1,176 research outputs found
Low Frequency Radio Observations of X-ray Ghost Bubbles in Abell 2597: A History of Radio Activity in the Core
A previous analysis of the Chandra X-ray image of the center of the cooling
core cluster Abell 2597 showed two ``ghost holes'' in the X-ray emission to the
west and northeast of the central radio galaxy PKS 2322-123. Previous radio
observations did not detect any radio emission coming from the interior of the
X-ray holes. We present new low frequency radio observations of Abell 2597. At
330 MHz, radio emission extends into the interior of the western ghost bubble,
but not the northeast one. Our re-analysis of the archival Chandra data shows
evidence for an X-ray tunnel (elongated region of reduced X-ray emission)
extending from near the center of the cD out to the west ghost bubble. We also
detect a smaller X-ray hole to the northeast of the center of the cD and closer
than the outer ghost bubbles. Radio observations at 1.3 GHz show extensions to
the west along the X-ray tunnel toward the west ghost bubble, to the northeast
into the new X-ray hole, and to the northwest. All of these structures are much
larger than the two inner radio lobes seen previously at 8 GHz. The X-ray
tunnel suggests that the west ghost bubble is part of a continuous flow of
radio plasma out from the active galactic nucleus, rather than a detached
buoyant old radio lobe, and thus it may be an intermediate case between an
active radio galaxy and a buoyant lobe.Comment: ApJ accepted, 5 page
Variability of Surface Pigment Concentrations in the South Atlantic Bight
A 1âyear time sequence (November 1978 through October 1979) of surface pigment images from the South Atlantic Bight (SAB) was derived from the Nimbus 7 coastal zone color scanner. This data set is augmented with in situ observations of hydrographic parameters, freshwater discharge, sea level, coastal winds, and currents for the purpose of examining the coupling between physical processes and the spatial and temporal variability of the surface pigment fields. The SAB is divided into three regions: the east Florida shelf, the GeorgiaâSouth Carolina shelf and the Carolina Capes. Sixâmonth seasonal mean pigment fields and time series of mean values within subregions were generated. While the seasonal mean isopleths were closely oriented along isobaths, significant differences between seasons in each region were found to exist. These differences are explained by correlating the pigment time series with physical parameters and processes known to be important in the SAB. Specifically, summertime concentrations between Cape Romain and Cape Canaveral were greater than those in winter, but the opposite was true north of Cape Romain. It is suggested that during the abnormally high freshwater discharge in the winterâspring of 1979, Cape Romain and Cape Fear were the major sites of crossâshelf transport, while the crossâshelf exchange during the fall of 1979 occurred just north of Cape Canaveral. Finally, the alongshore band of high pigment concentrations increased in width throughout the year in the vicinity of Charleston, but near Jacksonville it exhibited a minimum width in the summer and a maximum width in the fall of 1979
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