Hour time-scale QPOs in the X-ray and radio emission of LS I +61$^{\circ}$303

TL;DR

This study reports the discovery of hour-scale quasi-periodic oscillations in both radio and X-ray emissions of LS I +61$^{\

Contribution

It presents the first detection of stable 55-minute radio QPOs and 2-hour X-ray QPOs in LS I +61$^{\circ}$303, linking them to the radio outburst phenomena.

Findings

Radio QPOs of 55 minutes detected over 4 days.

X-ray QPOs of about 2 hours detected over 21 hours.

QPOs are associated with radio outbursts, regardless of amplitude.

Abstract

LS I +61$^{\circ}$303 is an X-ray binary with a radio outburst every ~27 days. Previous studies of the stellar system revealed radio microflares superimposed on the large radio outburst. We present here new radio observations of LS I +61$^{\circ}$303 at 2.2 GHz with the Westerbork Synthesis Radio Telescope (WSRT). Using various timing analysis methods we find significant Quasi-Periodic Oscillations (QPOs) of 55 minutes stable over the duration of 4 days. We also use archival data obtained from the Suzaku satellite at X-ray wavelengths. We report here for the first time significant X-ray QPOs of about 2 hours present over the time span of 21 hours. We compare our results with the previously reported QPO observations and we conclude that the QPOs seem to be associated with the radio outburst, independent of the amplitude of the outburst. Finally, the different QPO time-scales are discussed in the context of magnetic reconnection.