Supergiant, fast, but not so transient 4U 1907+09

TL;DR

This study examines the dipping activity in the high-mass X-ray binary 4U 1907+09, suggesting it may serve as a link between supergiant fast X-ray transients and typical accreting pulsars, based on pulsation behavior during dips.

Contribution

The paper proposes that 4U 1907+09 exhibits behavior bridging SFXTs and regular pulsars, supporting the gated accretion model for its dipping activity.

Findings

Pulsations continue during 'off' states.

Transition between states can be dip-like or flare-like.

Supports the gated accretion scenario.

Abstract

We have investigated the dipping activity observed in the high-mass X-ray binary 4U 1907+09 and shown that the source continues to pulsate in the "off" state, noting that the transition between the "on" and "off" states may be either dip-like or flare-like. This behavior may be explained in the framework of the "gated accretion" scenario proposed to explain the flares in supergiant fast X-ray transients (SFXTs). We conclude that 4U 1907+09 might prove to be a missing link between the SFXTs and ordinary accreting pulsars.