arXiv subjects

Girjesh Gupta

Publications and source records attributed to Girjesh Gupta.

4 recordsLinked to original sources

arXiv2026

Spectroscopic diagnostics of coronal fan loops using EIS/Hinode and AIA/SDO

We utilize spectroscopic and imaging data from the EIS/Hinode and the AIA/SDO to determine plasma and wave parameters along coronal fan loops. We determined the temperature along the loop lengths using the EM-loci method with EIS spectral lines and identified multi-thermal plasma components at temperatures ranging from 0.8-1.05, 1.2-1.4, and 1.6-1.8 MK. We further compared these temperature distributions along the loops with those derived from DEM analysis carried out using AIA coronal passbands. The multi-thermal nature of coronal fan loops can be well resolved using EIS spectroscopic data. We determined the density along the loop using the line-ratio method from the EIS Fe XII line pair. We found that density decreases slowly from the expected hydrostatic equilibrium. Our results demonstrate the multi-thermal nature of overdense loops, which can be well resolved with EIS spectroscopic data. We also determined the velocity amplitude of Alfvén waves from the non-thermal broadening of EIS Fe XII spectral line profiles. We further estimated the Alfvén wave energy flux in the corona by combining these parameters with the recently reported magnetic field strength of $\approx$200 G at the coronal footpoint of fan loops. The estimated Alfvén wave energy flux is $\approx$ 2$\times 10^7$ erg cm$^{-2}$ s$^{-1}$, significantly higher than those reported in earlier studies, and can contribute to coronal losses due to radiation along the fan loops in the active region.

astro-ph.SR↗

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↗

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↗