Ryuichi Usui, Mikio Morii, Nobuyuki Kawai, Takayuki Yamamoto, Tatehiro Mihara, Mutsumi Sugizaki, Masaru Matsuoka, Kazuo Hiroi, Masaki Ishikawa, Naoki Isobe, Masashi Kimura, Hiroki Kitayama, Mitsuhiro Kohama, Takanori Matsumura, Satoshi Nakahira, Motoki Nakajima, Hitoshi Negoro, Motoko Serino, Megumi Shidatsu, Tetsuya Sootome, Kousuke Sugimori, Fumitoshi Suwa, Takahiro Toizumi, Hiroshi Tomida, Yoko Tsuboi, Hiroshi Tsunemi, Yoshihiro Ueda, Shiro Ueno, Kazutaka Yamaoka, Kyohei Yamazaki, Atsumasa Yoshida
We report on the first observation of an X-ray outburst of a Be/X-ray binary
pulsar LS V +44 17/RX J0440.9+4431, and the discovery of an absorption dip
structure in the pulse profile. An outburst of this source was discovered by
MAXI GSC in 2010 April. It was the first detection of the transient activity of
LS V +44 17 since the source was identified as a Be/X-ray binary in 1997. From
the data of the follow-up RXTE observation near the peak of the outburst, we
found a narrow dip structure in its pulse profile which was clearer in the
lower energy bands. The pulse-phase-averaged energy spectra in the 3$-$100 keV
band can be fitted with a continuum model containing a power-law function with
an exponential cutoff and a blackbody component, which are modified at low
energy by an absorption component. A weak iron K$\alpha$ emission line is also
detected in the spectra. From the pulse-phase-resolved spectroscopy we found
that the absorption column density at the dip phase was much higher than those
in the other phases. The dip was not seen in the subsequent RXTE observations
at lower flux levels. These results suggest that the dip in the pulse profile
originates from the eclipse of the radiation from the neutron star by the
accretion column.
View original:
http://arxiv.org/abs/1201.6491
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