| Name: Sumanth A. Rotti |
| Affiliation: Aryabhatta Research Institute of Observational Sciences |
| Conference ID: ASI2026_482 |
| Title: Characterization of Hot Onset Precursor Event (HOPE) Features in Solar Flares During Solar Cycle 25 |
| Abstract Type: Poster |
| Abstract Category: Sun, Solar System, Exoplanets, and Astrobiology |
| Author(s) and Co-Author(s) with Affiliation: Sumanth A. Rotti(Aryabhatta Research Institute of Observational Sciences, Nainital - 263001, India), Kiran Lakshmipathaiah(U. R. Rao Satellite Centre, Bengaluru - 560037, India), Abhilash R. Sarwade(U. R. Rao Satellite Centre, Bengaluru - 560037, India), Srikar Paavan Tadepalli(U. R. Rao Satellite Centre, Bengaluru - 560037, India), Vaibhav Pant(Indian Institute of Technology Delhi, New Delhi - 110016, India), Krishna Prasad S.(Aryabhatta Research Institute of Observational Sciences, Nainital - 263001, India), Sankarasubramanian K.(U. R. Rao Satellite Centre, Bengaluru - 560037, India) |
| Abstract: The Hot Onset Precursor Event (HOPE) phenomenon represents the earliest detectable signature of flare-associated coronal heating. It precedes the onset of strong chromospheric evaporation and the impulsive rise of soft X-ray flux to its peak. In this study, we examine the behavior of the HOPE phase using a statistically filtered set of 62 isolated >=M1.0 flares observed between January 2024 and August 2025. Solar (soft and hard) X-ray data from the Aditya-L1 mission are used to analyze the HOPE phase of flares, and the findings are validated using data from the Geostationary Operational Environmental Satellite (GOES). Reliable plasma parameters, i.e., temperature (T) and emission measure (EM), from Aditya-L1's Solar Low-Energy X-ray Spectrometer (SoLEXS) data are estimated via spectral fitting. Additionally, hard X-ray spectrograms from the High Energy L-1 Orbiting X-ray Spectrometer (HEL1OS) onboard Aditya-L1 are used to examine sub-minute fluctuations in the HOPE phase. For GOES X-ray data, T and EM are determined using the flux-ratio inversion method available within the Sunpy library.
Our results indicate that the HOPE intervals (i) are generally brief (<10 minutes), (ii) have a median flare temperature ranging from 6 to 14 MK, (iii) show impulsive onsets at intermediate temperatures between 8 and 17 MK, and (iv) exhibit mildly nonlinear slopes in the T–EM space. The narrow HOPE phase durations and slope patterns indicate a relatively uniform early reconnection and continued heating process across the samples studied here. At the same time, the observed temperature distributions reflect event-to-event variability in energy deposition. Following the HOPE phase, a peak flare temperature of 10-25 MK is observed, accompanied by a rapid increase in EM. Overall, these findings support the characterization of the HOPE phase as a diagnostically significant stage in flare evolution, indicative of distinct coronal heating mechanisms prior to substantial mass loading. |
