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首页> 外文期刊>PASJ: Publications of the Astronomical Society of Japan >Spectral Evolution of a New X-Ray Transient MAXIJ0556--332 Observed by MAXI, Swift, and RXTE
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Spectral Evolution of a New X-Ray Transient MAXIJ0556--332 Observed by MAXI, Swift, and RXTE

机译：MAXI，Swift和RXTE观测的新型X射线瞬态MAXIJ0556--332的光谱演化

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摘要

We report on the spectral evolution of a new X-ray transient, MAXIJ0556-332, observed by MAXI, Swift, and RXTE. The source was discovered on 2011 January 11 (MJD = 55572) by the MAXI Gas Slit Camera allsky survey at (l, b) = (238.°9, -25.°2), relatively away from the Galactic plane. Swift/XRT follow-up observations identified it with a previously uncatalogued bright X-ray source, which led to optical identification. For more than one year since its appearance, MAXIJ0556-332 has been X-ray active, with a 2–10 keV intensity above 30 mCrab. The MAXI/GSC data revealed rapid X-ray brightening in the first five days, and a hard-to-soft transition in the meantime. For the following ~70 days, the 0.5–30 keV spectra, obtained by the Swift/XRT and the RXTE/PCA on an almost daily basis, show a gradual hardening, with large flux variability. These spectra are approximated by a cutoff power-law with a photon index of 0.4–1 and a high-energy exponential cutoff at 1.5–5 keV, throughout the initial 10 months where the spectral evolution is mainly represented by a change of the cutoff energy. To be more physical, the spectra are consistently explained by thermal emission from an accretion disk plus Comptonized emission from a boundary layer around a neutron star. This supports the source identification as being a neutron-star X-ray binary. The obtained spectral parameters agree with those of neutron-star X-ray binaries in the soft state, whose luminosity is higher than 1.8 × 10~(37) erg s~(-1). This suggests a source distance of >17 kpc.
机译：我们报告了由MAXI，Swift和RXTE观察到的新X射线瞬变MAXIJ0556-332的光谱演化。 MAXI气体狭缝相机全天候勘测在2011年1月11日（MJD = 55572）发现了气源，其相对（l，b）=（238.°9，-25。°2），相对于银河系飞机较远。 Swift / XRT的后续观察将其识别为先前未编录的明亮X射线源，从而进行了光学识别。自问世以来，MAXIJ0556-332具有X射线活性，在30 mCrab以上的强度为2–10 keV。 MAXI / GSC数据显示前五天X射线快速变亮，与此同时，从难到难的转变。在接下来的约70天中，由Swift / XRT和RXTE / PCA几乎每天获得的0.5–30 keV光谱显示出逐渐硬化，且通量变化较大。在整个最初的10个月中，这些光谱通过光子指数为0.4–1的截止幂律和1.5–5 keV的高能指数截止进行近似，其中光谱演变主要由截止能量的变化表示。为了更加物理化，通过吸积盘的热辐射加上中子星周围边界层的康普顿辐射一致地解释了光谱。这支持将源识别为中子星X射线双星。所获得的光谱参数与软状态下的中子星X射线双星光谱参数一致，其光度高于1.8×10〜（37）erg s〜（-1）。这表明光源距离> 17 kpc。

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