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Low-mass X-ray binaries are binary systems composed of a compact object and alow-mass star. Recently, a new class of these systems, known as symbiotic$X$-ray binaries (with a neutron star with a M-type giant companion), has beendiscovered. Here, we present long-duration ${\it XMM}$ observations of thesource 1RXS J180431.1-273932. Temporal and spectral analysis of the source wasperformed along with a search for an optical counterpart. We used aLomb-Scargle periodogram analysis for the period search and evaluated theconfidence level using Monte-Carlo simulations. The source is characterized byregular pulses so that it is most likely a neutron star. A modulation of$494.1\pm0.2$ s (3$\sigma$ error) was found with a confidence level of $>$99%.Evidence of variability is also present, since the data show a rate of changein the signal of $\sim -7.7\times 10^{-4}$ counts s$^{-1}$ hr$^{-1}$. A longerobservation will be necessary in order to determine if the source shows anyperiodic behavior. The spectrum can be described by a power law with photonindex $\Gamma\sim 1$ and a Gaussian line at 6.6 keV. The X-ray flux in the0.2--10 keV energy band is $5.4\times 10^{-12}$ erg s$^{-1}$ cm$^{-2}$. Theidentification of an optical counterpart (possibly an M6III red-giant star withan apparent visual magnitude of $\simeq 17.6$) allows a conservative distanceof $\sim 10$ kpc to be estimated. Other possibilities are also discussed. Oncethe distance was estimated, we got an $X$-ray luminosity of $L_X\ut<6\times10^{34}$ erg s$^{-1}$, which is consistent with the typical $X$-ray luminosityof a symbiotic LMXB system.

XMM observation of 1RXS J180431.1-273932: a new M-type X-ray binary with a 494 s-pulse period neutron star?