Disk vs wind accretion in X-ray pulsar GX 301-2

Abstract

GX 301-2 provides a rare opportunity to study both disk and wind accretion in a same target. We report Insight-HXMT observations of the spin-up event of GX 301-2 happened in 2019 and compare with those of wind-fed state. The pulse profiles of the initial rapid spin-up period are dominated by one main peak, while those of the later slow spin-up period are composed of two similar peaks, as those of wind-fed state. These behaviors are confirmed by Fermi/GBM data, which also show that during the rapid spin-up period, the main peak increases with luminosity up to 8 × 10 37 erg s −1 , but the faint peak keeps almost constant. The absorption column densities during the spin-up period are ∼ 1.5 × 10 23 cm −2 , much less than those of wind-fed state at similar luminosity (∼ 9 × 10 23 cm −2 ), supporting the scenario that most of material is condensed into a disk during the spin-up period. We discuss possible differences between disk and wind accretion that may explain the observed different trend of pulse profiles.