Eric A. Petersen

REVERBERATION MAPPING MEASUREMENTS OF BLACK HOLE MASSES IN SIX LOCAL SEYFERT GALAXIES

We present the final results from a high sampling rate, multi-month, spectrophotometric reverberation mapping campaign undertaken to obtain either new or improved Hβ reverberation lag measurements for several relatively low-luminosity active galactic nuclei (AGNs). We have reliably measured the time delay between variations in the continuum and Hβ emission line in six local Seyfert 1 galaxies. These measurements are used to calculate the mass of the supermassive black hole at the center of each of these AGNs. We place our results in context to the most current calibration of the broad-line region (BLR) RBLR–L relationship, where our results remove outliers and reduce the scatter at the low-luminosity end of this relationship. We also present velocity-resolved Hβ time-delay measurements for our complete sample, though the clearest velocity-resolved kinematic signatures have already been published.

Disk-Jet Connection in the Radio Galaxy 3C 120

We present the results of extensive multi-frequency monitoring of the radio galaxy 3C 120 between 2002 and 2007 at X-ray (2-10 keV), optical (R and V bands), and radio (14.5 and 37 GHz) wave bands, as well as imaging with the Very Long Baseline Array (VLBA) at 43 GHz. Over the 5 yr of observation, significant dips in the X-ray light curve are followed by ejections of bright superluminal knots in the VLBA images. Consistent with this, the X-ray flux and 37 GHz flux are anti-correlated with X-ray leading the radio variations. Furthermore, the total radiative output of a radio flare is related to the equivalent width of the corresponding X-ray dip. This implies that, in this radio galaxy, the radiative state of accretion disk plus corona system, where the X-rays are produced, has a direct effect on the events in the jet, where the radio emission originates. The X-ray power spectral density of 3C 120 shows a break, with steeper slope at shorter timescale and the break timescale is commensurate with the mass of the central black hole (BH) based on observations of Seyfert galaxies and black hole X-ray binaries (BHXRBs). These findings provide support for the paradigm that BHXRBs and both radio-loud and radio-quiet active galactic nuclei are fundamentally similar systems, with characteristic time and size scales linearly proportional to the mass of the central BH. The X-ray and optical variations are strongly correlated in 3C 120, which implies that the optical emission in this object arises from the same general region as the X-rays, i.e., in the accretion disk-corona system. We numerically model multi-wavelength light curves of 3C 120 from such a system with the optical-UV emission produced in the disk and the X-rays generated by scattering of thermal photons by hot electrons in the corona. From the comparison of the temporal properties of the model light curves to that of the observed variability, we constrain the physical size of the corona and the distances of the emitting regions from the central BH. In addition, we discuss physical scenarios for the disk-jet connection that are consistent with our observations.

A REVISED BROAD-LINE REGION RADIUS AND BLACK HOLE MASS FOR THE NARROW-LINE SEYFERT 1 NGC 4051

We present the first results from a high sampling rate, multimonth reverberation mapping campaign undertaken primarily at MDM Observatory with supporting observations from telescopes around the world. The primary goal of this campaign was to obtain either new or improved Hβ reverberation lag measurements for several relatively low luminosity active galactic nuclei (AGNs). We feature results for NGC 4051 here because, until now, this object has been a significant outlier from AGN scaling relationships, e.g., it was previously a ∼2–3σ outlier on the relationship between the broad-line region (BLR) radius and the optical continuum luminosity—the RBLR–L relationship. Our new measurements of the lag time between variations in the continuum and Hβ emission line made from spectroscopic monitoring of NGC 4051 lead to a measured BLR radius of RBLR = 1.87 +0.54 −0.50 light days and black hole mass of MBH = (1.73 +0.55 −0.52 ) × 10 6 M� . This radius is consistent with that expected from the RBLR–L relationship, based on the present luminosity of NGC 4051 and the most current calibration of the relation by Bentz et al.. We also present a preliminary look at velocity-resolved Hβ light curves and time delay measurements, although we are unable to reconstruct an unambiguous velocity-resolved reverberation signal.

DIVERSE KINEMATIC SIGNATURES FROM REVERBERATION MAPPING OF THE BROAD-LINE REGION IN AGNs

A detailed analysis of the data from a high sampling rate, multi-month reverberation mapping campaign, undertaken primarily at MDM Observatory with supporting observations from telescopes around the world, reveals that the Hbeta emission region within the broad line regions (BLRs) of several nearby AGNs exhibit a variety of kinematic behaviors. While the primary goal of this campaign was to obtain either new or improved Hbeta reverberation lag measurements for several relatively low luminosity AGNs (presented in a separate work), we were also able to unambiguously reconstruct velocity-resolved reverberation signals from a subset of our targets. Through high cadence spectroscopic monitoring of the optical continuum and broad Hbeta emission line variations observed in the nuclear regions of NGC 3227, NGC 3516, and NGC 5548, we clearly see evidence for outflowing, infalling, and virialized BLR gas motions, respectively.

Experiments on focusing and use of acoustic energy to enhance the rate of polymer healing

We consider the effects of acoustic pressure on the curing of a two-part epoxy, which can be considered analogous to the polymer healing process. An epoxy sample is loaded into a tube and monitored throughout the early stages of curing by measuring its vibrational response upon periodic impulses. By tracing the natural frequencies of the epoxy-tube system and cross-checking the temperature of the epoxy, the progress of the curing can be quantified. Acoustic stimulation at three different frequencies is investigated and compared to the unstimulated case. We find that external acoustic pressure does seem to affect the curing, though much work remains to be completed.

Effect of a Crack on the Response of a Membrane Strip to In-Plane Actuation

This paper presents recent results from an ongoing investigation on the use of a single actuator/receiver pair to enable dynamic testing of a thin membrane strip in order to detect cracks. The current focus is on understanding the frequency response function of a Kapton membrane strip excited at one end by a polyvinilidine fluoride (PVDF) actuator. A receiver of identical specifications is located at the other end. The actuator operates in the d31 mode, which under sinusoidal excitation leads to a periodic variation in membrane tension. Experimental results obtained as a part of this work are discussed to motivate the need for a detailed dynamic analysis. It is argued in this paper that the membrane strip dynamics in this case can be analyzed with the help of the Mathieu equation. In this paper the response of the membrane strip is computed both with and without a crack and it is shown that under some conditions, the presence of a crack leads to a significantly dierent response, which could translate into an easily detectable signature in a practical application of this method.

Behavior of thin lightweight structures under propagating waves

In this study, we examine the propagation of mechanical waves on thin lightweight structures, with the aim of developing a method of crack detection in such structures. By comparing the response of healthy and cracked samples, we are sometimes able to differentiate between the two. Using a network of sensors it would be possible to determine the presence of a crack on a structure that is remote. Experimental work has been performed with single-crystal Silicon thin plates and a thin rectangular sheet of steel. The Silicon plates were tested healthy and cracked, and the steel was only tested when healthy. Piezo-ceramic stacks were used to provide actuation and sensing, and wave solutions to the equation of motion are obtained for the Silicon plate. Calculated and experimental results agree reasonably well.

Electronic Control of Stiffness and Dissipation of Piezoelectric Polymer Membranes

This paper discusses a method of stiffness and dissipation control based on piezoelectric coupling with applications in vibration damping. The study focuses on thin piezoelectric film strips modeled with a non-vanishing thickness and a constant boundary tension. Both flexural stiffness and in-plane tension are accounted for in setting up the partial differential equation of motion. Simulation results are presented and compared with experimental results based on harmonic excitation. Nomenclature T e ⎡⎤ = 3 × 3 matrix of electric permittivity coefficients at constant stress

Wave Propagation on Thin Lightweight Structures

One of the goals of this research is to investigate the use of controlled stress-wave propagation for structural healing. The paper begins with a review of the recent literature in the area of self-healing materials with a view to understanding possible use of acoustic energy to accelerate the healing process. Using a simple 1-dimensional propagation example, the paper investigates time reversed acoustics as a method to deliver focused acoustic energy at the defect. Also reported are results form wave propagation experiments that were conducted on synthetic membranes with and without different types of defects such as scratches, slices, holes, and cracks. The analytical work shows that energy in a series of wave pulses scattered by a defect can be captured using transducers and focused at the site of the defect. Since both pressure and temperature affect the healing process, further theoretical and experimental investigations are needed in order to provide an understanding of the effect of acoustic focusing on the rate and nature of healing. HE current aim of this study of wave propagation across thin lightweight structures is to observe the behavior of wave feedback in real time. As the waves travel across the membrane and the frequency response is observed, one may deduce the behavior of not only the wave, but also the membrane. In this study, wave propagation across a synthetic collagen-like membrane is studied. The wave, phase, and frequency response patterns are studied with the goal of detecting an imperfection in the surface. Among the defects considered are scratches, cracks, slices, and holes. A survey of the state of the art was conducted to obtain a realistic impression of current wave studies and membrane healing projects. In theory, if the energy from the waves could be harnessed, it could also be reversed and used to create concentrated constructive or destructive interference focused at the defect. In an ideal system, the acoustic energy harnessed would induce healing of the membrane. To illustrate the healing process, it was animated using the Java Swing programming language.

In-plane vibration of membrane strips and sheets with piezoelectric actuation and sensing

The studies reported on in this paper are of relevance to automated diagnosis of light weight space structures based on membranes. We investigate in-plane vibration response of membranes to in-plane actuation. Identically shaped piezoelectric polymer strips are used both for actuation and sensing. For membrane strips, the frequency response function is obtained using an in-plane vibration model. The model for the intact membrane is then modified to analyze the effect of a transverse crack at mid-span. The theoretical results are compared with experimental measurements. Experiments on a cracked strip show small differences in the frequency response function, which are qualitatively borne out by the theoretical calculations. Some experimental results on membrane sheets are also presented.