arXiv subjects

Ananya Rawat

Publications and source records attributed to Ananya Rawat.

5 recordsLinked to original sources

arXiv2026

Investigating the propagation of small-scale flare energy in the lower and upper atmosphere of solar active region

During solar flares, a considerable portion of the flare atmosphere becomes heated; however, the energy deposition process is still unclear, especially in the lower solar atmosphere. Here, we present spectroscopic and imaging observations of a small-scale transient of lifetime $<$1-min and further formation of a hot loop of lifetime $\approx$2-min in a solar active region. The observed transient shows the appearance of hot plasma $>$10 MK at the loop foot-point and the subsequent formation of a small-scale transient loop with a loop-top temperature $>$8 MK. The transient shows an enhancement in intensities in several AIA and IRIS passbands. Light curves obtained from several lower atmospheric passbands show consistent time lags in several peak intensities, which, to our knowledge, has never been reported before. Beneath the transient, associated HMI magnetogram shows evidence of flux emergence of both polarities. Using the IRIS \ion{O}{IV} line pair, we obtained the average electron number density of $10^{11.22}$ cm$^{-3}$ at the transient. IRIS transition region lines such as \ion{O}{IV} and \ion{Si}{IV} show a redshift of 10-15 km s$^{-1}$, whereas neutral lines such as \ion{C}{I} and \ion{S}{I} show a redshift of about 5 km s$^{-1}$. These Doppler shifts suggest a down-flowing warmer plasma in the lower atmosphere. The appearance of \ion{Mg}{II} triplets in emission is also observed. We interpret these enhancements in intensities in the lower atmosphere as a result of heating due to both non-thermal electrons and thermal conduction operating simultaneously.

astro-ph.SR↗

arXiv2025

Understanding the magnetic field and plasma-$β$ along umbral fan loops traced using 3-min slow waves

The plasma-$β$ is an important fundamental physical quantity in solar plasma physics, which determines the dominating process in the solar atmosphere, i.e., magnetic or thermodynamic processes. Here, for the first time, we provide variations of magnetic field and plasma-$β$ along magnetically structured loops from the photosphere to the corona. We have selected several fan loops rooted in sunspot umbra observed simultaneously by the Interface Region Imaging Spectrograph and Solar Dynamics Observatory. The 3-min slow waves enabled us to trace and analyze several fan loops with cross-sectional areas in the lower atmosphere and locate their footpoints at the photosphere. We find the RMS magnetic field strengths in the range 1596-2269 G at the photospheric footpoints of the fan loops, which decrease rapidly to 158-236 G at the coronal footpoints. We estimated the plasma-$β$ at the photospheric and coronal footpoints in the range 0.2-0.5 and 0.0001-0.001, respectively. We found plasma-$β$$<$$1$ along the whole loop, whereas the plasma-$β$$\approx$$1$ layer is found to be at sub-photospheric heights. We compared our findings for isolated individual fan loops with a previously established model for active regions and found an almost similar pattern in variations with height, but with different plasma-$β$ values. Our results demonstrate the seismological potential of 3-min slow waves omnipresent in the umbral sunspot atmosphere to probe and map isolated loops and determine magnetic field and plasma-$β$ along these loops. The obtained parameters provide crucial ingredients for the theoretical modeling of the umbral atmosphere and wave dynamics along loops.

astro-ph.SR↗

arXiv2024

Effect of area divergence and frequency on damping of slow magnetoacoustic waves propagating along umbral fan loops

Waves play an important role in the heating of solar atmosphere, however, observations of wave propagation and damping from the solar photosphere to corona through chromosphere and transition region are very rare. Recent observations have shown propagation of 3-min slow magnetoacoustic waves (SMAWs) along fan loops from the solar photosphere to corona. In this work, we investigate the role of area divergence and frequencies on the damping of SMAWs propagating from the photosphere to the corona along several fan loops rooted in the sunspot umbra. We study the Fourier power spectra of oscillations along fan loops at each atmospheric height which showed significant enhancements in 1--2 min, 2.3--3.6 min and 4.2--6 min period bands. Amplitude of intensity oscillations in different period bands and heights are extracted after normalizing the filtered light curves with low-frequency background. We find damping of SMAW energy flux propagating along the fan loop 6 with damping lengths ~170 km and ~208 km for 1.5-min and 3-min period bands. We also show the decay of total wave energy content with height after incorporating area divergence effect, and present actual damping of SMAWs from photosphere to corona. Actual damping lengths in this case increases to ~172 km and ~303 km for 1.5-min and 3-min period bands. All the fan loops show such increase in actual damping lengths, and thus highlight the importance of area divergence effect. Results also show some frequency-dependent damping of SMAW energy fluxes with height where high-frequency waves are damped faster than low-frequency waves.

astro-ph.SR↗

arXiv2023

Exploring magnetic coupling of solar atmosphere through frequency modulations of 3-min slow magnetoacoustic waves

Coronal fan loops rooted in sunspot umbra show outward propagating waves with subsonic phase speed and period around 3-min. However, their source region in the lower atmosphere is still ambiguous. We performed multi-wavelength observations of a clean fan loop system rooted in sunspot observed by Interface Region Imaging Spectrograph (IRIS) and Solar Dynamics Observatory (SDO). We utilised less explored property of frequency modulation of these 3-min waves from the photosphere to corona, and found them to be periodic with the ranges in 14-20 min, and 24-35 min. Based on our findings, we interpret that 3-min slow waves observed in the coronal fan loops are driven by 3-min oscillations observed at the photospheric footpoints of these fan loops in the umbral region. We also explored any connection between 3-min and 5-min oscillations observed at the photosphere, and found them to be poorly understood. Results provide clear evidence of magnetic coupling of the solar umbral atmosphere through propagation of 3-min waves along the fan loops at different atmospheric heights.

astro-ph.SR↗

arXiv2023

Exploring source region of 3-min slow magnetoacoustic waves observed in coronal fan loops rooted in sunspot umbra

Sunspots host various oscillations and wave phenomena like umbral flashes, umbral oscillations, running penumbral waves, and coronal waves. All fan loops rooted in sunspot umbra constantly show a 3-min period propagating slow magnetoacoustic waves in the corona. However, their origin in the lower atmosphere is still unclear. In this work, we studied these oscillations in detail along a clean fan loop system rooted in active region AR12553 for a duration of 4-hour on June 16, 2016 observed by Interface Region Imaging Spectrograph (IRIS) and Solar Dynamics Observatory (SDO). We traced foot-points of several fan loops by identifying their locations at different atmospheric heights from the corona to the photosphere. We found presence of 3-min oscillations at foot-points of all the loops and at all atmospheric heights. We further traced origin of these waves by utilising their amplitude modulation characteristics while propagating in the solar atmosphere. We found several amplitude modulation periods in the range of 9-14 min, 20-24 min, and 30-40 min of these 3-min waves at all heights. Based on our findings, we interpret that 3-min slow magnetoacoustic waves propagating in coronal fan loops are driven by 3-min oscillations observed at the photospheric foot-points of these fan loops in the umbral region. We also explored any connection between 3-min and 5-min oscillations observed at the photospheric foot-points of these loops and found them to be weakly coupled. Results provide clear evidence of magnetic coupling of the solar atmosphere through propagation of 3-min waves along fan loops at different atmospheric heights.

astro-ph.SR↗