Chandra reveals a possible ultrafast outflow in the super-Eddington Be/X-ray binary Swift J0243.6+6124

J Van Den Eijnden,A Bahramian,C O Heinke,N Degenaar,J A Kennea,R Wijnands,M A Nowak,N S Schulz,T D Russell,J V Hernández Santisteban,T J Maccarone

doi:10.1093/mnras/stz1548

Abstract

Accretion at super-Eddington rates is expected to be accompanied by strong outflows. Such outflows are observed in Galactic X-ray binaries and extragalactic Ultra-luminous X-ray sources (ULXs). However, due to their large source distances, ULX outflows are challenging to detect and study in detail. Galactic neutron stars accreting from a Be-star companion at super-Eddington rates show many similarities to ULX pulsars, and therefore offer an alternative approach to study outflows in this accretion regime. Here, we present Chandra high-resolution spectroscopy of such a super-Eddington accreting neutron star, Swift J0243.6+6124, to search for wind outflow signatures during the peak of its 2017/2018 giant outburst. We detect narrow emission features at rest from Ne, Mg, S, Si, and Fe. In addition, we detect a collection of absorption features which can be identified in two ways: either as all Fe transitions at rest (with a possible contribution from Mg), or a combination of three blue-shifted Ne and Mg lines at $\sim 0.22c$, while the remaining lines are at rest. The second scenario would imply an outflow with a velocity similar to those seen in ULXs, including the ULX pulsar NGC 300 ULX-1. This result would also imply that Swift J0243.6+6124 launches both a jet, detected in radio and reported previously, and an ultra-fast wind outflow simultaneously at super-Eddington accretion rates.

Highlights

The accretion and subsequent ejection of matter is a ubiquitous process in the Universe, occurring in objects ranging from young stellar objects and planet-forming systems (e.g. Kuiper, Yorke & Turner 2015; Beltran & de Wit 2016) to X-ray binaries (XRBs; see e.g. Fender, Belloni & Gallo 2004; Migliari & Fender 2006, for overviews) and active galactic nuclei (e.g. Merloni, Heinz & di Matteo 2003; Falcke, Kording & Markoff 2004)
We show the high-energy grating (HEG) and medium energy grating (MEG) spectra
To deal with the 7 Å jump, two different splines are used for the HEG spectrum, while the range between 7 and 7.1 Å is removed from the analysis

Summary

Introduction

The accretion and subsequent ejection of matter is a ubiquitous process in the Universe, occurring in objects ranging from young stellar objects and planet-forming systems (e.g. Kuiper, Yorke & Turner 2015; Beltran & de Wit 2016) to X-ray binaries (XRBs; see e.g. Fender, Belloni & Gallo 2004; Migliari & Fender 2006, for overviews) and active galactic nuclei (e.g. Merloni, Heinz & di Matteo 2003; Falcke, Kording & Markoff 2004). XRBs. Accretion in XRBs is often accompanied by the ejection of matter, either through disc winds or via jets. Accretion in XRBs is often accompanied by the ejection of matter, either through disc winds or via jets The latter are strongly collimated outflows travelling near the speed of light, launched from the inner accretion flow, while winds are launched further out from the accreting object at lower velocities (ranging from hundreds of km s−1 to ∼0.3c) and with wider opening angles.

Objectives

Results

Conclusion