Dr Sargam Mulay

Scopus Publications

First time delay observation between two mid-infrared channels in solar flare footpoints
Miguel Rojas-Quesada, Lyndsay Fletcher, Hugh Hudson, Sargam M Mulay, Paulo J A Simões
Monthly Notices of the Royal Astronomical Society, 2026
The strong correlation between energy injection and mid-infrared (mid-IR) emission observed during solar flares can be used to probe energy deposition throughout the chromosphere, since the IR tracks prompt flare-induced changes in electron density. Despite its diagnostic value, solar mid-IR observations are relatively recent, with sporadic campaigns over the last decade resulting in only a few recorded flares. Earlier studies found time lags between mid-IR emissions from spatially resolved footpoints, offering clues about flare energy transport. Building on this, we analyse the time lags between emissions at two wavelengths (5.2 and 8.2 $\mu$m) for each footpoint. Using a local cross-correlation function, we show for the first time that the 8.2 $\mu$m emission channel peaks 0.3–0.45 $\mathrm{s}$ before the 5.2 $\mu$m channel. We investigate the origin of this lag, obtaining infrared emission estimates using results from the RADYN radiation hydrodynamics code. The theoretical lag values fall within the range of the observed ones. Variations in opacity primarily due to flare-induced ionization explain the wavelength-dependent temporal shift between emission maxima. In particular, longer wavelengths exhibit a smaller lag between the peak of energy injection and peak of intensity. These results contribute to a better understanding of how energy deposition during a flare affects the chromospheric layers of the atmosphere. Future observations with higher temporal resolution could exploit measurements of these time lags to more fully characterize the dynamics of energy deposition during solar flares, opening a new avenue for studying heating and energy transport processes in the solar atmosphere.
Extremely Energetic Extreme-ultraviolet Late Phase of a Pair of C-class Flares Caused by a Noneruptive Sigmoid
Ya Wang, Sargam M. Mulay, Lyndsay Fletcher
Astrophysical Journal, 2026
The extreme-ultraviolet (EUV) late phase (ELP) is the second increase of the irradiance of warm coronal lines during solar flares, and has a crucial impact on the Earth’s ionosphere. In this paper, we report on the extremely energetic ELP of a pair of C-class flares (SOL2012-06-17T17:26:11) observed on 2012 June 17 in NOAA active region 11504 by the Atmospheric Imaging Assembly (AIA) instrument on board the Solar Dynamics Observatory. The light curves integrated over the flaring region show that a factor of 4.2 more energy is released in the “warm-temperature” (2–3 × 10 6 K) passbands (e.g., AIA 335 Å) during the late phase than during the main peaks. The origin of the emission in this extremely energetic ELP is a noneruptive sigmoid situated in a multipolar magnetic field configuration, which is rapidly energized by C-class flares. The sigmoid plasma appears to reach temperatures in excess of 10 7 K, before cooling to produce the ELP emission. This is seen in high-temperature passbands (e.g., AIA 131 Å) and by using differential emission measure analysis. Magnetic extrapolations indicate that the sigmoid is consistent with formation by magnetic reconnection between previously existing J-shaped loops. The sigmoid experienced fast and slow cooling stages, both of which were dominated by conductive cooling. The estimated total cooling time of the sigmoid is shorter than the observed value. So, we proposed that the noneruptive sigmoid, heated by continuous magnetic reconnection, leads to the extremely energetic ELP.
Origin of the Unusual Composition of 3He-rich Solar Energetic Particles
Radoslav Bučík, Glenn M. Mason, Sargam M. Mulay, George C. Ho, Robert F. Wimmer-Schweingruber, Javier Rodríguez-Pacheco
Astrophysical Journal, 2025
We examine 3He-rich solar energetic particles (SEPs) detected on 2023 October 24–25 by Solar Orbiter at 0.47 au. Measurements reveal that heavy-ion enhancements increase irregularly with mass, peaking at S. C, and especially N, Si, and S, stand out in the enhancement pattern with large abundances. Except for 3He, heavy-ion spectra can only be measured below 0.5 MeV nucleon−1. At 0.386 MeV nucleon−1, the event shows a huge 3He/4He ratio of 75.2 ± 33.9, larger than previously observed. Solar Dynamics Observatory extreme-ultraviolet data show a minifilament eruption at the solar source of 3He-rich SEPs that triggered a straight tiny jet. Located at the boundary of a low-latitude coronal hole, the jet base is a bright, small-scale region with a supergranulation scale size. The emission measure (EM) provides relatively cold source temperatures of 1.5–1.7 MK between the filament eruption and nonthermal type III radio burst onset. Analysis suggests that the EM distribution of temperature in the solar source could be a factor that affects the preferential selection of heavy ions for heating or acceleration, thus shaping the observed enhancement pattern. Including previously reported similar events indicates that the eruption of the minifilament is a common feature of events with heavy-ion enhancement not ordered by mass. Surprisingly, sources with weak magnetic fields show extreme 3He enrichment in these events. Moreover, the energy attained by heavy ions seems to be influenced by the size and form of the jets.
Simultaneous Eruption and Shrinkage of Preexisting Flare Loops during a Subsequent Solar Eruption
Huadong 华东 Chen 陈, Lyndsay Fletcher, Guiping 桂萍 Zhou 周, Xin 鑫 Cheng 程, Ya 亚 Wang 汪, Sargam Mulay, Ruisheng 瑞生 Zheng 郑, Suli 素丽 Ma 马, Xiaofan 小凡 Zhang 张
Astrophysical Journal, 2024
We investigated two consecutive solar eruption events in the solar active region 12994 at the solar eastern limb on 2022 April 15. We found that the flare loops formed by the first eruption were involved in the second eruption. During the initial stage of the second flare, the middle part of these flare loops (E-loops) erupted outward along with the flux ropes below, while the parts of the flare loops (I-loops1 and I-loops2) on either side of the E-loops first rose and then contracted. Approximately 1 hr after the eruption, the heights of I-loops1 and I-loops2 decreased by 9 Mm and 45 Mm, respectively, compared to before the eruption. Their maximum descent velocities were 30 km s−1 and 130 km s−1, respectively. The differential emission measure results indicate that the plasma above I-loops1 and I-loops2 began to be heated about 23 minutes and 44 minutes after the start of the second flare, respectively. Within ∼20 minutes, the plasma temperature in these regions increased from ∼3 MK to ∼6 MK. We proposed an adiabatic heating mechanism where magnetic energy would be converted into thermal and kinetic energy when the prestretched loops contract. Our calculations show that the magnetic energy required to heat the two high-temperature regions are 1029–1030 erg, which correspond to a loss of field strength of 2–3 G.
Enhanced Three-minute Oscillation above a Sunspot during a Solar Flare
Ya Wang, Lyndsay Fletcher, Sargam Mulay, Haisheng Ji, Wenda Cao
Astrophysical Journal, 2024
Three-minute oscillations are a common phenomenon in the solar chromosphere above a sunspot. Oscillations can be affected by the energy release process related to solar flares. In this paper, we report on an enhanced oscillation in flare event SOL2012-07-05T21:42 with a period of around 3 minutes that occurred at the location of a flare ribbon at a sunspot umbral–penumbral boundary and was observed in both chromospheric and coronal passbands. An analysis of this oscillation was carried out using simultaneous ground-based observations from the Goode Solar Telescope at the Big Bear Solar Observatory and space-based observations from the Solar Dynamics Observatory. A frequency shift was observed before and after the flare, with the running penumbral wave that was present with a period of about 200 s before the flare coexisting with a strengthened oscillation with a period of 180 s at the same locations after the flare. We also found a phase difference between different passbands, with the oscillation occurring from high-temperature to low-temperature passbands. Theoretically, the change in frequency was strongly dependent on the variation of the inclination of the magnetic field and the chromospheric temperature. Following an analysis of the properties of the region, we found the frequency change was caused by a slight decrease of the magnetic inclination angle with respect to the local vertical. In addition, we suggest that the enhanced 3 minute oscillation was related to the additional heating, maybe due to the downflow, during the EUV late phase of the flare.
Behaviour of molecular hydrogen emission in three solar flares
Sargam M Mulay, Lyndsay Fletcher, Hugh Hudson, Nicolas Labrosse
Monthly Notices of the Royal Astronomical Society, 2023
We have systematically investigated ultraviolet (UV) emission from molecular hydrogen (H2) using the Interface Region Imaging Spectrograph (IRIS), during three X-ray flares of C5.1, C9.7, and X1.0 classes on 2014 October 25. Significant emission from five H2 spectral lines appeared in the flare ribbons, interpreted as photoexcitation (fluorescence) due to the absorption of UV radiation from two Si iv spectral lines. The H2 profiles were broad and consisted of two non-stationary components in red and in the blue wings of the line in addition to the stationary component. The red-wing (blue-wing) components showed small redshifts (blueshifts) of ∼5–15 km s−1 (∼5–10 km s−1). The non-thermal velocities were found to be ∼5–15 km s−1. The interrelation between intensities of H2 lines and their branching ratios confirmed that H2 emission formed under optically thin plasma conditions. There is a strong spatial and temporal correlation between Si iv and H2 emissions, but the H2 emission is more extended and diffuse, further suggesting H2 fluorescence, and – by analogy with flare ‘back-warming’ – providing a means to estimate the depth from which the H2 emission originates. We find that this is 1871 ± 157 and 1207 ± 112 km below the source of the Si iv emission, in two different ribbon locations.
Formation and thermodynamic evolution of plasmoids in active region jets
Sargam M Mulay, Durgesh Tripathi, Helen Mason, Giulio Del Zanna, Vasilis Archontis
Monthly Notices of the Royal Astronomical Society, 2023
We have carried out a comprehensive study of the temperature structure of plasmoids, which successively occurred in recurrent active region jets. The multithermal plasmoids were seen to be travelling along the multithreaded spire as well as at the footpoint region in the EUV/UV images recorded by the Atmospheric Imaging Assembly (AIA). The differential emission measure (DEM) analysis was performed using EUV AIA images, and the high-temperature part of the DEM was constrained by combining X-ray images from the X-ray telescope (XRT/Hinode). We observed a systematic rise and fall in brightness, electron number densities and the peak temperatures of the spire plasmoid during its propagation along the jet. The plasmoids at the footpoint (FPs) (1.0–2.5 MK) and plasmoids at the spire (SPs) (1.0–2.24 MK) were found to have similar peak temperatures, whereas the FPs have higher DEM weighted temperatures (2.2–5.7 MK) than the SPs (1.3–3.0 MK). A lower limit to the electron number densities of plasmoids – SPs (FPs) were obtained that ranged between 3.4–6.1 × 108 (3.3–5.9 × 108) cm−3 whereas for the spire, it ranged from 2.6–3.2 × 108 cm−3. Our analysis shows that the emission of these plasmoids starts close to the base of the jet(s), where we believe that a strong current interface is formed. This suggests that the blobs are plasmoids induced by a tearing-mode instability.
Fast prograde coronal flows in solar active regions
Hugh S Hudson, Sargam M Mulay, Lyndsay Fletcher, Jennifer Docherty, Jimmy Fitzpatrick, Eleanor Pike, Morven Strong, Phillip C Chamberlin, Thomas N Woods
Monthly Notices of the Royal Astronomical Society Letters, 2022
We report the discovery and characterization of high-speed (&gt;100 km s−1) horizontal flows in solar active regions, making use of the Sun-as-a-star spectroscopy in the range 5–105 nm provided by the EVE (Extreme Ultraviolet Variability Experiment) spectrometers on the Solar Dynamics Observatory. These apparent flows are persistent on time-scales of days, and are well observed in lines of Mg x, Si xii, and Fe xvi for example. They are prograde, as evidenced directly by blueshifts/redshifts peaking at the east/west limb passages of isolated active regions. The high-speed flow behaviour does not depend upon active-region latitude or solar cycle, with similar behaviour in Cycles 24 and 25.
Evidence of chromospheric molecular hydrogen emission in a solar flare observed by the IRIS satellite
Sargam M Mulay, Lyndsay Fletcher
Monthly Notices of the Royal Astronomical Society, 2021
We have carried out the first comprehensive investigation of enhanced line emission from molecular hydrogen, H2 at 1333.79 Å, observed at flare ribbons in SOL2014-04-18T13:03. The cool H2 emission is known to be fluorescently excited by Si iv 1402.77 Å UV radiation and provides a unique view of the temperature minimum region (TMR). Strong H2 emission was observed when the Si iv 1402.77 Å emission was bright during the flare impulsive phase and gradual decay phase, but it dimmed during the GOES peak. H2 line broadening showed non-thermal speeds in the range 7–18 $\\rm {km\\,s}^{-1}$, possibly corresponding to turbulent plasma flows. Small red (blue) shifts, up to 1.8 (4.9) $\\rm {km\\,s}^{-1}$ were measured. The intensity ratio of Si iv 1393.76 Å and Si iv 1402.77 Å confirmed that plasma was optically thin to Si iv (where the ratio = 2) during the impulsive phase of the flare in locations where strong H2 emission was observed. In contrast, the ratio differs from optically thin value of 2 in parts of ribbons, indicating a role for opacity effects. A strong spatial and temporal correlation between H2 and Si iv emission was evident supporting the notion that fluorescent excitation is responsible.
Thermodynamic evolution of a sigmoidal active region with associated flares
Sargam M Mulay, Durgesh Tripathi, Helen Mason
Monthly Notices of the Royal Astronomical Society, 2021
Active regions often show S-shaped structures in the corona called sigmoids. These are highly sheared and twisted loops formed along the polarity inversion line. They are considered to be one of the best pre-eruption signatures for CMEs. Here, we investigate the thermodynamic evolution of an on-disc sigmoid observed during 2015 December 24–28. For this purpose, we have employed Emission Measure (EM) and filter-ratio techniques on the observations recorded by the Atmospheric Imaging Assembly (AIA) on-board the Solar Dynamics Observatory (SDO) and X-ray Telescope (XRT) on-board Hinode. The EM analysis showed multithermal plasma along the sigmoid and provided a peak temperature of ∼10–12.5 MK for all observed flares. The sigmoidal structure showed emission from Fe xviii (93.93 Å) and Fe xxi (128.75 Å) lines in the AIA 94 and 131 Å channels, respectively. Our results show that the hot plasma is often confined to very hot strands. The temperature obtained from the EM analysis was found to be in good agreement with that obtained using the XRT, AIA, and GOES filter-ratio methods. These results provide important constraints for the thermodynamic modelling of sigmoidal structures in the core of active regions. Moreover, this study also benchmarks different techniques available for temperature estimation in solar coronal structures.
Temperature in Solar Sources of 3He-rich Solar Energetic Particles and Relation to Ion Abundances
Radoslav Bučík, Sargam M. Mulay, Glenn M. Mason, Nariaki V. Nitta, Mihir I. Desai, Maher A. Dayeh
Astrophysical Journal, 2021
Study of the spatial association between an active region jet and a nonthermal type III radio burst
Sargam M. Mulay, Rohit Sharma, Gherardo Valori, Alberto M. Vásquez, Giulio Del Zanna, Helen Mason, Divya Oberoi
Astronomy and Astrophysics, 2019
Flare-related Recurring Active Region Jets: Evidence for Very Hot Plasma
Sargam M. Mulay, Sarah Matthews, Takahiro Hasegawa, Giulio Del Zanna, Helen Mason, Toshifumi Shimizu
Solar Physics, 2018
Cool and hot emission in a recurring active region jet
Sargam M. Mulay, Giulio Del Zanna, Helen Mason
Astronomy and Astrophysics, 2017
Temperature and density structure of a recurring active region jet
Sargam M. Mulay, Giulio Del Zanna, Helen Mason
Astronomy and Astrophysics, 2017
Slipping magnetic reconnection, chromospheric evaporation, implosion, and precursors in the 2014 September 10 X1.6-class solar flare
Jaroslav Dudík, Vanessa Polito, Miho Janvier, Sargam M. Mulay, Marian Karlický, Guillaume Aulanier, Giulio Del Zanna, Elena Dzifčáková, Helen E. Mason, Brigitte Schmieder
Astrophysical Journal, 2016
Multiwavelength study of 20 jets that emanate from the periphery of active regions
Sargam M. Mulay, Durgesh Tripathi, Giulio Del Zanna, Helen Mason
Astronomy and Astrophysics, 2016
Sunspot waves and triggering of homologous active region jets
R. Chandra, G. R. Gupta, Sargam Mulay, Durgesh Tripathi
Monthly Notices of the Royal Astronomical Society, 2015
Initiation of coronal mass ejection event observed on 2010 november 3: Multi-wavelength perspective
Sargam Mulay, Srividya Subramanian, Durgesh Tripathi, Hiroaki Isobe, Lindsay Glesener
Astrophysical Journal, 2014
Low-frequency observations of drifting, non-thermal continuum radio emission associated with the solar coronal mass ejections
R. Ramesh, P. Kishore, Sargam M. Mulay, Indrajit V. Barve, C. Kathiravan, T. J. Wang
Astrophysical Journal, 2013

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Scopus Publications