12 research outputs found
VLBA 24 and 43 GHz observations of massive binary black hole candidate PKS 1155+251
PKS 1155+251 is a radio-loud quasar source at z=0.203. Observations using
very long baseline interferometry (VLBI) at ~2, 5, 8 and 15 GHz show that the
structure of the radio source is quite complicated on parsec scales and that
the outer hot spots are apparently undergoing a significant contraction.
Because these results cannot be fully explained based on the compact symmetric
object (CSO) scenario with a radio core located between the northern and
southern complexes, we made observations with the Very Long Baseline Array
(VLBA) at 24 and 43 GHz to search for compact substructures and alternative
interpretations. The results show that the radio core revealed in the previous
VLBI observations remains compact with a flat spectrum in our
sub-milli-arcsecond--resolution images; the northern lobe emission becomes
faint at 24 GHz and is mostly resolving out at 43 GHz; the southern complex is
more bright but has been resolved into the brightest southern-end (S1) and jet
or tail alike components westwards. Explaining the southern components aligned
westward with a standard CSO scenario alone remains a challenge. As for the
flatter spectral index of the southern-end component S1 between 24 and 43 GHz
in our observations and the significant 15 GHz VLBA flux variability of S1, an
alternative scenario is that the southern complex may be powered by a secondary
black hole residing at S1. But more sensitive and high-resolution VLBI
monitoring is required to discriminate the CSO and the binary black hole
scenarios.Comment: 7 pages, 3 figures, accepted by MNRA
Correlations between the peak flux density and the position angle of inner-jet in three blazars
We aim to investigate the relation between the long-term flux density and the
position angle (PA) evolution of inner-jet in blazars. We have carried out the
elliptic Gaussian model-fit to the `core' of 50 blazars from 15 GHz VLBA data,
and analyzed the variability properties of three blazars from the model-fit
results. Diverse correlations between the long-term peak flux density and the
PA evolution of the major axis of the `core' have been found in 20% of
the 50 sources. Of them, three typical blazars have been analyzed, which also
show quasi-periodic flux variations of a few years (T). The correlation between
the peak flux density and the PA of inner-jet is positive for S5~0716+714, and
negative for S4~1807+698. The two sources cannot be explained with the
ballistic jet models, the non-ballistic models have been analyzed to explain
the two sub-luminal blazars. A correlation between the peak flux density and
the PA (with a T/4 time lag) of inner-jet is found in [HB89]~1823+568, this
correlation can be explained with a ballistic precession jet model. All the
explanations are based mainly on the geometric beaming effect; physical flux
density variations from the jet base would be considered for more complicated
situations in future, which could account for the no or less significance of
the correlation between the peak flux density and the PA of inner-jet in the
majority blazars of our sample.Comment: 6 pages, 7 figures, accepted for publication in Astrophysics and
Space Scienc
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CEPC Conceptual Design Report: Volume 2 - Physics & Detector
The Circular Electron Positron Collider (CEPC) is a large international scientific facility proposed by the Chinese particle physics community to explore the Higgs boson and provide critical tests of the underlying fundamental physics principles of the Standard Model that might reveal new physics. The CEPC, to be hosted in China in a circular underground tunnel of approximately 100 km in circumference, is designed to operate as a Higgs factory producing electron-positron collisions with a center-of-mass energy of 240 GeV. The collider will also operate at around 91.2 GeV, as a Z factory, and at the WW production threshold (around 160 GeV). The CEPC will produce close to one trillion Z bosons, 100 million W bosons and over one million Higgs bosons. The vast amount of bottom quarks, charm quarks and tau-leptons produced in the decays of the Z bosons also makes the CEPC an effective B-factory and tau-charm factory. The CEPC will have two interaction points where two large detectors will be located. This document is the second volume of the CEPC Conceptual Design Report (CDR). It presents the physics case for the CEPC, describes conceptual designs of possible detectors and their technological options, highlights the expected detector and physics performance, and discusses future plans for detector R&D and physics investigations. The final CEPC detectors will be proposed and built by international collaborations but they are likely to be composed of the detector technologies included in the conceptual designs described in this document. A separate volume, Volume I, recently released, describes the design of the CEPC accelerator complex, its associated civil engineering, and strategic alternative scenarios