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arXiv 2103.00332astro-ph.HE
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哈勃太空望远镜对老脉冲星PSR J0108-1431的观测

Hubble Space Telescope observations of the old pulsar PSR J0108-1431

Vadim Abramkin, Yuriy Shibanov, Roberto P. Mignani, George G. Pavlov

备注：
14 pages, 7 figures, 7 tables. Accepted to ApJ
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摘要：

本文介绍了利用哈勃空间望远镜对2亿年前的旋转动力射电脉冲星J 0108 $-$ 1431进行的光紫外观测结果。我们发现了一个远紫外（FUV）脉冲星对应物的假定候选者，其通量密度为$λ= 1528$ nJy，为$f_ν= 9.0\pm 3.2$。然而，在更长的波长下没有探测到脉冲星，$3σ$的上限分别为52、37和87 nJy，$λ=$ 4326、3355和2366 nJy。假设脉冲星对应物确实在FUV中被探测到，并且之前报道的用甚大望远镜边缘探测到的$U$和$B$是真实的，那么脉冲星的光学紫外光谱可以用幂律模型描述，具有几乎平坦的$f_ν$光谱。与光学探测到的年轻恒星相似，非热谱的斜率在X射线范围内变陡。脉冲星在1500- 6000 nm波长范围内的光度，$L \sim 1.2\times 10^{27} (d/210\,{\rm pc})^2$ erg s $^{-1}$，对应于脉冲星旋转能量损失率$\dot {E}$到光紫外辐射的高转换效率，$η= L/\dot{E} \sim (1$ - $6)\times 10^{-4}$，取决于距离和光谱斜率的不确定值。体中子星表面的亮度温度不超过59，000 K（$3σ$上限），就像远距离观测者看到的那样。如果我们假设FUV通量是由热分量主导的，那么表面温度可以在27，000 - 55，000 K的范围内，需要一个加热机制在老中子星中运行。

英文摘要：

We present results of optical-UV observations of the 200 Myr old rotation-powered radio pulsar J0108$-$1431 with the Hubble Space Telescope. We found a putative candidate for the far-UV (FUV) pulsar counterpart, with the flux density $f_ν= 9.0\pm 3.2$ nJy at $λ= 1528$ Å. The pulsar was not detected, however, at longer wavelengths, with $3σ$ upper limits of 52, 37, and 87 nJy at $λ=$ 4326, 3355, and 2366 Å, respectively. Assuming that the pulsar counterpart was indeed detected in FUV, and the previously reported marginal $U$ and $B$ detections with the Very Large Telescope were real, the optical-UV spectrum of the pulsar can be described by a power-law model with a nearly flat $f_ν$ spectrum. Similar to younger pulsars detected in the optical, the slope of the nonthermal spectrum steepens in the X-ray range. The pulsar's luminosity in the 1500--6000 Åwavelength range, $L \sim 1.2\times 10^{27} (d/210\,{\rm pc})^2$ erg s$^{-1}$, corresponds to a high efficiency of conversion of pulsar rotation energy loss rate $\dot {E}$ to the optical-UV radiation, $η= L/\dot{E} \sim (1$--$6)\times 10^{-4}$, depending on somewhat uncertain values of distance and spectral slope. The brightness temperature of the bulk neutron star surface does not exceed 59,000 K ($3σ$ upper bound), as seen by a distant observer. If we assume that the FUV flux is dominated by a thermal component, then the surface temperature can be in the range of 27,000--55,000 K, requiring a heating mechanism to operate in old neutron stars.

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