Signatures of transition region explosive events in hydrogen Lyβ profiles

Aims. We search for signatures of transition region explosive events (EEs) in hydrogen Ly beta profiles. The relationship between the peak emission of Ly beta profiles and the wing emission of C II and O VI during EEs is investigated. Methods. Two rasters made by the SUMER (Solar Ultraviolet Measurements of Emitted Radiation) instrument onboard SOHO in a quiet-Sun region and an equatorial coronal hole were selected for our study. Transition-region explosive events were identified from profiles of C II 1037 angstrom and O VI 1032 angstrom, respectively. We compared Ly beta profiles during EEs with those averaged in the entire quiet- Sun and coronal-hole regions. Results. We find that the central part of Ly beta profiles reverses more and the distance of the two peaks becomes larger during EEs, both in the coronal hole and in the quiet Sun. The average Ly beta profile of the EEs detected by C II has an obviously stronger blue peak. During EEs, there is a clear correlation between the increased peak emission of Ly beta profiles and the enhanced wing emission of the C II and O VI lines. The correlation is more pronounced for the Ly beta peaks and C ii wings, and less significant for the Ly beta blue peak and O vi blue wing. We also find that the Ly beta profiles are more reversed in the coronal hole than in the quiet Sun. Conclusions. We suggest that the jets produced by EEs emit the Doppler-shifted Ly beta photons, causing enhanced emission at positions of the peaks of Ly beta profiles. The more-reversed Ly beta profiles confirm the presence of higher opacity in the coronal hole than in the quiet Sun. The finding that EEs modify the Ly beta line profile in QS and CIIs implies that one should be careful in the modeling and interpretation of relevant observational data.