A Multiwavelength Study of the Jets in FR-I Radio Galaxies:I.Data and Analysis

We compile a sample of 11 Fanaroff-Riley type I Radio Galaxies （FR-I RGs） with multi-wavelength observations to address the dynamic behavior of jets in these objects. Optical images acquired by the Hubble Space Telescope （HST） are carefully analyzed. The method and reduction procedure are described in detail. Unresolved optical cores emerge after having properly removed starlight from the host galaxies in eight of the FR-I RGs, of which five are new identifications. Broad band spectral properties of these newly identified compact cores are compared with that previously found in FR-I RGs, as well as the low-energy-peaked BL Lac objects. The similarity between them argues for the same non-thermal synchrotron origin. Well-resolved optical jets with knotty morphologies are found in three FR-I RGs in our sample, namely 3C 15, 3C 66B and B2 0755＋37. The optical counterparts to the inner radio/X-ray jets are identified and a clear one-to-one correspondence between the optical, radio and X-ray knots is found. The structure and information on the optical jets are discussed. Physical parameters such as the knots position, flux and size are also presented. Detailed comparison between the multi-wavelength data and radiative and dynamic models of jet will be made in a forthcoming paper.

Reflections and standing waves on the Tianlai cylinder array

In 21 cm intensity mapping,the spectral smoothness of the foreground is exploited to separate it from the much weaker 21 cm signal.However,the non-smooth frequency response of the instrument complicates this process.Reflections and standing waves generate modulations on the frequency response.Here we report the analysis of the standing waves in the bandpass of the signal channels of the Tianlai Cylinder Array.By Fourier transforming the bandpass into the delay time domain,we find various standing waves generated on the telescope.A standing wave with time delay at~142 ns is most clearly identified which is produced in the 15-meter feed cable.We also identify a strong peak at a shorter delay ofτ<50 ns,which may be a mix of the standing wave between the reflector and feed,and the standing wave on the 4 m intermediate frequency(IF)cable.We also show that a smoother frequency response could be partially recovered by removing the reflection-inducted modulations.However,the standing wave on the antenna is direction-dependent,which poses a more difficult challenge for high precision calibration.

The Tianlai Cylinder Pathfinder array: System functions and basic performance analysis

The Tianlai Cylinder Pathfinder is a radio interferometer array designed to test techniques for 21 cm intensity mapping in the post-reionization Universe,with the ultimate aim of mapping the large scale structure and measuring cosmological parameters such as the dark energy equation of state.Each of its three parallel cylinder reflectors is oriented in the north-south direction,and the array has a large field of view.As the Earth rotates,the northern sky is observed by drift scanning.The array is located in Hongliuxia,a radio-quiet site in Xinjiang,and saw its first light in September 2016.In this first data analysis paper for the Tianlai cylinder array,we discuss the sub-system qualification tests,and present basic system performance obtained from preliminary analysis of the commissioning observations during 2016-2018.We show typical interferometric visibility data,from which we derive the actual beam profile in the east-west direction and the frequency band-pass response.We describe also the calibration process to determine the complex gains for the array elements,either using bright astronomical point sources,or an artificial on site calibrator source,and discuss the instrument response stability,crucial for transit interferometry.Based on this analysis,we find a system temperature of about 90 K,and we also estimate the sensitivity of the array.