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 similar to I hr. Coherent pulsations with a period of 4.7394 +/- 0.0008 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 similar to I plus a narrow Gaussian line at the center energy of 6.4 keV. The interstellar column density of similar to 3 X 10(22)cm(-2) may indicate that AX J1841.0-0536 is located at a tangential point of the Scutum arm at similar to 10kpc distance. The coherent pulsations, large flux variability, and the spectral shape suggest that AX J1841.0-0536 is a Be/X-ray binary pulsar.