arXiv subjects

T. Samanta

Publications and source records attributed to T. Samanta.

5 recordsLinked to original sources

arXiv2018

Penumbral Waves driving Solar chromospheric fan-shaped jets

We use H$\alpha$ imaging spectroscopy taken via the Swedish 1-m Solar Telescope (SST) to investigate the occurrence of fan-shaped jets at the solar limb. We show evidence for near-simultaneous photospheric reconnection at a sunspot edge leading to the jets appearance, with upward velocities of 30\ks, and extensions up to 8~Mm. The brightening at the base of the jets appears recurrent, with a periodicity matching that of the nearby sunspot penumbra, implying running penumbral waves could be the driver of the jets. The jets' constant extension velocity implies that a driver counteracting solar gravity exists, possibly as a result of the recurrent reconnection erupting material into the chromosphere. These jets also show signatures in higher temperature lines captured from the Solar Dynamics Observatory (SDO), indicating a very hot jet front, leaving behind optically thick cool plasma in its wake.

astro-ph.SR↗

arXiv2016

The effects of transients on photospheric and chromospheric power distributions

We have observed a quiet Sun region with the Swedish 1-meter Solar Telescope (SST) equipped with CRISP Imaging SpectroPolarimeter. High-resolution, high-cadence, H$\alpha$ line scanning images were taken to observe different layers of the solar atmosphere from the photosphere to upper chromosphere. We study the distribution of power in different period-bands at different heights. Power maps of the upper photosphere and the lower chromosphere show suppressed power surrounding the magnetic-network elements, known as "magnetic shadows". These also show enhanced power close to the photosphere, traditionally referred to as "power halos". The interaction between acoustic waves and inclined magnetic fields is generally believed to be responsible for these two effects. In this study we explore if small-scale transients can influence the distribution of power at different heights. We show that the presence of transients, like mottles, Rapid Blueshifted Excursions (RBEs) and Rapid Redshifted Excursions (RREs), can strongly influence the power-maps. The short and finite lifetime of these events strongly affects all powermaps, potentially influencing the observed power distribution. We show that Doppler-shifted transients like RBEs and RREs that occur ubiquitously, can have a dominant effect on the formation of the power halos in the quiet Sun. For magnetic shadows, transients like mottles do not seem to have a significant effect in the power suppression around 3 minutes and wave interaction may play a key role here. Our high cadence observations reveal that flows, waves and shocks manifest in presence of magnetic fields to form a non-linear magnetohydrodynamic system.

astro-ph.SR↗

arXiv2016

Complex superconductivity in the noncentrosymmetric compound Re$_{6}$Zr

We report the electronic structure, synthesis, and measurements of the magnetic, transport, and thermal properties of the polycrystalline noncentrosymmetric compound Re$_{6}$Zr. We observed a bulk superconducting transition at temperature $T_{c}$ $\sim$ 6.7 K, and measured the resistivity, heat capacity, thermal conductivity, and the London penetration depth below the transition, as well as performed doping and pressure studies. From these measurements we extracted the critical field, and the superconducting parameters of Re$_{6}$Zr. Our measurements indicate a relatively weak to moderate contribution from a triplet component to the order parameter, and favor a full superconducting gap, although we cannot exclude the existence of point nodes based on our data.

cond-mat.supr-con↗

arXiv2015

Detection of high frequency oscillations and damping from multi-slit spectroscopic observations of the corona

During the total solar eclipse of 11 July 2010, multi-slit spectroscopic observations of the solar corona were performed from Easter Island, Chile. To search for high-frequency waves, observations were taken at a high cadence in the green line at 5303 A due to [Fe xiv] and the red line at 6374 A due to [Fe x]. The data are analyzed to study the periodic variations in the intensity, Doppler velocity and line width using wavelet analysis. The data with high spectral and temporal resolution enabled us to study the rapid dynamical changes within coronal structures. We find that at certain locations each parameter shows significant oscillation with periods ranging from 6 - 25 s. For the first time, we could detect damping of high-frequency oscillations with periods of the order of 10 s. If the observed damped oscillations are due to magnetohydrodynamic (MHD) waves then they can contribute significantly in the heating of the corona. From a statistical study we try to characterize the nature of the observed oscillations while looking at the distribution of power in different line parameters.

astro-ph.SR↗

arXiv2015

Propagating Disturbances along fan-like coronal loops in an active region

Propagating disturbances are often observed in active region fan-like coronal loops. They were thought to be due to slow mode MHD waves based on some of the observed properties. But the recent studies involving spectroscopy indicate that they could be due to high speed quasi-periodic upflows which are difficult to distinguish from upward propagating slow waves. In this context, we have studied a fan loop structure in the active region AR 11465 using simultaneous spectroscopic and imaging observations from Extreme-ultraviolet Imaging Spectrometer (EIS) on board Hinode and Atmospheric Imaging Assembly (AIA) on board SDO. Analysis of the data shows significant oscillations at different locations. We explore the variations in different line parameters to determine whether the waves or flows could cause these oscillations to improve the current understanding on the nature of these disturbances.

astro-ph.SR↗