Driving the Beat: Time-resolved Spectra of the White Dwarf Pulsar AR Scorpii
Driving the Beat: Time-resolved Spectra of the White Dwarf Pulsar AR Scorpii
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DOI：
10.3847/1538-4357/aafb2c
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发表时间：
2018-12
期刊：
影响因子：
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通讯作者：
P. Garnavich;C. Littlefield;S. Kafka;M. Kennedy;P. Callanan;D. Balsara;M. Lyutikov
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文献类型：
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作者：
P. Garnavich;C. Littlefield;S. Kafka;M. Kennedy;P. Callanan;D. Balsara;M. Lyutikov
我们获得了覆盖近一个轨道的异常双星AR-Scorpii(AR-Sco)的高时间分辨率光谱。Hα发射显示出一种复杂的线结构，类似于某些极点在静止时所看到的结构。这种辐射被认为是源于红矮星上的长寿命日冕。AR Sco与其他系统的一个不同之处在于，AR Sco中的白矮星(WD)相对于轨道周期快速自转。稳定在3到5个恒星半径的“弹射”日冕需要表面磁场在100到500G之间，这与次要天体表面附近的WD磁场强度相当。我们的时间分辨光谱还显示了发射通量、谱线当量宽度和连续谱颜色随系统的轨道和拍频/自旋周期的变化。在轨道的大部分时间里，光学光谱的变化与同步辐射是一致的，最高能量的电子在脉冲之间冷却。在拍频/自旋周期的时间尺度上，我们观测到了红移和蓝移的Hα发射闪光，其速度达到700kM S−1。红移的巴尔默发射闪光与连续谱拍频脉冲的亮相位相关，而蓝移的闪光似乎偏爱于拍频光曲线上的最小时间。我们认为在AR Sco中产生的大部分能量来自发生在次星内面附近的快速磁重联事件，并且我们证明了磁重联产生的能量可以解释观测到的来自系统的过量光度。
We obtained high temporal resolution spectroscopy of the unusual binary system AR Scorpii (AR Sco) covering nearly an orbit. The Hα emission shows a complex line structure similar to that seen in some polars during quiescence. Such emission is thought to be due to long-lived prominences originating on the red dwarf. A difference between AR Sco and these other systems is that the white dwarf (WD) in AR Sco is rapidly spinning relative to the orbital period. “Slingshot” prominences stable at 3 to 5 stellar radii require surface magnetic fields between 100 and 500 G. This is comparable to the estimated WD magnetic field strength near the surface of the secondary. Our time-resolved spectra also show emission fluxes, line equivalent widths, and continuum color varying over the orbit and the beat/spin periods of the system. During much of the orbit, the optical spectral variations are consistent with synchrotron emission with the highest energy electrons cooling between pulses. On the timescale of the beat/spin period we detect red- and blueshifted Hα emission flashes that reach velocities of 700 km s−1. Redshifted Balmer-emission flashes are correlated with the bright phases of the continuum beat pulses while blueshifted flashes appear to prefer the time of minimum in the beat light curve. We propose that much of the energy generated in AR Sco comes from fast magnetic reconnection events occurring near the inward face of the secondary and we show that the energy generated by magnetic reconnection can account for the observed excess luminosity from the system.