甚高能平谱射电类星体 PKS 0903-57 的光学光谱研究
Optical spectroscopy of the VHE flat-spectrum radio quasar PKS 0903-57
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中文总结 AI 辅助
本文通过甚大望远镜等高分辨率光学光谱观测，首次精确测定耀变体 PKS 0903-57 的红移为 0.2621，并发现宽窄发射线间约 1500 km/s 的速度位移，暗示其可能存在双黑洞或反冲黑洞等特殊动力学结构。
中文摘要 AI 辅助
我们报告了伽马射线耀变体 PKS 0903-57 的新光学光谱观测结果。由于一颗明亮的前景恒星与该耀变体仅相距 0.67 角秒，该源的光学特性历来难以确定。在 2020 年至 2022 年期间其强烈的高能（HE）和甚高能（VHE）伽马射线耀发阶段，南非大望远镜和甚大望远镜（VLT）对其光学对应体进行了光谱观测。快速眼（REM）望远镜的光度监测补充了这些观测。观测结果尚无定论。2024 年，在极佳视宁度条件下使用 0.5 角秒狭缝重复 VLT 观测，取得了重大进展。这导致在光谱中探测到五个窄发射特征，从而获得了可靠的红移测量值 z = 0.2621 ± 0.0006。我们还在光谱中探测到一个宽对称的 Hα 发射成分，其半高全宽为 4020 ± 30 km/s。发现非热喷流发射主导了连续谱，支持将 PKS 0903-57 归类为平谱射电类星体。另一个有趣的观测结果是宽 Hα 谱线与其对应的窄谱线之间存在约 1500 km/s 的显著速度位移。这种位移可能与宽线区或吸积流中的异常动力学、包含两个超大质量黑洞的系统，或超大质量黑洞合并后产生的反冲黑洞有关。基于这些结果，我们在 2024 年底和 2025 年期间进行了额外的 VLT、REM 和 Swift 观测。本文介绍了对这些新数据进行分析的初步结果。
英文摘要
We report new optical spectroscopic results for the gamma-ray blazar PKS~0903$-$57. The optical properties of this source have historically been complicated to establish, due to a bright foreground star separated from the blazar by only 0.67$^{\prime\prime}$. During its strong high-energy (HE) and very high-energy (VHE) gamma-ray flaring period between 2020 and 2022, the Southern African Large Telescope and Very Large Telescope (VLT) took spectra of its optical counterpart. Photometric monitoring with the Rapid Eye Mount (REM) telescope complemented the observations. The observational results were inconclusive. A major improvement was achieved with a repeat of the VLT observations in 2024 using a 0.5$^{\prime\prime}$ slit under excellent seeing conditions. This led to the detection of five narrow emission features in the spectra, yielding a robust redshift measurement of $z$ = 0.2621 $\pm$ 0.0006. We also detected a broad symmetric H$α$ emission component with a full width at half maximum of 4020 $\pm$ 30 km/s in the spectra. Non-thermal jet emission was found to dominate the continuum, supporting the classification of PKS~0903$-$57 as a flat-spectrum radio quasar. Another interesting observation was a significant velocity displacement of $\sim$1500~km/s between the broad H$α$ line and its corresponding narrow line. Such a displacement may be associated with unusual dynamics in the broad-line region or accretion flow, a system containing two supermassive black holes, or a recoiling black hole produced following a supermassive black-hole merger. Building on these results, we carried out additional VLT, REM, and \emph{Swift} observations towards the end of 2024 and during 2025. We present in this paper the preliminary results from the analysis of these new data.
