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arXiv · 1102.4232

Discovery of a Cyclotron Resonance Feature in the X-ray Spectrum of GX 304-1 with RXTE and Suzaku during Outbursts Detected by MAXI in 2010

Takayuki Yamamoto·Mutsumi Sugizaki·Tatehiro Mihara·Motoki Nakajima·Kazutaka Yamaoka·Masaru Matsuoka·Mikio Morii·Kazuo Makishima
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Abstract

We report the discovery of a cyclotron resonance scattering feature (CRSF) in the X-ray spectrum of GX 304-1, obtained by RXTE and Suzaku during major outbursts detected by MAXI in 2010. The peak intensity in August reached 600 mCrab in the 2-20 keV band, which is the highest ever observed from this source. The RXTE observations on more than twenty occasions and one Suzaku observation revealed a spectral absorption feature at around 54 keV, which is the first CRSF detection from this source. The estimated strength of surface magnetic field, $4.7 \times 10^{12}$ G, is one of the highest among binary X-ray pulsars from which CRSFs have ever been detected. The RXTE spectra taken during the August outburst also suggest that the CRSF energy changed over 50-54 keV, possibly in a positive correlation with the X-ray flux. The behavior is qualitatively similar to that observed from Her X-1 on long time scales, or from A 0535+26, but different from the negative correlation observed from 4U 0115+63 and X 0331+53.

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Takayuki Yamamoto, Mutsumi Sugizaki, Tatehiro Mihara, Motoki Nakajima, Kazutaka Yamaoka, Masaru Matsuoka, Mikio Morii, Kazuo Makishima. 2011-02-21. Discovery of a Cyclotron Resonance Feature in the X-ray Spectrum of GX 304-1 with RXTE and Suzaku during Outbursts Detected by MAXI in 2010. https://doi.org/10.1093/pasj%2F63.sp3.s751

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