[论文解读] Optical spectroscopic observations of gamma-ray blazar candidates II. The 2013 KPNO campaign in the Northern Hemisphere

F. Massaro, Marco Landoni+6 more|arXiv (Cornell University)|Mar 13, 2015

Astrophysics and Cosmic Phenomena参考文献 1被引用 21

一句话总结

本研究基于2013年KPNO北半球巡天，对39个伽马射线耀变体候选源进行了光学谱线观测，确认了6个新的耀变体，并将8个此前分类不确定的活动星系验证为BL Lac对象。结果表明，结合红外与射电选星标准与光学谱线观测，可有效识别费米未关联伽马射线源的低能对应体。

ABSTRACT

We recently started a systematic search of low-energy counterparts of the unidentified gamma-ray sources (UGSs) listed in the Fermi-Large Area Telescope (LAT) First Source Catalog (1FGL) and the Fermi-LAT 2-Year Source Catalog (2FGL).} The main goal of our investigation is to find active galaxies belonging to the blazar class that lie within the positional uncertainty region of the UGSs and thus could be their potential low-energy counterparts. To achieve our aims, we first adopted several procedures based on the peculiar observational properties of blazars in the radio and in the IR. Then we carried out a follow-up spectroscopic campaign in the optical band to verify the nature of the candidates selected as potential counterparts of the UGSs. Here we present the results of the observations carried out in 2013 in the Northern Hemisphere at Kitt Peak National Observatory (KPNO). Optical spectroscopy is crucial to confirm the nature of the sources and can be used to estimate their redshifts; it will also allow us to test the robustness of our methods when the whole campaign is completed. Here we present the optical spectroscopic observations of 39 sources. Within our sample we found that 6 sources are blazars, candidates to be low-energy counterparts of the UGSs listed in the 2FGL. We confirm that an additional 8 sources, previously classified as active galaxies of uncertain type and associated in the 2FGL, are also all BL Lac objects. Moreover, we also present 20 new spectra for known blazars listed in the Multi-frequency Catalogue of Blazars as having an uncertain redshift and/or being classified as BL Lac candidates. We conclude that our methods for selecting gamma-ray blazar candidates allows us to discover new blazars and increase the list of potential low-energy counterparts for the Fermi UGSs.

研究动机与目标

• 通过基于红外和射电性质选择的耀变体候选源，识别费米未关联伽马射线源（UGSs）的低能对应体。
• 检验多波段选星方法（特别是红外颜色与平谱射电）在分离真实耀变体方面的稳健性。
• 通过光学谱线观测确认候选体的耀变体性质，解决仅依赖测光与射电数据时的模糊性。
• 改进已知但表征不足的耀变体（列于Roma-BZCAT中）的红移估计，其分类或红移存在不确定性。
• 为多波段研究与源关联提供日益增长的确认伽马射线辐射耀变体样本。

提出的方法

• 利用WISE全天巡天的红外颜色与档案射电巡天的平谱射电性质筛选候选源。
• 优先选择具有耀变体特征的源：无谱线的光学光谱、高偏振度、非热谱能分布（SED）。
• 在KPNO的梅拉尔4米望远镜上开展后续光学谱线观测，以确认光谱类型并测量红移。
• 采用中分辨率谱线观测检测发射线/吸收线，或确认BL Lac对象特有的无特征连续谱。
• 与Roma-BZCAT v4.1进行交叉匹配，以验证或修正分类与红移估计。
• 评估信噪比（S/N）与归一化光谱，以确保数据质量与分类可靠性。

实验结果

研究问题

• RQ1 结合WISE红外颜色与平谱射电性质的多波段选星标准，能否有效从费米未关联伽马射线源中分离出真实的耀变体候选源？
• RQ2 光学谱线观测在多大程度上解决了将活动星系分类为BL Lac对象或平谱射电类星体的模糊性？
• RQ3 Roma-BZCAT中分类不确定的BL Lac候选源的红移估计有多可靠？
• RQ4 通过谱线后续观测，利用红外与射电性质识别的费米未关联伽马射线源候选源中，有多少比例被证实为耀变体？
• RQ5 谱线观测能否确认此前未分类或分类不确定的活动星系为伽马射线辐射耀变体？

主要发现

• 在观测的39个源中，确认了6个新的耀变体，为费米未关联伽马射线源的低能对应体提供了强有力候选。
• 此前分类为类型不确定的8个活动星系，通过无特征光学光谱及不可检测发射线，被确认为BL Lac对象。
• 为Roma-BZCAT中分类或红移存在不确定性的已知耀变体获取了20个新光谱，改善了其天体物理表征。
• 光学谱线观测成功验证了14个源（6个新确认，8个重新分类）的耀变体性质，证明该方法在确认非热、无特征连续谱方面的可靠性。
• 由于信噪比低或无可检测谱线，Roma-BZCAT中的部分源红移估计无法确认，凸显了光谱验证的必要性。
• 该巡天证实，结合WISE红外颜色、平谱射电性质与光学谱线观测，可显著提升耀变体候选源筛选的效率与准确性。