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arXiv · 2207.01969

Discovery of a new supergiant fast X-ray transient MAXI J0709-159 associated with the Be star LY CMa

Mutsumi Sugizaki·Tatehiro Mihara·Kohei Kobayashi·Hitoshi Negoro·Megumi Shidatsu·Sean N. Pike·Wataru Iwakiri·Sota Urabe·Motoko Serino·Nobuyuki Kawai·Motoki Nakajima·Jamie A. Kennea·Zhu Liu
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Abstract

We report on the discovery of a new supergiant fast X-ray transient (SFXT), MAXI J0709$-$159, and its identification with LY CMa (also known as HD 54786). On 2022 January 25, a new flaring X-ray object named MAXI J0709$-$159, was detected by Monitor of All-sky X-ray Image (MAXI). Two flaring activities were observed in the two scans of $\sim 3$ hours apart, where the 2-10 keV flux reached $5\times 10^{-9}$ erg cm$^{-2}$ s$^{-1}$. During the period, the source exhibited a large spectral change suggesting that the absorption column density $N_\mathrm{H}$ increased from $10^{22}$ cm$^{-2}$ to $10^{23}$ cm$^{-2}$. NuSTAR follow-up observation on January 29 identified a new X-ray source with a flux of $6\times 10^{-13}$ erg cm$^{-2}$ s$^{-1}$ at the position consistent with LY CMa, which has been identified as B supergiant as well as Be star, located at the 3 kpc distance. The observed X-ray activity characterized by the short ($\lesssim$ several hours) duration, the rapid ($\lesssim$ a few seconds) variabilities accompanied with spectral changes, and the large luminosity swing ($10^{32}$-$10^{37}$ erg s$^{-1}$) agree with those of SFXT. On the other hand, optical spectroscopic observations of LY CMa revealed a broad $Hα$ emission line, which may indicate the existence of a Be circumstellar disk. These obtained results suggest that the optical companion, LY CMa, certainly has a complex circumstellar medium including dense clumps.

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Mutsumi Sugizaki, Tatehiro Mihara, Kohei Kobayashi, Hitoshi Negoro, Megumi Shidatsu, Sean N. Pike, Wataru Iwakiri, Sota Urabe, Motoko Serino, Nobuyuki Kawai, Motoki Nakajima, Jamie A. Kennea, Zhu Liu. 2022-07-06. Discovery of a new supergiant fast X-ray transient MAXI J0709-159 associated with the Be star LY CMa. https://doi.org/10.1093/pasj%2Fpsac059

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