标题： Cas A中的致密中心天体：极帽炽热的中子星还是黑洞？ 显示英文标题

标题： The Compact Central Object in Cas A: A Neutron Star with Hot Polar Caps or a Black Hole?

摘要： 卡西尼超新星遗迹的中心点源在钱德拉首次曝光观测中被发现，并在档案中的ROSAT和爱因斯坦图像中后来也被发现。 这些数据的分析并未显示出源的统计显著变化。 对于d=3.4千秒的距离，幂律拟合得到光子指数为2.6-4.1，光度为(2-60)e34erg/s。 幂律指数更高，光度更低，与非常年轻的脉冲星所观测到的相比。 同样可以用黑体模型很好地拟合光谱，T=6-8MK，R=0.2-0.5km，L=(1.4-1.9)e33erg/s。 推断出的半径太小，温度太高，无法将辐射解释为来自均匀加热的中子星整个表面。 使用中子星大气模型可以增加半径并降低温度，但这些参数仍然与年轻中子星预期的有很大不同。 然而，不能排除观测到的发射来自较冷中子星表面热点的可能性。 由于强烈的星际吸收，可能的低温成分对观测光谱贡献很小；（引力红移）表面温度的上限为<1.9-2.3MK。 在几种可能的解释中，我们倾向于一个强磁化中子星模型，其磁场约束了氢或氦极帽在较冷铁表面上。 或者，观测到的辐射可以解释为由吸积自化石盘或晚期矮星的致密天体（更可能是黑洞）发出的。 显示英文摘要

摘要： The central pointlike X-ray source of the Cas A supernova remnant was discovered in the Chandra First Light Observation and found later in the archival ROSAT and Einstein images. The analysis of these data does not show statistically significant variability of the source. The power-law fit yields the photon index 2.6-4.1, and luminosity (2-60)e34 erg/s, for d=3.4 kpc. The power-law index is higher, and the luminosity lower, than those observed fromvery young pulsars. One can fit the spectrum equally well with a blackbody model with T=6-8 MK, R=0.2-0.5 km, L=(1.4-1.9)e33 erg/s. The inferred radii are too small, and the temperatures too high, for the radiationcould be interpreted as emitted from the whole surface of a uniformly heated neutron star. Fits with the neutron star atmosphere models increase the radius and reduce the temperature, but these parameters are still substantially different from those expected for a young neutron star. One cannot exclude, however, that the observed emission originates from hot spots on a cooler neutron star surface. Because of strong interstellar absorption, the possible low-temperature component gives a small contribution to the observed spectrum; an upper limit on the (gravitationally redshifted) surface temperature is < 1.9-2.3 MK. Amongst several possible interpretations, we favor a model of a strongly magnetized neutron star with magnetically confined hydrogen or helium polar caps on a cooler iron surface. Alternatively, the observed radiation may be interpreted as emitted by a compact object (more likely, a black hole) accreting from a fossil disk or from a late-type dwarf in a close binary.