LBA observations for project V578 semester 2019OCTS

Blazars are radio-loud active galactic nuclei whose jets point very close to the line of sight. High-resolution VLBI observations can provide the ultimate evidence for the blazar nature of a source, by revealing the compact, bright, high brightness temperature core with flat radio spectrum. Zywucka et al. (2018) selected the blazar candidates from the Magellanic Quasar Survey. The selection method based mainly on the optical variability and the radio-loudness of the sources. Using the infrared color-color selection for blazars derived from the data of the WISE satellite by Massaro et al. (2012) we found that 10 of the 27 WISE-detected sources are outside of the blazar gamma-ray strip. We propose to observe 7 sources from these list and additional 7 sources as a control sample which fall within the blazar strip. We want to compare the mas-scale properties of the two samples to asses whether (i) additional criteria is needed select blazar sources (ii) and if yes the WISE color-color criteria is able to improve the selection method. Optical emission and variability is thought to be dominated by the beamed jet in blazars while in non-beamed (and not radio-loud) sources it originates in the accretion disks thus governed by accretion processes. Therefore, if the physical mechanism causing the optical variability is intended to be studies the nature of the variable source is important to be ascertained.耀变体（blazar）是射电强的活动星系核（active galactic nuclei），其喷流方向极接近视线方向。高分辨率甚长基线干涉测量（Very Long Baseline Interferometry, VLBI）观测可通过揭示源的致密、明亮且具有平坦射电谱的高亮温度核，为源的耀变体本质提供决定性证据。Zywucka等人（2018）从麦哲伦类星体巡天（Magellanic Quasar Survey）中筛选出耀变体候选体，其筛选方法主要基于源的光学变异性与射电强特性。利用Massaro等人（2012）基于广域红外巡天探测器（Wide-field Infrared Survey Explorer, WISE）卫星数据推导的耀变体红外颜色-颜色筛选标准，我们发现27个经WISE探测到的源中有10个处于耀变体伽马射线带之外。我们提议对该列表中的7个源，以及另外7个处于耀变体伽马射线带内的源作为对照样本开展观测，旨在比较两个样本的毫角秒（milliarcsecond, mas）尺度特性，以评估两点：(i) 是否需要额外判据来筛选耀变体源；(ii) 若需要，WISE颜色-颜色判据能否优化筛选方法。学界普遍认为，耀变体的光学辐射与变异性主要由定向喷流主导；而非定向（且非射电强）源的光学辐射则起源于吸积盘，由吸积过程支配。因此，若要研究引发光学变异性的物理机制，明确变源的本质至关重要。