Discovery of a New X-Ray Transient Source in the Scutum Region with Suzaku

During an observation of the Galactic plane in the Scutum region with the Suzaku satellite, we discovered a new X-ray transient source, designated Suzaku J1844 $-$ 0404. Compared with previous Chandra observations of the same field, four Chandra X-ray sources exist within the current positional uncertainty of Suzaku J1844 $-$ 0404. A firm identification is not possible. From the beginning of the observation, the X-ray intensity was significant at $\sim 5 \times 10^{-14} \,\mathrm{erg} \,\mathrm{s}^{-1} \,\mathrm{cm}^{-2}$ (2–10 keV), which may be a possible precursor. Later, the source exhibited a flare with a peak flux of $\sim 10^{-12} \,\mathrm{erg} \,\mathrm{s}^{-1} \,\mathrm{cm}^{-2}$ (2–10 keV). A strong and narrow emission line at $\sim 6.66 \,\mathrm{keV}$ was observed during the flare, most likely the He-like Fe line. The spectrum in 1–10 keV is consistent with a heavily absorbed ( $N_{\mathrm{H}} \sim 3 \times 10^{22} \,\mathrm{H} \,\mathrm{cm}^{-2}$ ) thin thermal emission with $kT$ as high as $\sim 7 \,\mathrm{keV}$ . A single short flare, as observed, is rather unlikely for a cataclysmic variable. The source is probably an active binary star or a young stellar object.