26 research outputs found
Interferometric Phase Calibration Sources in the Declination Range 0deg to -30deg
We present a catalog of 321 compact radio sources in the declination range
0deg > delta > -30deg. The positions of these sources have been measured with a
two-dimensional rms accuracy of 35 milliarcseconds using the NRAO Very Large
Array. Each source has a peak flux density >50 mJy at 8.4 GHz. We intend for
this catalog to be used mainly for selection of phase calibration sources for
radio interferometers, although compact radio sources have other scientific
uses.Comment: 9 pages. To appear in ApJS. Catalog (Table 3) is abbreviated in
printed version. Complete catalog available at
ftp://ftp.aoc.nrao.edu/pub/staff/jwrobel/WPW2003_ApJS.tx
A nearly symmetric double-image gravitational lens
We report the discovery of a new double-image gravitational lens resulting
from our search for lenses in the southern sky. Radio source PMN J2004-1349 is
composed of two compact components separated by 1.13 arcseconds in VLA, MERLIN
and VLBA images. The components have a flux ratio of 1:1 at radio frequencies
ranging from 5 GHz to 22 GHz. The I-band optical counterpart is also an equal
double, with roughly the same separation and position angle as the radio
double. Upon subtraction of the components from the I-band image, we identify a
dim pattern of residuals as the lens galaxy. While the present observations are
sufficient to establish that J2004-1349 is a gravitational lens, additional
information will be necessary (such as the redshifts of the galaxy and quasar,
and precise astrometry and photometry of the lens galaxy) before constructing
detailed mass models.Comment: 17 pp., 5 bitmapped figs. (contact [email protected] for nicer figs), in
press, A.J. (substantially revised
PMN J1632-0033: A new gravitationally lensed quasar
We report the discovery of a gravitationally lensed quasar resulting from our
survey for lenses in the southern sky. Radio images of PMN J1632-0033 with the
VLA and ATCA exhibit two compact, flat-spectrum components with separation
1.47" and flux density ratio 13.2. Images with the HST reveal the optical
counterparts to the radio components and also the lens galaxy. An optical
spectrum of the bright component, obtained with the first Magellan telescope,
reveals quasar emission lines at redshift 3.42. Deeper radio images with MERLIN
and the VLBA reveal a faint third radio component located near the center of
the lens galaxy, which is either a third image of the background quasar or
faint emission from the lens galaxy.Comment: 21 pp., including 4 figures; thoroughly revised in light of new
MERLIN/HST data; accepted for publication in A
Venous thromboembolism following hematopoietic stem cell transplantation-a systematic review and meta-analysis
Venous thromboembolism (VTE) is a common complication of hematopoietic stem cell transplantation (HSCT). Graft-versus-host disease (GVHD) is another complication of HSCT that may modify the risk of VTE. Our objective was to explore the incidence of VTE (deep venous thrombosis and pulmonary embolism) following HSCT and to evaluate its association with GVHD. A comprehensive search of Medline In-Process & Other Non-Indexed Citations, MEDLINE, EMBASE, Cochrane Central Register of Controlled Trials, and Scopus was conducted to search for both retrospective and prospective HSCT studies which had reported VTE. Random-effects meta-analysis was used to pool incidence rates. We included 17 studies reporting on allogeneic- and 10 on autologous-HSCT; enrolling 6693 patients; of which 5 were randomized. The overall incidence of VTE after HSCT was 5%(4-7%). Incidence in allogeneic-HSCT was 4%(2-6%) and in autologous-HSCT was 4%(1-15%). Eleven and nine studies reported data on acute and chronic GVHD, respectively. The incidence of VTE in chronic GVHD was 35%(20-54%), whereas in acute GVHD it was 47%(32-62%). Based on the results of this meta-analysis, VTE is a fairly common complication after HSCT, emphasizing the importance of assimilating guidelines for both treatment and prophylaxis in this patient population
A major radio outburst in III Zw 2 with an extremely inverted, millimeter-peaked spectrum
III Zw 2 is a spiral galaxy with an optical spectrum and faint extended radio
structure typical of a Seyfert galaxy, but also with an extremely variable,
blazar-like radio core. We have now discovered a new radio flare where the
source has brightened more than twenty-fold within less than two years. A
broad-band radio spectrum between 1.4 and 666 GHz shows a textbook-like
synchrotron spectrum peaking at 43 GHz, with a self-absorbed synchrotron
spectral index +2.5 at frequencies below 43 GHz and an optically thin spectral
index -0.75 at frequencies above 43 GHz. The outburst spectrum can be well
fitted by two homogenous, spherical components with equipartition sizes of 0.1
and 0.2 pc at 43 and 15 GHz, and with magnetic fields of 0.4 and 1 Gauss. VLBA
observations at 43 GHz confirm this double structure and these sizes. Time
scale arguments suggest that the emitting regions are shocks which are
continuously accelerating particles. This could be explained by a frustrated
jet scenario with very compact hotspots. Similar millimeter-peaked spectrum
(MPS) sources could have escaped our attention because of their low flux
density at typical survey frequencies and their strong variability.Comment: ApJ Letters, in press, (AAS)LaTeX, 3 figures, available at
http://www2.mpifr-bonn.mpg.de/staff/hfalcke/publications.html#iiizw2 or in a
few weeks at
http://www.mpifr-bonn.mpg.de/staff/falcke/publications.html#iiizw
EVN+MERLIN Observations of Radio-Intermediate Quasars: Evidence for Boosted Radio-Weak Quasars
We present VLBI (EVN+MERLIN) observations of a sample of three low-redshift
radio-intermediate PG quasars (RIQ) with flat and variable radio spectrum (III
Zw 2, PG 1309+355, PG 2209+184). Their radio-to-optical flux ratio (R) is
slightly lower than the average R for steep-spectrum quasars, but their radio
spectral properties are those of core-dominated quasars. It was proposed
previously that these sources might be relativistically boosted jets in
radio-weak quasars. Our VLBI observations now indeed confirm the presence of a
high brightness temperature core in all three of these objects --- two of them
have lower limits on T_B well in excess of 10^10 Kelvin. Moreover, we find no
``missing-flux'' which means that basically all the flux of these quasars is
concentrated in the compact radio core. As the total radio flux is already at
the low end for radio-loud quasars, we can place a strong limit on the presence
of any extended emission. This limit is consistent with the extended emission
in radio-weak quasars, but excludes that the flat-spectrum RIQ reside in
typical radio-loud quasars. The observations therefore strongly support the
idea that relativistic jets are present in radio-weak quasars and hence that
radio-loud and radio-weak quasars have very similar central engines.Comment: ApJ Letters, accepted for publication, 7 pages, 4 PS Figures, AASTeX,
also available at http://www.astro.umd.edu/~hfalcke/publications.html#riqvlb