Connection between orbital modulation of H α and gamma-rays in the Be/X-ray binary LS I+61 ̊ 303

Abstract

We studied the average orbital modulation of various parameters (γ-ray flux, Hα emission line, optical V band brightness) of the radio-and γ-ray emitting Be/X-ray binary LS I + 61 303. Using the Spearman rank correlation test, we found highly significant correlations between the orbital variability of the equivalent width of the blue hump of the Hα and Fermi-LAT flux with a Spearman p-value ~2 × 10-5, and the equivalent widths ratio EWB/EWR and Fermi-LAT flux with p-value ~9 × 10-5. We also found a significant anti-correlation between Fermi-LAT flux and V band magnitude with a p-value ~7 × 10 -4. All these correlations refer to the average orbital variability, and we conclude that the Hα and γ-ray emission processes in LS I + 61 303 are connected. The possible physical scenario is briefly discussed. © 2013 ESO.