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

¹ Institute of Astronomy and National Astronomical Observatory, Bulgarian Academy of Sciences, 72 Tsarigradsko Shose Blvd., 1784 Sofia, Bulgaria
e-mail: rkz@astro.bas.bg; kstoyanov@astro.bas.bg; tomov@astro.bas.bg, jmarti@ujaen.es
² Departamento de Física (EPSJ), Universidad de Jaén, Campus Las Lagunillas, A3-420, 23071 Jaén, Spain

Received: 29 October 2013
Accepted: 26 November 2013

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 EW_B/EW_R 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.