AI 中文总结
本研究分析亚秒差距SMBHB候选体PG 1302-102的19年ATCA多频射电光变曲线，发现其射电带内谱指数周期性与光学一致，射电-光学周期性耦合支持SMBHB解释，为相关研究提供案例。
AI 中文摘要
亚秒差距（sub-pc）轨道间距的超大质量黑洞双星（SMBHB）候选体是稀有且具有高价值的系统，被认为是近期探测到的纳赫兹（nHz）引力波（GW）背景的主要来源。除了脉冲星计时阵列对SMBHB产生的局域纳赫兹引力波源的搜寻外，越来越多的候选体通过对大尺度类星体光学光变曲线的长期巡天识别出来，这些巡天的时间基线不断延长。红移z=0.278的类星体PG 1302-102的光学光变曲线在约20年的时间里呈现出明显、平滑变化的周期性信号，周期约为5.2年。尽管这种周期性的成因仍存在争议，但一个合理的解释是它由两个亚秒差距间距的超大质量黑洞组成的双星系统导致。在如此近的距离下，PG 1302-102中质量为10^8.3-9.4 M⊙的核黑洞预计仅通过引力波辐射会在约10^5年内合并。我们对PG 1302-102进行了多频射电光变曲线分析，覆盖约19年的时间基线，观测数据来自2005年至2024年的澳大利亚望远镜致密阵列（ATCA）。ATCA的射电光变曲线在5.5 GHz波段变化剧烈，但未显示出与光学波段相同的周期性的显著证据。不过，我们报告在5.5 GHz的带内谱指数时间序列中存在相对更强的周期性证据，其周期与光学周期性一致。此外，近期报道的光学周期性变化也出现在射电带内谱指数光变曲线中。这两个结果表明，尽管射电和光学的辐射机制差异极大，二者的周期性可能存在物理耦合。我们认为，这种射电-光学耦合支持了SMBHB的解释，即便光学周期性发生了变化，也为LSST-SKAO时代之前的相关研究提供了引人关注的案例。
英文摘要
Supermassive black hole binary (SMBHB) candidates with sub-parsec (sub-pc) orbital separations are rare, high-value systems, thought to be the dominant sources of the recently detected nanoHertz (nHz) gravitational wave (GW) background. Alongside pulsar-timing-array searches for localized nHz GW sources from SMBHBs, an increasing number of candidates have been identified from synoptic surveys of large quasar optical light curves over increasingly long baselines. The optical light curve of the quasar PG~1302-102 at a redshift of $z=0.278$ exhibits a pronounced, smoothly varying periodic signal of ~5.2 years over approximately 20 years. Although the cause of this periodicity remains debated, a plausible explanation is a binary system of two SMBHs with a sub-pc separation. At this close distance, the $10^{8.3-9.4} M_{\odot}$ nuclear black holes in PG 1302-102 are expected to merge within $\sim$$10^{5}$ yr solely due to GW emission. We present a multi-frequency radio light curve analysis of PG~1302-102 spanning a $\sim$19-year baseline, with observations between 2005 and 2024 drawn from the Australian Telescope Compact Array (ATCA). The ATCA radio light curve is highly variable at 5.5~GHz but shows no significant evidence of the periodicity seen at optical wavelengths. However, we report fractionally stronger evidence of periodicity in the in-band spectral index time-series at 5.5~GHz, with a period consistent with the optical periodicity. Furthermore, the recently reported change in optical periodicity is also present in the radio in-band spectral index light curve. These two results suggest that radio and optical periodicity may be physically coupled despite very different emission mechanisms. We argue that this radio-optical coupling reinforces the SMBHB interpretation, despite the optical periodicity change, and provides an intriguing case study ahead of the LSST-SKAO era.
