX spectral modeling

We fitted the *Chandra* spectrum using the X-ray spectral fitting package [XSPEC]{} (@1996ASPC..101...17A) v12.7.1 in the 0.2 to 10.0 keV energy range. Two models were used: an absorbed multicolor disk-blackbody model (*wabs\*diskbb*) and a power-law model (*wabs\*pow*). The fits were performed using the minimum $\chi^{2}$ method (i.e. Gehrels Chisq statistics). The fitting results of each model are shown in Table \[chandra\], while a plot of the power-law spectral fit is shown in Fig. \[chandrapow\].

Both the *pow* and the *diskbb* model provide acceptable statistical fits (i.e. null-hypothesis probability $>$ 5%, so rejection likelihood $<$ 95%), with values of $N_\mathrm{H}\sim$ 10–15 times larger than the Galactic column density (i.e. $N_\mathrm{H} = 2 \times 10^{20}$ cm$^{-2}$, @2003ApJ...588..805K). The data are insufficient to statistically distinguish between models. The disk-blackbody model provides an inner disk temperature $kT_\mathrm{in}$ = 2.5 keV, too high for a standard disk. The power-law fit provides a very hard photon index $\Gamma$ = 1.1 and unabsorbed flux = 1.7 $\times 10^{-13}$ erg s$^{-1}$ cm$^{2}$, from which we derive an X-ray luminosity $L_\mathrm{0.2-10.0 keV}$ = 3.4 $\times\ 10^{39}$ erg s$^{-1}$.

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