AI 中文总结
研究共生星V648 Car的X射线反射，发现其康普顿反射贡献强、缩放因子高，推测吸积天体为非磁性白矮星，提出多反射模型解释反射特征异常强度。
AI 中文摘要
V648 Car是一颗δ型共生星，以强硬热X射线辐射、强局域光电吸收和随机变异性著称。我们分析了NuSTAR观测数据，并辅以几乎同期的Swift/XRT观测数据，以验证其X射线谱中康普顿反射的预期存在及物理含义。我们用X射线模型拟合了光谱，该模型涵盖热等离子体成分、量化内禀吸收的不同方案、6.4 keV处的荧光铁线以及反射成分。结果显示，强康普顿反射贡献了3-50 keV波段总未吸收流量的约37%；纳入反射项显著提升了光谱拟合质量，并使最大等离子体温度值降低了2倍（从约49 keV降至25 keV）。若将最大温度归因于开普勒流的强激波，推算出的白矮星质量从约20%（1.2 M⊙降至0.95 M⊙），表明忽略反射会导致该参数的显著高估。反射模型给出高反射缩放因子（R~2），与反射盘上方单一X射线源的简单图像不符。时序分析显示存在随机闪烁变异性，无相干周期调制的证据，因此吸积天体很可能是一颗非磁性白矮星。我们提出多反射模型以解释V648 Car中反射特征的异常强度。
英文摘要
V648 Car is a $δ$-type symbiotic star known for its strong hard thermal X-ray emission, heavy local photoelectric absorption, and stochastic variability. We analyze NuSTAR observations, complemented by nearly contemporaneous Swift/XRT observations, to check for the expected presence and physical implications of Compton reflection in its X-ray spectrum. The spectra were fitted with X-ray models that accounted for thermal plasma components, different prescriptions to quantify the intrinsic absorption, the presence of the fluorescent iron line at 6.4 keV, and a reflection component. Our results reveal a strong Compton reflection contribution, accounting for approximately 37% of the total unabsorbed flux in the 3-50 keV band. The inclusion of reflection significantly improves the spectral fits and reduces the value for the maximum plasma temperature by a factor of 2 (from about 49 keV to 25 keV). If the maximum temperature is attributed to strong shock of a Keplerian flow, the inferred white dwarf mass decreases from about 20% (from $1.2$ to $0.95\,M_{\odot}$), demonstrating that neglecting reflection can lead to significant overestimates of this parameter. Reflection models yield high reflection scaling factors ($R \sim 2$), inconsistent with a simple picture of a primary X-ray source above a reflecting disk. The timing analysis reveals stochastic flickering variability with no evidence for coherent periodic modulations, thus the accreting object is likely a non-magnetic white dwarf. We propose a multiple-reflection model to explain the extraordinary strength of reflection features in V648 Car.
CommentsAccepted for publication in ApJ
