VLBI observations of the H2O gigamaser in TXS 2226-184
VLBI observations of the H2O gigamaser in TXS 2226-184
复制标题
TXS 2226-184 中 H2O gigaser 的 VLBI 观测
DOI：
10.1051/0004-6361/201937380
复制
发表时间：
2020
影响因子：
6.5
通讯作者：
P. Castangia
中科院分区：
文献类型：
--
作者：
G. Surcis;A. Tarchi;P. Castangia
上下文在银河系外，最明亮的22 GHz的H2O脉泽，称为超脉泽，因为它们的极端亮度相对于银河系和河外的H2O脉泽与星星的形成，主要是在活动星系核检测。在TXS 2226-184星系的核区发现的H2O脉泽，是第一次使用吉加脉泽这个术语。然而，这种非常明亮的H2O脉泽发射的起源从未被详细研究过。
目标。通过首次以毫角秒分辨率测量TXS 2226-184中22 GHz H_2O千兆赫脉泽的绝对位置、比较20年后在甚长基线干涉测量（VLBI）尺度上脉泽发射的形态和特征以及尝试探测其偏振发射，研究了TXS 2226-184中22 GHz H_2O千兆赫脉泽的性质。
方法.我们三次观测到TXS 2226-184的22 GHz H2O脉泽发射：第一次是用NRAO甚长基线阵列（VLBA，2017.45），接下来两次是用欧洲VLBI网络（EVN，2017.83和2018.44）。前两个历元（2017.45和2017.83）是在相位参考模式下观察到的，而最后一个历元（2018.44）是在全偏振模式下观察到的，但不是在相位参考模式下观察到的，以增加在源积分时间。我们还检索和分析了VLBA档案数据在22 GHz的TXS 2226-184在1998.40观测。
结果我们在2017.45历元（VLBA）中检测到六个H2O脉泽特征，在2017.83历元（EVN）中检测到一个，在2018.44历元（EVN）中检测到两个。除了一个是红移相对于TXS 2226-184的系统速度，我们只检测到一个蓝移脉泽功能，它是最弱的一个。所有的水脉泽功能，但蓝移一个是由两个组件具有非常不同的线宽。我们第一次能够测量的绝对位置的H2O脉泽功能的误差低于1毫角秒。未检测到线偏振和圆偏振。
结论.我们能够将TXS 2226-184中的H2O脉泽特征与文献中报道的最明亮的射电连续谱团联系起来。历元1998.40和2017.45之间的比较揭示了脉泽特征的形态和速度的差异，这可以解释脉泽的可变性。
Context. Outside the Milky Way the most luminous H2O masers at 22 GHz, called megamasers because of their extreme luminosity with respect to the Galactic and extragalactic H2O masers associated with star formation, are mainly detected in active galactic nuclei. In the case of the H2O maser detected in the nuclear region of the galaxy TXS 2226-184, the term gigamaser was used for the first time. However, the origin of this very luminous H2O maser emission has never been investigated in detail.
Aims. We study the nature of the 22 GHz H2O gigamaser in TXS 2226-184 by measuring its absolute position for the first time at milliarcsecond resolution, by comparing the morphology and characteristics of the maser emission on very long baseline interferometry (VLBI) scales after about 20 years, and by trying to detect its polarized emission.
Methods. We observed the 22 GHz H2O maser emission toward TXS 2226-184 three times: the very first time with the NRAO Very Long Baseline Array (VLBA, epoch 2017.45) and the next two times with the European VLBI Network (EVN, epochs 2017.83 and 2018.44). The first two epochs (2017.45 and 2017.83) were observed in phase-reference mode, while the last epoch (2018.44) was observed in full-polarization mode, but not in phase-reference mode to increase the on-source integration time. We also retrieved and analyzed the VLBA archival data at 22 GHz of TXS 2226-184 observed in epoch 1998.40.
Results. We detected six H2O maser features in epoch 2017.45 (VLBA), one in epoch 2017.83 (EVN), and two in epoch 2018.44 (EVN). All but one are red-shifted with respect to the systemic velocity of TXS 2226-184; we detected only one blue-shifted maser feature and it is the weakest one. All the H2O maser features but the blue-shifted one are composed of two components with very different linewidths. For the first time we were able to measure the absolute position of the H2O maser features with errors below 1 milliarcsec. No linear and circular polarization was detected.
Conclusions. We were able to associate the H2O maser features in TXS 2226-184 with the most luminous radio continuum clump reported in the literature. The comparison between epochs 1998.40 and 2017.45 reveals a difference in the morphology and velocity of the maser features that can be justified accounting for maser variability.
水巨型微波射电星系3C 403的最内部区域
影响因子：
6.5
作者：
Tarchi A;Brunthaler A;Henkel C;Menten K.M;Braatz J;Weiss A.
通讯作者：
Weiss A.