Exploring stellar activity in a sample of active M dwarfs

Most M dwarfs show higher chromospheric activity, often exceeding solar levels. Characterizing stellar activity is essential, particularly since these stars are prime targets in the search for habitable exoplanets. We investigate the stellar activity of active M dwarfs using TESS photometry combined with spectroscopic observations. We explore relations between flare occurrence rate (FOR), flare energies, rotation period, starspot filling factor, and chromospheric indicators. We also examine correlations between flare amplitude, duration, and cumulative flare frequency distributions to probe the mechanisms behind magnetic activity. We find that FOR is flat across spectral types M0-M4 but declines for cooler M dwarfs. Rapid rotators ($P_{\rm rot} < 1$ day) display significantly higher FOR and flare activity. M dwarfs with higher FOR tend to have lower flare amplitudes, suggesting that frequent flares are generally less energetic. For stars with 0.15--0.76 $M_\odot$, the median $L_{Hα}/L_{\rm bol}$ varies by a factor of 2.5 across mass bins of 0.1 $M_\odot$, while $Δ$EW decreases by 92\%. The cumulative flare frequency distributions show a decrease in the power-law slope from M0 to M5, with $α$ ranging from 1.68 to 1.95. Our results indicate a transition in stellar activity near M4, where stronger H$α$ emission coincides with higher FOR. We confirm that chromospheric and flare activity follow a power-law relation, highlighting the interplay between magnetic fields and flaring in M dwarfs. We also find that fast rotators sustain frequent flaring through strong dynamos, and that highly active stars dissipate magnetic energy via numerous low-energy flares rather than rare high-energy ones.

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