Radio QPO in the ${\gamma}$-ray-loud X-ray binary LS I +61${^\circ}$303

TL;DR

This study reports the detection of 15-hour radio QPOs in the gamma-ray loud X-ray binary LS I +61°303, suggesting they may originate from multiple shocks in its jet, based on multi-frequency radio observations and spectral analysis.

Contribution

It provides the first detailed timing analysis of radio microflares in LS I +61°303, linking QPOs to jet shock phenomena and comparing radio and gamma-ray spectral evolution.

Findings

Radio QPOs of 15 hours detected at multiple frequencies.

Spectral index evolution correlates with photon index changes.

QPOs likely caused by multiple shocks in the jet.

Abstract

LS I +61${^\circ}$303 is a $\gamma$-ray emitting X-ray binary with periodic radio outbursts with time scales of one month. Previous observations have revealed microflares superimposed on these large outbursts with periods ranging from a few minutes to hours. This makes LS I +61${^\circ}$303, along with Cyg X-1, the only TeV emitting X-ray binary exhibiting radio microflares. To further investigate these microflaring activity in LS I +61${^\circ}$303 we observed the source with the 100-m Effelsberg radio telescope at 4.85, 8.35, and 10.45 GHz and performed timing analysis on the obtained data. Radio oscillations of 15 hours time scales are detected at all three frequencies. We also compare the spectral index evolution of radio data to that of the photon index of GeV data observed by Fermi-LAT. We conclude that the observed QPO could result from multiple shocks in a jet.