We report a serendipitous detection of an intense X-ray flare from the Tycho reference source HD 161084 during a Suzaku observation of the Galactic Center region for \sim 20 ks .
The X-ray Imaging Spectrometer ( XIS ) recorded a flare from this A1-type dwarf or subgiant star with a flux of \sim 1.4 \times 10 ^ { -12 } erg s ^ { -1 } cm ^ { -2 } ( 0.5–10 keV ) and a decay time scale of \sim 0.5 hr .
The spectrum is hard with a prominent Fe \emissiontype XXV K \alpha emission line at 6.7 keV , which is explained by a \sim 5 keV thin-thermal plasma model attenuated by a \sim 1.4 \times 10 ^ { 21 } cm ^ { -2 } extinction .
The low extinction , which is consistent with the optical reddening , indicates that the source is a foreground star toward the Galactic Center region .
Based on the spectroscopic parallax distance of \sim 530 pc , the peak X-ray luminosity amounts to \sim 1 \times 10 ^ { 32 } erg s ^ { -1 } ( 0.5–10 keV ) .
This is much larger than the X-ray luminosity of ordinary late-type main-sequence stars , and the X-ray emission is unattributable to a hidden late-type companion that comprises a wide binary system with the A-star .
We discuss possible natures of HD 161084 and suggest that it is most likely an interacting binary with elevated magnetic activity in the companion such as the Algol-type system .
The flux detected by Suzaku during the burst is \sim 100 times larger than the quiescent level measured using the archived XMM-Newton and Chandra data .
The large flux amplification makes this star a unique example among sources of this class .