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| Autori principali: | , , , , , , , , , |
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| Natura: | Preprint |
| Pubblicazione: |
2025
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| Soggetti: | |
| Accesso online: | https://arxiv.org/abs/2508.15107 |
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| _version_ | 1866918176943505408 |
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| author | Hu, Yifan Brightman, Murray Favata, Fabio Pan, Haiwu Grefenstette, Brian Harrison, Fiona A. Stern, Daniel Yuan, Weimin Yung, Yuk L. Zhao, Xiurui |
| author_facet | Hu, Yifan Brightman, Murray Favata, Fabio Pan, Haiwu Grefenstette, Brian Harrison, Fiona A. Stern, Daniel Yuan, Weimin Yung, Yuk L. Zhao, Xiurui |
| contents | Stellar flares are potent drivers of atmospheric evolution on orbiting exoplanets, primarily through extreme ultraviolet (EUV) and soft X-ray (XUV) irradiation. However, the contribution of hard X-rays (HXR; 3--20 keV)-which penetrate deeper into planetary atmospheres-to mass loss and particle acceleration has remained poorly understood. To quantify the HXR share of the total radiative budget, we conducted quasi-simultaneous observations of the active M-dwarf AU Mic using NuSTAR, Swift, and the Einstein Probe. Our analysis detected two major flares, and we performed an empirical check by deriving a quiescent-phase soft X-ray (SXR; 0.3--3 keV)-HXR relation and then applying it to the flares. By combining this with the quiescent coronal SXR-EUV relations conversion of J. Sanz-Forcada et al. (2011), we computed the total high-energy flux (EUV + SXR + HXR) and assessed the relative role of HXR in atmospheric escape. We find that HXR accounts for only a few percent of the total radiative energy budget during both quiescent and flaring states. While a high-energy spectral tail is detected in the second flare, time-resolved spectroscopy reveals a dominant chromospheric-evaporation signature, indicating that the flare energetics are primarily thermal. |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2508_15107 |
| institution | arXiv |
| publishDate | 2025 |
| record_format | arxiv |
| spellingShingle | Hard X-ray Emission in AU Mic Flares: A Minor Contributor to Planetary Atmospheric Escape Hu, Yifan Brightman, Murray Favata, Fabio Pan, Haiwu Grefenstette, Brian Harrison, Fiona A. Stern, Daniel Yuan, Weimin Yung, Yuk L. Zhao, Xiurui Solar and Stellar Astrophysics Earth and Planetary Astrophysics High Energy Astrophysical Phenomena Stellar flares are potent drivers of atmospheric evolution on orbiting exoplanets, primarily through extreme ultraviolet (EUV) and soft X-ray (XUV) irradiation. However, the contribution of hard X-rays (HXR; 3--20 keV)-which penetrate deeper into planetary atmospheres-to mass loss and particle acceleration has remained poorly understood. To quantify the HXR share of the total radiative budget, we conducted quasi-simultaneous observations of the active M-dwarf AU Mic using NuSTAR, Swift, and the Einstein Probe. Our analysis detected two major flares, and we performed an empirical check by deriving a quiescent-phase soft X-ray (SXR; 0.3--3 keV)-HXR relation and then applying it to the flares. By combining this with the quiescent coronal SXR-EUV relations conversion of J. Sanz-Forcada et al. (2011), we computed the total high-energy flux (EUV + SXR + HXR) and assessed the relative role of HXR in atmospheric escape. We find that HXR accounts for only a few percent of the total radiative energy budget during both quiescent and flaring states. While a high-energy spectral tail is detected in the second flare, time-resolved spectroscopy reveals a dominant chromospheric-evaporation signature, indicating that the flare energetics are primarily thermal. |
| title | Hard X-ray Emission in AU Mic Flares: A Minor Contributor to Planetary Atmospheric Escape |
| topic | Solar and Stellar Astrophysics Earth and Planetary Astrophysics High Energy Astrophysical Phenomena |
| url | https://arxiv.org/abs/2508.15107 |