4,897 research outputs found
Two-sided radio emission in ON231 (W Comae)
Recent radio images of the BL Lac object ON231 (W Com, 1219+285) show
remarkable new features in the source structure compared to those previously
published. The images were obtained from observations made with the European
VLBI Network plus MERLIN at 1.6 GHz and 5 GHz after the exceptional optical
outburst occurred in Spring 1998. The up-to-date B band historic light curve of
ON231 is also presented together with the R band luminosity evolution in the
period 1994--1999. We identify the source core in the radio images with the
brightest component having the flattest spectrum. A consequence of this
assumption is the existence of a two--sided emission in ON231 not detected in
previous VLBI images. A further new feature is a large bend in the jet at about
10 mas from the core. The emission extends for about 20 mas after the bend,
which might be due to strong interaction with the environment surrounding the
nucleus. We suggest some possible interpretations to relate the changes in the
source structure with the optical and radio flux density variation in the frame
of the unification model.Comment: 8 pages, 8 figure
Multi-frequency Analysis of the two CSS quasars 3C 43 & 3C 298
We present and discuss observations made with MERLIN and VLBI at 1.7 and 5 GHz of the two CSS quasars 3C 43 and 3C 298. They show quite different morphologies, the former being a very distorted triple radio source, the latter a small FRII type object. Relativistic effects and structural distortions are discussed. Source ages are evaluated to be of the order of ~10^5 years, therefore 3C 43 and 3C 298 can be considered fairly ''young'' radio sources. Some inference is also derived on the properties of the medium surrounding the radio emitting regions in these sub-galactic objects, whose density could be as low as 10^-3 cm^-3
Naturalness of the Coleman-Glashow Mass Relation in the 1/N_c Expansion: an Update
A new measurement of the Xi^0 mass verifies the accuracy of the
Coleman-Glashow relation at the level predicted by the 1/N_c expansion. Values
for other baryon isospin mass splittings are updated, and continue to agree
with the 1/N_c hierarchy.Comment: 6 pages, revte
X-ray Properties of the GigaHertz-Peaked and Compact Steep Spectrum Sources
We present {\it Chandra} X-ray Observatory observations of Giga-Hertz Peaked
Spectrum (GPS) and Compact Steep Spectrum (CSS) radio sources. The {\it
Chandra} sample contains 13 quasars and 3 galaxies with measured 2-10 keV X-ray
luminosity within erg s. We detect all of the
sources, five of which are observed in X-ray for the first time. We study the
X-ray spectral properties of the sample. The measured absorption columns in the
quasars are different than those in the galaxies in the sense that the quasars
show no absorption (with limits ) while the galaxies
have large absorption columns () consistent with
previous findings. The median photon index of the sources with high S/N is
and it is larger than the typical index of radio loud
quasars. The arcsec resolution of {\it Chandra} telescope allows us to
investigate X-ray extended emission, and look for diffuse components and X-ray
jets. We found X-ray jets in two quasars (PKS 1127-145, B2 0738+32), an X-ray
cluster surrounding a CSS quasar (z=1.1, 3C 186), detected a possible binary
structure in 0941-080 galaxy and an extended diffuse emission in galaxy PKS B2
1345+12. We discuss our results in the context of X-ray emission processes and
radio source evolution. We conclude that the X-ray emission in these sources is
most likely unrelated to a relativistic jet, while the sources' radio-loudness
may suggest a high radiative efficiency of the jet power in these sources.Comment: 15 pages, to be published in Ap
FIRST-based survey of Compact Steep Spectrum sources I. MERLIN images of arc-second scale objects
Compact Steep Spectrum (CSS) sources are powerful extragalactic radio sources
with angular dimensions of the order of a few arcseconds or less. Such a
compactness is apparently linked to the youth of these objects. The majority of
CSSs investigated so far have been known since the early 1980s. This paper is
the first in a series where we report the results of an observational campaign
targeted on a completely new sample of CSSs which are significantly weaker than
those investigated before. The ultimate goal of that campaign is to find out
how ``weak'' CSSs compare to ``strong'', classical ones, especially with regard
to the morphologies. Here we present an analysis of morphological and physical
properties of five relatively large sources based on MERLIN observations at 1.6
and 5 GHz.Comment: 8 pages, 7 figures, A&A in pres
Multifrequency Study of The Radio Galaxy NGC326
We present the results of a multi-frequency study of the inversion symmetric
radio galaxy NGC326 based on Very Large Array observations at 1.4, 1.6, 4.8,
8.5 and 14.9 GHz. The morphological, spectral and polarization properties of
this peculiar object are studied at different levels of spatial resolutions.
The interpretation of the data will be discussed in forthcoming papers.Comment: 15 pages, 15 ps figures, accepted by A&
Coulomb interaction effects on nonlinear optical response in C60, C70, and higher fullerenes
Nonlinear optical properties in the fullerene C and the extracted
higher fullerenes -- C, C, C, and C -- are
theoretically investigated by using the exciton formalism and the
sum-over-states method. We find that off-resonant third order susceptibilities
of higher fullerenes are a few times larger than those of C. The
magnitude of nonlinearity increases as the optical gap decreases in higher
fullerenes. The nonlinearity is nearly proportional to the fourth power of the
carbon number when the onsite Coulomb repulsion is or , being the
nearest neighbor hopping integral. This result, indicating important roles of
Coulomb interactions, agrees with quantum chemical calculations of higher
fullerenes.Comment: 8 pages; 3 figures; Figures should be requested to the author
(E-mail: [email protected]
Weak CSS Sources from FIRST Survey
We report early results of an observational campaign targeted on a sample of
compact steep spectrum sources selected from the FIRST survey which are
significantly weaker than those investigated before. The selection criteria and
procedure are given in detail. We present here an assortment of MERLIN and VLBI
observations and make some general comments based on the morphologies of the
sources presented.Comment: A contribution to The Third Workshop on GHz-Peaked Spectrum and
Compact Steep Spectrum Radio Sources, Kerastari, Greece, May 28-31, 2002.
Refereed and accepted by Publications of the Astronomical Society of
Australia. Final version copyedited by PASA Edito
ISO observations of a sample of Compact Steep Spectrum and GHz Peaked Spectrum Radio Galaxies
We present results from observations obtained with ISOPHOT, on board the ISO
satellite, of a representative sample of seventeen CSS/GPS radio galaxies and
of a control sample of sixteen extended radio galaxies spanning similar ranges
in redshift (0.2 = 10^26 W/Hz).
The observations have been performed at lambda = 60, 90, 174 and 200 microns.
Seven of the CSS/GPS sources have detections >= 3 sigma at one or more
wavelengths, one of which is detected at >= 5 sigma. By co-adding the data we
have obtained average flux densities at the four wavelengths. We found no
evidence that the FIR luminosities of the CSS/GPS sources are significantly
different from those of the extended objects and therefore there is not any
support for CSS/GPS sources being objects "frustrated" by an abnormally dense
ambient medium. The two samples were then combined, providing FIR information
on a new sample of radio galaxies at intermediate redshifts. We compare this
information with what previously known from IRAS and discuss the average
properties of radio galaxies in the redshift range 0.2 - 0.8. The FIR emission
cannot be accounted for by extrapolation of the synchrotron radio spectrum and
we attribute it to thermal dust emission. The average FIR luminosity is >=
6*10^11 L_sun. Over the observed frequency range the infrared spectrum can be
described by a power law with spectral index alpha >~1.0 +/- 0.2. Assuming the
emission to be due to dust, a range of temperatures is required, from >=80 K to
\~25 K. The dust masses required to explain the FIR emission range from 5*10^5
M_sun for the hotter component up to 2*10^8 M_sun for the colder one.
(abridged)Comment: Astronomy & Astrophysics, in press, 16 pages, 2 Figure
New specimen of the rare requiem shark Eogaleus bolcensis from the Bolca Lagerst\ue4tte, Italy
A rare carcharhinid specimen (slab and counter-slab, MSNPV 24625-24626) from the world-renowned Eocene Bolca locality was recently rediscovered during a restoration project started in 1989 by the Museo di Storia Naturale di Pavia. The individual, the largest Eogaleus bolcensis known from Bolca, is disarticulated and lies in a massive limestone matrix, suggesting its provenience from the Monte Postale site. While assessing its taxonomic status, multiple morphological affinities and ontogenetic trends within the Bolca Carcharhiniformes assemblage where documented. Eogaleus bolcensis is here distinguished from the school shark Galeorhinus cuvieri exclusively according to dermal denticle morphology, suggesting partial overlap of ecologic and trophic niches between the two species. Further, measurements and meristic counts taken on different traits of E. bolcensis (two individuals) and G. cuvieri (five individuals) specimens show high degree of similarities. The ratios "trunk length/total length"and "sum of vertebral centra (head region)/total length"of four complete individuals of the fossil assemblage were averaged and employed to estimates the total length of MSNPV 24625-24626. Here, the total length of MSNPV 24625-24626 is estimated in about 172.1\ub10.1 cm. The same approach is applied to MCSNV T.311 (E. bolcensis, holotype) and MNHN F.Bol.516 (G. cuvieri, holotype), two partially-preserved fossil individuals from Bolca locality. To support the ontogenetic variability among the Bolca shark assemblage, the age of the fossil individuals was estimated following the Von Bertalanffy Growth Function, using the modern chondrichthyans growth parameters as a reference. Data presented here suggest that all G. cuvieri specimens are juvenile individuals, whereas the E. bolcensis specimens were young-adult
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