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Perlman E.S.,Florida Institute of Technology | Adams S.C.,University of Georgia | Cara M.,Florida Institute of Technology | Cara M.,Case Western Reserve University | And 13 more authors.
Astrophysical Journal | Year: 2011

During the last decade, M87's jet has been the site of an extraordinary variability event, with one knot (HST-1) increasing by over a factor 100 in brightness. Variability has also been seen on timescales of months in the nuclear flux. Here we discuss the optical-UV polarization and spectral variability of these components, which show vastly different behavior. HST-1 shows a highly significant correlation between flux and polarization, with P increasing from 20% at minimum to >40% at maximum, while the orientation of its electric vector stayed constant. HST-1's optical-UV spectrum is very hard (αUV-O 0.5, F ν ∞ ν-α), and displays "hard lags" during epochs 2004.9-2005.5, including the peak of the flare, with soft lags at later epochs. We interpret the behavior of HST-1 as enhanced particle acceleration in a shock, with cooling from both particle aging and the relaxation of the compression. We set 2σ upper limits of 0.5δ pc and 1.02c on the size and advance speed of the flaring region. The slight deviation of the electric vector orientation from the jet position angle (P.A.) makes it likely that on smaller scales the flaring region has either a double or twisted structure. By contrast, the nucleus displays much more rapid variability, with a highly variable electric vector orientation and "looping" in the (I, P) plane. The nucleus has a much steeper spectrum (αUV-O ∼ 1.5) but does not show UV-optical spectral variability. Its behavior can be interpreted as either a helical distortion to a steady jet or a shock propagating through a helical jet. © 2011. The American Astronomical Society. All rights reserved. Source


Hodges-Kluck E.J.,University of Maryland University College | Reynolds C.S.,University of Maryland University College | Cheung C.C.,NASA | Cheung C.C.,National Research Council Research Associate | Miller M.C.,University of Maryland University College
Astrophysical Journal | Year: 2010

We present new and archival Chandra X-ray Observatory observations of -shaped radio galaxies (XRGs) within z ∼ 0.1 alongside a comparison sample of normal double-lobed FR I and II radio galaxies. By fitting elliptical distributions to the observed diffuse hot X-ray emitting atmospheres (either the interstellar or intragroup medium), we find that the ellipticity and the position angle of the hot gas follow that of the stellar light distribution for radio galaxy hosts in general. Moreover, compared to the control sample, we find a strong tendency for -shaped morphology to be associated with wings directed along the minor axis of the hot gas distribution. Taken at face value, this result favors the hydrodynamic backflow models for the formation of XRGs which naturally explain the geometry; the merger-induced rapid reorientation models make no obvious prediction about orientation. © 2010 The American Astronomical Society. Source


Takeuchi Y.,Waseda University | Kataoka J.,Waseda University | Stawarz L.,Japan Aerospace Exploration Agency | Stawarz L.,Jagiellonian University | And 8 more authors.
Astrophysical Journal | Year: 2012

We report the results of a Suzaku X-ray imaging study of NGC6251, a nearby giant radio galaxy with intermediate FRI/II radio properties. Our pointing direction was centered on the γ-ray emission peak recently discovered with the Fermi Large Area Telescope (LAT) around the position of the northwest (NW) radio lobe 15 arcmin offset from the nucleus. After subtracting two "off-source" pointings adjacent to the radio lobe and removing possible contaminants in the X-ray Imaging Spectrometer field of view, we found significant residual X-ray emission most likely diffuse in nature. The spectrum of the excess X-ray emission is well fitted by a power law with a photon index Γ = 1.90 ± 0.15 and a 0.5-8keV flux of 4 × 10 -13ergcm-2s-1. We interpret this diffuse X-ray emission component as being due to inverse Compton upscattering of the cosmic microwave background photons by ultrarelativistic electrons within the lobe, with only a minor contribution from the beamed emission of the large-scale jet. Utilizing archival radio data for the source, we demonstrate by means of broadband spectral modeling that the γ-ray flux of the Fermi-LAT source 2FGLJ1629.4+8236 may well be accounted for by the high-energy tail of the inverse Compton continuum of the lobe. Thus, this claimed association of γ-rays from the NW lobe of NGC6251, together with the recent Fermi-LAT imaging of the extended lobes of CentaurusA, indicates that particles may be efficiently (re-)accelerated up to ultrarelativistic energies within extended radio lobes of nearby radio galaxies in general. © © 2012. The American Astronomical Society. All rights reserved. Source


Takahashi Y.,Waseda University | Kataoka J.,Waseda University | Nakamori T.,Waseda University | Maeda K.,Waseda University | And 10 more authors.
Astrophysical Journal | Year: 2012

We report on our second-year campaign of X-ray follow-up observations of unidentified Fermi Large Area Telescope (LAT) γ-ray sources at high Galactic latitudes (|b| > 10°) using the X-ray Imaging Spectrometer on board the Suzaku X-ray Observatory. In this second year of the project, seven new targets were selected from the First Fermi-LAT Catalog, and studied with 20-40ks effective Suzaku exposures. We detected an X-ray point source coincident with the position of the recently discovered millisecond pulsar (MSP) PSR J2302+4442 within the 95% confidence error circle of 1FGLJ2302.8+4443. The X-ray spectrum of the detected counterpart was well fit by a blackbody model with temperature of kT ≃ 0.3keV, consistent with an origin of the observed X-ray photons from the surface of a rotating magnetized neutron star. For four other targets that were also recently identified with a normal pulsar (1FGLJ0106.7+4853) and MSPs (1FGLJ1312.6+0048, J1902.0-5110, and J2043.2+1709), only upper limits in the 0.5-10keV band were obtained at the flux levels of ≃ 10-14ergcm-2s-1. A weak X-ray source was found in the field of 1FGLJ1739.4+8717, but its association with the variable γ-ray emitter could not be confirmed with the available Suzaku data alone. For the remaining Fermi-LAT object 1FGLJ1743.8-7620 no X-ray source was detected within the LAT 95% error ellipse. We briefly discuss the general properties of the observed high Galactic-latitude Fermi-LAT objects by comparing their multiwavelength properties with those of known blazars and MSPs. © 2012. The American Astronomical Society. All rights reserved. Source


Bandilla K.W.,National Research Council Research Associate | Kraemer S.R.,Office of Research and Development ORD | Birkholzer J.T.,Lawrence Berkeley National Laboratory
International Journal of Greenhouse Gas Control | Year: 2012

This study examines using the threshold critical pressure increase and the extent of the carbon dioxide (CO 2) plume to delineate the area of potential impact (AoPI) for geologic CO 2 storage projects. The combined area covering both the CO 2 plume and the region where the pressure is greater than the threshold critical pressure increase is defined as the AoPI. The threshold critical pressure increase is defined as the pressure needed to lift formation brine up the length of an unplugged well to an underground source of drinking water. Using parameter values based on existing and planned CO 2 injection sites, in combination with a simple conceptual model, semi-analytic solutions are used to find the radial pressure response and spread of the CO 2 plume. A set of sensitivity analyses investigates the parameters that have the strongest impact on the size of the AoPI. The sensitivity analyses show that the injection formation salinity and the vertical distance between injection formation and drinking water source have a strong impact on the threshold critical pressure increase. In addition, the formation permeability has a strong impact on the radius at which the threshold critical pressure is reached, as does the amount of diffuse leakage into neighboring formations. The radius of the CO 2 plume is mainly impacted by the available storage space (thickness and porosity), the formation permeability and the injection rate. The radius of the AoPI is determined by the threshold critical pressure increase in about half of 1458 sensitivity cases, the rest are determined by the maximum extent of the free phase CO 2 plume. When brine leakage into and through the cap rock is considered, the size of the AoPI is determined by the threshold critical pressure increase for only about 29% of the cases. © 2012 Elsevier Ltd. Source

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