9,269 research outputs found
A Bayesian Approach to Estimate the Size and Structure of the Broad-line Region in Active Galactic Nuclei Using Reverberation Mapping Data
This is the first paper in a series devoted to systematic study of the size
and structure of the broad-line region (BLR) in active galactic nuclei (AGNs)
using reverberation mapping (RM) data. We employ a recently developed Bayesian
approach that statistically describes the variabibility as a damped random walk
process and delineates the BLR structure using a flexible disk geometry that
can account for a variety of shapes, including disks, rings, shells, and
spheres. We allow for the possibility that the line emission may respond
non-linearly to the continuum, and we detrend the light curves when there is
clear evidence for secular variation. We use a Markov Chain Monte Carlo
implementation based on Bayesian statistics to recover the parameters and
uncertainties for the BLR model. The corresponding transfer function is
obtained self-consistently. We tentatively constrain the virial factor used to
estimate black hole masses; more accurate determinations will have to await
velocity-resolved RM data. Application of our method to RM data with Hbeta
monitoring for about 40 objects shows that the assumed BLR geometry can
reproduce quite well the observed emission-line fluxes from the continuum light
curves. We find that the Hbeta BLR sizes obtained from our method are on
average ~20% larger than those derived from the traditional cross-correlation
method. Nevertheless, we still find a tight BLR size-luminosity relation with a
slope of alpha=0.55\pm0.03 and an intrinsic scatter of ~0.18 dex. In
particular, we demonstrate that our approach yields appropriate BLR sizes for
some objects (such as Mrk 142 and PG 2130+099) where traditional methods
previously encountered difficulties.Comment: 17 pages, 10 figures, 2 tables; minor reversion to match the
published versio
Discovery of gamma-ray emission from a strongly lobe-dominated quasar 3C 275.1
We systematically analyze the 6-year {\it Fermi}/LAT data of the
lobe-dominated quasars (LDQs) in the complete LDQ sample from 3CRR survey and
report the discovery of high-energy -ray emission from 3C 275.1. The
-ray emission of 3C 207 is confirmed and significant variability of the
lightcurve is identified. We do not find statistically significant -ray
emission from other LDQs. 3C 275.1 is the known -ray quasar with the
lowest core dominance parameter (i.e., ). We also show that both the
northern radio hotspot and parsec jet models can reasonably reproduce the
-ray data. The parsec jet model, however, is favored by the potential
-ray variability at the timescale of months. We suggest that some
dimmer -ray LDQs will be detected in the future and LDQs could
contribute non-negligibly to the extragalactic -ray background.Comment: 26 pages, 10 figures, 3 tables; ApJ in pres
Platinum composite nanowires for ultrasensitive mass detection
Platinum (Pt) composite nanowires were grown on the tip of tungsten (W) microprobes by focused-electron-beam induced chemical vapor deposition (FEB-CVD). An electrical field was used to drive a transversal mechanical vibration of the nanowires. Such nanowire vibrations were found to display the first and second harmonic resonances with frequencies in the range of tens of MHz. The Young's modulus of the nanowires was estimated to be in the range of (1.4 ± 0.1) × 102 GPa to (4.7 ± 0.2) × 102 GPa, dependent on the wire size. A mass responsivity of 2.1 × 1021 Hz/kg Hz/kg was demonstrated with the minimum detectable mass of about 0.4 attogram. Our results indicated the potentials of FEB-CVD for the fabrication of nano-balances on any surface for ultra-sensitive mechanical applications
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