University of Maryland, Baltimore County

About: University of Maryland, Baltimore County is a education organization based out in Baltimore, Maryland, United States. It is known for research contribution in the topics: Population & Aerosol. The organization has 8749 authors who have published 20843 publications receiving 795706 citations. The organization is also known as: UMBC.

The Suzaku view of highly ionized outflows in AGN – I. Statistical detection and global absorber properties

Abstract: We present the results of a new spectroscopic study of Fe K-band absorption in Active Galactic Nuclei (AGN). Using data obtained from the Suzaku public archive we have performed a statistically driven blind search for Fexxv He and/or Fexxvi Ly absorption lines in a large sample of 51 type 1:0 1:9 AGN. Through extensive Monte Carlo simulations we nd that statistically signicant absorption is detected at E & 6:7 keV in 20/51 sources at the PMC > 95% level, which corresponds to 40% of the total sample. In all cases, individual absorption lines are detected independently and simultaneously amongst the two (or three) available XIS detectors which conrms the robustness of the line detections. The most frequently observed outow phenomenology consists of two discrete absorption troughs corresponding to Fexxv He and Fexxvi Ly at a common velocity shift. From xstar tting the mean column density and ionisation parameter for the Fe K absorption components are log(NH=cm 2 ) 23 and log(= erg cm s 1 ) 4:5, respectively. Measured outow velocities span a continuous range from < 1; 500 km s 1 up to 100; 000 km s 1 , with mean and median values of 0:1 c and 0:056 c, respectively. The results of this work are consistent with those recently obtained using XMM-Newton and independently provides strong evidence for the existence of very highly-ionised circumnuclear material in a signicant fraction of both radio-quiet and radio-loud AGN in the local universe.

Absolute accuracy of water vapor measurements from six operational radiosonde types launched during AWEX-G and implications for AIRS validation

Abstract: [1] A detailed assessment of radiosonde water vapor measurement accuracy throughout the tropospheric column is needed for assessing the impact of observational error on applications that use the radiosonde data as input, such as forecast modeling, radiative transfer calculations, remote sensor retrieval validation, climate trend studies, and development of climatologies and cloud and radiation parameterizations. Six operational radiosonde types were flown together in various combinations with a reference-quality hygrometer during the Atmospheric Infrared Sounder (AIRS) Water Vapor Experiment-Ground (AWEX-G), while simultaneous measurements were acquired from Raman lidar and microwave radiometers. This study determines the mean accuracy and variability of the radiosonde water vapor measurements relative to simultaneous measurements from the University of Colorado (CU) Cryogenic Frostpoint Hygrometer (CFH), a reference-quality standard of known absolute accuracy. The accuracy and performance characteristics of the following radiosonde types are evaluated: Vaisala RS80-H, RS90, and RS92; Sippican Mark IIa; Modem GL98; and the Meteolabor Snow White hygrometer. A validated correction for sensor time lag error is found to improve the accuracy and reduce the variability of upper tropospheric water vapor measurements from the Vaisala radiosondes. The AWEX data set is also used to derive and validate a new empirical correction that improves the mean calibration accuracy of Vaisala measurements by an amount that depends on the temperature, relative humidity, and sensor type. Fully corrected Vaisala radiosonde measurements are found to be suitably accurate for AIRS validation throughout the troposphere, whereas the other radiosonde types are suitably accurate under only a subset of tropospheric conditions. Although this study focuses on the accuracy of nighttime radiosonde measurements, comparison of Vaisala RS90 measurements to water vapor retrievals from a microwave radiometer reveals a 6–8% dry bias in daytime RS90 measurements that is caused by solar heating of the sensor. An AWEX-like data set of daytime measurements is highly desirable to complete the accuracy assessment, ideally from a tropical location where the full range of tropospheric temperatures can be sampled.

Fermi Gamma-Ray Imaging of a Radio Galaxy

Abstract: The Fermi Gamma-ray Space Telescope has detected the gamma-ray glow emanating from the giant radio lobes of the radio galaxy Centaurus A. The resolved gamma-ray image shows the lobes clearly separated from the central active source. In contrast to all other active galaxies detected so far in high-energy gamma-rays, the lobe flux constitutes a considerable portion (greater than one-half) of the total source emission. The gamma-ray emission from the lobes is interpreted as inverse Compton-scattered relic radiation from the cosmic microwave background, with additional contribution at higher energies from the infrared-to-optical extragalactic background light. These measurements provide gamma-ray constraints on the magnetic field and particle energy content in radio galaxy lobes, as well as a promising method to probe the cosmic relic photon fields.

Metastable Chaos: The Transition to Sustained Chaotic Behavior in the Lorenz Model

Abstract: The system of equations introduced by Lorenz to model turbulent convective flow is studied here for Rayleigh numbersr somewhat smaller than the critical value required for sustained chaotic behavior. In this regime the system is found to exhibit transient chaotic behavior. Some statistical properties of this transient chaos are examined numerically. A mean decay time from chaos to steady flow is found and its dependence uponr is studied both numerically and (very close to the criticalr) analytically.