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 $3.33 \times 10^{-10} {\rm ~erg ~cm^{-2} ~s^{-1}}$, over 30 times brighter than in quiescence. During the rising phase, the X-ray spectrum of PKS 2005-489 hardened considerably, reaching $\alpha = 1.32~ (F_\nu \propto \nu^{-\alpha})$ near maximum. During the declining phase, the X-ray spectrum steepened rapidly, reaching $\alpha = 1.82$, then became somewhat harder towards the end of December ($\alpha \sim 1.6$). 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