Chandra grating spectroscopy of the Be/X-ray binary 1A 0535+262

TL;DR

This paper presents the first CCD grating spectra of the Be/X-ray binary 1A 0535+262 during a giant outburst, revealing a highly ionized outflow and detailed spectral features that inform accretion flow models.

Contribution

First CCD grating spectra of a Be/X-ray binary during a giant outburst, detecting a highly ionized outflow and analyzing its properties.

Findings

Detection of a narrow Fe K_alpha emission line with FWHM ~ 5000 km/s.

First evidence of a highly ionized outflow in a Be/X-ray binary.

Estimated outflow velocities of ~1500 km/s to ~3000 km/s depending on ionization modeling.

Abstract

We present Chandra HETGS spectroscopy of the Be/X-ray binary 1A 0535+262 obtained during the 2009/2010 giant outburst. These are the first CCD grating spectra of this type of system during a giant outburst. Our spectra reveal a number of lines including a narrow Fe K_alpha emission line with a FWHM of ~ 5000 km s^-1. For the first time, we detect the presence of a highly ionized outflow in a Be/X-ray binary. Assuming that the line is He-like Fe XXV, fits with a simple Gaussian imply an outflow velocity of ~ 1500 km s^-1. However, self-consistent photoionization modeling with XSTAR suggests that Fe XXIII-XXIV must also contribute. In this case, an outflow velocity of ~ 3000 km s^-1 is implied. These results are discussed in the context of the accretion flow in Be-star, neutron star, and black hole X-ray binaries.