3,219 research outputs found
The HI Environment of Nearby Lyman-alpha Absorbers
We present the results of a VLA and WSRT search for HI emission from the
vicinity of seven nearby clouds, which were observed in Lya absorption with HST
toward Mrk335, Mrk501 and PKS2155-304. We searched a volume of 40' x 40' x 1000
km/s. The HI mass sensitivity (5 sigma) varies from 5x10^6 to 5x10^8 Msun. We
detected HI emission in the vicinity of four out of seven absorbers. The
closest galaxy is a small dwarf galaxy at a projected distance of 68/h kpc from
the sight line toward Mrk335. It has the same velocity (V=1970 km/s) as one of
the absorbers, and has an HI mass of only 4x10^7 Msun. We found a more luminous
galaxy at the velocity (V=5100 km/s) of one of the absorbers toward
PKS2155-304, 230/h kpc from the sight line. Two other, stronger absorbers
toward PKS2155-304 at V=17,000 km/s are associated with a loose group of three
bright spiral galaxies, at projected distances of 300 to 600/h kpc. These
results support the conclusion that most nearby Lya forest clouds trace the
large-scale structures outlined by optically luminous galaxies. We do not find
any evidence for a physical association between an absorber and its closest
galaxy.Comment: 4 Tables, 11 Figures, to be published in Astron J. (Oct 1996) Vol 11
X-Ray Spectral Variability of PKS 2005-489 During the Spectacular November 1998 Flare
We report on monitoring of the BL Lac object PKS 2005-489 by the Rossi X-ray
Timing Explorer (RXTE) in October-December 1998. During these months, the
source underwent a spectacular flare; at its peak on November 10, its 2-10 keV
flux was , over 30 times
brighter than in quiescence. During the rising phase, the X-ray spectrum of PKS
2005-489 hardened considerably, reaching near maximum. During the declining phase, the X-ray spectrum
steepened rapidly, reaching , then became somewhat harder
towards the end of December (). While such behavior has been
seen before, the simplicity, magnitude and duration of this flare allowed us to
study it in great detail. We argue that this flare was caused by either the
injection of particles into the jet or {\it in situ} particle acceleration, and
that the spectral steepening which followed the flare maximum was the result of
synchrotron cooling. Contrary to other recently observed blazar flares (e.g.,
Mkn 501, 3C 279, PKS 2155-304), our results do not imply a major shift in the
location of the synchrotron peak during this flare.Comment: ApJ Letters in press, 6 pages, 2 figures Corrected reference
INTRAOSSEOUS SARCOIDOSIS MIMICKING AS BONE METASTASES ON 18F- FDG PET/CT
A 62-year-old male with known prostate cancer underwent 18F- uorodeoxyglucose positron emission tomography/ computed tomography (18F-FDG PET/CT) scan for suspected osseous metastases after a magnetic resonance imaging of the pelvis, done for chronic low back pain and demonstrated a number of suspicious T1 hypointense/T2 hyperintense lesions in the sacrum, iliac bones and right proximal femur.18F-FDG PET/CT showed abnormal foci of increased tracer uptake in the sacrum, iliac bones and right proximal femur. Core biopsies from the sacrum were performed, showing intertrabecular non-caseating granulomata with surrounding small lymphocytes. Acid-fast bacilli and Gomori methenamine silver stains were negative, consistent with intraosseous sarcoidosis. Key words: 18F- uorodeoxyglucose positron emission tomography/computed tomography, non-caseating granulomata, sarcoidosis
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