Discovery of a keV-X-ray Excess in RX J1856.5--3754
Discovery of a keV-X-ray Excess in RX J1856.5--3754
复制标题
DOI：
10.1093/pasj/psx025
复制
发表时间：
2017-03
期刊：
影响因子：
--
通讯作者：
T. Yoneyama;K. Hayashida;H. Nakajima;S. Inoue;H. Tsunemi
中科院分区：
文献类型：
--
作者：
T. Yoneyama;K. Hayashida;H. Nakajima;S. Inoue;H. Tsunemi
RX J1856.5 $-$3754是热发射孤立中子星中最亮和最近的（$\sim 120 $pc）源。它的光谱与{\sl XMM-Newton}和{\sl Chandra}卫星观测到的两个温度（$kT ^\infty\sim $32和63 eV）黑体模型很好地拟合。用双温黑体模型拟合了10组来自{\sl Suzaku} XIS 0，XIS 1，XIS 3和{\sl XMM-Newton} EPIC-pn的数据，发现在0.8 - 1.2\，keV范围内有16 - 26\ %的过量发射。我们研究了这种keV-X射线过剩的可能原因;背景的不确定性，低能光子的堆积和其他来源的混乱。他们都没有成功地解释keV-X射线过剩观察到不同的仪器。因此，我们认为这种keV-X射线过量最有可能起源于RX J1856.5 $-3754 $。然而，这是很难约束的keV-X射线过剩的光谱形状。第三个黑体分量的kT ^\infty = 137 ^{+18}_{-14}$eV，附加的幂律分量的光子指数$\Gamma = 3.4 ^{+0.5}_{-0.6}$，或康普顿化的黑体种子光子到幂律的光子指数$\Gamma_c = 4.3 ^{+0.8}_{-0.8}$可以再现keV-X射线过剩。由于在XMM Newton EPIC-pn数据（1.5）中发现了0.15 - 1.2keV波段的7.055 s脉动，我们还对0.8 - 1.2keV波段的周期性进行了研究。在keV-X射线过剩中，我们只得到脉冲分数<3%的上限。我们简短地讨论了keV-X射线过剩的可能来源，如同步辐射和黑体光子的康普顿化。
RX J1856.5$-$3754 is the brightest and nearest ($\sim 120$ pc) source among thermally emitting isolated neutron stars. Its spectra observed with {\sl XMM-Newton} and {\sl Chandra} satellites are well-fitted with the two-temperature ($kT^\infty \sim$ 32 and 63 eV) blackbody model. Fitting ten sets of the data from {\sl Suzaku} XIS0, XIS1, XIS3 and {\sl XMM-Newton} EPIC-pn with the two-temperature blackbody model, we discover an excess emission, 16--26\% in 0.8--1.2\,keV. We examine possible causes of this keV-X-ray excess; uncertainty in the background, pile up of the low energy photons and confusion of other sources. None of them succeeds in explaining the keV-X-ray excess observed with different instruments. We thus consider this keV-X-ray excess is most likely originated in RX J1856.5$-$3754. However, it is difficult to constrain the spectral shape of the keV-X-ray excess. The third blackbody component with $kT^\infty = 137^{+18}_{-14}$ eV, additional power-law component with a photon index $\Gamma = 3.4^{+0.5}_{-0.6}$, or Comptonization of blackbody seed photons into power-law with a photon index $\Gamma_c = 4.3^{+0.8}_{-0.8}$ can reproduce the keV-X-ray excess. We also search for the periodicity of 0.8--1.2\,keV data, since 7.055 s pulsation is discovered from 0.15--1.2\,keV band in the XMM Newton EPIC-pn data ($\sim$1.5\%). We only obtain the upper limit of pulsed fraction $<$ 3\% in the keV-X-ray excess. We shortly discuss the possible origin of the keV-X-ray excess, such as synchrotron radiation and Comptonization of blackbody photons.