PROPERTIES OF CYCLOTRON LINES IN A LINE-FORMING REGION INJECTED BY AN ANISOTROPIC CONTINUUM IN ACCRETING X-RAY PULSARS

Abstract

I examine the characteristics of profiles of cyclotron lines formed by the superposition of a number of lines formed at a number of altitudes in line-forming regions illuminated by anisotropic injections in an accretion column, which formed around the polar cap of Roche-lobe-type accretion-powered X-ray pulsars. In the present paper, I consider the line-forming region near the walls of a cylindrical geometry illuminated from the inside of the cylinder. I also examine how the direction of the peak of a beam pattern affects the profiles of cyclotron lines. I found that the width and depth of the line in a phase-averaged spectrum provide information concerning the direction of a beam. I demonstrate that the cyclotron line has a pure absorption in the phase-averaged spectrum regardless of the height of the cylinder, which is expected to change with luminosity. On the other hand, in phase-resolved spectra, an emission-like feature can be formed in the phase with lower intensity in a short cylinder, which is expected at erg s−1, while a pure absorption feature tends to appear in all phases due to the superposition of a large number of lines in a tall cylinder, which is expected at erg s−1.