BL Lacertae (BL Lac) objects are the prominent members of the third {\it Fermi} Large Area Telescope catalog of $γ$-ray sources. Half of the BL Lac population ($\sim$ 300) lack redshift measurements, which is due to the absence of lines in their optical spectrum, thereby making it difficult to utilize spectroscopic methods. Our photometric drop-out technique can be used to establish the redshift for a fraction of these sources. This work employed 6 filters mounted on the $Swift$-UVOT and 4 optical filters on two telescopes, the 0.65 m SARA-CTIO in Chile and 1.0 m SARA-ORM in the Canary Islands, Spain. A sample of 15 sources was extracted from the $Swift$ archival data for which 6 filter UVOT observations were conducted. By complementing the {\it Swift} observations with the SARA ones, we were able to discover two high redshift sources: 3FGL J1155.4-3417 and 3FGL J1156.7-2250 at $z=1.83^{+0.10}_{-0.13}$ and $z=1.73^{+0.11}_{-0.19}$ , respectively, resulting from the dropouts in the powerlaw template fits to these data. The discoveries add to the important (26 total) sample of high-redshift BL Lacs. While the sample of high-z BL Lacs is still rather small, these objects do not seem to fit well within known schemes of the blazar population and represent the best probes of the extragalactic background light.
Hunting for extreme high-energy-peaked BL Lacs: Rare to find and difficult to classify
INAF – Osservatorio di Astrofisica e Scienza dello Spazio（国家天体物理研究所空间科学与天体物理观测台）；Instituto de Astrofisica, Universidad Andres Bello（安第斯贝尔托大学 Astrophysics 研究所）
An emerging population of BL Lacs with extreme properties: towards a class of EBL and cosmic magnetic field probes?
最近，对极端BL Lac天体（如1 ES 0229+200或1 ES 0347-121）的高能观测引起了人们对耀变体和喷流物理以及对河外背景光和星系间磁场估计的兴趣。然而，这些极端高峰值BL Lac天体（EHBL）的数量仍然相当少。为了增加它们的数量，我们从Plotkin等人的BL Lac样本中选择了一组EHBL候选者。（2011），考虑到费米星上的大面积望远镜未检测到（或仅勉强检测到）的那些，并以高X射线与射电通量比为特征。我们收集了由此产生的9个源的多波长光谱能量分布，利用Swift，Galex和Fermi卫星进行的公开档案观测，确认了它们的性质。通过一个简单的单区同步自康普顿模型，我们估计预期的VHE通量，发现在大多数情况下，它是在本代切伦科夫阵列或即将到来的切伦科夫望远镜阵列（CTA）的范围内。
Extreme BL Lacs: probes for cosmology and UHECR candidates
最近，对极端BL Lac天体（如1 ES 0229 +200或1 ES 0347-121）的高能观测引起了人们对耀变体和喷流物理以及河外背景光和星系间磁场估计的兴趣。此外，它们的神秘特性已经在一种场景中得到解释，在这种场景中，它们的主要高能输出是通过高能强子束。然而，尽管它们可能在所有这些主题中发挥重要作用，但这些极端高峰值BL Lac天体（EHBL）的数量仍然相当少。为了增加它们的数量，我们选择了一组EHBL候选者，考虑那些未被LAT机载费米探测到（或几乎没有探测到）的EHBL候选者，其特征在于高X射线与射电通量比。我们使用Swift，GALEX和Fermi卫星的可用档案数据，收集了由此产生的9个源的多波长光谱能量分布，确认了它们的性质。通过一个简单的单区同步自康普顿模型，我们估计预期的非常高的能量通量，发现在大多数情况下，它是在本代切伦科夫阵列或即将到来的CTA的范围内。
Using Neural Networks to Differentiate Newly Discovered BL Lacs and FSRQs among the 4FGL Unassociated Sources Employing Gamma-ray, X-ray, UV/Optical and IR Data
A new look at the extragalactic Very High Energy sky: searching for TeV-emitting candidates among the X-ray bright, non-Fermi detected blazar population
Constraining the synchrotron peak and estimating the VHE brightness of a sample of extreme high synchrotron peak blazars
Università di Bologna（博洛尼亚大学）；INAF-Osservatorio di Astrofisica e Scienza dello Spazio (OAS)（意大利国家天体物理研究所空间科学与天体物理观测台）；Clemson University（克莱姆森大学）；INFN Sezione di Padova and Università degli Studi di Padova（帕多瓦大学意大利国家核物理研究所帕多瓦分部）；Deutsches Elektronen-Synchrotron DESY（德国电子同步辐射研究所）
