Ionized Reflection Spectra from Accretion Disks Illuminated by X-ray Pulsars

TL;DR

This paper develops ionized X-ray reflection models for accretion disks illuminated by hard X-ray spectra and applies them to Suzaku data of the pulsar LMC X-4, revealing insights into inner disk dynamics.

Contribution

It introduces new ionized reflection models tailored for hard X-ray illumination and demonstrates their application to pulsar data, highlighting the inner disk's complex dynamics.

Findings

Good spectral fits with highly ionized reflector

Detection of Doppler broadening and redshifted features

Inner disk dynamics influence reflection signatures

Abstract

X-ray reflection signatures are observed around multiple classes of accreting compact objects. Modelling these features yield important constraints on the physics of accretion disks, motivating the development of X-ray reflection models appropriate for a variety of systems and illumination conditions. Here, constant density ionized X-ray reflection models are presented for a disk irradiated with a very hard power-law X-ray spectrum (\Gamma < 1) and a variable high-energy cutoff. These models are then applied to the Suzaku data of the accreting X-ray pulsar LMC X-4, where very good fits are obtained with a highly ionized reflector responsible for both the broad Fe K line and the soft excess. The ionized reflector shows strong evidence for significant Doppler broadening and is redshifted by ~10^4 km/s. These features indicate that the reflecting material is associated with the complex dynamics occurring at the inner region of the magnetically-truncated accretion disk. Thus, reflection studies of X-ray pulsar spectra may give important insights into the accretion physics at the magnetospheric radius.