954 research outputs found
Giant Radio Sources
We present multi-frequency VLA observations of two giant quasars, 0437-244
and 1025-229, from the Molonglo Complete Sample. These sources have
well-defined FRII radio structure, possible one-sided jets, no significant
depolarization between 1365 and 4935 MHz and low rotation measure (). The giant sources are defined to be those whose overall
projected size is 1 Mpc. We have compiled a sample of about 50 known
giant radio sources from the literature, and have compared some of their
properties with a complete sample of 3CR radio sources of smaller sizes to
investigate the evolution of giant sources, and test their consistency with the
unified scheme for radio galaxies and quasars. We find an inverse correlation
between the degree of core prominence and total radio luminosity, and show that
the giant radio sources have similar core strengths to the smaller sources of
similar total luminosity. Hence their large sizes are unlikely to be due to
stronger nuclear activity. The degree of collinearity of the giant sources is
also similar to the sample of smaller sources. The luminosity-size diagram
shows that the giant sources are less luminous than our sample of smaller-sized
3CR sources, consistent with evolutionary scenarios where the giants have
evolved from the smaller sources losing energy as they expand to these large
dimensions. For the smaller sources, radiative losses due to synchrotron
radiation is more significant while for the giant sources the equipartition
magnetic fields are smaller and inverse Compton losses with the microwave
background radiation is the dominant process. The radio properties of the giant
radio galaxies and quasars are consistent with the unified scheme.Comment: 14 pages with 12 figures, MNRAS LaTex. Accepted for publication in
MNRAS. Minor changes in the text and couple of references adde
Dispersionless motion in a driven periodic potential
Recently, dispersionless (coherent) motion of (noninteracting) massive
Brownian particles, at intermediate time scales, was reported in a sinusoidal
potential with a constant tilt. The coherent motion persists for a finite
length of time before the motion becomes diffusive. We show that such coherent
motion can be obtained repeatedly by applying an external zero-mean square-wave
drive of appropriate period and amplitude, instead of a constant tilt. Thus,
the cumulative duration of coherent motion of particles is prolonged. Moreover,
by taking an appropriate combination of periods of the external field, one can
postpone the beginning of the coherent motion and can even have coherent motion
at a lower value of position dispersion than in the constant tilt case.Comment: 4 pages, 4 figure
Multicomponent Materials to Improve Solubility: Eutectics of Drug Aminoglutethimide
Here, we report the synthesis and experimental characterization of three drug-drug eutectic mixtures of drug aminoglutethimide (AMG) with caffeine (CAF), nicotinamide (NIC) and ethenzamide (ZMD). The eutectic mixtures i.e., AMG-CAF (1:0.4, molar ratio), AMG-NIC (1:1.9, molar ratio) and AMG-ZMD (1:1.4, molar ratio) demonstrate significant melting point depressions ranging from 99.2 to 127.2 °C compared to the melting point of the drug AMG (151 °C) and also show moderately higher aqueous solubilities than that of the AMG. The results presented include the determination of the binary melt phase diagrams and accompanying analytical characterization via X-ray powder diffraction, FT-IR spectroscopy and scanning electron microscopy
The Dynamics of Radio Galaxies and Double-Double Radio Galaxies
Relativistic and magnetised plasma ejected by radio loud AGNs through jets
form the diffuse lobes of radio galaxies. The radiating particles
(electron/electron-positron) in lobes emit in radio via the synchrotron process
and X-ray via inverse-Compton scattering of cosmic microwave background
photons. The thermal environment around radio galaxies emits X-rays via the
thermal bremsstrahlung process. By combining information from these processes
we can measure physical conditions in and around the radio lobes and thus study
the dynamics of radio galaxies, including double-double radio galaxies.Comment: 11 pages, 4 figures, Diffuse Radio Plasma Conference proceedings
(held in Raman Research Institute, Bangalore, India
A low-frequency study of recently identified double-double radio galaxies
In order to understand the possible mechanisms of recurrent jet activity in
radio galaxies and quasars, which are still unclear, we have identified such
sources with a large range of linear sizes (220 917 kpc), and hence time
scales of episodic activity. Here we present high-sensitivity 607-MHz Giant
Metrewave Radio Telescope (GMRT) images of 21 possible double-double radio
galaxies (DDRGs) identified from the FIRST survey to confirm their episodic
nature. These GMRT observations show that none of the inner compact components
suspected to be hot-spots of the inner doubles are cores having a flat radio
spectrum, confirming the episodic nature of these radio sources. We have
indentified a new DDRG with a candidate quasar, and have estimated the upper
spectral age limits for eight sources which showed marginal evidence of
steepening at higher frequencies. The estimated age limits (11 52 Myr) are
smaller than those of the large-sized ( 1 Mpc) DDRGs.Comment: Accepted for publication in MNRAS. 14 pages, 7 figure
Discovery of a red quasar with recurrent activity
We report a new double-double radio quasar, DDRQ, J07464526 which exhibits
two cycles of episodic activity. From radio continuum observations at 607 MHz
using the GMRT and 1400 MHz from the FIRST survey we confirm its episodic
nature. We examine the SDSS optical spectrum and estimate the black hole mass
to be (8.20.3)10M from its observed MgII emission
line, and the Eddington ratio to be 0.03. The black hole mass is significantly
smaller than for the other reported DDRQ, J0935+0204, while the Eddington
ratios are comparable. The SDSS spectrum is significantly red continuum
dominated suggesting that it is highly obscured with
mag. This high obscuration further indicates the
existence of a large quantity of dust and gas along the line of sight, which
may have a key role in triggering the recurrent jet activity in such objects.Comment: 5 pages, 3 figures, 1 table. Accepted for publication in Ap
A study of the environments of large radio galaxies using SDSS
The distributions of galaxies in the environments of 16 large radio sources
have been examined using the Sloan Digital Sky Survey. In the giant radio
galaxy J1552+2005 (3C326) which has the highest arm-length ratio, the shorter
arm is found to interact with a group of galaxies which forms part of a
filamentary structure. Although most large sources occur in regions of low
galaxy density, the shorter arm is brighter in most cases suggesting
asymmetries in the intergalactic medium which may not be apparent in the
distribution of galaxies. In two cases with strong and variable cores,
J0313+4120 and J1147+3501, the large flux density asymmetries are possibly also
caused by the effects of relativistic motion.Comment: Accepted for publication in MNRA
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