Generation of unstable whistler mode is investigated in the presence of kinetic Alfven wave turbulence (KAW) field in a burning plasma. KAW turbulence is supported by plasma inhomogeneity in a ...burning plasma. The propagation of this low frequency KAW in inhomogeneous magnetized plasma is expected to play a significant role in heating energetic particles such as deuterium and tritium and the exchange of energy among waves to develop instability in fusion reactors. Whistler mode in a burning plasma may be amplified when the accelerated energetic particles transfer their energy to whistler mode nonlinearly through a modulated field. Considering a Maxwellian model of ion distribution function for inhomogeneous plasma with the involvement of a uniform force
F
, we have evaluated fluctuating parts of the distribution function due to KAW turbulence using the Vlasov equation. We have also obtained nonlinear fluctuating parts of the ion distribution function due to modulated waves as well as nonlinear whistler mode. We have estimated the growth rate of the whistler mode using a nonlinear dispersion relation for the whistler mode.
The BL Lac object PKS 1413+135 was observed by the Large Survey Project MeerKAT Absorption Line Survey (MALS) in the
L
-band, at 1139 MHz and 1293–1379 MHz, targeting the H
I
and OH lines in ...absorption at
z
= 0.24671. The radio continuum might come from the nucleus of the absorbing galaxy or from a background object at redshift lower than 0.5, as suggested by the absence of gravitational images. The H
I
absorption line is detected at a high signal-to-noise ratio, with a narrow central component, and with a red wing, confirming previous results. The OH 1720 MHz line is clearly detected in (maser) emission, peaking at a velocity shifted by −10 to −15 km s
−1
with respect to the H
I
peak. The 1612 MHz line is lost due to radio frequency interference. The OH 1667 MHz main line is tentatively detected in absorption, but not the 1665 MHz line. Over 30 years a high variability is observed in optical depths, due to the rapid changes of the line of sight caused by the superluminal motions of the radio knots. The H
I
line has varied by 20% in depth, while the OH-1720 MHz depth has varied by a factor of ∼3. The position of the central velocity and the widths also varied. The absorbing galaxy is an early-type spiral (maybe S0) seen edge-on, with a prominent dust lane, covering the whole disk. Given the measured mass concentration and the radio continuum size at centimeter wavelengths (100 mas corresponding to 400 pc at
z
= 0.25), the width of the absorption lines from the nuclear regions are expected up to 250 km s
−1
. The narrowness of the observed lines (< 15 km s
−1
) suggests that the absorption comes from an outer gas ring, as frequently observed in S0 galaxies. The millimetric lines are even narrower (< 1 km s
−1
), which corresponds to the continuum size restricted to the core. The radio core is covered by individual 1 pc molecular clouds, whose column density is a few 10
22
cm
−2
, which is compatible with the gas screen detected in X-rays.
Drift waves exist universally in inhomogeneous plasmas and play a major role in the cross-field transport of particles, energy, and momentum in space and laboratory plasmas. In this article, we ...present our investigation on the amplification of the Langmuir waves in the presence of the drift wave turbulent field through nonlinear wave particle interaction process called the plasma-maser effect. The drift wave turbulent field interacts with plasma particles as it is in the resonant mode and its energy is transferred to accelerate the plasma particles. The accelerated plasma particles transfer their energy to Langmuir waves through a modulated field. We have obtained Fourier components of drift wave turbulent field and the non-linear Langmuir waves using linearized Vlasov-Poisson system of equations. From the non-linear dispersion relation of Langmuir waves, we have calculated growth rates of the Langmuir waves using observational data set of the topside polar ionosphere of the Earth’s magnetosphere. The calculations demonstrate that Langmuir waves amplification is feasible at the expense of collisionless electron drift wave turbulent energy.
Abstract
We report the detection of stimulated hydrogen radio recombination line (RRL) emission from ionized gas in a
z
= 0.89 galaxy using 580–1670 MHz observations from the MeerKAT Absorption Line ...Survey. The RRL emission originates in a galaxy that intercepts and strongly lenses the radio blazar PKS 1830−211 (
z
= 2.5). This is the second detection of RRLs outside of the local Universe and the first clearly associated with hydrogen. We detect effective H144
α
(and H163
α
) transitions at observed frequencies of 1156 (798) MHz by stacking 17 (27) RRLs with 21
σ
(14
σ
) significance. The RRL emission contains two main velocity components and is coincident in velocity with H
i
21 cm and OH 18 cm absorption. We use the RRL spectral line energy distribution and a Bayesian analysis to constrain the density (
n
e
) and the volume-averaged path length (
ℓ
) of the ionized gas. We determine
log
(
n
e
)
=
2.0
−
0.7
+
1.0
cm
−3
and
log
(
ℓ
)
=
−
0.7
−
1.1
+
1.1
pc toward the northeast (NE) lensed image, likely tracing the diffuse thermal phase of the ionized ISM in a thin disk. Toward the southwest (SW) lensed image, we determine
log
(
n
e
)
=
3.2
−
1.0
+
0.4
cm
−3
and
log
(
ℓ
)
=
−
2.7
−
0.2
+
1.8
pc, tracing gas that is more reminiscent of H scii regions. We estimate a star formation (surface density) rate of Σ
SFR
∼ 0.6
M
⊙
yr
−1
kpc
−2
or SFR ∼ 50
M
⊙
yr
−1
, consistent with a star-forming main-sequence galaxy of
M
⋆
∼ 10
11
M
⊙
. The discovery presented here opens up the possibility of studying ionized gas at high redshifts using RRL observations from current and future (e.g., SKA and ngVLA) radio facilities.
Abstract
Planar hypercoordinate structures are gaining immense attention due to the shift from common paradigm. Herein, our high level ab initio calculations predict that planar pentacoordinate ...aluminium and gallium centres in Cu
5
Al
2+
and Cu
5
Ga
2+
clusters are global minima in their singlet ground states. These clusters are thermodynamically and kinetically very stable. Detailed electronic structure analyses reveal the presence of σ-aromaticity which is the driving force for the stability of the planar form.
The instability of electron Bernstein mode has been investigated in presence of drifts due to density and temperature gradient. Nonlinear resonant interaction of drift mode is considered for the ...investigation of the instability. We have considered a uniform force field
F
which is the cause of
F
×
B
drift due to temperature perpendicular to the magnetic field
B
in the system. Using Vlasov-Poissons system of equations and Maxwellian type distribution function of particles that involve the effect of
F
associated with density and temperature gradient. We have derived a nonlinear dispersion relation for electron Bernstein mode and then estimated its growth rate. We have analyzed various aspects of the growth rate of electron Bernstein mode associated with the variation of the gradients of the density and temperature by using experimental data in tokamak plasmas.
The impact of an external periodic force on the characteristics of dust ion-acoustic solitary waves in a superthermal magnetised plasma is investigated. To obtain the forced Zakharov–Kuznetsov (FZK) ...equation from fundamental governing equations, the well-known reductive perturbation technique is used. Furthermore, the ZK equation is transformed into planar dynamical systems to analyse the phase portrait of the system. Based on the approximated analytical solution of the FZK equation, it is observed that both positive potential compressive and negative potential rarefactive solitons exist in this model. The amplitudes of positive potential solitons are found to increase along with the increase in external periodic force, whereas the amplitudes of negative potential solitons are found to decrease. It is observed that due to the presence of external forced potential, the amplitude of solitons naturally takes on a variety of peak forms, whereas in the absence of this external force, the phenomenon of variety in peak formation does not happen. The results of this present investigation are interesting and may be helpful in understanding nonlinear phenomena in space and astrophysical plasma, such as the ionosphere, terrestrial plasma sheet, mesosphere and lower thermosphere.
We report a new, rare detection of H I 21 cm absorption associated with a quasar (only six quasars are known at 1 < z < 2) toward J2339−5523 at z em = 1.3531, discovered through the MeerKAT ...Absorption Line Survey (MALS). The absorption profile is broad (∼400 km s −1 ), and the peak is redshifted by ∼200 km s −1 from z em . Interestingly, optical/far-UV spectra of the quasar from the Magellan-MIKE/HST-COS spectrographs do not show any absorption features associated with the 21 cm absorption, despite the coincident presence of the optical quasar and the radio core inferred from a flat-spectrum component with a flux density of ∼65 mJy at high frequencies (> 5 GHz). The simplest explanation would be that no large H I column ( N (H I ) > 10 17 cm −2 ) is present toward the radio core and the optical active galactic nucleus. Based on the joint optical and radio analysis of a heterogeneous sample of 16 quasars ( z median = 0.7) and 19 radio galaxies ( z median = 0.4) with H I 21 cm absorption detection and matched in 1.4 GHz luminosity ( L 1.4 GHz ), a consistent picture emerges according to which quasars primarily trace the gas in the inner circumnuclear disk and cocoon created by the interaction of the jet with interstellar medium. They (i.e., quasars) exhibit a L 1.4 GHz – Δ V null correlation and a frequent mismatch of the radio and optical spectral lines. The radio galaxies show no such correlation and likely trace the gas from the cocoon and the galaxy-wide interstellar medium outside the photoionization cone. The analysis presented here demonstrates the potential of radio spectroscopic observations to reveal the origin of the absorbing gas associated with active galactic nuclei that may be missed in optical observations.
Abstract
The MeerKAT Absorption Line Survey (MALS) has observed 391 telescope pointings at the
L
band (900–1670 MHz) at
δ
≲ +20°. We present radio continuum images and a catalog of 495,325 (240,321) ...radio sources detected at a signal-to-noise ratio (S/N) > 5 over an area of 2289 deg
2
(1132 deg
2
) at 1006 MHz (1381 MHz). Every MALS pointing contains a central bright radio source (
S
1 GHz
≳ 0.2 Jy). The median spatial resolution is 12″ (8″). The median rms noise away from the pointing center is 25
μ
Jy beam
−1
(22
μ
Jy beam
−1
) and is within ∼15% of the achievable theoretical sensitivity. The flux density scale ratio and astrometric accuracy deduced from multiply observed sources in MALS are <1% (8% scatter) and 1″, respectively. Through comparisons with NVSS and FIRST at 1.4 GHz, we establish the catalog’s accuracy in the flux density scale and astrometry to be better than 6% (15% scatter) and 0.″8, respectively. The median flux density offset is higher (9%) for an alternate beam model based on holographic measurements. The MALS radio source counts at 1.4 GHz are in agreement with literature. We estimate spectral indices (
α
) of a subset of 125,621 sources (S/N > 8), confirm the flattening of spectral indices with decreasing flux density, and identify 140 ultra-steep-spectrum (
α
< −1.3) sources as prospective high-
z
radio galaxies (
z
> 2). We have identified 1308 variable and 122 transient radio sources comprising primarily active galactic nuclei that demonstrate long-term (26 yr) variability in their observed flux densities. The MALS catalogs and images are publicly available at
https://mals.iucaa.in
.
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