arXiv subjects

Suraj Sahu

Publications and source records attributed to Suraj Sahu.

4 recordsLinked to original sources

arXiv2026

Phase-drifting with emitting plasma temperature in the quasi-periodic pulsations of an X-class solar flare

Recent multi-wavelength observations of solar flares have provided new constraints on the physical origin of quasi-periodic pulsations (QPPs). In an X-class flare, we detect a short-lived $\sim$5-minute QPP simultaneously in hard X-rays, extreme-ultraviolet (EUV), and soft X-ray emissions, exhibiting a clear phase-drifting behavior with emitting plasma temperature. Based on phase-resolved timing analysis, it is found that (i) the QPPs in all diagnostics share nearly identical oscillation periods, (ii) a systematic temperature-dependent phase drifting is present, with the phase delay relative to the hard X-ray emission increases systematically from the hottest to cooler EUV channels, and (iii) the QPP persists for only a few cycles during the impulsive phase. These properties imply that periodic magnetic reconnection, possibly triggered by the leakage of 5-minute oscillations from the lower atmosphere, modulates the non-thermal electrons responsible for the leading Hard X-ray QPPs. Subsequently, plasma heating and cooling processes manifest sequentially across passbands with different temperature responses, resulting in the observed temperature-dependent phase drifting. These results provide novel observational evidence supporting the use of multi-temperature, multi-wavelength phase relationships to constrain the temporal evolution of flare energy release and the origins of QPPs.

astro-ph.SR↗

arXiv2022

Evolution of magnetic fields and energy release processes during homologous eruptive flares

We explore the processes of repetitive build-up and explosive release of magnetic energy together with the formation of magnetic flux ropes that eventually resulted into three homologous eruptive flares of successively increasing intensities (i.e., M2.0, M2.6, and X1.0). The flares originated from NOAA active region 12017 during 2014 March 28-29. EUV observations and magnetogram measurements together with coronal magnetic field modeling suggest that the flares were triggered by the eruption of flux ropes embedded by a densely packed system of loops within a small part of the active region. In X-rays, the first and second events show similar evolution with single, compact sources, while the third event exhibits multiple emission centroids with a set of strong non-thermal conjugate sources at 50-100 keV during the HXR peak. The photospheric magnetic field over an interval of approximately 44 hr encompassing the three flares undergoes important phases of emergence and cancellation processes together with significant changes near the polarity inversion lines within the flaring region. Our observations point toward the tether-cutting mechanism as the plausible triggering process of the eruptions. Between the second and third event, we observe a prominent phase of flux emergence which temporally correlates with the build-up phase of free magnetic energy in the active region corona. In conclusion, our analysis reveals an efficient coupling between the rapidly evolving photospheric and coronal magnetic fields in the active region that led to a continued phase of the build-up of free energy, resulting into the homologous flares of successively increasing intensities.

astro-ph.SR↗

arXiv2022

Homologous compact major blowout-eruption solar flares and their production of broad CMEs

We analyze the formation mechanism of three homologous broad coronal mass ejections (CMEs) resulting from a series of solar blowout-eruption flares with successively increasing intensities (M2.0, M2.6, and X1.0). The flares originated from active region NOAA 12017 during 2014 March 28-29 within an interval of approximately 24 hr. Coronal magnetic field modeling based on nonlinear-force-free-field extrapolation helps to identify low-lying closed bipolar loops within the flaring region enclosing magnetic flux ropes. We obtain a double flux rope system under closed bipolar fields for the all the events. The sequential eruption of the flux ropes led to homologous flares, each followed by a CME. Each of the three CMEs formed from the eruptions gradually attain a large angular width, after expanding from the compact eruption-source site. We find these eruptions and CMEs to be consistent with the 'magnetic-arch-blowout' scenario: each compact-flare blowout eruption was seated in one foot of a far-reaching magnetic arch, exploded up the encasing leg of the arch, and blew out the arch to make a broad CME.

astro-ph.SR↗

arXiv2020

HXR emission from an activated flux rope and subsequent evolution of an eruptive long duration solar flare

In this paper, we present a comprehensive study of the evolutionary phases of a major M6.6 long duration event (LDE) with special emphasize on its pre-flare phase. The event occurred in NOAA 12371 on 2015 June 22. A remarkable aspect of the event was an active pre-flare phase lasting for about an hour during which a hot EUV coronal channel was in build-up stage and displayed co-spatial hard X-ray (HXR) emission up to energies of 25 keV. As such, this is the first evidence of HXR coronal channel. The coronal magnetic field configuration based on NLFFF modeling clearly exhibited a magnetic flux rope (MFR) oriented along the polarity inversion line (PIL) and co-spatial with the coronal channel. We observed significant changes in the AR's photospheric magnetic field during an extended period of $\approx$42 hours in the form of rotation of sunspots, moving magnetic features, and flux cancellation along the PIL. Prior to the flare onset, the MFR underwent a slow rise phase ($\approx$14 km s$^{-1}$) for $\approx$12 min which we attribute to the faster build-up and activation of the MFR by tether-cutting reconnection occurring at multiple locations along the MFR itself. The sudden transition in the kinematic evolution of the MFR from the phase of slow to fast rise ($\approx$109 km s$^{-1}$ with acceleration $\approx$110 m s$^{-2}$) precisely divides the pre-flare and impulsive phase of the flare, which points toward the feedback process between the early dynamics of the eruption and the strength of the flare magnetic reconnection.

astro-ph.SR↗