1,081 research outputs found
Parsec Scale Properties of Markarian 501
We present the results of a high angular resolution study of the BL Lac
object Markarian 501 in the radio band. We consider data taken at 14 different
epochs, ranging between 1.6 GHz and 22 GHz in frequency, and including new
Space VLBI observations obtained on 2001 March 5 and 6 at 1.6 and 5 GHz. We
study the kinematics of the parsec-scale jet and estimate its bulk velocity and
orientation with respect to the line of sight. Limb brightened structure in the
jet is clearly visible in our data and we discuss its possible origin in terms
of velocity gradients in the jet. Quasi-simultaneous multi-wavelength
observations allow us to map the spectral index distribution and to compare it
to the jet morphology. Finally, we estimate the physical parameters of the
parsec-scale jet.Comment: accepted for publication in ApJ; 24 pages with 17 figures (fig. 1 and
fig. 2 available only as .jpg files
Obscuration and Origin of Nuclear X-ray emission in FR I Radio Galaxies
We present X-ray observations of the nuclear region of 25 Fanaroff-Riley I
radio galaxies from the 3CRR and B2 catalogs, using data from the Chandra and
XMM archives. We find the presence of a X-ray Central Compact Core (CCCX) in
13/25 sources, in 3/25 sources the detection of a CCCX is uncertain, while in
the remaining 9/25 sources no CCCX is found. All the sources are embedded in a
diffuse soft X-ray component, generally on kpc-scales, which is in agreement
with the halo of the host galaxy and/or with the intracluster medium. The X-ray
spectra of the cores are described by a power law with photon indices Gamma=1.1
- 2.6. In 8 sources excess absorption over the Galactic value is detected, with
rest-frame column densities N_H^z ~ 10^20 - 10^21 cm^-2; thus, we confirm the
previous claim based on optical data that most FRI radio galaxies lack a
standard optically-thick torus. We find significant correlations between the
X-ray core luminosity and the radio and optical luminosities, suggesting that
at least a fraction of the X-ray emission originates in a jet; however, the
origin of the X-rays remains ambiguous. If the X-ray emission is entirely
attributed to an isotropic, accretion-related component, we find very small
Eddington ratios, L_bol/L_Edd ~ 10^-3 - 10^-8, and we calculate the radiative
efficiency to be eta ~ 10^-2 - 10^-6, based on the Bondi accretion rates from
the spatial analysis. This suggests that radiatively inefficient accretion
flows are present in the cores of low-power radio galaxies.Comment: 20 pages, 7 figures, accepted for publication in The Astrophysical
Journa
A nationwide inventory of the availability of alcohol-based handrub in Dutch acute care hospitals
IRAS F02044+0957: radio source in interacting system of galaxies
The steep spectrum of IRAS F02044+0957 was obtained with the RATAN-600 radio
telescope at four frequencies. Optical spectroscopy of the system components,
was carried out with the 2.1m telescope of the Guillermo Haro Observatory.
Observational data allow us to conclude that this object is a pair of
interacting galaxies, a LINER and a HII galaxy, at .Comment: 2 pages, 2 EPS-figures, uses newpasp.sty. To appear in Proc. IAU
Colloq. 184, AGN Surveys, ed. R. F. Green, E. Ye. Khachikian, & D. B. Sanders
(San Francisco: ASP
Evolution of the number of accreting white dwarfs with shell nuclear burning and of occurrence rate of SN Ia
We analyze temporal evolution of the number of accreting white dwarfs with
shell hydrogen burning in semidetached and detached binaries. We consider a
stellar system in which star formation lasts for 10 Gyr with a constant rate,
as well as a system in which the same amount of stars is formed in a single
burst lasting for 1 Gyr. Evolution of the number of white dwarfs is confronted
to the evolution of occurrence rate of events that usually are identified with
SN Ia or accretion-induced collapses, i.e. with accumulation of Chandrasekhar
mass by a white dwarf or a merger of a pair of CO white dwarfs with total mass
not lower than the Chandrasekhar one. In the systems with a burst of star
formation, at 10 Gyr observed supersoft X-ray sources, most probably, are
not precursors of SN Ia. The same is true for an overwhelming majority of the
sources in the systems with constant star formation rate. In the systems of
both kinds mergers of white dwarfs is the dominant SN Ia scenario. In symbiotic
binaries, accreting CO-dwarfs do not accumulate enough mass for SN Ia
explosion, while ONeMg-dwarfs finish their evolution by an accretion-induced
collapse with formation of a neutron star.Comment: 11 pages, 2 figures, accepted by Astronomy Letter
Radio emission of Shakhbazian Compact Galaxy Groups
Three hundred fifty three radio sources from the NRAO VLA Sky Survey (NVSS)
(Condon et al. 1998) and the FIRST Survey (White et al. 1997}, are detected in
the areas of 179 Shakhbazian Compact Groups (ShCGs) of galaxies. Ninety three
of them are identified with galaxies in 74 ShCGs. Six radio sources have
complex structure. The radio spectra of 22 sources are determined. Radio
luminosities of galaxies in ShCGs are in general higher than that of galaxies
in Hickson Compact Groups (HCGs). The comparison of radio (at 1.4 GHz) and FIR
(at 60 m) fluxes of ShCG galaxies with that of HCG galaxies shows that
galaxies in ShCGs are relatively stronger emitters at radio wavelengths, while
galaxies in HCGs have relatively stronger FIR emission. The reasons of such
difference is discussed.Comment: 35 pages, 6 Postscript figures, ApJS in pres
Optical Identification of the ASCA Large Sky Survey
We present results of optical identification of the X-ray sources detected in
the ASCA Large Sky Survey. Optical spectroscopic observations were done for 34
X-ray sources which were detected with the SIS in the 2-7 keV band above 3.5
sigma. The sources are identified with 30 AGNs, 2 clusters of galaxies, and 1
galactic star. Only 1 source is still unidentified. The flux limit of the
sample corresponds to 1 x 10^{-13} erg s^{-1} cm^{-2} in the 2-10 keV band.
Based on the sample, the paper discusses optical and X-ray spectral
properties of the AGNs, contribution of the sources to the Cosmic X-ray
Background, and redshift and luminosity distributions of the AGNs. An
interesting result is that the redshift distribution of the AGNs suggests a
deficiency of high-redshift (0.5 10^{44}
erg s^{-1}) absorbed narrow-line AGNs (so called type 2 QSOs).Comment: Accepted for publication in ApJ. 57 pages with 13 figures, 9 JPG
plates, 5 additional PS tables. Original EPS plates (gzipped format
~1Mbyte/plate) and TeX tables are available from
ftp://ftp.kusastro.kyoto-u.ac.jp/pub/akiyama/0001289
- …