► Design of artificial microRNAs (amiRs). ► Tomato transgenics expressing amiRs. ► Transgenics showing tolerance to infectious ToLCV clones. ► amiR cleavage of target sites. ► T2 level transgenics ...show high tolerance against virus challenges.
Designing artificial microRNAs (amiRs) targeting the genes responsible for viral replication, transmission and symptom development after viral infection offers a promising strategy to contain the multiplication and spread of geminiviruses in host plants. Here, we report the design of two amiRs targeting the middle region of the AV1 (coat protein) transcript (amiR-AV1-3) and the overlapping region of the AV1 and AV2 (pre-coat protein) transcripts (amiR-AV1-1) of a model geminivirus, Tomato leaf curl virus (ToLCV). Our analyses demonstrate that transgenic tomato plants expressing amiR-AV1-1, propagated until the T2 generation and were highly tolerant to Tomato leaf curl New Delhi virus (ToLCNDV), whereas those harboring amiR-AV1-3 exhibited only moderate tolerance. Biochemical analyses revealed that in these cases, the amiRs acted through the slicing mechanism, cleaving their respective targets. Although ToLCVs are generally difficult targets for manipulations related to virus resistance, our data reveal that an amiR strategy could be employed to protect plants in an effective manner.
ABSTRACT
Supernova remnants (SNRs) have a variety of overall morphology as well as rich structures over a wide range of scales. Quantitative study of these structures can potentially reveal ...fluctuations of density and magnetic field originating from the interaction with ambient medium and turbulence in the expanding ejecta. We have used 1.5 GHz (L band) and 5 GHz (C band) VLA data to estimate the angular power spectrum Cℓ of the synchrotron emission fluctuations of the Kepler SNR. This is done using the novel, visibility-based, Tapered Gridded Estimator of Cℓ. We have found that, for ℓ = (1.9–6.9) × 104, the power spectrum is a broken power law with a break at ℓ = 3.3 × 104, and power-law index of −2.84 ± 0.07 and −4.39 ± 0.04 before and after the break, respectively. The slope −2.84 is consistent with 2D Kolmogorov turbulence and earlier measurements for the Tycho SNR. We interpret the break to be related to the shell thickness of the SNR (0.35 pc) which approximately matches ℓ = 3.3 × 104 (i.e. 0.48 pc). However, for ℓ > 6.9 × 104, the estimated Cℓ of L band is likely to have dominant contribution from the foregrounds while for C band the power-law slope −3.07 ± 0.02 is roughly consistent with 3D Kolmogorov turbulence like that observed at large ℓ for Cas A and Crab SNRs.
Abstract Empirical studies of cold gas content are essential for comprehending the star formation activities and evolution in galaxies. However, it is not straightforward to understand these ...processes because they depend on various physical properties of the interstellar medium. Massive Faranoff–Riley I/II type radio galaxies rich in molecular hydrogen with lower star formation activities are known as radio molecular hydrogen emission galaxies (MOHEGs). We present a study of neutral hydrogen-gas-associated radio MOHEGs at redshifts <0.2 probed via the H i 21 cm absorption line. Neutral hydrogen is detected in 70% of these galaxies, which are located at a distance of 8–120 kpc from the neighboring galaxies. These galaxies show a scarcity of H i gas as compared to merging galaxies at similar redshifts. We found no strong correlation between N (H i ), N H , and the galaxy properties, regardless of whether the H i is assumed to be cold or warm, indicating that the atomic gas probably plays no important role in star formation. The relation between the total hydrogen gas surface density and the star formation surface density deviates from the standard Kennicutt–Schmidt law. Our study highlights the importance of H i studies and offers insights into the role of atomic and molecular hydrogen gas in explaining the properties of these galaxies. In the upcoming H i 21 cm absorption surveys with next-generation radio telescopes such as the Square Kilometre Array and pathfinder instruments, it may be possible to provide better constraints for these correlations.
Abstract
Very-high-energy (VHE; 100 GeV <
E
≤ 100 TeV) and high-energy (HE; 100 MeV <
E
≤ 100 GeV) gamma rays were observed from the symbiotic recurrent nova RS Ophiuchi (RS Oph) during its outburst ...in 2021 August by various observatories, such as the High Energy Stereoscopic System (HESS), Major Atmospheric Gamma Imaging Cherenkov (MAGIC), and Fermi-Large Area Telescope (LAT). The models that have been explored so far tend to favor a hadronic scenario of particle acceleration over an alternative leptonic scenario. This paper explores a time-dependent lepto-hadronic scenario to explain the emission from the RS Oph source region. We have used simultaneous low-frequency radio data observed by various observatories along with the data provided by HESS, MAGIC, and Fermi-LAT to explain the multiwavelength spectral energy distributions corresponding to 4 days after the outburst. Our results show that a lepto-hadronic interpretation of the source not only explains the observed HE-VHE gamma-ray data but the corresponding model synchrotron component is also consistent with the first 4 days of low-radio-frequency data, indicating the presence of nonthermal radio emission at the initial stage of the nova outburst. We have also calculated the expected neutrino flux from the source region and discuss the possibility of detecting neutrinos.
Abstract
Characterizing the diffuse Galactic synchrotron emission at arcminute angular scales is needed to reliably remove foregrounds in cosmological 21-cm measurements. The study of this emission ...is also interesting in its own right. Here, we quantify the fluctuations of the diffuse Galactic synchrotron emission using visibility data for two of the fields observed by the TIFR GMRT Sky Survey. We have used the 2D Tapered Gridded Estimator to estimate the angular power spectrum (C
ℓ) from the visibilities. We find that the sky signal, after subtracting the point sources, is likely dominated by the diffuse Galactic synchrotron radiation across the angular multipole range 240 ≤ ℓ ≲ 500. We present a power-law fit,
$C_{\ell }=A\times \big (\frac{1000}{l}\big )^{\beta }$
, to the measured C
ℓ over this ℓ range. We find that (A, β) have values (356 ± 109 mK2, 2.8 ± 0.3) and (54 ± 26 mK2, 2.2 ± 0.4) in the two fields. For the second field, however, there is indication of a significant residual point source contribution and for this field we interpret the measured C
ℓ as an upper limit for the diffuse Galactic synchrotron emission. While in both fields the slopes are consistent with earlier measurements, the second field appears to have an amplitude that is considerably smaller compared to similar measurements in other parts of the sky.
Abstract Low-radio-frequency spectral index measurements are a powerful tool for distinguishing between different emission mechanisms and, in turn, understanding the nature of the sources. Besides ...the standard method of estimating the “broadband” spectral index of sources from observations in two different frequency “bands,” if the observations were made with large instantaneous bandwidth, the “in-band” spectral index can be determined, either using images of emission at multiple frequency ranges within a band or using the novel Multi Term-Multi Frequency Synthesis (MT-MFS) imaging algorithm. Here, using simulated upgraded Giant Metrewave Radio Telescope (uGMRT) data, we have systematically studied the reliability of various methods of spectral index estimation for sources with a wide range of signal-to-noise ratios (S/Ns). It is found that for synthetic uGMRT point-source data, the MT-MFS imaging algorithm produces in-band spectral indices for S/N ≲ 100 that have errors ≳0.2, making them unreliable. However, at a similar S/N, the sub-band splitting method produces errors ≲0.2, which are more accurate and unbiased than the in-band spectral indices. The broadband spectral indices produce errors ≲0.2 even for S/N ≳ 15, and hence they are most reliable if there are no higher-order variations in the spectral index. These results may be used to improve the uGMRT observation and data analysis strategies, depending on the brightness of the target source.
We discuss physical conditions in Galactic neutral hydrogen based on deep, high-velocity resolution interferometric H i-21 cm absorption spectroscopy towards 33 compact extragalactic radio sources. ...The H i-21 cm optical depth spectra have root-mean-square noise values 10−3 per 1 km s−1 velocity channel, i.e. sufficiently sensitive to detect H i-21 cm absorption by the warm neutral medium (WNM). Comparing these spectra with H i-21 cm emission spectra from the Leiden-Argentine-Bonn (LAB) survey, we show that some of the absorption detected on most sightlines must arise in gas with temperatures higher than that in the stable cold neutral medium (CNM). A multi-Gaussian decomposition of 30 of the H i-21 cm absorption spectra yielded very few components with linewidths in the temperature range of stable WNM, with no such WNM components detected for 16 of the 30 sightlines. We find that some of the detected H i-21 cm absorption along 13 of these sightlines must arise in gas with spin temperatures larger than the CNM range. For these sightlines, we use very conservative estimates of the CNM spin temperature and the non-thermal broadening to derive strict upper limits to the gas column densities in the CNM and WNM phases. Comparing these upper limits to the total H i
column density, we find that typically at least 28 per cent of the gas must have temperatures in the thermally unstable range (200-5000 K). Our observations hence robustly indicate that a significant fraction of the gas in the Galactic interstellar medium has temperatures outside the ranges expected for thermally stable gas in two-phase models.
Abstract
Photodissociation regions (PDRs), where the (far-)ultraviolet light from hot young stars interact with the gas in surrounding molecular clouds, provide laboratories for understanding the ...nature and role of feedback by star formation on the interstellar medium. While the general nature of PDRs is well understood—at least under simplified conditions—the detailed dynamics and chemistry of these regions, including gas clumping, evolution over time, etc., can be very complex. We present interferometric observations of the 21 cm atomic hydrogen line, combined with C
ii
158
μ
m observations, toward the nearby reflection nebula IC 63. We find a clumpy H
i
structure in the PDR, and a ring morphology for the H
i
emission at the tip of IC 63. We further unveil kinematic substructure, of the order of 1 km s
−1
, in the PDR layers and several legs that will disperse IC 63 in <0.5 Myr. We find that the dynamics in the PDR explain the observed clumpy H
i
distribution and lack of a well-defined H
i
/H
2
transition front. However, it is currently not possible to conclude whether H
i
self-absorption and nonequilibrium chemistry also contribute to this clumpy morphology and missing H
i
/H
2
transition front.
ABSTRACT
The shell type supernova remnant (SNR) Cas A exhibits structures at nearly all angular scales. Previous studies show the angular power spectrum (Cℓ) of the radio emission to be a broken ...power law, consistent with MHD turbulence. The break has been identified with the transition from 2D to 3D turbulence at the angular scale corresponding to the shell thickness. Alternatively, this can also be explained as 2D inverse cascade driven by energy injection from knot–shock interactions. Here we present Cℓ measured from archival VLA 5-GHz (C band) data, and Chandra X-ray data in the energy ranges ${\rm A}=0.6{-}1.0$ and ${\rm B} =4.2{-}6.0 \,{\rm keV}$, both of which are continuum dominated. The different emissions all trace fluctuations in the underlying plasma and possibly also the magnetic field, and we expect them to be correlated. We quantify this using the cross-Cℓ between the different emissions. We find that X-ray B is strongly correlated with both radio and X-ray A; however, X-ray A is only very weakly correlated with radio. This supports a picture where X-ray A is predominantly thermal bremsstrahlung, whereas X-ray B is a composite of thermal bremsstrahlung and non-thermal synchrotron emission. The various Cℓ measured here, all show a broken power-law behaviour. However, the slopes are typically shallower than those in radio and the position of the break also corresponds to smaller angular scales. These findings provide observational inputs regarding the nature of turbulence and the emission mechanisms in Cas A.
ABSTRACT
How are accretion discs affected by their outflows? To address this question for white dwarfs accreting from cool giants, we performed optical, radio, X-ray, and ultraviolet observations of ...the outflow-driving symbiotic star MWC 560 (≡V694 Mon) during its 2016 optical high state. We tracked multi-wavelength changes that signalled an abrupt increase in outflow power at the initiation of a months-long outflow fast state, just as the optical flux peaked: (1) an abrupt doubling of Balmer absorption velocities; (2) the onset of a 20 μJy per month increase in radio flux; and (3) an order-of-magnitude increase in soft X-ray flux. Juxtaposing to prior X-ray observations and their coeval optical spectra, we infer that both high-velocity and low-velocity optical outflow components must be simultaneously present to yield a large soft X-ray flux, which may originate in shocks where these fast and slow absorbers collide. Our optical and ultraviolet spectra indicate that the broad absorption-line gas was fast, stable, and dense (≳106.5 cm−3) throughout the 2016 outflow fast state, steadily feeding a lower density (≲105.5 cm−3) region of radio-emitting gas. Persistent optical and ultraviolet flickering indicate that the accretion disc remained intact. The stability of these properties in 2016 contrasts to their instability during MWC 560’s 1990 outburst, even though the disc reached a similar accretion rate. We propose that the self-regulatory effect of a steady fast outflow from the disc in 2016 prevented a catastrophic ejection of the inner disc. This behaviour in a symbiotic binary resembles disc/outflow relationships governing accretion state changes in X-ray binaries.
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