| 1. |
- Su, Bu-Mei, et al.
(författare)
-
Sub-milliarcsecond radio structure of three quasars
- 2001
-
Ingår i: Chinese Astronomy and Astrophysics. - : Elsevier. - 0275-1062 .- 1879-128X. ; 25:1, s. 23-28
-
Tidskriftsartikel (refereegranskat)abstract
- The quasars, 0420-014, 0748+126 and 2251+158 (3C 454.3), have been observed at 1.3 cm with a global VLBI network. We have obtained the hybrid maps of the quasars at sub-milliarcsecond resolution. The brightness distribution is revealed in their nuclear regions. The observed data are fitted with a small number of Gaussian components. 2251+158 shows a core-jet structure, and its nuclear region is elongated in the direction PA= -130o. The jet is curved. Its observations at the epoch 1992.9 show it to be in the course of a large burst, accompanied by several smaller ones. The strongest component has a flux of ~ 4.11 Jy (67% of the total detected flux), mostly from an area of 0.16 x 0.01 mas. Doppler boosting is probably responsible for raising the brightness temperature up to 2.6 x 1012 K.
|
|
| 2. |
- Yang, Y., et al.
(författare)
-
A New Smoothing Algorithm and its Application in Gravitational Lensing
- 2009
-
Ingår i: Chinese Astronomy and Astrophysics. - 0275-1062. ; 33:2, s. 121-132
-
Tidskriftsartikel (refereegranskat)abstract
- Based on the DWT (discrete wavelet transform) method, we propose a new smoothing algorithm for computing surface densities from 3D numerical simulation samples. To check its effectiveness, we have applied this algorithm to two Monte-Carlo samples of gravitational lens simulation with different mass resolutions, generated from the isothermal ellipsoid model of dark matter halos. The calculated results indicate that this algorithm can reconstruct accurately the surface density distribution of the gravitational lens simulation sample, and that the lens caustics and critical curves derived from the surface densities agree well with the theoretical curves. We have compared the results calculated by using 3 different wavelet bases (Daub4, Daub6 and B-spline 3th), and identified the best one. Without sacrificing its smoothing capability, this algorithm has a very fast computing speed, suitable for later N-body numerical simulations, which require even higher resolutions.
|
|
| 3. |
- Ye, Wu, et al.
(författare)
-
A Statistical Study of a Large Sample of Changing-look Active Galactic Nuclei with Multi-frequency Radio Sky Surveys
- 2023
-
Ingår i: Chinese Astronomy and Astrophysics. - 0275-1062. ; 47:2, s. 285-308
-
Tidskriftsartikel (refereegranskat)abstract
- Optically “changing-look” active galactic nuclei (AGNs) are a class of objects that exhibit appearance or disappearance of broad lines. Recent studies have shown that these “changing-look” activities very likely result from the accretion activities of the central supermassive black holes. Large variation of the accretion rate might cause jet ejection and fading events, thus lead to a certain variability of observational radio properties. From the published literature, 74 “changing-look” AGNs and 90 “changing-look” AGNs candidates identified in optical observations were collected. Based on this largest, complex, and incomplete sample to date, the radio properties of “changing-look” AGNs were investigated. The radio counterparts of 51 “changing-look” AGNs (including 21 candidates) were discovered from the all-sky surveys conducted by the Australian Square Kilometre Array Pathfinder (ASKAP) and Very Large Array (VLA) covering the frequency range of 0.9–3 GHz. This corresponds to a detection rate of about 41 percent, which is similar to general AGNs. The radio spectral indices between 0.9 and 1.4 GHz and between 1.4 and 3 GHz were calculated, which suggest that these “changing-look” AGNs tend to have flatter radio spectra than normal AGNs. This statistical result indicates that “changing-look” AGNs might host some young, compact, and faint radio jets.
|
|
