Discovery of a Transient X-Ray Pulsar, AX J1841.0$-$0536, in the Scutum Arm Region with ASCA

We report on the discovery of a transient X-ray pulsar, AX J1841.0$$-$$0536, serendipitously found in the Scutum arm region with the ASCA in two separate observations. The X-ray flux is very faint at the beginning, but exhibits two flares in the second observation. The flare flux increases by a factor 10 within only $$\sim 1 \,\mathrm{hr}$$. Coherent pulsations with a period of $$4.7394 \pm 0.0008 \,\mathrm{s}$$ were detected in the brightest flare phase. The X-ray spectra in the quiescent and flare phases were fitted with an absorbed power-law model with a photon index $$\sim 1$$ plus a narrow Gaussian line at the center energy of 6.4 keV. The interstellar column density of $$\sim 3\times 10^{22} \,\mathrm{cm}^{-2}$$ may indicate that AX J1841.0$$-$$0536 is located at a tangential point of the Scutum arm at $$\sim 10 \,\mathrm{kpc}$$ distance. The coherent pulsations, large flux variability, and the spectral shape suggest that AX J1841.0$$-$$0536 is a Be/X-ray binary pulsar.