15928792
VLBI observations of nineteen GHz-peaked-spectrum radio sources at 1.6 GHz
$\mathsfsl{Aims~and~Methods}$. We present the results of VLBI observations of nineteen GHz-peaked-spectrum (GPS) radio sources at 1.6 GHz. Of them, 15 sources are selected from the Parkes half-jansky (PHJ) sample (Snellen et al. 2002, MNRAS, 337, 981), and 4 others are from our previous observation list. We aimed at imaging the structure of GPS sources, searching for compact symmetric objects (CSOs) and studying the absorption for the convex radio spectra of GPS sources. $\mathsfsl{Results}$. We obtained total-intensity 1.6 GHz VLBI images of 17 sources for the first time. Of them, 80% show a mini-double-lobe radio structure, indicating that they are CSOs or candidates, and their host AGNs could be edge-on to us. This result suggests that there is a high incidence of mini double-lobe sources (or CSOs) in the PHJ sample. The sources J0323+0534, J1135-0021, J1352+0232, J2058+0540, J2123-0112, and J2325-0344 are classified as CSOs with measured redshift, showing double-lobe structure with sizes of <1 kpc. Three sources J1057+0012, J1600-0037, and J1753+2750 are considered as core-jet sources according to their morphologies and flux variability.
7519824
Seven-frequency VLBI Observations of the GHz-Peaked-Spectrum Source OQ 208
We present quasi-simultaneous VLBI images of the GHz-Peaked-Spectrum radio source OQ 208 obtained with the Very Long Baseline Array at 1.4, 1.7, 2.3, 5.0, 8.4, 15.4 GHz and the European VLBI Network at 6.7 GHz. The low frequency (1.4, 1.7 and 2.3 GHz) observations reveal a weak and extended steep-spectrum component at about 30mas away at position angle -110 degrees, which may be a remnant emission. The radio structure of OQ 208 consists of two mini-lobes at 5.0, 6.7, 8.4 and 15.4 GHz. Our spectral analysis further confirms that the southwest lobe undergoes free-free absorption and finds that the free-free absorption is stronger in the inner region. By fitting the 8.4 GHz images from 1994 to 2005, we obtain a separation speed of 0.031+/-0.006 mas yr(-1) between the two mini-lobes. This indicates a jet proper motion of 0.105+/-0.020 c and a kinematic age of 219+/-42 yr for the radio source.
118574295
Position Angle Changes of Inner-Jets in a Sample of Blazars
We have carried out the Gaussian model-fitting to 15 GHz VLBA cores for a sample of blazars from the MOJAVE database, analysed the correlations in the model-fitted parameters and studied the variability properties for different group of sources. We found that the Fermi LAT-detected blazars have on an average higher position angle changes of cores than the non-LAT detected blazars, and that the LAT-detected ones are associated with more variable cores in flux density.
118431275
IDV observations & study of the quasar 0917+624
We carried out intra-day variability (IDV) observations from August 2005 to January 2010 with the Urumqi 25 m radio telescope for a dozen IDV sources including the quasar 0917+624. This target exhibited pronounced centimeter-band, intra-day variability during the 1980s–1990s, but its strong IDV phase ceased in 2000. The source showed no IDV in the majority of the Urumqi observing sessions, although weak IDV activity was detected in some. Multifrequency UMRAO data for 0917+624 show that the spectral index is steeper during the weak and non-IDV phases than during the strong IDV phase, supporting the idea that the size of the scintillating component may be enlarged in the weak/non IDV phases.
119119786
Radio observations of the first three-months of Fermi AGN at 4.8 GHz
Using the Urumqi 25 m radio telescope, sources from the first t hree months of the Fermi-large area telescope detected active galactic nuclei (AGN) catalog with a declination of > 0 ◦ were observed in 2009 at 4.8 GHz. The radio flux density ap- peared to correlate with the -ray intensity. Intra-day variability (IDV) observations were performed in March, April and May 2009 for 42 selected -ray bright blazars, and ∼60% of them showed evidence of flux variability at 4.8 GHz duri ng the IDV observations. The IDV detection rate was higher than that in previous flat-spectrum AGN samples. IDV appeared more often in the very long baseline interferometry-core dominant blazars, and the non-IDV blazars showed relatively "steeper" spectral in- dices than the IDV blazars. Pronounced inter-month variability was also found in two BL Lac objects: J0112+2244 and J0238+1636.
119289992
Is radio jet power linearly proportional to the product of central black hole mass and Eddington ratio in AGN?
A model for the relation between radio jet power and the product of central black hole (BH) mass and Eddington ratio of AGN is proposed, and the model is examined with data from the literature. We find that radio jet power positively correlates but not linearly with the product of BH mass (m in solar mass) and Eddington ratio (λ), and the power law indices (μ) are significantly less than unity for relatively low accretion (λ<0.1) AGN, Pj∝(λm)μ, in the radio galaxies and the Seyfert galaxies. This leads to a negative correlation between radio loudness and λm for the low luminosity AGN, i.e. R∝(λm)ρ with ρ=(7/6)μ−1<0, which may be attributed to a contribution of BH spin to total jet power assuming that the spin induced jet is gradually suppressed as the accretion rate increases. Whereas, for the high-z quasars which often show the slope μ≥1, a positive correlation between the radio loudness and disc luminosity is predicted. We discuss that the jet powers of the high-z FRII quasars are likely dominated by the accretion disc rather than by the BH spin.
122412335
Study of baryon octet charge form factors in perturbative chiral quark model
The charge form factors of baryon octet are studied in the perturbative chiral quark model (PCQM). The relativistic quark wave function is extracted by fitting the theoretical results of the nucleon charge form factors to the experimental data and the predetermined quark wave function is applied to study the charge form factors of other octet baryons. The PCQM results are found, based on the predetermined quark wave function, in good agreement with the experimental data.
118434102
Study of baryon octet electromagnetic form factors in perturbative chiral quark model
The electromagnetic properties of baryon octet are studied in the perturbative chiral quark model (PCQM). The relativistic quark wave function is extracted by fitting the theoretical results of the proton charge form factor to experimental data and the predetermined quark wave function is applied to study the electromagnetic form factors of other octet baryons as well as magnetic moments, charge and magnetic radii. The PCQM results are found, based on the predetermined quark wave function, in good agreement with experimental data.
118798867
A hunt for dual radio active galactic nuclei in the VLASS
This whitepaper describes how the VLASS could be designed in a manner to allow the identification of candidate dual active galactic nuclei (AGN) at separations <7 kpc. Dual AGN represent a clear marker of two supermassive black holes within an ongoing merger. A dual AGN survey will provide a wealth of studies in structure growth and gravitational-wave science. Radio wavelengths are ideal for identifying close pairs, as disturbed stellar and gaseous material can obscure their presence in optical and shorter wavelengths. With sufficiently high resolution and sensitivity, a large-scale radio imaging survey like the VLASS will uncover many of these systems and provide the means to broadly study the radio properties of candidate dual systems revealed at other wavelengths. We determine that the ideal survey for our purposes will be at as high a resolution as possible, with significantly more science return in A array at L-band or higher, or B array at C-band or higher. We describe a range of potential survey parameters within this document. Based on the analysis outlined in this whitepaper, our ideal survey would create a catalogue of $\gtrsim$100 dual AGN in either: 1) a medium-sensitivity (~1 mJy detection threshold), wide-field (few thousand square degree) survey, or 2) a high-sensitivity (~10 uJy threshold) survey of several hundred square degrees.
118442162
The two-body hadronic decays of Bc meson in the perturbative QCD approach: a short review
Along with the running of Large Hadron Collider (LHC) located at CERN in November 2009, a large number of data samples of $$B_c$$Bc meson have been collected and some hadronic $$B_c$$Bc decay modes have been measured by the LHC experiments. In view of the special and important roles of $$B_c$$Bc meson decays playing in the heavy flavor sector, we here give a short review on the status of two body hadronic decays $$B_c \rightarrow M_1 M_2$$Bc→M1M2 at both experimental and theoretical aspects. For the theoretical progresses, specifically, we will show lots of theoretical studies on two body hadronic $$B_c$$Bc decays involving pseudoscalar, vector, scalar, axial-vector, even tensor meson(s) in the final states by employing the perturbative QCD (pQCD) factorization approach. We will present a general analysis about the two-body hadronic decays of the heavy $$B_c$$Bc meson and also provide some expectations for the future developments.
119236452
CONSTRAINING SUB-PARSEC BINARY SUPERMASSIVE BLACK HOLES IN QUASARS WITH MULTI-EPOCH SPECTROSCOPY. II. THE POPULATION WITH KINEMATICALLY OFFSET BROAD BALMER EMISSION LINES*
A small fraction of quasars have long been known to show bulk velocity offsets (of a few hundred to thousands of km s–1) in the broad Balmer lines with respect to the systemic redshift of the host galaxy. Models to explain these offsets usually invoke broad-line region gas kinematics/asymmetry around single black holes (BHs), orbital motion of massive (~sub-parsec (sub-pc)) binary black holes (BBHs), or recoil BHs, but single-epoch spectra are unable to distinguish between these scenarios. The line-of-sight (LOS) radial velocity (RV) shifts from long-term spectroscopic monitoring can be used to test the BBH hypothesis. We have selected a sample of 399 quasars with kinematically offset broad Hβ lines from the Sloan Digital Sky Survey (SDSS) Seventh Data Release quasar catalog, and have conducted second-epoch optical spectroscopy for 50 of them. Combined with the existing SDSS spectra, the new observations enable us to constrain the LOS RV shifts of broad Hβ lines with a rest-frame baseline of a few years to nearly a decade. While previous work focused on objects with extreme velocity offset (>103 km s–1), we explore the parameter space with smaller (a few hundred km s–1) yet significant offsets (99.7% confidence). Using cross-correlation analysis, we detect significant (99% confidence) radial accelerations in the broad Hβ lines in 24 of the 50 objects, of ~10-200 km s–1 yr–1 with a median measurement uncertainty of ~10 km s–1 yr–1, implying a high fraction of variability of the broad-line velocity on multi-year timescales. We suggest that 9 of the 24 detections are sub-pc BBH candidates, which show consistent velocity shifts independently measured from a second broad line (either Hα or Mg II) without significant changes in the broad-line profiles. Combining the results on the general quasar population studied in Paper I, we find a tentative anti-correlation between the velocity offset in the first-epoch spectrum and the average acceleration between two epochs, which could be explained by orbital phase modulation when the time separation between two epochs is a non-negligible fraction of the orbital period of the motion causing the line displacement. We discuss the implications of our results for the identification of sub-pc BBH candidates in offset-line quasars and for the constraints on their frequency and orbital parameters.